Cat Centerboards Single vs Twin.

[Zed]

Could a single central board match the traditional setup of one in each hull?

[Doug Lord]

Originally Posted by Zed

Could a single central board match the traditional setup of one in each hull?

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Yes ,if the surface piercing nature of the foil was understood and dealt with.
The bi-plane rigged cat "Happy Feet" uses such an arrangement. They seem to have good speed but break things too often.
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I just remembered the 27' Stilleto had a single board and was/is a fairly high performance cat: "Stiletto has an unusual single centerboard that varies her draft from a maximum of four feet to a minimum of nine inches; with her kickup rudders, she is easily beachable. "
http://www.thebeachcats.com/Article124.html

[Zed]

Originally Posted by Doug Lord

Yes ,if the surface piercing nature of the foil was understood and dealt with.

Meaning?

Simple Engrish PLS!

[Zed]

Originally Posted by Doug Lord

I just remembered the 27' Stilleto had a single board and was/is a fairly high performance cat: "Stiletto has an unusual single centerboard that varies her draft from a maximum of four feet to a minimum of nine inches; with her kickup rudders, she is easily beachable. "
http://www.thebeachcats.com/Article124.html

Cool, thanks.

Any benefit in tacking?

[Doug Lord]

Originally Posted by Zed

Meaning?

Simple Engrish PLS!

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1) angling the board slightly forward( about 7 degrees) of vertical to reduce the chance of ventilation
2) and,if necessary, adding a fence to the board a few inches below the point the waters surface contacts the board when the windward hull is just slightly out of the water.

multiple fences:

[Zed]

This is because of the lack of a hull/end plate so to speak... no?

[Doug Lord]

Originally Posted by Zed

Cool, thanks.

Any benefit in tacking?

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Thats a good question. A cat with twin boards can use twin asymetric boards or "toe-in" the daggerboard trunks so the boards eliminate the hull drag associated with leeway. A single board would either have to use a trailing edge flap or rotate a few degrees to windward tack to tack(gybing board) to match the effectiveness of the asymetrical/toed-in boards. Even with this the single board has an edge in weight and ease of handling.
However, if you want to generate vertical lift there is a whole 'nother set of considerations.....
Tacking is not affected one way or the other that I have been able to tell.

[Doug Lord]

Originally Posted by Zed

This is because of the lack of a hull/end plate so to speak... no?

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Yes, sure. The hydrofoil Moth has a similar problem when sailed upwind level and to a lesser extent when sailed with veal heel. They've used the angled forward daggerboard "trick" successfuly w/o fences.

[Zed]

[Doug Lord]

Cool-thanks!

[sabahcat]

comment at 55 seconds

"so busy trying to make money at the moment its great"

Always someone to fleece in Thailand eh

[Zed]

Yeah noticed that comment!

I like the boom gooseneck/vang configuration.

How to they manage mainsail twist? Or don't they?

[ThomD]

Didn't simpson do a cat like that, and Chris White has one, ad K-designs.... .

A lot of them have been done, and yet it really never seems to become standard. So for instance consider the Tikis, somewhere in there Wharram gets the religion on foils and starts adding these relatively hidious fixed keels. If there were some standard well understood details for a mid mounted one that could be pulled in when the next Perfect Storm comes along it would seem a natural. Not making a point, just wonder about it from time to time.

Also, it depends what you mean by "match". A similar boat with central spar and lateral boards woould structurally be possible in wood, while I suspect Happy feet had to step it up to carbon fiber.

[rayaldridge]

I think a better approach than a central board is one daggerboard in one hull. There's really no necessity to have twin boards. All of John Shuttleworths cruising designs use a single board, I believe, and he says he conducted thorough tank tests.

The Stiletto was fast with a single central board, but faster with boards endstopped by the hull.

[Zed]

I want to avoid cases exiting into the water on a moored boat.

Thom,

I would like to retain windward performance as much as is possible. Yes it never has caught on so I ask why? What don't I know? Am I missing something big?