# Foldable catamaran

Discussion in 'Boat Design' started by skatun, Nov 20, 2018.

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?

## Feasible?

3 vote(s)
60.0%
2. ### No

2 vote(s)
40.0%
1. Joined: Mar 2018
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Location: Europe

### DejaySenior Newbie

Thanks for the calculations! Just to avoid confusion, the numbers I posted was meant as an estimate for displacement power needed at 6 kts btw, not hydrofoiling.

What lift/drag ratios are realistic? I saw somewhere foils with > 80 or even >100 l/d ratio, but I don't know at what reynolds number. Is this L/D possible if you design for cruising speed? Assuming you solve the takeoff problem with e.g. ladder foils. I used a coefficient of lift of 1 and coefficient of drag of 0.012 in my initial naive calculations, arriving at 4.2kW power needed with a 0.64m² foil at 20 kts. Seems too good to be true though!

I still need to learn and understand more, and to find good tables on hydrofoils lift/drag for different reynolds numbers. I've been playing around with javafoil but ideally I'd learn openFOAM to optimize a hydrofoil design.

Do you definitely want to design your boat as a hydrofoiling boat? Or just as an maybe option for later? I have a rather crazy idea for a more specialized hydrofoiling motor yacht.

And I'm really curious why there seem to be no designs for a hydrofoiling motor cruising yacht. From what I understand they should always be more energy efficient.

BTW TANSL posted something about calculating the beam here but it's promptly been hotly debated I also have to learn more about structural engineering...

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### skatunJunior Member

How did they managed that? Best glilders have glideratio of 70 and an extreme aspect ratio....
Well I would rather just do AOA change and then reduce power when on foils...

3. Joined: Mar 2018
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### DejaySenior Newbie

Oh of course I don't find it again now... But it was definitely ignoring aspect ratio and possibly purely theoretical. But I found one article about a hydro bike design with high L/D hydrofoils here with used this "Wortmann FX 74-CL5-140" which supposedly has an L/D of 152.6 at 4.5° and rn=1.000.000. But that is an Xfoil prediction.

Honestly no idea, I'd love to know what numbers are ballpark realistic for highest energy efficiency hydrofoiling, just for rough estimations. Assuming you'd design for staying in the drag bucket with laminar flow and high aspect ratio.

About the ladder foils, they could also be useful to give lift a boat some lift at slower speeds to reduce power needed. And help with the liftoff and higher speeds. Only using AOA means Vmax ~ 2 x Vtakeoff.

4. Joined: Sep 2010
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### skatunJunior Member

@Dejay So we are at about the same magnitude, however Xfoil is just 2d and does not take into effect any 3d effects and hence is way to low.

This yacht here :
Sunreef Supreme 68 Power - Sunreef Yachts https://www.sunreef-yachts.com/en/supreme-68-power

Seems to have an extreme low bridge clearance,

this seems to have a bit more bridge clearance:

SILENT 55 https://www.silent-yachts.com/silent55/

However they are both extremly heavy!

I will keep digging more into over the next few months, stay tuned.

5. Joined: Mar 2018
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Location: Europe

### DejaySenior Newbie

Yeah that looks very low on the sunreef but I guess maybe you can make that compromise if you want more space and nicer bedrooms and just do trips in calmer seas. But if it slaps in the marina it would be properly bad.

And yeah the silent55... awesome but heavy. Seems to be the same as the "SolarWave 54" or maybe renamed for the US. They commented they can do 4kts on solar alone 24/7, or much faster of course if you only travel for 8 hours and then recharge the next days. The concept works for the right use profile and with some limitations. And in sunnier regions

The 60kWh battery of the Chevrolet Volt costs something around \$15.000. Quite cheap per kWh but I think it's high voltage and won't be easy to get your hands on.

And yeah I need to learn more about wing loading and reynolds numbers and factor in aspect ratio losses etc, my calculations were just extremely preliminary to see if this could work at all and if it's worth pursuing. I've found one foil NACA 16-1012 that has a Cl=1.092 and a Drag of 0.00334 at a=0° according to JavaFoil, which gives it a L/D ratio of 327. Something that can't be quite right haha.

PS: If you want to see light, the harry proa 50 weights 2 tons empty for a 15m and 10m hull. Much more utilitarian of course.

6. Joined: Sep 2010
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### skatunJunior Member

Has anyone tried to make a parametrized hull?

I would like to give it some boundary condition such as max beam, LWL and max draft, min displacement the do a kriegen optimization in Openfoam for the hull shape. Has anyone gone down this path before?

7. Joined: Mar 2018
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Location: Europe

### DejaySenior Newbie

Marcus Bole talks about something like it for big ships here for his polycad. He also has parametric yacht hulls. TLDR for catamarans is light, long, slender.
There was this one paper to generate a catamaran hull form with openfoam to cancel out the wave interference but I can't find it now. Looked like two opposite S shapes.

Godzilla is using genetic algorithm to optimize hull dimensions and multihull stagger and sizes. I *think* you can use mathematically defined hull shapes that are being varied too. It's based on michlet and michel's thin ship theory so it's very fast.

I'd love to do something like this in openfoam to evaluate hydrofoils. But it's daunting to learn how to use the software and the simulation is much much slower. Do you have experience with openFoam? I'm sure lots of people would love to see your results. Is "kriegen" Norwegian for greedy optimization?

BTW you can buy "like new" 24V Tesla battery modules now for about 270€/kWh on eu ebay now.

8. Joined: Sep 2010
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### skatunJunior Member

Link? Most be something wrong with the numbers

9. Joined: Mar 2018
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Location: Europe

### DejaySenior Newbie

Got the "pm"? Not sure what the policy is on spammy ebay links.
You can also buy single "Panasonic NCR18650B 3350mAh – 6.7A" for the same kwh price from nkon.nl. Which is close to what they used, but possibly with QA and selection process and they are already welded in a module and fused for safety (I think).

Prices will likely continue to come down.

10. Joined: Sep 2010
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Location: Aachen

### skatunJunior Member

so with the price that @Dejay provided it looks like this:

for boatmass 5000kg and like this for 7000kg:

For longer distances we need to sail.... or recharge battery by solar...

11. Joined: Sep 2010
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Location: Aachen

### skatunJunior Member

Just a quick update, its been way to long, but its summer time and hence we have been busy with our current boat, but there has been some progress.
• We went to the USA and talked to a company about welding of the structure
• We have 3d printed and laser cut parts to test folding mechanism in scale 1/10
• We started to gather information in one place: skatun/boat https://github.com/skatun/boat/wiki
• We have done some more windows calculations and research
• We bought a house with docking possibilities
So stay tuned for more updates..

12. Joined: Mar 2018
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Location: Europe

### DejaySenior Newbie

Having a piece of land with my own dock would be awesome

Having a place to build, live in a caravan while building, launch, repair and also to store things when away.

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