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-   -   How does a fixed keel boat differ from keel+centerboard? (http://www.sailnet.com/forums/general-discussion-sailing-related/55235-how-does-fixed-keel-boat-differ-keel-centerboard.html)

phboujon 06-11-2009 04:47 PM

How does a fixed keel boat differ from keel+centerboard?
 
Hi,

I am curious to understand the difference between a fixed keel boat and a keel + centerboard IF the displacement & ballast are close in both version. For example:

Valiant 40 - Keel + Centerboard (rare but it's an example only)
LOA: 40'
LWL: 34'
Beam: 12'4"
Displacement: 22,500 lbs
Draft: 4'-6'
Ballast: 7,7000 lbs

Valiant 40 - Fixed Keel:
LOA: 39'11"
LWL: 34'
Beam: 12'4"
Displacement: 22500
Draft: 6'
Ballast: 7800

If I was to calculate all common sailboat ratios related to speed, stability, capsize risk, none is ever related to the depth of the keel, but more often to the LWL, Beam, Displacement, Ballast and Sail Area.

Therefore, what would be the drawback of purchasing a keel + centerboard sailboat for offshore cruising/sailing, versus a fixed keel one? Does it impact safety? stability? or only speed?

Thank you
Philippe

speciald 06-11-2009 04:59 PM

The righting moment, center of effort, and center of gravity are determined not only by the weight of the ballast but where that weight is placed so a keel boat will have more weight lower, be stiffer, and point better as the weight and the center of effort will be lower. Also centerboard boats tend to be noisier and risk the board jambing in thetrunk.

sailingdog 06-11-2009 05:14 PM

A properly designed Keel/Centerboard boat is a great bluewater boat and has the advantage of a shallower draft for when in coastal waters. The major issue with it is the slightly increased maintenance that the centerboard requires.

As for what SpecialD said, that really depends on the boats in question. A keel boat may be stiffer, and may have weight lower, but if the keel/CB design is a good one, it won't point any higher. The height of the COE has little to do with the boat's ability to point.

tweitz 06-11-2009 05:15 PM

On the other hand, the centerboard Valiant will be a lot more fun to sail in 5 feet of water.

chef2sail 06-11-2009 08:56 PM

Many centerboards such as our C&C 35 MKIII have no issues with noise and in fact give us geater flexibility than the fixed keel models. For instance our centerboard drops down to over 6 feet giving us an advantage over fixed shoal keel C&C 35's in terms of stability and can be pulled up to 4'6 to allow us to go up many of the smaller tributaries of the Chesapeake.

As long as you take care of the pivioting mechanism and maintain it as SD has indicated a k/c can give you the best of all worlds.

The only disadvantage I have found is a shallower bilge.

Dave

phboujon 06-11-2009 09:42 PM

Thanks, I appreciate the insights. If you can expand on the "noise" issue since I am not sure to understand. Aren't they supposed to be locked in placed once down?

So, based on what the few of you already said, that would bring my next question: Since most bluewater/offshore cruisers tend to have keels longer than 5'2" (what I have been said to be the max you want in the small tributaries of the Chesapeak, ICW, Caribbeans), what bluewater cruisers with a good keel/CB design exists out there? The Valiant was only one example, and I am trying to find others of the same caliber.

Thanks again for the replies!
Philippe

Omatako 06-11-2009 09:52 PM

It's very important that it locks in the down position especially in heavy weather because if you have a knock-down and the keel slides up into it's bay, it will take considerably longer for the boat to stand up again.

I also fear the reality of the keel being seriously damaged in a grounding (having lost a fixed-keel boat through that once before) but then I guess that fear could just be due to unfamiliarity with the workings of a drop-keel.

CrazyRu 06-11-2009 10:06 PM

Quote:

Originally Posted by phboujon (Post 495416)
The Valiant was only one example, and I am trying to find others of the same caliber.

Thanks again for the replies!
Philippe

All these manufacturers have had models with centerboards:

Freedom,
Able,
1987 Able Custom Sloop/Cutter - Boats.com
Packet Island

and somewhat arguably lesser caliber
C&C,
Tartan,
Bristol,
Sabre,
Person,
Benetau, and many others.

T37Chef 06-11-2009 10:08 PM

and Hinckley.

The centerboard on my Tartan is really designed only for pointing ability, I adds little or no stability. If it were bad weather I would just retract it so not to cause any damage from a knockdown and the board crashing into the slot unexpectedly.

Maintenance is an issue, but for where we sail, it is worth the extra time needed to maintain it IMO. Just recently, I replace the pennant and the tube connecting the mast tube to the thu hull fitting, it was a SOB but I got it on.

I have heard it make some noise, but only when I was at anchor or sailing downwind with a following sea and had forgot to bring it up ;)

T37Chef 06-11-2009 10:29 PM

Quote:

Originally Posted by CrazyRu (Post 495434)
All these manufacturers have had models with centerboards:

Freedom,
Able,
1987 Able Custom Sloop/Cutter - Boats.com
Packet Island

and somewhat arguably lesser caliber
C&C,
Tartan,
Bristol,
Sabre,
Person,
Benetau, and many others.

Haven't heard of some of those boats; person, packet island and lesser caliber :D

JeffH...where are you????


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