Daggerboard versus keel fin on cruiser

[Mick@itc]

Hi
The boat design I like has both a daggerboard or keel fin option. The boat will be purely cruising so there is not a racing reason. But to those who have an opinion on the subject...please tell me which you think is better for a 55 foot cruising catamaran.
Looking forward to hearing from you!
Mick

[michael pierzga]

A dagger board is a one trick pony.

A keel is versatile. the boat can sit on it, it protects your drive gear and it can be used as a fuel, water or waste tank.

[cavalier mk2]

I'd say use shallow keels for beaching, grounding protection and thin water use and a daggerboard for the trick it does so much better. If you must have a larger keel put the waste tank there so you don't lose your fuel or water in a bad grounding.

[michael pierzga]

yes indeed...waste tank. Because multihulls are so shallow bilged they have great difficulty with " downhill" plumbing and drainage. A box keel solves this issue. I see a rather nice , 15 meter, Sporty, carbon rigged cruising cat hauled at the shipyard. She has both stubby keels for grounding and tankage plus daggerboards. It looks like an expensive professionally designed, custom built boat.

[Corley]

Chris White's Atlantic catamarans have a LAR keel plus a daggerboard (or it could be a centreboard) mounted in the LAR keel housing it looks like a very good system.

[Mick@itc]

Thanks for the replies all...good feedback. What's a LAR?
Thanks
Mick

[Corley]

A LAR equals Low Aspect Ratio keel. Its similar to the normal beaching keels seen on lots of cruising cats.

[Mick@itc]

Also just after I posted I found this...
http://www.sailingcatamarans.com/Keelsvboards.htm

That's good as it gives me the understanding...now would like to hear opinion of users of both.

Thanks to all

Mick

[CatBuilder]

The thread is going in the right direction.

The best bet for simple cruising is a LAR (very small) keel - just enough to rest the boat flat, but not more, combined with a dagger board that comes out of the middle of the LAR.

This is the LAR on a Chris White. A bit too much keel, IMO, but it works.



If you want skinny draft and better performance (which means sailing instead of motoring, not pushing the limits), you go for dagger boards without the LAR.

The article by Richard Woods linked to above really nails it too. Nothing in there that isn't true.

Regular keels though... are for monohulls.

[michael pierzga]

The fast French cruising cat hauled at the shipyard has two daggerboards and long stubby box keels. The boards penatrate the hull skin on the outboard side of the hulls, at or just below the waterline. The lifting tackle is a halyard. Looks logical and easy to use.

[catsketcher]

I have the very shallow keel and daggerboard set up on my cat and I like it. It gives me a knockabout place to rest my boat on when out of the water and I get the benefits of daggerboards because personally I value sailing performance highly.

We can beat very well to windward. A lot of our fellow cruisers motor instead. We tend to get there at the same time or in front when they motor. Also a boat that really goes to windward well will feel fabulous when eased off 15 degrees. A boat that can't point will still feel hard on the wind.

My wife prefers the motion of our cat going to windward rather than running.

cheers

Phil

[cavalier mk2]

The big keel addition on our boat created a speed bump on a fast hull. Richard Woods site comments really nail it. We are going back in the other direction to shallow, thinner keels for beaching and putting in a trunk because we sail to windward and motor very little. In defense of keels I think it important for sailors to identify what kind of sailors they are. There is nothing wrong with the keel approach, for many people cruising has plenty to keep them busy and they aren't looking for every knot. As their skills sharpen though performance becomes worth pursuing for some. We actually go sailing to sail so we try to take the bumps out of the performance envelope.

[michael pierzga]

Im out on the water two hundred days a year with a 4 meter draft fin keeler with inboard sheet leads and it hauls ass to windward. I rarely see any boat sailing to windward.

Its logical that if you prefer not to beat that you avoid expensive apendages , tight sheeting angle deck layouts which increase windward ability, stress the yachts structure and comprimise livabilty. . A boat that can get 40 degree ap wind angles is OK for 99 percent of all cruisers.

[cavalier mk2]

We even see people motoring downwind ! In the NW the wind usually channels through the inlets so it is either upwind or down wind. We actually do pretty well to windward but are after all improvement for what amounts to 50% of conditions. 4 meters of draft would eliminate many destinations open to daggerboard boats or shoal keelers....

[Bruce Woods]

Originally Posted by CatBuilder

The thread is going in the right direction.

The best bet for simple cruising is a LAR (very small) keel - just enough to rest the boat flat, but not more, combined with a dagger board that comes out of the middle of the LAR.

This is the LAR on a Chris White. A bit too much keel, IMO, but it works.



If you want skinny draft and better performance (which means sailing instead of motoring, not pushing the limits), you go for dagger boards without the LAR.

The article by Richard Woods linked to above really nails it too. Nothing in there that isn't true.

Regular keels though... are for monohulls.

You seem very knowledgeable. Have you more experience than chris white?
Check out whites latest atlantic keel setup.....

From his website.....


Beneath the waterline:
Forget the daggerboards! I know, I know, this is heresy. Burn me at the stake!

It's clear from the performance of the Atlantic 55 and A57, which have fixed fins and retractable boards, that upwind performance with the boards retracted is still quite good. Basically, if a cat is reasonably light, has an efficient sail plan and some type of fin under the hull, it will sail well. Daggerboards are vulnerable to breaking if you hit something. Both daggerboards and pivot centerboards are heavy, expensive to build and get in the way either on deck or inside the accommodation spaces. Everything has its price.

So the question becomes, what can be done to improve the efficiency of the hull fins to daggerboard level without making them excessively deep?

The answer: put a flap on the trailing edge of the fin. This makes so much sense. It is simpler to construct and maintain, weighs very little and is not vulnerable to damage. Yet a flap has the ability to dramatically improve the performance of the fin.

Let me explain: The typical symmetrical daggerboard creates zero lift unless the hull is sailing a little bit sideways in the water. In order for anything beneficial to result from the increased draft of the daggerboard it must go through the water at some "angle of attack" to the water flow. Normally a good sailboat going to windward will be "making leeway" of 3 to 5 degrees. This means that the boat is turned 3 to 5 degrees to the rush of water coming along the hulls, which is highly inefficient. Unless the hulls are operating at this inefficient angle to the water flow the boards have no angle of attack and cannot provide any lift to combat the sideways push from the sails. So in order to get "lift" from the board you need to accept an offsetting "drag" penalty from the hull.

What makes the most sense is to have an underwater foil that is adjustable so that it can provide lots of lift while the hull tracks nearly straight thru the water. By far the simplest way to do this is to install a flap on the trailing edge of a fixed fin.

I can see all sorts of beneficial uses for fin flaps beyond just sailing to windward. They can be used to balance the boat under different sail trim. They can be used to combat crosswinds in a docking situation. They can be very effective sailing down wind too. Flaps set at negative angles will reduce drag and help "push" the boat to leeward which is just what you want when deep reaching.

There is even the possibility for using the fin flaps as a built in drogue. By setting them in opposite directions at high deflection angles they will be very effective "brakes" and could be handy in conditions where you need to slow down. Each flap will have an independent control and will be adjustable from the helm station.

Regards