Semi-submersible Sailing vessel Ohanda One

Within our spectulative design project about buildig a zero emission ship, we have been working on a functioning prototype of the semi-submersible sailing vessel for Ohanda One: Good to go?! https://ohanda.one/good-to-go/
This is a request for comments on the suggested - yet to be optimized - principal semi-submerged design of Ohanda One. Thank you!

 

Building a small waterplane area sailing vessel is difficult because the whole point of the small waterplane area is to minimise responses not only in heave, but also roll and pitch, and the small waterplane area reduces roll and pitch by preventing the centre of buoyancy from moving much in response to where the waterline is. But the centre of buoyancy moving in response to where the waterline is, that is the primary source of stability for sailing vessels. You reduce stability, and sail carrying ability, by design.

That leaves you either reducing heeling moment quite radically, perhaps by using kites, which you don't do, or foil stabilisation, which I assume is what you plan to do. The length of the vessel relative to the height of the rig gives you plenty of lever arm for stabilisation in pitch. It seems quite narrow, so you don't have much for dealing with heeling moment. And if the vessel is ever forced to stop in heavy weather, will it have enough stability?

Why three hulls? That seems to increase wetted surface area a lot, so what is the compensating gain?

Given the design brief of a seakindly sailing vessel, I would go for a proa with a very long, deep, narrow lee hull, for a modest waterplane loading, and a very narrow ama, for high waterplane loading. Give it counterrotating spade rudders with propellers for motoring, and a Walker Wingsail.

 

Interesting concept.

15, 000 tonnes is a very heavy vessel

What passenger ports can accommodate 11m - 23m draft?

 

Thank you for your reply Robert! Yes, exactly, we are using dynamic ballast tanks on each side of the ship, plus four flapping fins, to control the heeling. Also the static horizontal and vertical fin formed struts help to stabilize it when sailing. The design was chosen to test its limits, so the vessel can only stop, when the ballast tanks are full of air and the vessel is then swimming on the water surface (harbour mode). When driving the vessel is semi-submerged to the red water line.

We needed the full volume of the outer two ballast tubes to create enough static and dynamic buoyancy to operate the vessel in the desired way, while the center hull is fully packed with batteries, motor, valves and pumps. Also the keel is packed with batteries for a second power supply.

I cannot fully imagine your design from the brief, yet, but yes, we would definitely want counterrotating spade rudders and wingsails for a larger version of it.

 

Can you post what the stability calculations are for the design? At least the basic ones like what the righting moment is at rest, and whether it is self ritghting or not.

 

That would have a very high centre of gravity, so limited in the wave height it can cope with. So at sea, you could only stop in good conditions? And power loss would severely affect seaworthiness?

It seems to me that you could achieve that by having two fatter hulls, using their midships sections to house all that stuff, and the ends for ballast tanks.

For hull configuration, a suitably scaled up version of this:





Apart from being seakindly, the vessel is also supposed to be zero emission. Zero emission during use doesn't help if you have higher emissions from building and decommissioning. Even before you work out the details, I think you should be able to estimate to within a factor 3 or so the lifecycle impact; the embodied energy (how much energy is needed to make the vessel and to maintain it), antifouling (is something free of biocides practical for this use?), decommissioning, and cumulative risk of collision with sealife. Compare that to flying, assuming a realistic transition to sustainable fuels.

I am not a fan of air travel, but seeing that people will travel, and that transporting people over appreciable distances by water tends to be more energy intensive than air travel, and that most will need to travel not just coast to coast but also inland (which you need to add to the environmental impact of your proposal), it will not be easy to make your alternative better for the environment.

 

For the existing first functional prototype we are still working on the adjustment. Right after the scale model (aka shiplet) got painted, we did a first test (see video at end of blog post Colorful High Hydrostatic Hopes https://ohanda.one/high-hydrostatic-hopes/). But it turned out, we had to add more electronics (weight) in the deck than we had expected. So just very recently and in preparation of the first test in a local lake with waves, we added a bit more buoyancy by prolonging the four ends of the ballast tubes.

When the shiplet is semi-submerged it is not self righting, but it just falls to one side, if it gets too slow or stops driving. We are aware that from a risk perspektive, it is unlikely to build a passanger ship in that manner. But to start with, we were just very curious and wanted to find out if we can manage to completely balance such a vessel just by dynamically adjusting the flapping fins and the ballast in the side tubes when driving. For a future design one could of course add more stabilizing by adding more lift to the struts and weight to the bottom. The deck is designed to be a ship in itself, so that it would swim when the balast tanks are fully flooded.

 

Thank you Robert for your challenging criticalness! I very much appreciate your comments.

Yes, you are right, as you can also read in my reply to gonzo here. That is our starting point. For prototyping we were thinking about it more like a modern airplane, assuming it has to drive to be stable or be in calmer waters or in save harbours to fully surface.

Yes, I agree that this is possible. One other thought about the trimaran with center hull was to put all the heavy mass there to make it easier to balance. But I agree that it needs further investigation to better understand the pros and cons and it might be better to go just with two hulls in the end.

I think you make a very relevant point here. Everything from production to end of lifcycle has to be taken into account. And yes, why build a ship that needs a lot of extra technology and adds a hell lot of complexity when the Polynesian solved most of the problems thousands of years ago already and their ships are super sustainable by design. Good point! The one argument that was driving us the most is, that we assume that people want a certain level of comfort and maximum stability on board a vessel, be it for the work and other activities they want to do on board, or be it for the fear of seasickness or for other psychological effects. And second, they want to go fast. The SWATH design has proven to provide good speed at rough sea. If we could really manage to achieve equal stability and speed without all the tech, then hell yes, please let's try it this way. On the other hand we know that foiling is driving the yacht races, but I'd assume it is not feasible and reasonable to try to completely lift a big ship with hundreds of passengers out of the water. So that's why going semi-submerged seamed to be the right goal.

I agree. In my ideas Ohanda One would not fully replace air travel, but add an alternative to it. If it really turnes out to be less biocompatible and environment friendly than flying one day, then maybe there is no point for it anymore. But from what I know, most airplaines are still burning fossil fules these days and it might take longer to change that, than to build more modern and sustainable sailing ships.

In regards of (wave) stability and speed, what would you estimate how the design you suggest would behave? Would you assume it was possible to build a larger version of it based on wood?

 

If the wings could lie flat and horizontal in difficult conditions it would become more stable, but then rely on powered propulsion. Replacing the wings with cylindrical drives, rotating drum or internal rotating air pump type may be beneficial, since eg. flettners apparently handle high winds and rough seas well. The interesting concept illustrated in the pdf reminds me of a cross between a floating oil drilling platform, and a futuristic space station.
What speeds do you anticipate under sail; would it keep up with the Cutty Sark for comparison to old world shipping ? Would it be constructed of steel, or aluminium, or composites like carbon fibre etc.? How much energy would the stabilising fins and ballast pumps need in rough weather ? What would the procedures be for riding out a hurricane, cyclone, typhoon, tornado, or even a tsunami ? Would it survive in a total power failure ?

 

Is this for an academic assignment?I suspect gonzo is gently directing thoughts to how a beam reach might impose forces that the SWATH hull isn't the ideal type to deal with and the height of the rig above the initial waterplane compounds matters.

 

The project has been a private initiative so far. It is intended to engage with academia to discuss the concept and its fundamental rationale and feasibility.

It is clear that the height is very relevant in terms of the forces resulting from that. On the other hand, for SWATH we need a reasonable clearance between deck and hull depending on the assumed wave height. The 1:100 prototype has been designed with a clearance of 22 meters. The beam of 42 meters seemed "reasonable" compared to other cruise liners. The resulting ratio could be further optimized in the future. Also, by applying rotating wing sails (the existing square-rigs are used for simplification and to test detrimental positions and situations) and a relatively leightweight deck contruction (compared to the hull) we would try to keep those forces as little as possible. The purpose of the flapping fins and dynamic balast tanks is to compensate the heeling lever (and to adjust and balance the draft) and to keep it stable. That's what we took as a design challange (Dilettante Design Deep Dive https://ohanda.one/dilettante-design-deep-dive/).

 

When we started, we were thinking of flettner rotors, then we switched to DynaRigs and now our preference might be inflatable wing sails. I think there is a lot of dynamic in the development of wind propulsion systems recently. Let's see where we get to until when it becomes relevant for us.

Nice! I like that.

These are all very good questions yet to be answered. Maybe we can gain more insights with a next iteration, since the balloon based balast tanks and other details of the 1:100 scale model do not aggregate the data we'd need to come up with reasonable results here, I suppose. (Balloon Blast https://ohanda.one/balloon-blast/)

 

The type of rig is irrelevant if you can't make a design that has a significant righting moment. A completely submerged hull is neutral and will have minimal stability.

 

15, 000 tonnes is a very heavy vessel

What passenger ports can accommodate 11m - 23m draft?

 

Yes, that's true for sure! In case of the existing 1:100 prototype when submerged the entire righting moment comes from the flapping fins and the automatic ajdustment of the ballast tanks on each side of the hull. I think that in a future version of Ohanda One one could add more static buoyancy and stability by increasing the vertical volumes, but due to the nature of the SWATH design in combimation with sails, the dynamic balancing will remain most relevant, I would say.