# Hull shape optimization

Discussion in 'Sailboats' started by rapscallion, Sep 2, 2007.

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### rapscallionSenior Member

Is there any software out there that I could use to find out if it is a fast shape?

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### tspeerSenior Member

If you are designing long slender hulls at zero leeway angle, take a look at Michlet.

3. ### Guest625101138Previous Member

Michlet has an optimising component termed Godzilla (Genetic Optimisation and Design of Zoomorphs Is Leo Lazauskas's Acronymworks) that is effective for displacement mode in smooth water. You can set a wide variety of constraints as well.

I have got good correlations for drag using Michlet with a variety of small displacement hulls having L/B in the range 4 to 30. Godzilla utilises Michlet by continually refining and testing hull shape variations at about 1000 iterations per second on a typical desktop computer.

I have built three hulls based on Godzilla output and they performed to expectations although I had to do some back calculating as I am never able to get the weight as low as I plan. (Just too optimistic)

It takes a while to learn how to use Michlet/Godzilla but it is definitely faster than building a boat and testing it. I have done primitive tow tests and Michlet is more accurate than I can achieve at scale level. I think you would need a large tow tank to avoid boundary conditions in order to achieve a more accurate result than Michlet can produce. Then think about all the variations on the model that you would need to make to better the 1000 a second that Godzilla can analyse.

If you have a problem that suits Godzilla I can get you started with it.

Rick W.

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### rapscallionSenior Member

Godzilla sounds exactly like what I'm looking for. I want to design an 8 meter sailboat that sails like a sportboat but has standing headroom.

would that work in Godzilla?

5. ### Chris OstlindPrevious Member

Tough sled at that length

Raps,

Godzilla and Michlet might be two tools which you would use for the hullform optimization of a boat as you describe, but they aren't going to address the business of obtaining standing headroom in an 8 meter craft that will go like a sportboat.

Sportboats do not, as a rule, have very roomy cabin environments. Making your optimal boat tall enough to allow for full standing will raise the cabin height. This will, in turn, make for higher windage drag as well as weight, making for a slower, non-sport boat-like performance potential.

If you really want to stand-up inside (without going to a poptop hatch) you'll probably need to make a bigger boat.

Here's an example from Jim Antrim about how to get full standing headroom in a fast multihull http://www.antrimdesign.com/trimarans/84cruiser.html and this one is 40' LOA.

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6. Joined: Feb 2002
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### tspeerSenior Member

When you say "sportboat" I assume you mean a hull that planes. Michlet cannot handle the dynamic lift of a planing hull. It's strictly for the displacement speed regime.

7. ### Chris OstlindPrevious Member

Raps,

Are you still searching for the headroom answer for the possible multihull in your dreams, or have you switched gears to address a monohull as Tom infers?

I remember this same question regarding the desire to build a trimaran with standing headroom a little while back and applied the answer as it would suit.

I don't see any reason why you couldn't apply the term, Sportboat, to a very fast 8m tri as well, headroom issues not withstanding.

8. ### Guest625101138Previous Member

I get the impression that you are talking about something going well beyond displacement speed for an 8m boat. You want hull/s that will plane readily. This is not a regime that suits Godzilla. Godzilla does not handle roll either so would not be much good for a monohull unless you plan on a canting keel or movable ballast to keep it upright.

If you were considering a multihull then you could optimise the light air performance of the hulls. It is possible to constrain sections and profile to flatter sections that would plane more easily. So Godzilla might be useful for getting bottom end performance optimised.

For displacement mode of operation, speed is related to length. If you want to sustain speeds above 10kts then you need to be considering something over 15m long.

This may seem ridiculous if you have a concept of a typical yacht. If you start thinking more along the lines of a beamy rowing 8 with sails then you can get a fast displacement boat that is very easily driven. The practicality will require some lateral thinking. A bit like what is applied to 16ft wide trailable cats and tris. You might want to be able to fold or collapse the hull. Some rowing 8s are made in pieces to make transport more practical.

I the last 50 years you see yachts getting longer and thinner hulls so this is just taking evolution to the optimum. Staying in displacement mode but going relatively fast. Weight and cost are related to volume not length so cost is not likely to be a constraint. Displacement mode means it is easily driven so you keep rig and loads low.

Rick W.

Are they?

10. ### Guest625101138Previous Member

I have an example of a 7.2m (24ft) low volume trimaran attached. The main hull is built from carbon fibre over a foam plug. It cost under AUD450 in materials. It has a design displacement of 100kg. This boat does 7kts with 150W.

If you move up to a 15m hull of similar proportions then displacement gets up to 1 tonne and the cost for the main hull estimated at AUD4,500. For real accomodation you need to go longer or beamier. Depends on what speed you want and still have an easily driven hull. Going up to 20m you would be looking at the hull costing around AUD20,000. Still a low cost for a 20m hull displacing around 3 tonne. Sails would be less than a typical 3t yacht because you have an easily driven hull capable of 12kts with very little effort.

What I am suggesting is to think of long narrow displacement hulls and very small rigs compared with wider higher powered planing hulls.

Rick W.

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11. Joined: Oct 2006
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### rapscallionSenior Member

I have 2 seperate projects in mind. The first one is a 30' multihull with standing headroom but faster than an F-27, and a Catry 27. I have help lined up with the build and I have a killer discount on materials.

The second boat I want to build is basically a Stealth 8M or a T8sc.... but altered a bit for standing head room. The stealth has 5'4" now, I just want to add 3" of freeboard and 3" to the deckhouse to get the headroom and build it out of s glass instead of carbon fiber.

Sportboat is the wrong word, how about performance cruiser?

12. ### Chris OstlindPrevious Member

The first one is easy, Raps. Go to Sweden, take the measurements off the SeaCart 30. Replicate the build techniques with all the exotic stuff you can muster and add a few personal amenities inside to get it just a bit more livable. Oh, yeah... push the deck height up to your suggested standing headroom and hope it still cranks like you want it when you sheet in.

The Seacart secret? Ultra-tech build methods with carbon everything all packed into a huge autoclave and Wham... out comes a really light and really stiff boat. Eliminate the heavy folding mechanisms and be willing to put-up with assembling the boat whenever you want to use it. Recognize that the interior is pretty darn Spartan to save a bunch more weight. And on and on the list goes until you have a really dedicated, near total, full-on race machine that will fly the main hull at will (no discussion here about planing main hulls because it doesn't matter much, you're flying the hull anytime you want)

The monohull is another set of problems, but similar outcomes when looking at the SeaCart build methods and material choices.

All this is going to be very large money, discounted materials and labor understood... but you already knew that. Not to put the hit on your design work, Raps, but if you are spending this kind of dough, why not get a big time designer like Marc Lombard, Nigel Irens, VPLP, or Jim Antrim to do the full tomatoe on the design function? With the cash you are saving from the build, you can now afford a hot pencil outfit like one of those shops and do the whole thing first class.... Leaving little doubt as to the claims you may make when the boat is done and on the water.

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13. ### xaraxPrevious Member

It seems that you have to go MUCH longer if you want standing headroom...

14. Joined: Oct 2006
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### rapscallionSenior Member

You are right... If I had the unlimited funds I would probably go with the seaon 9.6... but I don't have that kind of cash.... The best I could do (if I'm lucky) is build the D30 in sglass. And that can only happen if I can find a place to do it that won't cost me an arm and a leg...

I was just looking for tricks or insights into making the project more affordable/likely to succeed.

The monohull design seems to be the Ross 780. That boat fits all of the requirements on my list. I think I could build that boat for less money than it would cost to ship one to the states...

can you think of other designs similar to the 780?

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### PI DesignSenior Member

What about a Dragonfly 920 Extreme for the tri?

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