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Old 04-10-2016, 12:37   #1
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Beam vs Keel Depth - Which is more Efficient?

Can you fully replace a keel with a beamier design (or vice versa), or is there always a balance to be struck between beam and keel depth?
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Old 04-10-2016, 12:48   #2
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Re: Beam vs Keel Depth - Which is more Efficient?

You would hope that the yachts designer has done his homework and reached the best compromise. Many yachts have different keel options, this would be an interesting start point. Our bilge keels are about 600kgs heavier than the deep fin keel version, but you wouldn't know looking at the water line.

However, the one yacht (34 ft) I know which had a new cast iron keel fitted came to £7000 for the casting from the original foundry.

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Old 04-10-2016, 13:34   #3
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Re: Beam vs Keel Depth - Which is more Efficient?

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Can you fully replace a keel with a beamier design (or vice versa), or is there always a balance to be struck between beam and keel depth?
In a word, yes. Though at either end of the spectrum, the boats tend to be more extreme, as well as having a fair amount of drawbacks. And when it comes to design, the old saying is true (but for a few materials advances). In that "there's nothing (or little) which hasn't been tried before".

Spend some time at the Amateur Yacht Research Society www.AYRS.org They have info on all kinds of obscure, & unique boats & concepts, going back a looong way. And if you do much digging, you'll find things which are "new" to sailing, that were tried a century or more ago. Just look at Nat Herresoff.
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Old 04-10-2016, 13:41   #4
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Re: Beam vs Keel Depth - Which is more Efficient?

Yes. I gather you are thinking of resistance to heeling. Beamier boat: initially more resistant to heeling than a skinnier deeper keel, but there is a little more to the story than that. As far as "efficient" do you mean which keeps a boat up better or which delivers faster boat? My narrow boat goes faster when heeled. A beamier boat is designed to sail best with less heel than mine. Check Marchaj's book for the graphs comparing the different designs.
https://www.amazon.com/Sail-Performa...ywords=marchaj
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Old 04-10-2016, 13:49   #5
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Re: Beam vs Keel Depth - Which is more Efficient?

Yes, look at a catamaran. There are consequences to wide beam, no keel, means very poor or no self righting ability. You can go real skinny and deep. Not much room, heels easily. You can go narrow no keel, eg capt voss's sailing canoe Tillicum. But you lose much of your windward ability. You are always going to need some sort of centreboard or keel to make any ground to windward.

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Old 04-10-2016, 14:06   #6
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Re: Beam vs Keel Depth - Which is more Efficient?

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But you lose much of your windward ability. You are always going to need some sort of centreboard or keel to make any ground to windward.
Exactly. Still an interesting physics question (perhaps!) but a keel or skeg or whatever is necessary to keep a hull moving in the direction it is pointed and not side-slipping, something an increase in beam will not fix.
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Old 04-10-2016, 14:12   #7
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Re: Beam vs Keel Depth - Which is more Efficient?

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Originally Posted by TitoSoto View Post
Can you fully replace a keel with a beamier design (or vice versa), or is there always a balance to be struck between beam and keel depth?

If you get wide enough you can skip the keel altogether, but then you will be sailing a scow or a catamaran.


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Old 04-10-2016, 14:22   #8
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Re: Beam vs Keel Depth - Which is more Efficient?

I first posted this in the multihull thread but it got moved, so I suppose I meant this in the context of beam width of a multihull of some sort...
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Old 04-10-2016, 14:34   #9
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Re: Beam vs Keel Depth - Which is more Efficient?

Google initial stability and form stability.
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Old 04-10-2016, 16:07   #10
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Re: Beam vs Keel Depth - Which is more Efficient?

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Originally Posted by TitoSoto View Post
I first posted this in the multihull thread but it got moved, so I suppose I meant this in the context of beam width of a multihull of some sort...
In a monohull, a keel plays two main roles, controlling stability and leeway.
In a multihull, a keel does not contribute to stability, just to leeway.

For reducing leeway, beam width has little or no effect. Any form of keel or dagger board is the primary factor.

(Note, this is all an over simplification, but to a first approximation, it will do)
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Old 04-10-2016, 16:14   #11
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Re: Beam vs Keel Depth - Which is more Efficient?

Yes catamaran vs mono.
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Old 05-10-2016, 00:39   #12
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Re: Beam vs Keel Depth - Which is more Efficient?

This is the basic difference between a mono and a cat.


Yes a cat won't come back up if it rolls but it's far less likely to roll and it's far less likely to sink if it does roll. In the end unless you do something stupid, it's pretty much a non-issue.
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Old 05-10-2016, 08:59   #13
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Re: Beam vs Keel Depth - Which is more Efficient?

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Can you fully replace a keel with a beamier design (or vice versa), or is there always a balance to be struck between beam and keel depth?
Back in the late seventies, when a Belgium sailor (Patrick Van God), who wrote extensively in French sailing magasines, traded his full keel, heavy displacement 40' steel sailboat for a light displacement full centerboard sailboat, he started a centerboard sailboats "fashion" in France & elsewhere. I sailed, back then for a couple of months, on my C&N 31 full keel sailboat with two French people & their children. At "anchorage", they would lift the centerboards & put the nose of their sailboat right on the beach where their 3 kids could jump & play while they went fishing with us... Real cool He also brought back to France a "new" internal layout for cruising sailboats that he learned from a DIY american sailor from the West Coast i.e. The head at the foot of the companionway & forward, an open layout with the main centerboard housing in the middle of twin passages on port with the galley & on starboard with the chart table. The centerboard housing was excellent to hold yourself whether cocking or working on the charts & since you could use both to move forward it wasn't much of a nuisance Cheers
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Old 05-10-2016, 09:40   #14
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Re: Beam vs Keel Depth - Which is more Efficient?

Alain, thanks for posting pics and story. Enjoyed it.
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Old 05-10-2016, 09:45   #15
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Re: Beam vs Keel Depth - Which is more Efficient?

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Originally Posted by ALAIN97133 View Post
Back in the late seventies, when a Belgium sailor (Patrick Van God), who wrote extensively in French sailing magasines, traded his full keel, heavy displacement 40' steel sailboat for a light displacement full centerboard sailboat, he started a centerboard sailboats "fashion" in France & elsewhere. I sailed, back then for a couple of months, on my C&N 31 full keel sailboat with two French people & their children. At "anchorage", they would lift the centerboards & put the nose of their sailboat right on the beach where their 3 kids could jump & play while they went fishing with us... Real cool He also brought back to France a "new" internal layout for cruising sailboats that he learned from a DIY american sailor from the West Coast i.e. The head at the foot of the companionway & forward, an open layout with the main centerboard housing in the middle of twin passages on port with the galley & on starboard with the chart table. The centerboard housing was excellent to hold yourself whether cocking or working on the charts & since you could use both to move forward it wasn't much of a nuisance Cheers
I like it! In certain areas that would be great.. or how about...
https://farm1.staticflickr.com/118/2...0204961f_z.jpg
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