types of keel

[steve2k]

OK, my last stupid question, for today at least.

I always assumed there were 2 types of keel, a fixed keel and a centreboard. As centreboards are more often seen on dinghy's I assume that they are less stable (dinghy's capsize alot) and more suited to smaller boats than a fixed keel.

But looking around the internet this might not be true, however I can't find a useful site to explain the different keel options.

A key selling point for my girlfriend, would be that the boat will not capsize and kill everyone so the issue of keel becomes quite important to us.

Can anyone summarise the keel options?

Thanks,
Steve

<hr width=100% size=1>

 

[AndrewB]

Two previous threads that should help answer this question can be found HERE.

 

[steve2k]

perfect, just what I was looking for, thanks.

<hr width=100% size=1>

 

[boatless]

Fixed single keel. Can be deep with high aspect ratio (Long/thin) for high performance. Shallow, for better access to shallow places, perf not so good. Both may be enhanced by adding a bulb at the bottom, and/or being made of lead as opposed to cast iron.

Long keel. 'Old fashioned' runs down from bow all the way to stern, rudder hangs off the back of it. Looks like a Concord wing. Very easy to steer, not quite as good as fin for ultimate performance.

Twin or bilge keels (or even triple). Won't perform quite as well as a single, but usefully allows boat to sit happily on the ground.

Lifting. Maybe be heavy, perhaps also with bulb, in which case, performance wise it's as good as a fixed fin. Or light, which is easier to get up and down - this usually means that the boat will then have internal ballast. They can swing up, or be lifted vertically.

Stability. All depends on several things. Shape of boat - wide flat will give high 'initial' stability. (Doesn't tip much when you stand at the side). But will happily stay upside down if rolled. Narrow deep is the reverse. Ballast ratio (weight of boat compared to weight of ballast) is an important factor, but an allowance must be made for the depth of the centre of gravity of the keel relative to the centre of flotation. That is - less ballast mounted deeper can be equally effective.

All yachts will, technically, capsize - given a large enough wave. In practice, we all hope that the next big wave will roll it upright again. The angle at which this happens is the best indicator, and on a new yacht the info should be available.



<hr width=100% size=1>my opinion is complete rubbish, probably.

 

[danera]

You do get big centreboard monohulls, for example the aluminum ovni range from alubat in france, upto 45 feet. As other posters have mentioned they contain internal ballast to counteract the lack of a weighty keel.

Note that all recently built boats have to comply with the 'European Craft Directive' which enforces minimum stability requirements making them very unlikely to capsize in the conditions for which they are rated at.

<hr width=100% size=1>

 

[extravert]

Centreboards

Centreboards are used on some multihulls as well as dinghies, because multis do not rely on ballast to keep them upright. They need the board to stop them going sideways, as for dinghies.

For example, Dragonfly trimarans have a pivoting centreboard, Corsair trimarans have a lifting daggerboard.

<hr width=100% size=1>One day, I want to be a real sailor. In the mean time I'll just keep tri-ing.

 

[danera]

Re: Centreboards

To be pedantic, the Corsair F24 mark 1 had a centreboard and the mark 2 has a daggerboard...

<hr width=100% size=1>

 

[alant]

Re: types of keel - Baraccuda of Tarrant

"Baraccuda of Tarrant" the 45' boat featured on 'Howards Way' & built by Bob Fisher, has a big daggerboard - originally manually winched up, but changed a few years ago to an electric winch. Daggerboard held in position with pins (big ones) through the casing.
Also had twin rudders & sailed incredibly balanced & easily steered.

<hr width=100% size=1>