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Old 17-04-2015, 12:03   #1
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Need a Precise Explanation

Exactly what is a shoal keel with centerboard? What is each function? I know nothing Thanks for your usual expert help.
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Old 17-04-2015, 12:06   #2
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Re: Need a Precise Explanation

I imagine it's probably a weighted keel stub, with a centerboard that then extends out for better windward performance.


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Old 17-04-2015, 12:18   #3
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Re: Need a Precise Explanation

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Originally Posted by brownoarsman View Post
I imagine it's probably a weighted keel stub, with a centerboard that then extends out for better windward performance.


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It is a structure that is supposed to address two main issues facing upwind sailors. Ballast to keep the boat upright and the board to provide resistance to the wind pushing the boat sideways - all while allowing for maneuvering in shallow waters. I would be careful about using such a boat in open water - folks have done it but there are risks. Best for coastal gunkholing.
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Old 17-04-2015, 14:04   #4
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Re: Need a Precise Explanation

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It is a structure that is supposed to address two main issues facing upwind sailors. Ballast to keep the boat upright and the board to provide resistance to the wind pushing the boat sideways - all while allowing for maneuvering in shallow waters. I would be careful about using such a boat in open water - folks have done it but there are risks. Best for coastal gunkholing.
What are the risks? I have this on my Bristol 30' 1971. I"m aiming for offshore cruising eventually. What would i have to do to change this?
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Old 17-04-2015, 14:09   #5
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Re: Need a Precise Explanation

It's all about rig/sail area size and the amount of ballast you have. The more weight you have in the keel and the lower it is, the more stability you have. If you go out in a day sailor with just a center board and large sails, your boat will be more susceptible to being capsized. Those types of smaller boats rely more on the mobile crew to provide the weight where it is needed.

I have sailed boats with keels and centerboards. If you are thinking of single handing a boat off shore and it has an arrangement such as yours, you have to watch the weather very carefully and wear your PFD at all times.
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Old 17-04-2015, 14:21   #6
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Re: Need a Precise Explanation

COBG, I think you are getting a little over the top in your criticism of keel/centerboard designs. If properly designed (and I believe that Bristols are so considered), the stability curves are quite adequate for offshore usage. To say that one must constantly wear a PFD whilst sailing such a vessel because of the constant risk of capsize is simply nonsense.

For the OP, there are many offshore designs with centerboards. They don't go around capsizing in great numbers. Our own boat, a one-off design, was originally a centerboarder. It was modified to a fixed keel after a few thousand miles (Japan-Alaska), not because of stability issues but because of balance issues in sailing downwind in big seas and to windward in strong winds. Every time we need to get through a shallow channel with our 7'2" draft I wonder if it was a good trade off!

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Old 17-04-2015, 14:31   #7
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Re: Need a Precise Explanation

Your Bristol 30 is a beautiful Halsey Herreshoff design. It has a Keel/centerboard design (K/CB). This was done quite a bit in Bristol's later, refined by Ted Hood and his incomparable Hood 38 (built by Bistol, Little Harbor and Wauquiez).

These K/CB designs were made so that sailors could get into the shoal areas and still have stiff, upwind capability offshore. The CB does not contribute to the overall stability of the boat (the "vanishing stability"). That is accomplished by the high ballast to displacement ratio. In many of Ted Hood's boat, that is 50%. In your boat, it is 40%. But, your boat has a narrow beam and so its angle of vanishing stability (AVS) is very high (I believe, but do not know).

The CB in the K/CB:
The CB enables the boat to point higher, go to weather better and, when sailing very slowly, mitigate leeward slippage. That is all. You really do not need it or use it for most sailing conditions. Note that this is completely different from designs that are swing keel or purely centerboard designs....very different animal.

Your boat:
A high AVS DOES make for a good offshore boat. As does the a high ballast to displacement ratio. A high B/D can give a very high comfort ratio and make the boats movements very smooth and easy to take.

That said, the B30 is under 9,000 lbs displacement and has about a 22 ft LWL. So....you will not be going anywhere offshore fast and she is pretty light for a lot of sea conditions. But then, the 28ft Pearson Triton has sailed many ocean miles and is a similar boat...though...it is full keel.

If you are not going to cross oceans, and will keep a weather eye out, the B 30 should serve you in any capacity.

What do you want to do with her? Where do you want to go?

Hope this helps
best
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Old 17-04-2015, 14:37   #8
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Re: Need a Precise Explanation

No criticism involved. Stating reality. I own a Pearson Triton. I would take that small boat in a heavy seaway over a shoal draft keel/centerboard. Simple physics. Righting moment, etc. Just gotta watch what you are doing, is all. And don't we do that on any boat we are sailing? Peace
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Old 17-04-2015, 14:55   #9
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Re: Need a Precise Explanation

As to single handing:

I single handed my boat a lot. And every time, even if I was well within sight of land, I would wear an inflatable harness with a tether to the boat. Clipped to the harness were a waterproof hand held VHF radio, strobe, whistle and rigging knife.

Safety first and always.
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Old 17-04-2015, 14:59   #10
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Re: Need a Precise Explanation

Not just design, also maintenance. I looked at a lot of centerboard Morgans in my boat search. Often, the owners hadn't opened the bilge in years. The centerboard block was rusted in place, the cable about to snap, etc. When the centerboard falls down violently from gear failure, it can crack the trunk which creates room for water ingress.
So, not knowing how your boat is designed, before you go offshore, or at your next haulout, or if you like to snorkel, check the attachment point for the cable (if present) on your centerboard, check the cable run, and check the system in general.
If it does fall down on you (assuming no damage), just tie a rope around your boat to keep the board up and carry on


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Old 17-04-2015, 15:43   #11
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Re: Need a Precise Explanation

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Originally Posted by crazyoldboatguy View Post
It is a structure that is supposed to address two main issues facing upwind sailors. Ballast to keep the boat upright and the board to provide resistance to the wind pushing the boat sideways - all while allowing for maneuvering in shallow waters. I would be careful about using such a boat in open water - folks have done it but there are risks. Best for coastal gunkholing.
Ted Hood designed many boats for Bristol (and others), with a keel / centreboard setup, from the 31.1 up to the 54.4. Among them are some of the best blue water boats ever built. Any of them would have a better angle of vanishing stability than most of the cruisers made today. More on the subject can be found in Ted Hood's book on his design philosophy.

What are these risks you speak of?
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Old 17-04-2015, 16:19   #12
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Re: Need a Precise Explanation

The risk of having an opinion different from yours.
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Old 17-04-2015, 16:36   #13
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Re: Need a Precise Explanation

I think this is a shallow keel with a slot where the centerboard is fitted.

Killing all birds with one stone: perfect when perfectly designed and executed, but a disaster when a miss.

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Old 17-04-2015, 19:22   #14
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Re: Need a Precise Explanation

It is worth pointing out that all boats are compromises of some sort, and a shoal draft centerboard boat is a compromise, obviously aimed at skinny water. It trades draft for stability, to one extent or another. That said I've been on some big Little Harbors and Aldens with very deep centerboards that went to windward pretty damn well and were pretty stable.

Everything is relative. If I was going to spend a lot of time poking around the Bahamas, I'd think a shoal draft centerboard was a pretty excellent option, and I'm pretty sure I'd be comfortable sailing it offshore to get there, depending on the boat.
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Old 17-04-2015, 20:31   #15
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Re: Need a Precise Explanation

Bristol is a quality craft and well designed. When I bought my Little Harbor I contacted the web page to see if they still had drawings of the boat. Later that day, Ted Hood called me directly and my secretary said there was a Ted Hood on the line. I was quite surprised to say the least. He said the plans were destroyed in a fire but wanted to know what questions I had about the Little Harbor. I told him that I had some racing experience, mostly one design keel boats (J-24's mostly) and the boat I was looking at had three things that bothered me: 1. Centerboard which I never had before. 2. Center cockpit. 3. Windows in the Hull which I considered a high risk for leaks. He said, "the centerboard will let you into shallow water like in the Bahamas, the center cockpit will keep you dry, and when you are heeled twenty degrees in the Bahamas, you will enjoy watching the lobsters crawling on the sea bottom".


Having sailed the boat for almost nine years, I can attest to his comments. The boat is designed to sail with the board up and does so nicely. I drop the board down twenty five percent, or 15 turns of the CB winch to point the boat higher when close hauled and reaching conditions. I only drop the board completely 58 turns when off the wind, down wind to reduce the roll in moderate and heavy seas. The board is solid fiberglass and aside from its own weight, its ten feet long, it really has no ballast to right the boat. All the ballast is in the bottom of the boat. It's called a whale bottom design. I have no concerns with being in heavy air and seas with the design, and would expect you will not either. The primary benefit is to enjoy the shallower waters when the board is retracted. It opens up a lot of cruising ground. The biggest drawback is pointing to windward. But as it is often said, "gentlemen cruisers do not sail to windward" meaning that it is hard work and wet.


I don't know the Bristol that you have, but I suspect it is similar, and you should have no concerns. Just experiment going to weather to find the depth of the board that gives you your highest point to weather without sacrificing speed to your course made good, VMG. As conditions change, so changes the board depth.
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