Simple keel/daggerboard concepts for catamaran?

[dustman]

I'm looking for simple and easily deployed keel/daggerboard concepts for a small catamaran. Is there somewhere that has a collection of people's design ideas?

I want to have minimal draft for exploring extremely shallow areas in the bahamas so fixed keels are not really an option.

I have have racked my brain exploring many design ideas but all have drawbacks. Hoping someone out there has had a stroke of genius and shared it on the internets. Doesn't have to be fancy or look good.

The small sails and boards will be for backup propulsion, primary propulsion will be an outboard motor.

 

[bajansailor]

How big is your 'small' catamaran going to be?
Would it be feasible to have a pair of leeboards rather than daggerboards?
I have had thoughts about a cat with assymetric hulls (like a monohull sliced down the centreline), and assymetric foil shaped leeboards mounted on the flat vertical inboard sides of the hulls - you would only use one at a time, on the leeward side to give you some lift.
But I don't think anybody has really done this, so it probably would not work!

 

[dustman]

How big is your 'small' catamaran going to be?
Would it be feasible to have a pair of leeboards rather than daggerboards?
I have had thoughts about a cat with assymetric hulls (like a monohull sliced down the centreline), and assymetric foil shaped leeboards mounted on the flat vertical inboard sides of the hulls - you would only use one at a time, on the leeward side to give you some lift.
But I don't think anybody has really done this, so it probably would not work!

It will be 24-30' with 12' beam. I prefer to avoid any penetrations in hulls. And I want to maintain the highest possible hydrodynamic efficiency to keep powering requirements low, I don't think the asymmetric hull design really fits that bill, though I like that idea. I considered hulls like those of wharram designs where the hulls themselves act as lift devices, but that increases draft and wetted surface area.

What I really mean is any device that will give me lift underwater. Edit: horizontal lift.

There are two ideas I'm considering so far, one is to mount the board on a set pivoting arms so it could go straight up and down, kind of like a-arms on automotive suspension. The other is to have it swing down outboard of the hull on a single arm, so they would go from horizontal while stowed to vertical while deployed, if that makes any sense. The first would be more structurally sound. Both would be easy to deploy and stow even under load. However, I was hoping to have something that requires less infrastructure, something that I can add to the overall structure with a minimum of modification.

Another issue I'm having is deciding the area of the foil relative to sail area. I've seen figures anywhere from 4-10%.

 

[Rumars]

You want leeboards, or a bridgedeck centerboard. The foil doesn't have to look like it came from a dutch barge, you use a modern profiled foil. If you want it depth adjustable at any angle you put the foil into a casette first. It's up to you (and the size ot the board) if you use a pivoting casette or a fixed one with an open back.

 

[messabout]

Take a look at the Hobie 12,14, 16 footers. No boards, they worked pretty well. Yes, they had rudders but the rudders were hinged and cleverly controlled.