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Old 12-08-2013, 20:41   #1
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Two is Better than One: Keels

What are the design tradeoffs between one keel or two?

**Advantage one keel
Less leeway
Greater moment arm to resist gusts
? Thicker / stronger


**Advantage bilge keels
Less stress at keel hull joint
Less draft
Easy upright Beaching
More friction (against rolling)
Bounces off light incidental groundings (rolls a shoulder)
? Less likely to trip over keel in large waves

Is one keel definitely better for blue water?
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Old 12-08-2013, 20:46   #2
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pirate Re: Two is better than one: Keels

Only if your a stick up yer ass 'I can point higher' racer...
but for cruising.. probably better..
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Old 12-08-2013, 21:13   #3
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Re: Two is better than one: Keels

I like the 2 keels on my Nomad.

The original owner sailed it from the UK, across the Atlantic, and all around the Gulf, and eventually sold it in Houston.

She's a strong, reliable boat. Not fast, but what can you expect from a 22' boat anyway? If you want fast, get a Citation X!

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Old 12-08-2013, 21:45   #4
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Re: Two is better than one: Keels

Biggest drawback to bilge keels is dramatically increased wetted surface area=slow boat.
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Old 12-08-2013, 23:48   #5
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Re: Two is better than one: Keels

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Originally Posted by minaret View Post
Biggest drawback to bilge keels is dramatically increased wetted surface area=slow boat.
More of a pain in the ass to clean as well, but it's not like any of them are easy.

I'd be fine with a twin keel arrangement. Not really popular on the western coast of the US; I think it's a British thing primarily.
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Old 13-08-2013, 00:53   #6
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Re: Two is better than one: Keels

My bilge keels are awesome. Depends on the boat. The Centaurs go to weather fairly well, but the keels were well designed and provide lift. Shes easy to work on the bottom, drying out on the tide, and its motion in a seaway is very kind and a think a great part of that is her keels.
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Old 13-08-2013, 01:02   #7
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Re: Two is better than one: Keels

A lot of folks bag twin keels, or bilge keels as we knew them in the UK, but most of it is like a lot of things, more word of mouth than true experience. I learnt to sail way back in the sixties on a bilge keeler. 18' Caprice, a Robert Tucker design built by my father in the garage. I owe it a lot.

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Old 13-08-2013, 01:11   #8
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Re: Two is better than one: Keels

Twin keels are less efficient. Same reason there are not many biplanes around now. One wing is better than two.

The overall weight of the keels and therefore the overall displacement of the boat is higher, or the center of gravity is higher. Sailing performance is impacted either way.

If you run aground, you cannot reduce draught by heeling the boat.

Applying bottom paint is more of a P.I.T.A.

There is much more torsional strain on the hull to keel joint.

But,

not everyone is so worried about sailing efficiency,
Draught is lower, so less likely to run aground
You can park on the beach if the tidal range is sufficient
You can do simple jobs on the hull without craning out
You don't need a cradle if you are craned out.
You can use a drying mooring.

The choice depends on where you sail and how you sail.
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Old 13-08-2013, 01:17   #9
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Re: Two is better than one: Keels

I'm not finding the article I first found on the topic, but this is similar. Basically a twin keeler with a modern design could have as little wetted surface as a long fin keel boat and have better stability. I don't believe many that are currently out there fit this this category.


Small Craft Advisor - The Truth About Twins
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Old 13-08-2013, 02:33   #10
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Why not use twin keels on twin hulls?
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Old 13-08-2013, 03:03   #11
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Re: Two is better than one: Keels

Quote:
Originally Posted by SecondBase View Post
What are the design tradeoffs between one keel or two?

**Advantage one keel
Less leeway
Greater moment arm to resist gusts
? Thicker / stronger


**Advantage bilge keels
Less stress at keel hull joint - that is wrong, unless the fin keel is really flimsy
Less draft
Easy upright Beaching
More friction (against rolling)
Bounces off light incidental groundings (rolls a shoulder)
? Less likely to trip over keel in large waves

Is one keel definitely better for blue water?
The comparison depends on the boats - not all single keel and twin keelers are the same......and whether "Better" or not also depends on use.

Me has a triple keeler (full length keel, plus two wing keels).
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Old 13-08-2013, 03:46   #12
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Re: Two is better than one: Keels

I really like the idea of Bilge keels for a cruiser. your not too worried about the little bit of speed you're loosing due to the increase in whetted surface and you loose a little pointing ability but the shallower draft and self beaching ability seems like a good trade off. although I don't really know much about sailboats yet. I could change my mind tomorrow. also nothing I've looked at has bilge keels so although I may like the idea it doesn't seem to be too important to me
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Old 13-08-2013, 04:40   #13
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Re: Two is better than one: Keels

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Originally Posted by Unkle Toad View Post
I really like the idea of Bilge keels for a cruiser. your not too worried about the little bit of speed you're loosing due to the increase in whetted surface and you loose a little pointing ability but the shallower draft and self beaching ability seems like a good trade off.
I like the idea of bilge keels for much the same reasons. Speed is not an issue for me.
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Old 13-08-2013, 05:02   #14
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Re: Two is better than one: Keels

Location will be the big decider - over here have up to 40' tidal range (very small is a 26 footer).....and our harbours are all built on dry land! (Including 2 of our 3 Marinas! - albeit they are gated)..........so unless in Marina then being able to dry out means Bilge (or Triple) or Legs (a PITA) or a lifting keel or a floating wooden cradle (the pre marina solution for fin keelers)........the benefits of Twin keels come from that requirement, especially no haulouts.

If in the Med I would have a fin (also more choice on boat design and numbers built).
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Old 13-08-2013, 06:02   #15
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I owned a Sun Star 18 twin bilge keels as my first
Sailboat. Very stable, certainly not horrible to windward but .....when you stick a keel while sailing and both get stuck oh my! I would only go back to one for tidal reasons but plenty of good memories of the 1st boat. Champlain Sailor
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