Progress on Möbius’ hull for this week of July 30 through August 3rd of 2018 was very visible as the final row of hull plates were set in place so let’s jump right in.
Beginning of the week saw the Port side hull plates being fully fitted and tacked in place.
This shot from about mid ships on what will be the Port (left) side of the hull looking aft lets you see the final shape of the aft section now emerging.
As is the looking forward section up to the bow.
Up on the scaffolding and looking forward towards the bow you can see the slippery smooth shape of this critical section of the hull that will be under the waterline.
And turning around here is the shape going aft towards the prop tunnel and skeg which is that fin shaped extension where the prop shaft goes through. The propeller sits immediately behind this foil shaped skeg the shape of which you can start to make out from those curved thick vertical plates you see here. This will all be sheathed in aluminium plate in the coming weeks.
Moving aft you can see that Team Möbius has prepped all the edges of these 12mm/1/2” and 15mm/5/8” thick hull plates for the Starboard side and have them all stacked up and ready to be lifted up atop the upside down hull.
These piles of plates sitting behind Möbius have been getting smaller and smaller each week and by the time we get to the end of this week there won’t be too many left on the ground.
Must be time to call in the eXtremely long reaching crane again.
The quick clamp is locked in place on each plate and up they go.
Uğur and Umit are up on top of the hull to help set each plate in place.
The middle bottom area of the hull is the widest and the plates become long thin triangles where they fill in the area between the third upper row of plates you see here and the central keel bar so they set these plates up at the very top to await their turn to be fitted later in the process. Watch the video at the end to see this all in action.
Looking towards the bow you can see how the wider set of 3rd row plates are set in place resting on the large flat bars which have been welded along the whole length of the upper edge of the 2nd row plates to keep them perfectly aligned as the 3rd row plates butt up against them.
Looking aft you can see that the whole 3rd row of plates are now set in place with their overlapping edges being aptly similar to fish scales to my eyes. Bar clamps are for safety to ensure that the loose plates can slip off the flat bars.
With all those Starboard hull plates lifted in place this is all that is left of the piles of aluminium we started wtih a few months ago.
Nihat and Uğur start work on the 6m/20’ long bow plate by welding on this temporary tab to help them slide it forward into position up against the Stem Bar using a chain tackle and pry bars.
This closer look at the aft edge of that first 15mm/5/8” thick bow plate and the underlying WT bulkhead frame and stringers will give you a sense of the eXtreme strength of the underwater bow section.
If you look closely (click to enlarge) under my thumb you can see how the stringer has a step in it to accommodate the 12mm thick plate which will slide in here next.
Doesn’t take them long to have this first bow plate all tacked in position.
With the bow plate done they move aft to repeat the process and slide the next plate back into position.
Which goes very quickly and you can now see the smooth shape of the forward section of the hull. This is a very critical section of the hull as it makes the transition from the initial piercing of the water with the axe like shape of the Stem Bar and then widens out gradually as the beam of the hull widens. It is quite a tricky transition as we want the knife like slicing into the water and waves and at the same time we want to have good flotation or upward lift in large seas to prevent the bow from digging in. Some of this comes from careful design of these shapes and transitions and some comes from keeping this bow area as light as possible.
You may recall that the first meter of the bow is a fully air and water tight “collision” compartment and the next 3 meters are the relatively empty forepeak storage area so all these features combine to provide the just right combination of wave piercing and bow lift when needed.
Standing up where the 25mm thick Stem Bar makes its transition into the Keel Bar and looking almost straight down the Keel Bar you can see how this cutting edge of the bow is both knifelike sharp and yet ice splitting strong.
Sezgin soon went to work on welding the bow plate fully to the underlying framework.
In no time flat he soon has all those slots you’ve seen in previous postings all filled up with weld now. These will be ground down flush with the surrounding hull plate and disappear once we do the final finishing of all the exterior aluminium with rotary sanders and 3M abrasive pads to create a uniform finish to the beautiful raw aluminium.
Now that the hull plates are all in place at the bow, Sezgin and now do the final welding where the hull plates transition into the Stem and Keel Bar.
Producing our version of the BowTy and the Beast. Sorry, must be the Argon gas fumes from all the welding?
I captured much more of the process of living all the hull plates in place with video so be sure to watch the time lapse video compilation below of this week’s progress.
But wait, there’s more!!
There was also good progress on the new Naval Yachts shipyard a few blocks over this week as the steel structure of the large ship working area started to go up.
The roof trusses are due to go in next week so I will keep you posted as construction continues over there.
The stern shape facinates me
Apparently the bumps are to provide the bouyancy lost by the semi tunnel hull for the prop. Wounder what it does for the local flow and the fore and aft motion?
Not sure what you are meaning by “bumps” here John so can you help me understand what you are referring to?
Dennis would be best to provide the expert design explanation if he has time. Buoyancy wise at the stern we wanted to avoid having too much lift from a flat bottom stern so you can see that Dennis has kept the bottom on either side of the prop tunnel slopping up smoothly and quickly to the waterline so that the hull will disperse the lift of a stern wave to either side equally. Dennis also spent a lot of time with both software and human assistance in designing the tunnel shape for optimal flow of the water over the keel, prop and rudder. As with all the design really, this will all remain theoretical until we get her in the water but without the budget for full on hydrostatic testing of models in tanks, I think we have a hull which is going to perform extremely well for the criteria we have set.
In Goldilocks Has Her Skirt Up! June 25-28, 2018 there’s a nice screen grab that shows the hull to demonistrate the thickness of plating. I’ve been getting bloodied eyed trying to understand the “lift” that the stern will experience in a following sea. Appears from the lines that show flow that there are slight bumps on either side of the tunnel and a slight flatening of the hull lines as it goes to the rear. I get antsy about lifting the stern and making like a submarine espcially when there is a sharp forward entry with a controlled flare. BUT as you said, we’ll see what we’ll see when she hits the water.
By the by, what got me started were your comments “Which goes very quickly and you can now see the smooth shape of the forward section of the hull. This is a very critical section of the hull as it makes the transition from the initial piercing of the water with the axe like shape of the Stem Bar and then widens out gradually as the beam of the hull widens. It is quite a tricky transition as we want the knife like slicing into the water and waves and at the same time we want to have good flotation or upward lift in large seas to prevent the bow from digging in. Some of this comes from careful design of these shapes and transitions and some comes from keeping this bow area as light as possible.
You may recall that the first meter of the bow is a fully air and water tight “collision” compartment and the next 3 meters are the relatively empty forepeak storage area so all these features combine to provide the just right combination of wave piercing and bow lift when needed.”
I do have a tendency to chase rabbits. Also, I get very nervous when no one is worried about what worries me.
Got to say, you’ve got a fun site to keep the blood pumping and the brain cells snapping.
Thanks for kind compliment and glad we are keeping your heart and synapses in tip top shape John! 🙂
Don’t think there are any “bumps” per se anywhere John and may just be an anomaly of the relatively small screen grab. I will include some better views of the model and this whole area in this week’s update as we are putting in the hull plates around the skeg this week.
As I understand it, the hull shape in this aft area is created first without any tunnel and once the shape is working well then the tunnel shape, which has also been worked out extensively beforehand, is set into the hull. You could think of this as some subtractive modeling perhaps. As the water flows back along the hull when it starts to flow around the leading edge of the skeg it also starts to flow upwards along the very gradual arcs of the tunnel. As this water flow comes back together again around the aft end of the skeg it should now be quite “clean” and unified as it comes into contact with the prop blades and then flows around the rudder and is smoothly released just aft of the stern.
This week’s update will have lots of pictures of the framework for the skeg and the hull plates going in on either size and I will also include some screen shots from the model zoomed in on this area so you can see how this all works and what it looks like to you then. As you will see the below the waterline surface area of the stern narrows significantly in width and slopes well up to the sides so I think it will behave very well when surfing and being overtaken by following seas. And yes, all very theoretical and computer based right now so proof will come next year during sea trials and when we are our in the real world with Möbius.
I bet it will float forever if you can always keep the water on the sunny side!! 🙂
I think we are placing the same bet too Elton, but we aim to keep the water on the underside of the boat below us and the sun up on top above us right?!
Here’s yje Dashew comments from a 2015 aerticle that got me going on the stern “Dashew stresses the importance of balance in the shape of a yacht below the waterline. “Properly designed,” he wrote, “that waterline puts buoyancy at the end of a long lever arm, so it works harder, at the same time it allows the hull to penetrate the wave smoothly. On the other hand, if there is too much volume in the bow, the wave has more surface area to grab.
“As the wave travels down the hull,” Dashew continued, “how it interacts with the boat is a function of the hull shape it encounters in the middle and stern (as well as forward). You will notice that this design has modest beam at the stern, much finer than what you are used to seeing on other motorboats or even our sailing designs. If the boat had a broad, buoyant stern, when the wave got to the back end it would lift this area, forcing the bow down and deep into the oncoming wave crest. This is what causes hobby-horsing and heavy slamming loads. To get a hull comfortably (and quickly) through head seas you need to look at the distribution of volume along the total length, not just in the bow.” FPBs, like nearly every oceangoing motoryacht, use active stabilizers to damp rolling in beam seas. The trade-off in resistance is well worth the comfortable motion.”
Thanks for that quote John and we would concur with Steve’s basic observations. As per the previous comments and as you’ll see in this week’s update that will show the stern area in much more detail, I think you will see Mobius’, more so Dennis, has executed on the same quite well established principles of hull design. We often refer to these types of long, slender and slippery hulls as a “sailor’s motorboat’ and I think this is particularly true in the hull shaping. As with our sailboats, the bows have been very sharp and widening very gradually in the beam to just aft of center and then curving back in towards center as they go aft such that the aft end is both narrow in beam and well sloped so there is minimal buoyancy or lift. See what you think when you get a closer look at the aft area of the hull and the tunnel in this week’s update.
We have chosen a different route re stabilisation and will go with passive paravanes as our primary source of roll dampening though as you’ve seen the hull has been built with all the framing for active stabilisers, most like Magnus effect type rather than fins. We think that the paravanes will give us almost as good roll dampening as active and are much better aligned with our KISS principles and focus on efficiency.
However if we are wrong or if the subsequent XPM buyers feel differently, then retrofitting active stabilisers will be a relatively quick job.