Lifting keels in motor boats ?

A lifting ballasted keel would give adjustable static stability, so the roll period would be variable.

How about an electronic roll sensor that lowers the bulb keel if it detects a big roll motion, and lifts it up if it's only a small roll: just like active stabilisers but only acting in a vertical plane?

 

That design I posted is attributed to Dixon yachts, patented I think.

Looks very vulnerable to jamming!!!

 

Why not use a very large upside down 'wing' keel, just like an aeroplane wing, with lots of dihedral. This would give you dynamic anti roll force as you motor along. The more dihedral or v shape between two wings, the stronger the self centring force is exerted.

I used to fly RC models, and my first model had lots of dihedral: if a gust of wing blew it off course it would correct itself very quickly without any input from the pilot.

Not sure exactly how big the wing would have to be to exert enough self righting force, But A wing twice the size of a paravane would be about the correct size; and of course paravanes are wings but the wrong way up.

 

How much power would be needed to move the mass quickly enough?

 

The reason dihedral in the wing of an aircraft causes the aircraft to tend to return to an upright position when the aircraft rolls is slightly complex. When an aircraft rolls the lift vector is tilted and the aircraft moves sideways in the direction of the lowered wing. A wing positive dihedral (tips higher than center) which is moving sideways as well as forward will have increased lift on the side in the direction of the sideways motion, and decreased lift on the other side. This difference in lift between the two sides results in a moment which tends to roll the aircraft back to horizontal. Without the sideslip there would be no difference in lift between the two sides of the wing.

 

The bulb keel would weigh a lot, so it would drop very quickly under its own weight; as it dropped it could pressurise an air accumulator tank to assist raising the keel. A pneumatic system would be very simple to maintain and pressurise with a standard air compressor, either electric or engine driven.

 

Boats with conventional stabilisers yaw (same as side slip?)as they are stabilised by the fins, would that yawning motion also occur with a large wing keel with lots of dihedral?

 

A simpler way of controlling roll would be to put a small 'rudder fin' on the bottom of a very long keel leg, like a vertical aligned stabiliser fin. If the boat rolled to starboard the 'rudder fin' would turn to starboard which would produce a large dynamic force to counter balance the roll forces, and because it's on the end of a long 8' keel it would exert considerable leverage.

The advantages over conventional stabilisers would be:

Only one fin needed.
one through hull fitting.
One actuating mechanism with shaft.
Keel could swing backwards if struck.
No need to vary the length of the keel.

It would work rather like an asymetric dagger board, but with variable control.
Would this produce yaw?

 

Because of the large leverage at the end of a long daggerboard, a small rudder Something like this might work.




...or static and dynamic stability.......