Non rectangular sterns for non planning boats

[schakel]

Hi,

Today I visited the SA forums
http://forums.sailinganarchy.com/ind...howtopic=77355

And there the new Zeydon 60 is discussed.
http://www.zeydon.com/

I opened a reply there and I am interested in the answer I might get in another forum:

Does any body knows the effect of a non rectangular stern? I mean in the new VOR 70, the IMOCa's and the open 40's the trend is rectangular sterns. Well that is the state of the art isn't it?

But for a non planning boat this might work.

Are these boats rudder stable like a dragon in any angle of heel?

[gggGuest]

I'm not entirely sure what you mean... But its worth noting that like all racing boats the shape of these craft is very much influenced by the rules, which in this case make a lot of form stability from the hull shape desirable. These big wide shapes have, of course, huge form stability which counts for the job they have to do. I think the weight distribution is such that the steering characteristics aren't as upset by heel as you might expect, especially with the twin angled rudders. Don't forget that as soon as you wind on a bit of weather helm with a conventional rudder its tending to lift the stern and exaggerate the effects.

[schakel]

You mean a wipe out?

That's not so nice. I know Paul Cayard broke his ribs while aboard a VOR in a wipe out. There was a video of of the wipe out avaialble on the internet but I can't find it anymore. He was pulled of the ship with a helicopter.

Boy, that must have hurt.

[TYD]

In Naval architect you have to think (as a simplification) that you have a perfect hull shape for three inputs: Lenght, Weight, Stability (Righting Moment). In a sail Boat the Righting Moment dictate how much sail you can carry. Is the same as in a powerboat how much HP do you have. Then you can figure out HP's for as specific lenght and weight and on that point you have a lot of constraints.

For example, maybe the dragon is the perfect design for that weight and lenght. And probably the Open 60' or 40' have the perfect planning shapes for its weight/lenght/righting moment.

[TYD]

''Are these boats rudder stable like a dragon in any angle of heel? ''

Of course NOT.

[schakel]

I knew it,

Lots of of trimming on board. Nice when you have a trimmer on board.

Hey I want to sail the thing very relaxed together with my son and wife.

Okay, I can do the trimming as well but then I start to work realy hard and that is not what I had in mind with a nice daytrip.

Thanks

[gggGuest]

Originally Posted by TYD

''Are these boats rudder stable like a dragon in any angle of heel? ''

Of course NOT.

I'm not saying you're right or wrong, because I don't have enough time on those kind of boats. But are you speaking from experience or supposition? They are, after all, principally designed as singlehanded racers which are run by an autopilot much of the time. Surely they can't demand that much in the way trimming and rudder input, or is the electronics really that good?

[TYD]

From Hull shape nothing is more rudder stable than a Dragon or AC's boat at any angle of heel as ask Schakel. These class of boat are strictly designed to big angles of heel and upwind great performance. And they are practical a cilinder (to simplification purpose). So the hull lines and the Center of Buoyancy doesn't change to much at any angle of heel. On the other hand this Open 40', 60' etc.... were designed to REACH....so with the propper design of Daggerboards, TWO rudders, a AFT positioned Mast, etc.... you can have a CORRECTION the not easy (to drive) hull lines when the boat goes with high angle of heels. Another think is that this Hull (Open class for Ocean Races, not windward/leeward) have canting keel, so the righting moment come from the angle of the keel and not form the heel angle as ocurred on the Dragon or the AC's (maybe old AC's?....maybe the future is multihull?).

Cheers,

[schakel]

Originally Posted by gggGuest

I'm not saying you're right or wrong, because I don't have enough time on those kind of boats. But are you speaking from experience or supposition? They are, after all, principally designed as singlehanded racers which are run by an autopilot much of the time. Surely they can't demand that much in the way trimming and rudder input, or is the electronics really that good?

When you let the steering apparatus do all the work you do not develop the feeling for the wheel or tiller in the way my son develops trimming skills.
I agree with you if you say in the end the trimming isn't that bad.

I once sailed a 16 square metre designed by Bulthuis. When you sail-up wind without trimming, the rudder is almost 45 degrees and takes a bodybuilder to hold the tiller.

I speak from both experience and superposition, but more like sparring partner when it comes to brainstorming.

Once crewed a 13 metre long van der Stadt (Rebel) and she was very gentlle when she overtook wave by wave towards Zeebrugge. This is because she is rudder stable at any angle of heel. You can compensate what she does but you can let her drift along and then you gain most speed and the surfing is fabulous.

Yes sorry.. It is a very important question.

Well I believe these yachts are mighty fine and I would love to crew them when I have the occasion. I am in the middle of a very complex project right now which requirres every second of my attention.

C 'est directive, j me excuse, chapeau pour le awardwinning design