After the novella that I turned last week’s post into I will change the pace for this week and write about something else I get asked about a lot and that more people can likely relate to than last week’s Tech Talk deep dive into fuel maps and CPP props. And a lot shorter!
Hope you enjoy and let me know in your comments either way.
Green Grass Prototyping
In one of my former lives I was a drafting and CAD teacher and in the architecture classes I taught I showed my students the value of what I referred to as the “Green Grass” approach to prototyping.
I took this title from a practice that I had first run into when I was attending the University of British Columbia in Vancouver and they were doing some major construction projects on this hugely awesome 400 hectares/1000 acres campus. When it came time to put in the many sidewalks and pathways around the campus rather than do the typical set of engineering studies to determine minimum walking distances, foot traffic density and the like, they instead just planted all these areas in grass for the first year. After being used that first year they went back and simply put in sidewalks and walkways on top of all the well trodden pathways had been made by all the people walking on them for the past year. I thought this was a brilliant method that I admired for its humbleness of seeing that the users were the true experts and that “we is smarter than me” type of approach. I have gone on to use this approach for the rest of my life and applied it conceptually to most of my many “build” projects over the past 50 years, the latest of which is the design and building of our new boat Möbius. Hence this week’s title. Seemed all quite apropos that I should come across this perfect example on my walk to the bank yesterday in the small town of Finike Turkey where we are currently docked and working on Möbius at the Setur Finike Marina.
Pretty clear proof that the civil engineers who did this recent renovation miscalculated and forgot to put in this section of walkway that more people than me thought should be there! I find this Green Grass Prototyping to be one of those concepts that is so simple and easy to understand, yet ever so smart and powerful. I thought it was worth writing about both because I get a lot of related questions about some of the ways we have used this on Möbius and I also hope that it is a concept than many of you will find useful and powerful in some of your own projects. Here are a few examples we have right now on Möbius.
Shading & Cooling of Super Salon
After living aboard for over seven months now, we are eXtremely pleased with the 360 degree views we have through the 26mm/1” thick glass that surrounds the SuperSalon or Pilot House. It is a thrilling place to be both day and night. We knew that all this glass would require some additional attention to control the heat coming in from the sun as well as the heat going out at night and we have quite a few options as to how to control both of these. As with most parts of boat design it is all about juggling the various pros and cons of each option and deciding which one will be the just right, just for us, Goldilocks choice. In many cases this is exacerbated by the fact that in order to evaluate many options you need to live with it for awhile and experiment with different arrangements before you will know how each possible solution works and how well it does or does not fit you. For controlling the PH windows we have options that include applying some of the amazing new films that are being made, using blinds on the inside or using shade cloth on the outside. This is where the Green Grass prototyping really shines and so we have been applying it to the shading of the SuperSalon glass. For the past few months we have had this nylon mesh garden shade material draped around the sides and front of the SuperSalon. We bought a 20m length of 2m wide shade cloth that is readily available from home improvement and hardware stores as it is used extensively for everything from shaded overhangs on cafes to semi-privacy screening on link fencing.
And I used some of these plastic spring clamps in my Workshop to clamp the unused width of the cloth to the AL pipe handrails running all around the roof overhang.
This has been working really well as it allows us to lift it up out of the way entirely in a few seconds and so we can experiment with how much of a difference it makes in the morning vs afternoon sun, etc.. One of the unexpected things we’ve learned is that in addition to reducing the amount of UV and sunlight getting through the glass, this draped material keeps the glass itself much cooler and also forms a bit of an air insulation pocket in the large space between the cloth and the window glass. Being loose and not attached at the bottom seems to also help in that there is a natural breeze blowing through this space keeping it from trapping hot air inside. It looks completely blacked out from the outside but when you are inside there is still reasonably good visibility so you know what is going on around you. Still early in our prototyping phase with this but our current thinking is that we will still likely go ahead and put in some film on the outer surfaces that will reduce the UV and heat transfer without adding much tint or colorization. But we think we will also do a more finished installation of this shade cloth by putting in some tracks or fasteners around the top and bottom and sewing up a strip of the shade cloth to attach to these. Right now we are enjoying the HUGE difference this has made to the inside temperatures in the hot up to 40C/105F we’ve had this summer.
Another place where we have been applying the Green Grass approach is with the furniture in the large area up in the SkyBridge. We purposely left his large area open and then Christine found some inexpensive patio furniture that fit just right into the dimensions of this area. It is all loose and easily moved about so we are trying out different configurations of these furniture pieces for a month or so at a time while we enjoy it each breakfast and evening sundowner’s. We pay attention and talk about what we like, what’s working, what’s not with each configuration and I will use these when it comes time to build in a more permanent solution. A good example of where this prototyping really pays off is that I’ve realized that the AL frame running around the circumference of the windows where they transition from fixed tinted glass to removable panes of clear acrylic, ends up being at the same height as our eyes when we are sitting down. This gets in the way as you are looking out and showed us that we will want to install a raised platform for this area where the furniture will sit. This will also make it easy for me to convert the table to a pedestal style that can be raised and lowered and will give us some easy to access storage under the platform. I will build a prototype of this platform as well using PVC pipe and fittings for a framework and some plywood for the raised floor so we can Green Grass the platform as well and figure out the best shape and height.
Media Filter v2.0
I’ve also been doing some Green Grass prototyping with the media or sand filter that does the bulk of the work filtering the sea water being pumped into our Delfin 250L/hr watermaker.
Apparently my first attempt with this plastic tank pool filter wasn’t quite up to the job as the 45PSI feed pump pressure proved too much for the seam and it split. So I found a more robust model that I could get shipped in here which is no easy task let me assure you, and spent 2 days getting this bad boy installed. As you can see it is wrapped in glass fibre to withstand much higher pressures. Unfortunately the only size that would fit moved the six position valve (black plastic bit on top of the white watermaker) from the top to the side so it took me a bit longer to figure out how best to re-route all the hoses and get everything to fit. It was close but I ended up being able to get it to fit just nicely behind the Blue filter body and still allow me to see the various pressure gauges I have on the plumbing and to fit all the hoses coming in and out. The low pressure (45 PSI) Feed Pump first pushes the sea water from the sea chest through the Blue media filter which removes almost all of the algae, dirt, etc. and then it goes through the 25 micron filter on the Right here before going through the final 5 micron filter. All in all it worked out very well. These media filters are not commonly found in marine Watermakers but they really do dramatically reduce the amount of filter cleaning and maintenance. Without one of these I would typically need to clean each of the 5 & 25 micron filters before each use and replace them about once a month. In my previous boat, adding a media filter reduced this to changing these two filters about once a year and even then they were still very clean. Inside the big Blue filter body, I first fill the bottom 10cm/4” (similar to the “Grade 2” in this illustration) with crushed rock about 20mm / 3/4” in size These rocks cover the spokes or laterals in the bottom of the filter and prevent the mesh surfaces from clogging with the sand above. Super simple in operation, no moving parts, the water enters at the top and the water pressure pushes the seawater through the full height of the sand and then exits out the bottom outlet. Rather than typical pool sand, I use what is called Zeolite which is far superior to regular pool filter sand in that it traps MUCH more and much finer particles and it cleans out much easier when back flushed. From what I read Zeolite is a natural mineral formed millions of years ago in volcanic ash flows that settled in seas and lakes. Zeolite a filtration area of about 1,000 times greater than sand media beds and the key to the truly amazing performance of this all natural Zeolite is in its molecular structure which looks like this. Much more surface area to trap finer particles in much higher volume than grains of sand. After each run of the watermaker it takes me about 3 minutes to backflush the media filter with fresh seawater by simply moving the handle on the filter valve to “Backwash” and then about 30 seconds at “Rinse” and it is all clean and ready for the next run.
The mechanical pressure gauges and Maretron pressure sensors make it easy for me to monitor any clogging of any of the filters and know which one is clogged.
I could argue that fresh water is ultimately even more critical than diesel fuel for us in order to live the completely self sufficient and eXtremely remote life style we do, so having these extra layers of filtration and dramatically lowered maintenance tick of all four of our SCEM priorities of Safety Comfort Efficiency and Maintainability.
Self Sufficient Freedom
This is especially relevant when we are at the very tiny remote islands we so enjoy which often have very limited fresh water for themselves. This is one of many favorite such spots we’ve been to, here in the Lau Group of islands in Fiji with a total of about 120 residents ashore when we were there in 2015. In several instances in our past experiences our watermaker proved to be quite the relationship builder wherein we were able to add value to the lives of those ashore by providing them with more fresh water rather than showing up wanting to take it from them to fill up depleted fresh water tanks onboard. This is the Aur atoll in the Marshall Islands when I was there in 2012.
Having a watermaker is also a key factor in our #1 benefit of this lifestyle which is Freedom. Without a watermaker, passage making boats often have their schedules dictated by the range of the supplies they carry. This applies to electricity needing to recharge batteries with shore power, diesel fuel when your tanks are too small to allow greater range and to fresh water as I’ve outlined above.
Being able to make all the electricity and water we need and having enough fuel that we only need to fill up about every 18 months allows us to travel the world with an eXtremely clean and minimal wake of disruption of the world around us.
It means that when we reach our next destination we have no demands often constrained shoreside resources and no stress from desperately seeking more water, fuel or electrical power.
Thanks for joining me again this week, hope it was enjoyable and you learned something. Please add your comments, what you learned, what you are still curious about, in the “Join the Discussion” box below.
In the post two weeks ago, I posed the question in the title “What Moves a Boat?” and went on to fill in the blanks around the answer which is the propeller because the engine “just” spins the propeller. In that post I went on to outline the relationship between the different types of Horse Power or HP measurements such as theoretical maximum power, power in the propeller shaft and most importantly power that is absorbed by the propeller. A lot of this has a very direct bearing on one of the key metrics most of us keep track of and that is the fuel burn rate or how much fuel does it take to go a set distance on a given amount of diesel fuel. However I spent so much time going through the power and engine side of the equation that I didn’t get to the propeller part itself. So consider this Part II of the “What Moves a Boat?” question.
Since that post and throughout the build actually, I received quite a few questions along the lines of “OK, but what about the propeller then?” and “Why did you chose to use a CPP Controllable Pitch Propeller on Möbius?” so I will do my best to answer these and other questions I’ve received in today’s posting.
Those of you who don’t find these technical discussions to be your cup of tea, probably most of you, please feel free to take a break from your devoted reading of these Möbius World blogs and I’ll try to have something different for next week’s update. And I will issue a warning right up front here that reading the article below may well bring back memories of your high school math and physics courses. I’ll let you decide if that is a good thing or bad?!
It may also help you to know that I named my previous boat sv Learnativity for a very good reason and she definitely lived up to her name in the 15 years I spent sailing her around the world. For Christine and I, two former teachers as well, Learning and Loving are the keys to living life well and that is what we aspire to do every day. Might help you understand what drives us to do things like designing and building Möbius and then writing articles like this one and others here on the Möbius.World blog so we can share all of our lessons learned with you.
Horses for Courses:
I promise to get to propellers as quickly as possible but it is neccessary to understand a wee bit more about the engine power that turns every propeller. It is not widely understood that for most diesel engine models from most manufacturers, the same engine model can be configured for several different service ratings, each with their own different set of HP, torque and fuel burn ratings. This is done so that the same engine can be set up to match the use case of the vehicle or boat that it is installed in. I am oversimplifying it but in marine applications these different configurations typically go from Continuous for engines needing to run at full load aka WOT or Wide Open Throttle 24/7 for days and weeks at a time, up through a series of other models as the use rating goes down to where the engine is only needing to produce peak output for a few hours a day. As you might guess as you go “up” this range, the Horse Power and the RPM goes up with each step as does the fuel consumption. It should also be noted that these same engines also start acquiring some “add on” equipment such as turbochargers, after and inter coolers, etc. but the base engine, block, crank, pistons, etc. are the same.
For example, below is a well done explanation by John Deere for their “M rating” system for their marine diesel engines. (click HERE for link to full PDV version) Keep in mind that these M ratings apply to the same overall engine model, let’s say their JD 4 cylinder 4045 4.5 liter engines or their JD 6 cylinder 6068 6.8 Liter model.
M1 rating is for marine propulsion applications that may operate up to 24 hours per day at uninterrupted full power. These applications typically operate more than 3,000 hours per year and have load factors* over 65 percent. Possible applications: Line haul tugs and towboats, fish and shrimp trawlers/draggers, and displacement hull fishing boats over 18 m (60 ft).
M2: The M2 rating is for marine propulsion applications that operate up to 3,000 hours per year and have load factors* up to 65 percent. This rating is for applications that are in continuous use, and use full power for no more than 16 hours out of each 24 hours of operation. The remaining time of operation must be at cruising † speeds. Possible applications: Short-range tugs and towboats, long-range ferryboats, large passenger vessels, and offshore displacement hull fishing boats under 18 m (60 ft). Marine auxiliary power engines for dedicated hydraulic pump drives, dredge pumps, or other constant-load marine applications should use the M2 rating.
M3: The M3 rating is for marine propulsion applications that operate up to 2,000 hours per year and have load factors* up to 50 percent. This rating is for applications that use full power for no more than four hours out of each 12 hours of operation. The remaining time of operation must be at cruising† speeds. Possible applications: Coastal fishing boats, offshore crew boats, research boats, short-range ferryboats, and dinner cruise boats.
M4: The M4 rating is for marine propulsion applications that operate up to 800 hours per year and have load factors* below 40 percent. This rating is for applications that use full power for no more than one hour out of each 12 hours of operation. The remaining time of operation must be at cruising† speeds. Possible applications: Inshore crew boats, charter fishing boats, pilot boats, dive boats, and planing hull commercial fishing boats.
M5: The M5 rating is for marine recreational propulsion applications that operate 300 hours or less per year and have load factors* below 35 percent. This rating is for applications that use full power for no more than 30 minutes out of each eight hours and cruising† speed the remainder of the eight hours, and do not operate for the remaining 16 hours of the day. Possible applications: Recreational boats in the U.S., tactical military vessels, and rescue boats outside the U.S.
Probably easiest to understand in table format like this. Putting this all together, here is the table of the eight different models of the JD4045 four cylinder marine engines John Deere offers. As you can see the HP ratings range from 75HP @ 2400 RPM for the M1 version all the way up to 150HP @ 2600RPM for the M4 model.
Mr. Gee’s Power Curves:
Just before I finally jump into discussing our CPP propeller on Möbius, let me quickly summarize the power curves from Mr. Gee himself, our Gardner 6LXB six cylinder diesel engine that is fully NA or Naturally Aspirated with all mechanical fuel injection, no turbo, no inter/after cooler.
All 6LXB’s can be setup for several different configurations along the lines of the M ratings of the John Deere outlined above and in our case for Mr. Gee and our XPM hull and use cases, we have set it up for a 100% Continuous Duty able to produce 150HP @ 1650 RPM.
Thanks to Michael Harrison and the other great people at Gardner Marine Diesel in Canterbury England I was able to get this copy of an original graph of all the outputs of the Continuous 100% Duty Cycle version of the 6LXB taken directly while running on their dynamometer.
I took the best photo I could of this very old paper chart so you may want to click to enlarge to read it better.
As per this graph, there are 5 numbered curves mapped out:
Max. power available from engine
Max Shaft Power
Power required by typical propeller
Fuel consumption max power absorbed
Fuel consumption prop power absorbed. If it helps, I have done my best to extract the following data from these curves and put them into this brief chart:
As we now get into our discussion about CPP propellers (finally!), curve #3 is the most relative as this is the power that a “typical” fixed propeller can absorb at these different RPM so that’s the curve to keep in mind here.
Fixed vs Controllable Propellers
Fixed props FP are pretty straightforward and common so I don’t think I need to go into these in much detail. Their basic dimensions are outside diameter, pitch, # of blades, etc. Pitch refers to the angle of the blades and as this angle increases the propeller “bites” into the water more. You order a fixed propeller after carefully working with the manufacturer and providing them with the data about your boat such as hull type, displacement, engine power curves, cruising speed, etc. and they calculate the prop diameter and pitch and manufacture the propeller to match.
Tying this all together, a correctly pitched prop is one that allows the engine to achieve a few more RPM’s above its rated WOT or Wide Open Throttle. This is done to ensure that you can not overload the engine and damage it and most manufacturers will void the warranty if the boat has been “over propped”.
All very logical and reasonable until you start to look at it more closely or more likely you actually get out there and run a boat for awhile and see what the real world performance and fuel consumption numbers turn out to be.
What you end up discovering are two fundamental limitations of a fixed prop:
A FP is pitched to be just right at one RPM, one HP output and one set of conditions or load. In all other conditions the pitch is less and less optimal. In this one scenario the fixed prop can be more efficient because it has been designed to be able to absorb all the power the engine can produce. However, at any other RPM or set of conditions and load a fixed prop is either over pitched or under pitched, running less efficiently and consuming more fuel.
Most of the time in most conditions you need much less power and torque than the maximum power available and so you run the boat with much lower loads which usually reduces the lifespan of that engine. This is exacerbated by the trend for the past decade or more for boat manufacturers, under pressure from buyers, to put in more and more HP rated engines and so it is quite common for boats to spend most of their time running at 10 to 20% of their full load rating which sets them up for very nasty results such as glazing cylinder walls, running too cold, etc.
Engine manufacturers recommend ways to try to reduce the consequences of running their engines in these low load conditions such as running them at WOT for a percentage of the time you have been running them at low loads, but you can see how this is far from desirable and a very poor fit for an eXtreme eXploration Passage Maker XPM type of boat and use case.
In summary then, with a FP boat, in many situations you end up running the engine inefficiently, using more fuel and reducing the lifespan of the engine. I don’t want to overstate this too much and there are of course thousands if not millions of boats running with fixed props so please don’t misconstrue my overview above to be saying that fixed props do not work. They absolutely do and can work quite well.
But as I repeat ad nauseum perhaps, we have our four fundamental SCEM principles for Möbius and all XPM type boats Safety, Comfort, Efficiency, Maintenance and so we are always looking to maximize all four of these and IF there is a better overall solution that helps us optimize one or more of these SCEM principles without compromising the others, then that is usually the Goldilocks choice we make. In the case of FP vs CPP, it became clear to us that CPP helped us make gains in all four of the SCEM categories, and especially so for Efficiency.
The CPP Efficiency Factor
I am going to resist the temptation, lucky you, of writing my own version of a deep dive into how and why a CPP prop enables you to achieve otherwise unavailable efficiency of both fuel consumption and engine maintenance and life span. Instead I will off load that explanation to the following two very well written articles on CPP propulsion.
** There is also a thread on the Trawler Forum with a discussion about the pros and cons of FP vs CPP HERE
The first is THIS one “Controllable Pitch Propellers” by the Naval Architect Michael Kasten’s at Kasten Marine Design. It was written back in 2001 but nothing has changed in this regard since and Michael does a very good job of walking your through the benefits of a CPP propelled boat. I will reference this article again a bit later as he also does an excellent comparison of the costs of building a new boat with FP vs CPP.
The other very worthwhile read is THIS eXcellent posting on CPP props by Matt Marsh. Matt published this very well written article back in April 2013 as part of a much larger “book” of which this is one chapter. All this is over on the eXcellent Attainable Adventures blog that John Harries has eXpertly curated over many years. If you are unfamiliar with this blog I can highly recommend that you spend a few minutes checking it out and I think many of you will want to subscribe.
The Wonder of Fuel Maps!
We need a way to talk about fuel efficiency of engines and boats and by far the best tool for that job is a Fuel map such as the one here from Wikipedia. These are also called Efficiency Maps or Consumption Maps where the horizontal X axis is RPM and vertical Y axis is Torque typically expressed in BMEP (Brake Mean Effective Pressure”). This allows you to plot out colored lines of a given engine’s specific fuel consumption usually measured in units such as grams per kilo Watt hour g/kW/hr or grams per HP hour g/HP/hr and these colored lines are like a topographical map but instead of elevation of land, each curved line is a given amount of fuel consumption.
What is super helpful about Fuel Maps is that the specific fuel consumption lines are normalized so you can compare any two engines of any size because the lower the specific fuel consumption number, the more efficient the engine will be at that combination of RPM and torque. Does not matter if this is one of the world’s largest diesel engines such as the 14 cylinder Wärtsilä RT-flex96C that can produce over 100,000 HP @ 102 RPM (not a typo!) or a slightly smaller 2 cylinder Beta 10 engine that produces 10HP @ 3,000 RPM, you can directly compare their Brake Specific Fuel Consumption BSFC numbers.
Show Me the Money (numbers)!!
I know this has been a long and winding journey to get here and many of these acronyms and metrics can be overwhelming so let’s put this into more understandable every day units we can all understand.
While it may be counterintuitive to many the Wärtsilä RT consumes 171 g/kW/hr and the Beta 10 consumes about 330 g/kW/hr. Converting these numbers to efficiency, the Wärtsilä has a thermodynamic efficiency of 48.1% and the Beta 10 works out to about 24.8%. So as surprising as this may be, the Beta is about 50% less efficient and consumes twice the amount of fuel relative to its rated power output. Clearly I am choosing extreme examples as the Wärtsilä RT engine has held the record for the most efficient diesel engine in the world and it does weighs in with a dry weight of a svelte 2,300 tons so there is that, but you get the point of how handy it is to work wtih these BSFC.
Oh, and for those wondering, Mr. Gee, a Gardner 6LXB has a BSFC of 206 g/kW/hr which works out to be no less than 39.73%. If the engine is operated slightly below maximum torque, it does attain slightly more than 40% thermal efficiency. Now you can see why we chose to marry Mr. Gee to a CPP bride for truly outstanding efficiency, longevity and low maintenance,
If you’d like to know more about Fuel Maps, Matt also wrote up a very good explanation of these in his other post “Understanding an Engine Fuel Maps” HERE and reading that will help you understand what I’ve written below much better.
Fuel Maps for CPP driven boats
I will leave you to digest all these articles and charts above at our own choosing and speed but to get to the crux of it for our discussion of CPP props I will focus on the following 3 following three Fuel Maps from Matt’s great article above.
Here is an example of a “fuel map” that Matt created for his articles. This would equate to a typical 4L 100kW/135HP four stroke diesel engine. The thick Red line is peak Torque and the green circle is the sweet spot of fuel economy, power and torque we seek.
When we add in the Blue/Purple line of a Fixed propeller torque curve, the problem becomes very easy to see; the optimal green circle is a long ways away from the middle of that center Goldilocks Island we want and the prop torque curve never even gets close to Goldilocks Island at any RPM. With a FP this is just the way it is and there isn’t much you can do about it.
However, if we change to a Controllable Pitch Prop we can “pull” the green circle over here simply by changing the pitch and we now run right though that Goldilocks sweet spot! Being able to change the Pitch allows us to drag that torque curve pretty much anywhere we want it
I can imagine that some of you might feel that I am overstating the situation with FP boats to lead into the explanation of why we chose to go with a Controllable Pitch Prop or CPP, and perhaps I am. But all of these points above are based on the laws of physics to a large degree and just the way a FP and diesel engine works.
You might think about it this way; in a FP boat there is only one way that you can change the speed of the boat in a given set of conditions and that is by changing the RPM of the engine and prop. That works BUT these are often RPM’s that are much less efficient and you would otherwise not want to use if you had a choice. Turns out you do!
The ideal would be to be able to run your engine and prop ALL the time under ALL conditions, at their just right load conditions where they are most efficient fuel and power wise. As it turns out this isn’t all that difficult to achieve if we simply add the ability to change the pitch of the propeller at any time such that the engine is always running at its just right RPM and the boat is moving at whatever speed you want within its range. This is what a CPP does: just right load at any RPM and SOG (Speed Over Ground)
CPP props are not new or uncommon having been in daily use in boat airplanes and boats around the world for almost 100 years. For example almost all propeller driven airplanes have a CPP. Have you ever wondered how such a plane can sit there on the runway with its propeller/s whirring away and not be moving? Simple, the pilot adjusts a lever in the cockpit that changes the pitch to zero such that it is like a knife slicing through the air producing no thrust. When you’re ready to take off you just push that Pitch lever forward, the prop blades rotate more and more, producing more and more thrust and the plane zooms down the runway. Once the plane is in the air and finished climbing, the loads are much lower so you reduce the pitch accordingly.
Change the medium from air to water and the CPP in a boat works just the same way. Here is a short video that might help you see how a marine CPP works and looks as it is changing the pitch.
But Wait! There’s more!!!
Below is a short video of Uğur manually rotating our four bladed CPP on Möbius. This is from last year during the build but does a good job of showing you just what is going on under the water as we move our Pitch lever on Möbius.
There are several additional benefits that might not be immediately apparent until you get to know CPP a bit better and one of the biggest benefits worth pointing out is that if you can change the pitch from zero/neutral to full ahead, you can do the same in reverse by simply rotating the blades the opposite direction AND the shaft continues to rotate in the same direction.
Thus you eliminate the need for a fwd/rev transmission. You do still usually need a gear reduction box, ours is 3:1, to get the prop spinning much slower than the engine but no forward/reverse gears are involved. This has several positive consequences such as being much “kinder” to the engine and gearbox as there is no “clunking” in and out of gear and the other is that you can smoothly feather the prop from forward to reverse moving the boat just millimeters at a time if desired, which is eXtremely handy when maneuvering in close quarters, docking, etc.
Know the Load!
Just a very quick diversion to explain an eXtremely useful gauge on any boat and one that is of particular value on a CPP based boat and that is having a high temperature thermometer known as a Pyrometer or an Exhaust Gas Temperature EGT gauge. If you’ve been following along for the past few threads about engines, power and fuel consumption you will have noticed that the key metric that efficiency is based on is the % of load you are putting on an engine. To avoid confusion, keep in mind that Load is the power in either kW or HP that you are USING at any given time and NOT the total POTENTIAL power an engine can produce. Also keep in mind that load can not be measured by RPM, you can fully load or over/under load an engine at ANY RPM. Therein lies the challenge; If you can’t go by the RPM’s on the tachometer or the throttle position, how do you know what the load is at any given point?
It turns out to be rather simple to know the load when you understand that exhaust gas temperature or EGT is a direct proxy for load because as the load increases in a diesel engine, so too does the heat of the exhaust gas. Measuring the EGT is done very simply by having a thermometer that can measure high temperatures which is technically called a Pyrometer and what I will refer to here as an Exhaust Gas Temperature gauge. Very similar to what you might have to check the temperature of your oven or a meat thermometer, you insert a probe into the exhaust manifold, usually at the end or elbow where the exhaust is exiting the manifold.
My finger is pointing at the threaded fitting I have installed at the end of the exhaust manifold on Mr. Gee I am using a Maretron EGT probe as this makes it easy to put all the EGT data onto our N2K/NMEA2000 network that allows us to display the EGT gauge on any screen, anywhere, anytime. Installation is as simple as putting in the threaded adaptor that comes with the EGT probe, inserting the probe, tightening the nut and then connecting the wires into your N2K network.
There are also many gauge companies who make independent EGT gauges that just wires the probe to a dedicated display on your dashboard the same as you would do for things like oil pressure, oil/water temperature, RPM, etc.. Here is one example of a test setup Christine made to display EGT and Fuel Burn rate on any of our screens while we were doing our initial sea trials in July. For those interested, this is an example of some of the various ways we can chose to display our engine and boat data on our Maretron N2KView screens. You can have as many of these screens as you have time to create and this one is an example courtesy of our friends James and Jennifer on mv Dirona. OK, now that we know the exact EGT and therefore engine load at any given time, it is easy to adjust the Pitch lever to the Goldilocks load and efficiency we want at ANY speed and in ANY conditions. This is a significant advantage to any boat I would think but it turns out to be an eXtremely Big Deal on an XPM type of boat and use can in particular.
Why Does this all Matter?
If I have done a reasonable job of brining you this far, you now have a good answer to that question as the CPP enables us to operate near peak efficiency under almost any conditions and this adds up to significantly better fuel economy and lifespan for the whole propulsion system on any boat. Now put this in the context of an XPM style of boat that is intended to allow a couple to take their floating home across oceans to the far reaches of the seas which means that these boats will be underway on long passages running non stop for weeks or more and complete self sufficiency throughout their journeys. Therefore these boats have unusually large tank capacities for both fuel and water which adds up to a lot of weight that literally comes and goes over these passages and so the displacement (weight) of these boats changes a great deal from start to end of passage and over the course of a year. Thus the boat has a highly variable displacement and when you add into this equally as variable wind and sea conditions, an XPM’s propulsion system must bee able to handle ALL of these varied conditions and do so while continuing to be optimized for all of the Safety/Comfort/Efficiency/Maintenance priorities.
XPM liquid loads vary substantially during a passage and over the annual use of the boat and to put that into perspective, our total fuel tankage is 14,617L/3861USG = 12,410Kg and water is 7300L/1930USG = 7300 Kg/16100 Lbs for a total of 19,700 Kg/43,450 Lbs. That is a LOT of weight and amounts to the displacement of the boat changing by over 55% ! That is a huge range that the propulsion system needs to be able to deal with efficiently throughout and this is yet another way in which the CPP provides significant advantages. Being able to change the pitch in synch with the changes in overall displacement of the boat as the fuel and water volumes go up and down allows us to stay in that Goldilocks sweet spot on the Fuel and Efficiency Map ALL the time.
System Based Solution:
Another key benefit that helped convince me that CPP was the way to go for Möbius is that the CPP comes as an integrated solution. With a FP you typically need to spec, chose, install and buy each component; the FP itself, then a matching prop shaft, then cutlass bearings, prop tube, flanges, transmission, shaft seals, anti vibration mounts, Elecrical controls, and the list goes on.
In our case, we chose to go with Nogva a large Norwegian company that builds complete propulsion systems. They provided us with everything except the engine as we already had Mr. Gee, though Nogva does offer several major engine options from the likes of JD, Scania and Nanni.
We worked closely with the engineers at Nogva to provide them with all the details of the boat and how we wold be using it and came up with a propulsion system that consisted of their N4-215-65 CPP system that looks like this and includes literally every part you need from the prop at one end to the flange that bolts to the servo gearbox at the other. Installation of the whole prop tube and shaft assembly Nogva shipped was eXtremely easy as we just inserted the Nogva prop tube into the aluminium shaft log pipe that had been welded in as part of the hull months prior. These two tubes slid into each other with about 10mm / 3/8” clearance between them so it was a simple matter of aligning these two shafts concentrically and then pumping the space full of ChockFast an epoxy filler made for this job.
The bright red flange you can see on the far Right here is that flange on the N4 CPP which I am not bolting together with the brown Nogva HC-168-C servo gear reduction box using the standard SAE1 flange on the back of Mr. Gee which is the Silver/Aluminium part on the far Left.
I can not overstate the benefits of getting the entire propulsion system as a complete system from the same manufacturer as it made both the installation and the maintenance of this critical system eXtremely easy and reliable.
Additional Benefits of CPP
This does not apply to us on Möbius as we went all electric, but for boats that have hydraulic systems for things like thrusters, stabilizers, windlasses and winches, CPP provides a significant advantage in that not only is the pitch always just right for actual load, it also provides the ability to have higher engine revs needed for the hydraulic pumps even when you are docking or stopping the boat. With a FP it is challenging to keep the engine revs up just as you need that bow thruster and winches the most while the boat is near standstill while docking.
Slow Speed Maneuverings
Speaking of docking, with a CPP you can move the boat with silky smooth precision 1mm forward/astern with nothing more than small movements of the Pitch lever forward/aft.
Repairing Broken Props
Given our intent to cruise in icy locations in high latitude locations, as well as the always present danger of an errant underwater log or coral head that can take a bite out of your prop blades, the CPP provides a much more manageable repair than a FP. With a once piece FP if you bend or break a prop blade the whole propeller needs to be removed, often the shaft along with it and have it repaired or replaced by an all new one. I have had to do this on previous boats and it is a big job that takes a lot of time.
With the blades on a CPP being separate parts and the center hub being much stronger and more robust, it is relatively easy to remove and replace just one or two prop blades and this can be done while the remains in place.
When I spoke with the Nogva engineers about this scenario they agreed to machine an extra set of four blades in the same run and were able to provide these at a very low cost. I carry these four new blades along with a set of O-ring seals and grease just in case this should ever be a repair I need to do in some far flung spot. To fully validate all this and give me some advanced practice in such ideal conditions, I did a trial run by disassembling the prop and removing all four blades. It turned out to be a very quick operation with no special tools required.
I started by removing the eight SS Allen head SS bolts you can see here which let me easily remove the end side of the hub. This now exposed the bases of the four blades which rotate around the square bronze block you see in the center. Each blade is machined to precisely slide into place on the boat side of the hub and then the end side hub fits over that to fully capture the props. A rubber O-ring around the grooves you see here, seals each blade to keep the water out and the grease in. Some of you have asked “Isn’t this a very complex piece of equipment?” and while it can’t get more simpler than a single part fixed prop, these CPP props really are not complex at all.
And when you consider the whole propulsion system not having any gear changing transmission reduces the overall complexity considerably further. When you slide the blades off the only thing that remains inside is the end of the SS Pitch Adjustment rod and the single bronze block that each blade pivots on. No gears, no bearings, just a lot of grease. Slide each blade back in place, bolt the end cap back in place and you end up with a fully operational CPP. Before we splashed the boat back in February we of course put on the black International InterSleek silicone based Foul Release paint an all the underwater aluminium surfaces and coated the Nogva CPP with similar silicone PellerClean. Now seven months later with very little movement unfortunately, the good news is that there is almost no growth on either the CPP or the bottom surfaces and what little we’ve found comes off easily with a simple wipe with a cloth.
In my discussions with the Nogva engineers and other research before making my decision to go with a Nogva CPP, I was impressed by the attention Nogva had paid to the problem of prop blades transferring noise and vibration into the hull. As I understand it, Nogva provides propulsion systems for work boats used in aquaculture and the use case of these boats in particular need to have robust, efficient and reliable propulsion in their very demanding situations.
Like XPM’s these work boat hulls are usually made of aluminum, which can be prone to noise and vibration problems. Nogva’s solutions counteract these problems by minimizing the propeller’s impulses toward the hull.and they have gained a lot of experience though their R&D into this. I will need to get more nautical miles on our Nogva CPP to more fully understand how well this all works but based on our sea trials to date, the whole propulsion system is very smooth and working very well so far.
OK Wayne, but What about Cost?
This is perhaps the most asked question or concern when others are considering FP vs CPP for their boat. For those considering changing their current boat from fixed to CPP it would be a move costly conversion in terms of both time and money and I don’t think the payoff would be there. However the opposite is the case for those of us building a new boat where everything has to be purchased and installed either way. In this case the CPP turns out to be no more and some have suggested less total coast than a fixed prop.
Perhaps the best explanation of this is a very thorough comparison that Michael Kasten’s did and wrote about in that article I mentioned up near the beginning. HERE is that link again to save you from scrolling up to find it. Michael did this research back in early 2001 so the actual amounts he quotes have of course changed, but based on my more recent research and purchasing all the costs have scaled up equally and so I think his examples still hold up. In the beginning of this article Michael does a good job of providing an overview of how CPP props work and why he too sees them as a better and more efficient type of prop for the boats that he designs, but if you scroll down to “Part II Costs” you will find his comparison of pricing out a like for like Fixed Prop and a CPP.
Near the end of this comparison he goes on to cover some of the same points I mentioned above as to the cost and labour required to install a CPP vs a FP. He arrives at the same conclusion as I have with is that installing a CPP system is actually less time and effort than a FP. Installation wise there is little to no difference between installing a transmission for a FP vs installing a servo reduction gearbox for a CPP so that is a wash cost and difficulty wise. However installing a CPP shaft system is much easier than the more “distributed” FP components.
Michael ends with names and links to all the CPP manufacturers he was aware of at the time and these will provide those interested with a good starting point for doing their own research.
I had read Michaels article several years ago before we Möbius was even a twinkle in my eyes and so I referred back to it and used it to help me do my own research and comparison of the pros, cons and costs of FP vs CPP and I came to the exact same conclusion that a CPP is no more expensive or difficult to buy and install than a fixed prop and could be less. Given the significant advantages and benefits I’ve gone over up above you can hopefully understand why this became a “no brainer” decision for me to make. Nothing since then in our experience with buying, installing and now staring to use a Controllable Pitch Propeller has changed and it has already exceeded our hopes that this would be the Goldilocks propulsion system for Möbius. I fully expect that opinion will continue to improve over the entire time we are running Möbius and enjoying all these advantages of the increased Comfort and Efficiency our Nogva CPP provides as well as the significant reductions in fuel costs.
Isn’t a CPP Difficult to Operate?
Another of the most common questions I receive and so I will close out (bet you thought that would never happen!) by doing my best to answer this final question. A couple of quick caveats for context here. First there is no question that Christine and I are much more familiar with operating boats with a Fixed Prop and their typical Throttle + Fwd/Reverse levers or combined single lever versions. Switching over to CPP therefore presented us with some initial learning curve and at first it all felt very strange as everything was SO different. No “clunk” as we were used to when you put a FP into gear and you knew that the boat was going to move forward right away and increase speed as you increased the throttle and engine RPM. With the CPP there is no noise at all and the boat does not immediately jump forward, or reverse, and so at first you are a bit uncertain what is going to happen. You know the prop is turning at all times as you can see some of the turbulence coming out the sides even when you are in the Zero Pitch/Neutral position and moving the throttle forward increases the engine RPM but the boat just sits there. However, as you push the Pitch lever slowly forward in absolute silence and lack of any other indication, you notice that the boat is indeed moving forward and the more you push the Pitch lever forward, the faster you go. Pull the Pitch lever back and you very quickly slow down but again no other indication other than the visual confirmation of gauges and surroundings that you are slowing down and stopping.
We both spent some time out in some calm open waters to try out this all new propulsion control system and the strangeness soon faded away and began to feel more and more intuitive. Set the RPM where you want them and then increase the Pitch to move forward or reverse with extremely smooth and strong control.
Our first few experiences with docking this all new boat would have been challenging enough so with the added newness of a CPP it was all the more so. However all the surprises were very good ones as you were able to so smoothly and completely control the movement of the boat. With a very big four bladed of just over 1m diameter and an equally large rudder controlling the stern of the boat while docking is like having a stern thruster. We also have a very powerful electric bow thruster and as we have practiced using the combination of these fore and aft controls we have already gained a lot of confidence in our ability to control Möbius while doing such close quarter manoeuvring and even more so when we get underway. All still VERY early in our learning process but it has been a great start so far.
So the best answer I can provide at this early stage is that there is no question that learning to operate a CPP does take some time but it is time well spent and I’m not sure that this is very different than any system on a boat. Like all our systems, It takes a bit of time to learn where the sweet spots or Goldilocks settings are and become familiar with them so they become routine.
Operation of the CPP for cruising can be done in two different ways; set the Pitch and adjust the throttle to reach optimal loading of the engine or do the opposite, set the Pitch to where you have learned you think it will be best and then use the throttle to move you up to whatever speed you have found to be optimal for a given set of conditions. As I’ve covered in the sections up above about EGT we have learned that we basically run the boat based on the EGT reading once we are at the speed we want. We are learning to watch the EGT numbers to be sure we stay well below the maximum EGT/load which in the case of our Gardner 6LXB is about 450C/840F. If the EGT number gets too high, just back off the Pitch a bit. At this setting, the engine is powering the prop at its maximum ability, and runs well loaded at max. efficiency.
You don’t want to set the pitch too shallow as the engine will not be loaded by the prop and will run straight up to its maximum rpm. Nor do you want to set the pitch too steep either for the given rpm as that will overload the engine. Dark smoke and a increasing EGT are a signal for overload. In situations where you want to be moving much slower, you set the RPM lower and the Pitch higher to load the engine sufficiently at low power range and low fuel consumption. In opposite situations when going uphill in adverse weather we will set the RPM higher and the Pitch lower or more shallow to allow the engine to come up to speeds with higher power output. The recommended practice for docking with a single prop vessel is to set the RPMs higher rpm (about 60 to 80%) and then use the Pitch lever to do the needed and often hard over manoeuvres. We are learning to trust that we can push or pull the Pitch lever in either direction at these higher revs and it does not harm the system. This is quickly feels very comfortable as you experience the eXtremely fine control you have over moving the boat incrementally or quickly with just the Pitch lever.
Clearly I am in NO position to be offering advise here about running a CPP well and how to best handle a CPP powered boat, but these are my early lessons learned and I look forward to bringing you more and more as we get out there and log more hours and nautical smiles on Möbius.
Whew!! If you have made it this far, you are probably almost as tired from reading all this as I am from writing it. But even if it takes you, and me, more times to re read this and learn more, I do hope this has at least been interesting and informative for you no matter where you are at in the comparison between Fixed and Controllable Pitch propellers.
I will sign off for today with a “proof is in the pudding” shot of the stern wake we leave behind us while doing 9.2 knots at 1500 RPM burning 21.7L/hr EGT @ 305C.
VERY happy with how well Mr. Gee and his Nogva CPP bride get along and how they propel us with such eXcellent Safety, Comfort, Efficiency and Maintainability.
Thanks for coming along for this long and winding ride and please join the discussion by adding your comments and questions in the box below.
Our lives aboard Möbius have settled into the same pattern of working our way through the list of jobs needing to be finished before Möbius is fully sea worth and ready for us to get back to crossing oceans and eXploring the salt water world we both love so much. This work is far from “glamorous” or eXciting, just neccessary and a pattern we are accustomed to from our decades being full time live aboards and stewards of many boats before.
What IS eXtremely eXciting is the arrival of more and more members of our family of XPM style boats from the desk of our beloved Naval Architect and designer, Dennis Harjamaa who runs Artnautica Yacht Design in Auckland NZ. So let me provide a bit of background to help put this all in context.
Finding our Goldilocks NA and Designer for XPM78-01 Möbius
Back in 2016 when Christine and I got serious about switching from sail to power and designing and building our own new “Goldilocks” just right, just for us passage maker, we spent a year searching the world for our equally Goldilocks NA. There are a LOT of Naval Architects and boat design firms but what made our search so challenging was that we did not want to be just clients the designer worked FOR and end up with a boat design that was based on what the designer thought was best. Instead we wanted a designer who would work WITH us in a highly collaborative way to transform the very specific visions and specifications which we knew well from all our nautical smiles at sea. It took us almost a year and a lot of both nautical and air miles but we finally found and met up with Dennis when we had our previous boat in New Zealand and we knew right away that we had finally found our Goldilocks guy.
Winding the clock back a few years more, somewhere around 2010, after designing a lot of very successful smaller boats, Dennis set out to design the Goldilocks boat for himself and his partner Raquel to live aboard and enable them to start exploring the world by sea. What he came up with was the LRC58 which you see rendered here and hull #1 called “Koti” has been their full time home near Auckland since it launched in 2013.
Since then FIVE more LRC58’s have launched from the Aluboot yard in the Netherlands and you can read all about them HERE on the Artnautica.EU website. But wait! There’s more!!!
Not only did Dennis design the LRC58, he also built her almost single handedly! So now you are starting to understand why Dennis was and still is to this day our Goldilocks XPM designer!
The XPM Line of Boats Begins
Christine and I found the LRC name to be too generic and overused in the boating world and so we came up with the more specific eXtreme eXploration Passage Maker or XPM title to better suit this unique style of boats and therefore Möbius became hull #1 of the new XPM78 design.
We spent almost two years working with Dennis in what quickly became a collaborative work of art and engineering and resulted in the completed 3D model and drawings that were used by Naval Yachts to build XPM78-01 Möbius. This is a relatively new style of boat which do not yet have a common name or acronym but are all designed and built for a small but growing group of like minded people with a common set of priorities and use cases. They are most often a couple, sometimes with a child or two, who want to be able to have a floating home that can carry them across oceans and eXplore the most remote spots on the planet and do so with the highest degree of safety, comfort, efficiency and low maintenance. Such requirements tend to determine the overall characteristics of these boats so they are long, slender and slippery all aluminium hulls that are low to the water, self righting and efficient to run with as low amount of maintenance as possible to operate.
Since designing our XPM78-01 Möbius, more and more people have been intrigued by what Dennis calls his LRC or Long Range Cruising boats and have sought him out to design a Goldilocks version of an XPM for them and that’s what brings us to this post.
Over the years as more people became aware of our work building Möbius and chronicling it all with these weekly blog posts, Christine and I have been fielding more and more requests by people wanting to know more about these XPM boats, In spite of my Emails being even longer than my blog posts, some of these people have been brave enough to keep asking questions and receiving more and more of my novellas aka Emails as their interest grew. In several cases this has led to them coming to meet with us for lengthy tours of Möbius, Naval Yachts and the Antalya Free Zone and as you’re about to see, in several cases this ultimately led to several signing on the dotted line with Artnautica and Naval to design and build an XPM for them.
The first are an American couple, Chris and Sebrina and their son Rhys who not only endured hundreds of pages of my Emails but they also very courageously flew over to Antalya last December and we spent several days with them aboard Möbius as she was nearing the end of her build and showing them around Antalya and Naval Yachts. Apparently they liked what they saw as a few months later they had signed on with Artnautica and Naval to design and build what is now hull # 2 XPM78-02 Vanguard.
These are some relatively recent renders of how hull #2 has evolved. You can see the XPM78 family resemblance and she is based on the same models as Möbius. However Chris & Sebrina worked with Artnautica and Naval on some important modifications to make this the just right, just for them, XPM78. Keen eyed followers might notice that the Pilot House has been lengthened by about 1 from aka 1 meter which is a change that we recommended as well for all future XPM78’s. More significantly and perhaps controversial, the Pilot House has also been raised by about the same amount to enable the area underneath to become living space that includes a 3rd cabin. Some of the other key changes that Vanguard will have include:
Twin John Deer 4045 engines with double prop tunnels to keep the draft down.
electric hybrid propulsion by Praxis added to the propulsion from twin JD diesel engines
addition of a 3rd cabin
extending the PH as noted above to make the salon in particular more roomy.
raise the PH to convert what is the Basement on Möbius to all living space on Vanguard.
bulwarks wrapping around the side and bow decks
windows in the sides of the hull
Some will love those changes, others will question but all that matters is that this is what’s best for Chris, Sebrina and Rhys.
There are a growing number of designs similar to these XPM’s from other companies that have appeared in the past couple of years but almost none of these have gone on to be built. So pictures like this are a big deal IMHO!
Construction at Naval began in April and matches the way Möbius was built. A steel frame is built on the shop floor and then the hull is built upside down on top of this. For the curious, if you go back to posts here starting around April 2018 you can see when Möbius was at this same point and follow the construction from there if you’d like to look into the future of the building of Vanguard. This is the most recent photo I received from Chris which I think was taken a few weeks ago at the end of August.
I believe Chris and/or Naval will soon be creating a blog to cover this build and I’ll be sure to pass that on here for those interested.
Not to be outdone, another couple, Andrew and Lily, also from the USA have recently signed on with Artnautica and Naval to build XPM hull #3 and this one will be much larger at 85’ LOA. Covid travel restrictions have not allowed us to meet in person yet, but Christine and I have had some video calls with Andrew and Lily and they too have been subjected to my barrage of Emails as I attempt to answer all their questions. Unfortunately as you may have heard in the news, there has also been a Covid related shortage in the world’s aluminium supply so work on both XPM78-02 and XPM85-01 has been delayed but Naval has been busy getting ready for the aluminium to arrive by building the steel support structure that XPM85 will be built upon.
Dennis and Naval are still working with Andrew to finalize the design so I don’t have much more to show you yet but will bring you updates when I get them and we could not be more eXcited for Andrew & Lily as their dreams are transformed into very real aluminium. But wait! There is still MORE!!
Meanwhile, in the Netherlands
As if these new XPM builds were not enough eXcitement for one blog post, things have been equally as busy or more so over in the LRC world of Artnautica. Somewhere around 2018 Dennis was in conversation with the owner of LRC58-03 Britt which launched from the Aluboot yard in July 2017. Rob Westermann and his wife Janet have been touring the many waterways surrounding the Netherlands and their conversations with Dennis soon resulted in Rob setting up Artnautica Europe. Rob and I first met at the big METS marine trade show in Amsterdam back in 2018 and have gone on to become very good friends who have visited with us in Antalya several times. Rob is eXtremely bright and entrepreneurial and he has been a great partner with Dennis to extend and expand the LRC line of boats being built in the Netherlands as well.
Rob & Janet enjoyed their life aboard Britt so much that they decided they wanted not only more time but more boat and so began a conversation and a whole new design process that has now culminated in the LRC65 which will become the new home for them to continue to explore Europe and the world.
FYI, LRC58-03 Britt is therefore now for sale and can find out more about that and how to contact Rob HERE.
LRC65-01 Britt II
As you can imagine, Covid restrictions are doing their best to get in the way of getting LRC65-01 off the drawing board and into the build, but Rob is tenacious and very experienced so he was able to get in an order for some aluminium just as the supply was drying up and they expect to begin construction in about a month.
Dennis & Rob have created two layout versions GA 5 and GA 6 have each with different galley, settee, and helm station positions, as well as a different position of the staircase leading forward. This could be interchangeable between the two layout options. As you can see here in this rendering of the framework of LRC65, the LRC/XPM boat similarities are much more than just skin deep. Here is a similar shot of Mobius’ framework. When you peel away the outer aluminium plating, the familiar Artnautica framing signature is very clear to see.
There will be several propulsion options for the LRC65; twins of either Beta 75 or John Deere 4045 DTF 70 (80hp). The single-engine option will have a turbocharged four-cylinder, 130-160hp engine, likely supplied by SABB who make the CPP gearbox of choice and can therefore supply the whole driveline (Deutz, Iveco, and AGCO Sisu).
Phwew!!! That was quite the tour of the XPM Family Tree!
Coming around the XPM world full circle, I will leave you with this photo of the very first XPM, our beloved Möbius.
Hope you enjoyed the tour and if you have any questions or would like to consider creating your own XPM just let me know in the “Join the Discussion” box below or send me an Email to us at email@example.com
The cooling trend continues with the weather here in Finike Turkey as the daytime highs drop down below 34C/93F most days this week and the forecast calls for our first sub 30C/86F high next week. We are very fortunate in that we have a huge swimming pool here at Finike Marina, aka the Mediterranean Ocean, that is just a short walk down along the sea wall from where Möbius is docked. We are able to have our nightly swims thanks to a set of stairs up over the sea wall that the Finike municipality put in several years ago.
You can see more of our nightly swim spot in the fun video HERE which Christine put up last week of her first solo piloting of our Mavic Air 2 drone. So every evening around 7pm or so, we exchange our work clothes for our bathing suits and make the short walk down to this set of stairs up over the sea wall every evening after we stop working and swim off this landing for 15 minutes or so. We even a fresh water shower to rinse off all the salt on our way back to the boat.
Oh! AND we also have the AirCon working very well now for those days that are still a wee bit too warm, so we are very comfy and grateful to be here. I am running late here getting this blog written on Sunday afternoons as usual and it has been another very busy work week getting more and more of the jobs done on Möbius but I’d like to share some details on a set of related topics which I get asked quite about very often and which seems to be surrounded by SO much confusion and misinformation; Power, Load and fuel consumption.
What moves a boat?
Seems like such a simple question, and the answer really is equally as simple and yet, in talking with other boat owners over the years, both in person and online in various forums such as Trawler Forum, I’m often surprised at some of the things I hear otherwise very savvy and smart people say when it comes to things like Horse Power, fuel consumption, propellers and other aspects of the propulsion of their or other people’s boats. I was reminded of this again just this week by a post that Steve D’Antonio sent out in his August 2021 Newsletter “Full Throttle vs. Full Load”. If you are not already subscribed to Steve’s newsletter I recommend it highly as a super valuable source of very thoughtful advise and info on all things boating.
In this most recent article, Steve goes over the often confused differences between full throttle and full load and more importantly he links to a much longer and well written article of his called “Wide Open Throttle” from back in 2010 for Professional Boat magazine which I also recommend eXtremely highly if you are not already subscribed (free) as ProBoat is one of my best learning resources and I have their entire library of magazines.
Both of these articles are must reads in my opinion if you would like to understand the relationship of HP, fuel burn and power going to your propeller. However THE best explanation of this relatively simple set of relationships is written by Tony Athens at Seaboard Marine in his very well titled article “Propellers Move Boats, Engines Just Turn Them”. All three of these articles are very much worth your time and I will circle back around from what they address in a future article here to talk more about why we have a Controllable Pitch Propeller or CPP on Möbius. It will also address why we chose to have a Gardner 6LXB turn that CPP
Once you have read these over I think that you will clearly understand what so many don’t seem to. The major points are as follows:
The rated HP of any engine tells you very little about the amount of fuel it will burn or the load that engine will be running at.
When I am having these discussions my key point is that HP = amount of fuel burned, full stop, no other information or variables required.
However, to quote a much fuller explanation from Tony’s article the single best relationship to understand is “… the amount “FUEL BURNED” is the amount of “HORSEPOWER PRODUCED.” That is the COMMON DENOMINATOR, not ENGINE RPM, and NOT the actual rating of the engine. And, what makes the engine produce a given amount of horsepower is how the propeller loads the engine.”
Using one of the example’s Tony uses near the end of his article, if you have the same make and model of engine in two identical boats, but one is set up by the factory, to BE ABLE TO reach a maximum of 300 HP and the other boat with the same engine is set up by the factory to reach a maximum of 715HP, when these two identical boats are running side by side, their fuel consumption will be the SAME because the amount of HP that the boat requires is also the SAME.
Load can be very deceiving because it is based on the RATED HP of that engine and has very little to do with how long an engine will last. (assuming it is not overloaded). As Tony outlines in his article, you can set up the same Cummins QSM11 300HP to 715HP, for the otherwise exact same engine. So if the propeller requires 215HP to move this boat at a certain speed and set of conditions, then the load gauge on the 300HP engine would read 72% whereas the 715HP version would say the load was 30% and BOTH engines would last or have the same amount of “wear and tear”. So contrary to very popular opinion, load % has very little to do with how long any marine engine will last.
If this does not make sense to you, or you have always been told otherwise, please do give these articles above a read and then let me know in your comments if you still think this does not make sense or is not correct. Once we all have the same understanding of these basic components of boat propulsion and how they are related to each other, I will address one of the most asked questions I receive; why did you chose to use a CPP on your boat?
I know these more technical topics are not everyone’s cup of tea, but for those it is, I hope you enjoy the articles above and I look forward to any additional discussion or questions you have.