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Old 12-09-2007, 11:23   #1
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Center board vs keel vs twin keel vs twin centerboard

I am new here so...

I am looking for an Aluminium hull sailboat about 45 feet in length, I have only sailed single keel boats.

I read robert bray's discussion about twin keels etc.

What type of keel goes upwind the best,
What type of keel provides bad weather stability the best,
What type dries out the best?
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Old 12-09-2007, 12:04   #2
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To the questions you ask there is only one easy answer:

Twin keels go to ground best, but do almost nothing else better than the same boat with a "regular" keel.

To everything else any honest answer has "it depends". If you do not have restrictions on minimum draft, then a fixed keel will do better than a centerboard under most all conditions without the maintenance difficulties.

If you have a draft restriction, then a centerboard might be a good choice, or even a necessary one.

Like everything else on boats this is a compromise. It should be only one of the factors going into the selection of the boat and it all depends on how and where you are going to use it. There is no "right" answer.

Bill
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Old 12-09-2007, 12:37   #3
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twin keels generally have shallower draft than a single fixed keel as well. Although not usually as shallow as a centerboard.

Twin keels also are said to have stability as good or better than a single fixed keel of the same overall dimensions/weight

that said, they do not go to windward as well as other keels, and the increased surface area would probably slow them down a bit in other directions as well.


overall, the biggest benefit would probably be the ability to stay upright while sitting on it's bottom, good close in at low tide as well as after a haulout in a yard. In some situations, you could just forgo the yard altogether and do your work at low tide.

take my advice with a grain of salt, I've never owned a twin keel, but I was looking to buy one not too long ago and did a bit of research on it.
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Old 12-09-2007, 13:34   #4
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Okay I follow so far,

So which generally goes to windward best the keel or the centerboard?

And to put so minimum draft requirements to it, I would say 5 feet, from the water line.

I guess what I am trying to compare is something like the Allures boats, versus, the Alubat OVNI and the Alubat Cigale.

BTW are there any other good competitors for boats like these out there.
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Old 12-09-2007, 13:53   #5
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I have an alloy twin centreboarder that does everything for me, of course there is always a trade off so it depends what is important to you. windward ability is not bad with both boards down, you allow for leeway, you have to shorten sail earlier, but you can still maintain good windward speed. downwind sailing is fast although I tend to tack down wind for that little extra, eased sheets through to reaching you trim board (s) to suit, my hull draws 1m with the boards up,(2 with the main one down) it has a full keel and the base is 700mm at its widest point so it will support the hull for scrubbing on the beach or a designated area without legs although they can be used. <trismus.populus.org> is the Trismus site which has loads of info. you need to read French to get the best of it but the translation makes for an interesting read.
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Old 12-09-2007, 14:11   #6
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So what would your leeway be close hauled say about 45 degree off the wind?

I seem to end up at somewhere between 5 (if the wind can drive the boat fully) and 10 degrees in light wind. This is with fixed keels.
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Old 12-09-2007, 16:38   #7
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At best guestimate between 5 and 15 degrees depending on wind strength, it is not a boat that you can pinch up on, it needs to be sailed free, sail further but faster and you will arrive about the same time as an equivalent fixed keel or maybe even before.
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Old 12-09-2007, 18:02   #8
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If there were one best keel design there would be only one keel design. I think you are better off with your question in post 4. i.e. Which of these boats does XXX better.

Once you get agreement from the community on that (good luck) then you will find a completely different boat does YYY better.

Not trying to be a smarty pants and I may be pointing out the obvious. But the best boat to windward may be completely unliveable as a cruising boat. I'd rather spend 2 days longer on a boat I love to be on than 2 days shorter on a boat I hate...
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Old 13-09-2007, 08:13   #9
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I hear you.

Steve Pope's comment answers were very direct, and cleared up some of my questions.

So lets try again Steve can you compare the twin keel you have to a fixed keel boat, in rough seas, let's say 3m waves and 20 knots of wind. (Pretty common for me.)

From what I have read the twin keel with more and higher ballast should have a slower easier to take motion.

BTW I checked out the trismus site, and though I can plow through in french it is quite a sight.
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Old 13-09-2007, 08:18   #10
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Yes, pinching is a bad habit for sure on any sail boat.
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Old 13-09-2007, 11:47   #11
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jscott, just asking 'how high do you point' is an indication that a centerboard or bilge keel might not be your cup of tea. all said and done; it ends up you sail one mile further off shore than you would with a demon; probably a good idea anyway.
those frenchie alu boats will take you anywhere you want to go with comfort and speed.
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Old 13-09-2007, 12:08   #12
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No honest answer

There's really no way to say any one of these keel types is "better" than another without defining things a *lot* more closely. Like, what does "better" mean when in rough weather? 3m and 20kt of wind isn't "rough" in my area, and I've sailed that with my shallow draft modified full keel 25' sloop reefed tight. In my opinion, better in these conditions is able to put together something hot to eat without having anyone on the tiller. (It also happens to be some of my favourite conditions, so long as it isn't gusty.)

The twin keeler option sounds great in theory, but I watched a yard boss place one very tight in the yard, walk to the bow, and it tipped forward onto a car. Able to take the ground does not necessarily mean it's completely stable there. A better reason for the twin keeler is the shallow draught; that same boat would sail hard on the wind in 3' of water.

Twin keel v full keel in heavy weather would depend on both the weather and many other design factors like ballast distribution and waterlines. A balanced narrow hull with either would have a more comfortable motion than an unbalanced broad hull, but you'd be trading off internal volume and possibly design stability.

Higher ballast, remember, means reefing earlier/more often. Everything is a trade-off. Decide your real, honest use of the boat and determine your priorities based on that. Having a bullet proof deep blue cruiser isn't much fun for daysailing or weekend coasting.
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Old 13-09-2007, 12:33   #13
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Really the only big disadvantage I see is pointing for these types of boats. So I wanted to quantify the effect.

Also I will charter a maple leaf centerboarder shortly so I wanted to have an indication of where to sail it.
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Old 13-09-2007, 12:39   #14
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I follow the part about compromise in the designs.

But not sure I unserstand the rest of it.

So you sail 25 foot monohull shallow draft modified keel, (3m 20kn) and you can go below and comfortably make a meal up.

So I think what your saying is a well designed twin keel, centerboarder etc can do the same?

That would say to me that there is very little advantage other than perhaps some speed to be gained with a keel boat over the other types.

So unless speed (and pointing) are critical the type of keel, is not as important as the overall design of the boat.

I guess in a long day sailer to moderate open water boat you good safely go either way?
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Old 13-09-2007, 14:12   #15
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Quote:
Originally Posted by jscott View Post
I follow the part about compromise in the designs.

But not sure I unserstand the rest of it.

So you sail 25 foot monohull shallow draft modified keel, (3m 20kn) and you can go below and comfortably make a meal up.
No, I mean that's how I would measure "better" for heavy weather sailing. For other people it may mean being able to sail fast and point high in those conditions, or the ability to heave-to in 45 kt and 10m, or having a large enough engine/propeller to punch straight into the waves at hull speed. What do you want to do in weather you consider heavy in your area of sailing?

Quote:
Originally Posted by jscott View Post
So I think what your saying is a well designed twin keel, centerboarder etc can do the same?

That would say to me that there is very little advantage other than perhaps some speed to be gained with a keel boat over the other types.

So unless speed (and pointing) are critical the type of keel, is not as important as the overall design of the boat.

I guess in a long day sailer to moderate open water boat you good safely go either way?
Yes, you could safely choose almost any type of keel to do day sailing to moderate open water sailing. If for day sailing you plan to spend 12 hours working up and down your region, then how deep the local waters are becomes very important to you. If you have plenty of deep water like we do here, a fin keeler and a tall rig may give you more excitement. If you're near shallow cruising destinations, though, a centreboard or twin keel may give you a lot more places to poke into.

The problem is you haven't said *where* you'll sail, or what kind of sailing you already do. Without knowing the context it's impossible to say what keels might work well for you.
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