Bridge deck mounted centerboard/dagger board

[SV AURA II]

Looking for any information on catamarans with dagger board mounted under the bridge deck. Specifically larger cruising cats.
I have an 12m aluminum Cat and wanted to know if it is feasible to fit a pivot mounted dagger board under the mast compression point. I understand there would need to be some strengthening and lifting/lowering mechanism, possibly hydraulic.
Would one large board, midship, it provide the necessary lift to increase pointing ability and reduce leeway?
Photo for reference attached

Thanks

[GRIT]

Kelsall designed a few. They weren't popular though.

There was one in Georgetown Bahamas last week, and I believe it was 22m (72 feet) long, with centre board and centred rudder.

I also saw a 13 or so metre Kelsall cat with the same setup in Puerto Rico back in 2008.

Good luck.

Cheers.
Paul.

[SV AURA II]

Thanks Paul...I'll see if I can search some images.

[tkeithlu]

I'm thinking "be cautious" on a retrofit of this sort. The lateral load all the way up in the bridge deck is going to require some framing, first at the level of the pivot and then at the top, right in the middle of the cabin. The lever arm will be much longer than with a hull mounted centerboard and in an area that doesn't have the rigidity inherent to a hull. Then let's add strength to withstand an impact at speed. If you've got a leeway problem, I hope that you will compare dealing with it through two boards in the hulls with this design.

[smj]

Our old Cherokee 35 catamaran came from the factory with a bridgedeck mounted center board. I believe they realized it was a mistake and the later ones had mini keels, and most of the older ones opted to remove the center board and install the mini keels.
I couldn’t imagine how much seaweed and crap they would catch while sailing.

[psk125]

tkeithlu brings up pertinent structural and design questions. Putting centerboards in the hulls will disrupt the interior spaces. Would leeboards be at all feasible? They wouldn't need a trunk and might be simpler to engineer, fabricate, and use.

[tkeithlu]

Or maybe mini-keels long enough to still allow beaching?

[psk125]

Another good idea. Simpler and probably cheaper. They will add wetted surface, but if the goal is to avoid leeway, they should help. Brings us to the question as to whether the excessive leeway is due to pinching. Heading off can sometimes increase VMG to windward, and would automatically reduce leeway.

[Matt Johnson]

Crowther, Oram and a few others have designed cats with just a single large daggerboard in one hull. It seems like that would be easier to retrofit too.