Bridgedeck centreboard why don't they work???

I think that is approximately the position that my board arrangement assumed?
And I ended up with a larger base with shorter 'arm length' to leverage against?

 

Hey Doug,
What if this solid plate in the dwg was my flat plate nacelle down the centerline of the catamaran, and the two boards (one raised, one down) were the twin asymmetric boards as I have suggested.

Now what if those twin boards were 'modified a bit' (extended) into up-tip foils. :idea:
That just might work on a light-weight cat

 

actually the closing strip is "hinged to the backside of the board"
As the board rotates down, the hinge forces the closing strip (something like a batten) aft and downwards. The inward lip on the case stops the strip from falling out.

 

Gybing and Asymmetric Boards

Last night (asian time) I was going back thru discussions on this forum about gybing centerboards and daggerboards. I ran into this old discussion that got quite involved, and with some knowledgeable contributors,...and covered asymmetric board discussions as well.
http://www.boatdesign.net/forums/multihulls/gybing-center-boards-43772.html

As I've said it gets quite involved technical wise, so many might just well ignore it. Bottom line it appears as though there is only a little to be gained by employing these type boards,...certainly in the contect of cruising boat design,...and certainly if its adds to the complexity of an installation.

Having said that I still am going back to renew my look at the twin centerboard arrangement I have proposed, as I do not feel it will be that complicated to design and build,...in fact maybe even easier than 2 centerboards in the hulls of cats.

 

One of the primary reasons I chose to put that 'flat plate nacelle' down the center of my catamaran design was to give the vessel an extra 'backbone'....ala



http://www.boatdesign.net/forums/sailboats/sail-loading-rig-rig-loading-vessel-2293-3.html

Now that 'flat plate' doesn't really have to be a solid plate at all, it's just a convenient manner to describe it,....more when I find the old discussions/illustrations...

 

You might find this posting of interest, as well as a few others in that subject thread.

Vessel Substructure to Support Rigging Loads

Alinghi was an interesting vessel....

 

if you want kickup foilers here is one idea
these show the forward beam of the bridgedeck -- CRP pipe 40 cm diameter.
boat is moving from left to right and only starboard foil is shown.
The horizontal foil lies partly under the starboard hull - when it kicks back and up the cam forces the foil inboard clearing the inboard side of starboard hull.
There is a mechanical trip that holds the board carrier in position.
Each foil itself is 80 cm long with 40 cm chord
The foils are rotated forward when not in use
The demi-hulls are basically lengthened Woods Gypsy with flat bottoms, no keel.
There is a third foil on the aft cross beam to balance the front 2. It also trips but just straight back.

 

[Translation assistance by Google. No warranty provided. Use at your own risk.]

Dufour T7

Centerboard

A special feature of the Dufour T7. Jean-Louis Noir was an experimental and innovative designer. Later he build numbers of the T7 has provided a Derive Auto-orient able ', better known in English as "Gybing Center Board' which can be translated into Dutch as' Drop keel with self-aligning toe.


Operating principle centerboard to the hauled course




Daggerboard case and water lines



The advantage of a "Gybing Center Board" has never really been proven. My own T7 is - in collaboration with naval architect Peter Bosgraaf - includes a 'fixed' ballasted centerboard. Because the pivot point for more body and under the water line is allowed the length of the profiled sword blade become longer. More length is more effective than the toe. Additional advantages are that the sword loose rattling in the closet on downwind courses and self-falling and rising.

 

Happy Feet

-----------------------
Brian, might work on a boat with a lot of crew. Otherwise, the lift would probably reduce RM? The cat "Happy Feet" had a lifting foil on the forward cross arm(+rudder T-foil on the aft cross) but both were designed to slide to leeward to pick up more of the boats weight and affect RM less. However, they used a wand which could be set for a specific flying altitude after which it would automatically develop downforce, increasing RM. So it could maintain a preset angle of heel without sliding sideways or maintain altitude if it was to the lee side and lifted the whole boat.

Happy Feet ,post 60: the whole nacelle holding the main and rudder T-foils slid sideways....

 

Gybing Boards

I assume you may have seen these postings ?

It just doesn't appear that gybing boards are worth their complications?

 

Gybing Board

Funny about that. Some people swear by them others swear at them. Next comparisons: an asymmetric foil vs a gybing board and vs a symmetrical board. If I was doing it, I guess I'd probably stick with a single well mounted bridgedeck centerboard.....

 

I think what I would do Doug is just make a couple of my twin asymmetric boards out of wood to start out with...perhaps out of laminating up some good plywood. The two boards could be made out of one long length of asymmetric shaped 'board', then cut in half to get the two mirror images for either side.

This would allow one to experiment with several different foil shapes at a relatively cheap price, then either glass these wood boards over, or build molds and do a fancier job in glass, carbon, whatever. The prototypes being solid wood would preclude any fancy bearing fixture for the boards themselves,...just smooth bore holes to fit onto the UHMWPE bearing pins.

And its not like it would be a great problem to change out boards while experimenting,...no hauling of the vessel, and basically just one giant pivot pin mounting them to that flat plate nacelle beam.

KISS principle

 

brian, suggest you build your longitudinal beam with say four 10 mm dia holes for the thru bolt spaced fore-aft over a distance of 1 m to allow the sweet balance spot to be found on the water. Once found, you can then glass the pivot pin permanently into position. and the thru bolt then only has to restrain movement of the boards. Certainly impossible to do with dagger boards.

 

Here is another (concept) vessel that wants to make use of a center nacelle something like I was speaking of,... O yachts

 

O-yachts Spine Concept

'Spine Concept'





more here...
http://www.o-yachts.com/models/class-6