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post #1 of 9 Old 03-26-2011 Thread Starter
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Swing Keel Question

I have a New Bombay Trading Company Explorer 44. It has a swing keel which increases the draft from 5"6' to about 9"6'.

The keel is operated from the deck by a wire winch.

My question is what angle should I drop the keel to? I had always assumed that it should swing through 90 degrees, basically hanging straight down from the pivot but in another forum I read that it was not always correct to do this as it might over stress the casing. The boat seems to be well balanced when it is at 90 degrees and it certainly makes a difference to its pointing ability. It does clonk a bit though.
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post #2 of 9 Old 03-26-2011
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Sounds like a prime opportunity for you to go sailing and while on a reach try the swing keel at various angles. Watching where you have the most speed and the least leeway. This done on the various reaches.
To me it would be a good reason to go sailing. Of course assuming that you have a way of measuring the angle of the dangle on the swing keel. You do don't you?

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post #3 of 9 Old 03-27-2011
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These are good questions to ask the boat builder.

As for overstressing the swing keel's casing: I cannot believe a reputable builder would design a hull which would be overstressed by sailing with the keel fully deployed, even in heavy weather. It should take everything the sea can dish out with a safety factor of at least 3.

As for sailing technique: I'm with Boasun on this one. There are too many variables for an accurate calculation. I think your best bet is start with the answer the builder gives you and then refine it for your particular boat by empirical means.

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post #4 of 9 Old 03-27-2011 Thread Starter
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It is a 33 year old boat and the builders, The New Bombay Trading Company, have long since gone. I have been trying to track down the boats hull designer a Canadien called Maurice DeClerq or the production manager Ross James without success.

What I was worrying about was doing something silly that 'everyone else 'knew not to do. I.E. drop the keel fully. It looks like it is OK to do so then. When I had it dropped in the slings to A/F it it looked right fully dropped down.
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post #5 of 9 Old 03-27-2011
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I have a ceterboard boat, I sail with the board not quite all the way down, as I let it all the way then bring it back just enough so the cable has some load, if the boat was pitching so as the board swings I'd pull it in so as to stop it from slamming,
Then as you reef down you may want to change the board to balance the helm some, I haven't messed with that yet.
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post #6 of 9 Old 03-27-2011 Thread Starter
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Quote:
Originally Posted by P35juniper View Post
I have a ceterboard boat, I sail with the board not quite all the way down, as I let it all the way then bring it back just enough so the cable has some load, if the boat was pitching so as the board swings I'd pull it in so as to stop it from slamming,
Good tip thanks.
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post #7 of 9 Old 03-27-2011
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Advice given so far is all good.
The general rules of thumb for center board/swing keel boats is:
- when tacking/close reach the board is all the way down
- beam/broad reach the board can be raised to reduce wetted surface area drag
- dead downwind the board can be raised partially or all the way. You may roll a bit more without the stability of the board.

Really it mostly depends on the shape of your boats hull. If there is a partial keel or even full keel (as my boat is) then the dynamics can vary. Boasuns idea of trying out various settings is spot on.
Good luck.

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post #8 of 9 Old 03-28-2011
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I'm no expert but on my swing keel I would sail it with the keel raked back like you find most fix keels. I got to where I would let it down fully then crank it up 5 turns on the crank handle to get this position, i'm sure your may require different.
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post #9 of 9 Old 03-28-2011
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Here is a discussion of what technically happens when you adjust a centerboard. The issues raised here apply to any size boat (in varying degrees of course). In short, you have some fun experimenting ahead.

Partially raising a dinghy centerboard - Boat Design Forums
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