Design question

[caradow]

I have been trying to decide between a daggerboard vs. a fixed keel Cat.
I know the conventional issues with both and have actually owned a Voyage 440 for almost 5 years in the past. I originally picked that boat because it actually felt like you were in a sailboat and not a barge. Will not go into the other brands I have sailed but there were several.

I enjoyed the boat immensely as long as I wasn't going upwind or shaken by the loud slap of a low bridgedeck!

So the keel cats can't point and the daggerboard boats risk getting their saildrives and rudders taken off by a floating object such as a log. Not to mention the potential damage that could be done to the daggerboard trunk. That kind of worries me.

This may be a dumb question and I accept my ignorance but has anyone ever designed a cat with a hollow keel that would allow a hinged daggerboard?
Seems cool if it could be done.
Could this add to the actual pointing ability of a conventional cat?

Has anyone that personally sails a daggerboard boat ever sustained damage from floating debris ?

[James Shiers]

I've often wondered the same thing. I was very pleased with the drop keel in my old MacGregor 26X. It was located in an internal housing built into the hull and easily dropped to an infinite number of positions. The drop keel would "ride up" over bottom, rocks or debris and drop back into place. The X keel drafted 6+ feet, yet the boat would draft 9" with keel up and no water ballast. It was a grand design for lake sailing and much more convenient than the daggerboards of the later 26M. If you encounter an X, ask to check out the design ... pretty cool. I've never seen this arrangement in another boat.

[Matt Johnson]

Yes. Chris White did mini keels with a pivoting centerboard. Seemed to work well on the Atlantics that went that route.

But there are other ways to prevent the issues you're worried about. Kick-up rudders protect themselves in a grounding. Outboard motor driven helps too, or a good skegs around the prop shaft or saildrive protects that appendage.

[noelex 77]

I think the aluminium Portofino 52 is produced with a swing keel option.

However, the problem with swing keels is that the open casing creates a great deal of drag.

[caradow]

Ah ok so that defeats the purpose.
Guess then as Matt stated specially designed skeg ,kickup rudders and possibly outboard engines could help alleviate that problem.
So that would probably limit the field to a custom build.
Thank you all for your time and knowledge.

[Matt Johnson]

Not necessarily. The older Outremer had a skeg that protects the drive and rudders. I'm sure they aren't the only one with this, so may be worth checking out the underwater profile of the boats you are interested in.

It would greatly change the hull balance to add one after the fact. So don't think this is an option without a good designer guiding you.

[ozolli]

The Outremer 45v2 and the 49/51 too have a skeg ahead of the saildrive. Don't know for the newer ones though...

[Tin Tin]

Balance 526 has a choice of board or fin keel. The fin version though has a draft of 4.5ft which is deeper than some others. I read some where but can't find it, that the windward performance of the keel version was pretty good though.

[Tin Tin]

Found it

https://www.youtube.com/watch?v=EmkogXjR2sA

[catsketcher]

A large keel with daggerboard is not efficient. That is because the lift characteristics of the keel and daggerboard are very different. The daggerboard will produce lots of lift at low angles of leeway, so the keel, which needs higher angles of attack to produce lots of lift, just comes along for the ride.

So I would think that such a design should have a narrow keel, to reduce resistance of a parasitic foil, but having a long slot in the keel, and the forces of a pivoting centreboard, would require the keel to be wider. So you would get some of the problems of a keeled boat and also of a daggerboard boat.

https://www.youtube.com/watch?v=h5lFXp9u1w0

The above link shows the McConaghy cat with pivoting centreboards. After owning a boat with centreboards, I am dubious about the ability of the boards to deflect kelp and logs, and also the ability of the boards to move easily after a few months of immersion. Barnacles in the case are a pain, as are immersed pivot pins and the long case top is hard to waterproof. Daggerboard cases are surprisingly easy to keep clean, with just a little antifoul on the board bottom and a very close fit between case and board.

As Matt said, most medium sized dagger cats use kick up rudders and retractable motors. My mate's 13.2 metre Schionning uses lifting diesel outboards. I like outboards on my 11.6m cat and have kick up rudders. I hadn't run into anything with my daggers till last week, and although the rock was not floating, it showed how a well set up dagger system can reduce worries.

Phil Berman in his interesting talk, says an advantage of keels is that you can fix them easily after damage. I would agree in part. I damaged my daggers and instead of having to haul my boat again, I removed the dagger and it is now awaiting a new tip in my shed, saving me a huge amount of money compared to slipping and fixing a keel. And it is pretty easy to pop on a new tip compared to working on a damaged keel.

The incident where I hit the rocks with the keel is on another thread

https://www.cruisersforum.com/forums...se-275128.html

cheers

Phil

[Chotu]

I would also like to add one point about the dagger board situation

when you design and build a dagger board catamaran and the trunks, it’s built in such a way that the trunks are much more solid than the boards themselves. The boards are designed to break off if you hit something. That’s the proper way to design it.

so really that’s a non-issue. If you hit a big log with your dagger board or a rock, the dagger board breaks. And then you take the other dagger board and you make a new one from it. It serves as a great plug.

[Cavalier MK2]

Having a shoal keel with a centerboard is a design that goes back for decades. The big pluses are no impact on the interior and having the the pivot pin outside of the hull so no leaks, more hull strength is a plus too as frames and skin are uninterrupted by a slot.

Phil is right in that low aspect and high aspect foils have a different angle of attack but in a seaway that can help you, the low aspect keel is hard to stall and takes over if the boat falls off or slows, the centerboard leads when you get up to speed and keep in the groove. Keeping the slot clean is really a matter of use, you want to raise and lower the board frequently because it isn't as accessible as a daggerboard trunk.

[Kinkircating]

You can add the Kinetic KC54 to this list as well. It is one hell of a sweet full carbon fiber high tech catamaran, only problem it sets you back about $3.3M ready to go blue water cruising.

[Cheechako]

"So the keel cats can't point ..."
Is this true? Why would that be? Or are you talking about cats with just shallow stubs really? ....so little depth?

My Lagoon 42 had fixed keels and over 4 ft of draft and went to weather a bit. Not like a mono really though...

[pbmaise]

Study this picture to understand my opinion on fixed keel versus retractable dagger boards.

I spent over a man week trying and ultimately failing to shift this dagger aboard.

Apparently, a bolt or screw fell into the channel and was lodged in there.

I even inserted a wire rope, looped it around the obstruction and used winches to try and pull it up.

This was a second dagger board built into the main hull. It was located in the cockpit and the perfect spot for junk to fall into it. I ultimately ended up glassing in the dagger board and now had a fixed rear dagger board and retractable main dagger board.