on the design of ultra slim yachts

Bottom view

from the bottom angle

 

Looks like something that would interest Wardi, looks like a really well balanced hull ;-)

 

Henrik - much as I agree with you there, that was cruel (good, but cruel...)

 

This may qualify,

30' loa
5'8" beam on deck
7'0" draft
1900 lbs. displ.

 

excellent Paul, great renders,

your numbers I think are correct, but you may be using a waterline length of over 70 ft, redo them for 68ft, and you should get about 18,000lbs, and 350 square ft of wetted surface give or take. With such a shape, immersed inches up or down make a big difference.

I disagree though on you thinking the boat will not go. I did not really believe that I was going up against professional competition in an around the world race. It was for my own use.

Nevertheless I see no reason why such a configuration should not go to weather with a vengeance. My worry was running. You could not get a cleaner shape both aero and hydro-dynamically.

The idea stems from a discussion in Norwood, where he analyses the growth of frictional versus "form" resistance and concludes that a 13:1 ratio is the upper limit for displacement craft, before planing craft take the upper hand.

You are right, accomodation wise it stinks. I have designed the inside and at a pinch everything fits in, but you would not want to have a party or anything. The only way around it is to go to 7.5 ft diameter - that's where the 100 ft comes in. Then you got structural problems and on to your spiral. At 84ft one person could build and sail it, but at 100ft I say let the french do it.

Of couse, designing the boat for a toe to toe round the world race is not that hard-just make the boat smaller. I was looking for standing head room only-thus the 84ft length. In fact in the smaller sizes the idea may be even more successfull.

So far no one has explained why the boat won't work. I am delighted with the flack so far - it means that there is something worth thinking about here.

Think of this design, not as half a cat, but as 3 quarters of a proa.

 

yea, you see, its not that far fetched, thanks doug.

By the way Paul, there are no "inordinate" stresses in the boat except for the keel versus mast twist: the sail forces are relatively small - I'm talking about a righting moment of 50 to 70 thousand ft lbs - small stuff. I'm sure you would agree.

 

OK 68 feet of DWL

I have changed to a 68 foot DWL (8' overhang per end on 84 foot LOA). It looks like about 380 sq. ft of wetted surface, and about 23,700 pounds (using 64 lbs/ft^3).

The DWL is now 1' below the midline. The BWL is now about 6.2 feet. You are now down to about 11:1 on your DWL:BWL ratio.


The boat Doug shows is nowhere near as long and round as your idea, and by all accounts it is very tippy.

 

hmm...that cannot be right - maybe my mathematics is wrong - oh yea, forgot to mention - IT ALL DEPENDS ON THE SHAPE OF THE HULL - silly me. We are in the same ballpack Paul.

Check you prismatic coefficient - mine is about .57

If you like? I can post or email the excel spreadsheet formulae and calculations for the shape. That will settle queries about shape at least.

What I meant was that it at least is in the right direction. Tippy or not, is a matter of design - narrow does not mean tippy necessarily.

 

I was thinking that the shape was probably different. I followed your comment and simply made the midsection 6.5 feet diameter, and lofted to the ends 42 feet away. Your actual shape could have a sharper lead-in, lead out, becoming tangent to the longitudinal radius somewhere along the line. That would decrease the displacement.

I just made these models to get a good visual on what we are talking about. I don't think I need to spend the time to make a more precise (time consuming) loft to the actual offsets.

But once You do, please post them.

 

yep, no worries, but it will have to wait till after christmas

 

There's some historical precident here, such as the 110 one design by C. Raymond Hunt. I recommend using a VPP to optimize sail area & ballast, and Michlet to optimize hull shape.

Before committing yourself to something so big how about building a mini version using a catamaran hull? Note also: There are some very narrow monohulls in the Moth class.

 

Thanks Stephen,

I have used a vpp for this design, and I think I have optimised sail, keel and rudder- fair comparisons with the big cats, but as I said, the real problem is accomodation. I have to think that part through a bit more, but I will be building a 1 or 2 metre model.

This kind of boat has been raced with success in the model boat field. So there are precedents, apart from the moth class boats you mentioned.

Cheers

 

I should have mentioned the International Canoe class:
http://www.intcanoe.org/
What if you built your hull as an International Canoe? Good opportunity for on-the-water testing against knowledgable people with similar designs.

There was a very slender BOC 60 designed by Dave Gerr, though it never competed 'round-the-world to my knowledge.

You may want to consider whether you have enough room for your canting mechanism. Also be warned: I've heard stories of a canting keel boat with a single hydraulic ram that failed frequently. It was narrow and would just flop on its side in its slip when the hydraulics failed.

 

I have heard of Dave Gerr's boat, and will look up the International Class canoes.

This boat does not require a canting keel: the other alternative is a lifting dagger keel, but this has it's drawbacks too. It is no wonder people go for more conventional designs.

Cheers Stephen, and have a Happy Christmas.

 

Ultra-slim hulls
I don't want to deflect this thread! I just wnt to say that I am drooling over these beautifully rendered hulls and see them as a natural for ultra-slim power boats. I will start another thread sometime.
Will Jones