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Go Back   SailNet Community > General Interest > General Discussion (sailing related) > when to deploy the drop down keel?
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Thread: when to deploy the drop down keel? Reply to Thread
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Topic Review (Newest First)
06-20-2008 12:26 AM
arbarnhart It also has about 200 lbs of concrete in the hull around the whatever-it-is trunk to further confuse the issue. Even the manufacturer wasn't clear. In the specs they gave the max draft with "C.B. down" but in the text refer to it as a "retractable keel".
06-20-2008 12:17 AM
sailingdog A swing keel is just a heavily weighted centerboard generally. A lifting keel is a totally different beast. Swing keels and centerboards serve much the same purpose, in the same way, with the swing keel having a bit more to do with righting moment than an unweighted centerboard would.

This photo is of the lifting keel used in a Tide 28 sailboat.



My boat has a centerboard, which is made of wood. It is buoyant and must be held in the down position.

A Southerly 46RS has a swing keel, which is weighted and in the case of the Southerly RS weighs about 4800 lbs. Functionally, it combines the righting moment features of a lifting keel, with the center of lateral resistance features of a centerboard.
06-20-2008 12:03 AM
sailingfool
Quote:
Originally Posted by arbarnhart View Post
What is technically correct and what term is generally used and understood are not always the same. The big piece of steel that swings down on my boat weighs about 140 pounds and almost anywhere you find a listing for my boat or similar ones they will be referred to as a "swing keel".

Chuckles is right about needing more specific info, though. I have a planing hull with a shallow V, so I cannot point nearly as well without it if I am heeling.
Sounds like your boat has a swing keel then, not a centerboard, that makes some sense on a 17' foot boat, but not on a 32' which is four to five times larger and is again most likely equipped with a centerboard. Knowing what it is pretty key to knowing what it is for...
06-19-2008 11:44 PM
arbarnhart What is technically correct and what term is generally used and understood are not always the same. The big piece of steel that swings down on my boat weighs about 140 pounds and almost anywhere you find a listing for my boat or similar ones they will be referred to as a "swing keel".

Chuckles is right about needing more specific info, though. I have a planing hull with a shallow V, so I cannot point nearly as well without it if I am heeling.
06-19-2008 11:26 PM
Wayne25 I have a Helms 25 with a shallow fixed 1650# ballasted keel and a 6' long steel 300 pound centerboard. All good points above. I might add depending on the design of your boat, the amount the centerboard is lowered can be used to adjust your weather helm. Going close hauled, it's amazing how the tiller feel changes as the centerboard is lowered from zero to ten turns of the centerboard winch. 30 turns is full down.
06-19-2008 10:22 PM
sailingfool
Quote:
Originally Posted by ambianceack View Post
There has been a debate onboard regarding when to use the drop down keel on our 32 ft shoal draft cruiser.

Position A is always. For lack of the correct descriptive physics it seems to me that the counter forces of the sail and keel enable the sail plan.

Position B is that the keel may provide too much drag/resistant foce in light air thereby slowing the boats progress, and to only use it during heavy wind and or large wave action.
On a boat that size I would suspect that you have a centerboard, i.e a device designed to provide lateral resistence by being down when sailing upwind (right on PBzeer). It is probably not a 'keel" which would have signifacant weight intended to promote stability when deployed. Even a centerboard weighting only 1-2oo pounds will require a winch...but it isn't really a keel.

If you call it by the right name, you'll get more useful responses.
06-19-2008 09:42 PM
Banshi I would say if it is a swing keel you should always keep it down on a beat. The ability to point higher and slide sideways less will more than compensate for the added drag. Also raising it effects the CR of the boat and could create lee helm, depending on how your boat is balanced out, which if the wind suddenly picks up could put you in a bad situation. It is also acts as your ballast which could, if it was up in a heavy gust, cause a knock down that may otherwise have been avoided.
06-19-2008 04:37 PM
chucklesR Use of a 'drop down keel', whether it be centerboard, swing keel, or a true drop down depends on the boat, it's underwater shape etc..
For example, usually I'd say light air needs nothing down, even making to windward - and especially if you have a hard chine to bite the water and halt leeward drift.
Normally downwind you need no centerboard/keel action as it's (the keel/centerboard) meant to prevent leeward drift by providing upwind lift to the boat. Therefore downwind you raise as much as you can to prevent drag/minimalize submerged surface area.
Upwind use depends on wind speed, boat and a host of other variables, for instance I have to centerboards that are assymetrically shaped, I drop the windward one by stages depending on wind strength and only as much as needed to make my desired degrees off the wind with minimal helm and rudder drag.
OTH, when I'm single handing I often deploy both boards half down and leave them there as it's a good lazy man's solution.

Afraid we'd need to know more to answer more specifically.
06-19-2008 03:01 PM
sailingdog is it a lifting keel or a swing keel??? Not the same thing imho. A swing keel is essentially a glorified, weighted centerboard. A lifting keel is not.
Quote:
Originally Posted by ambianceack View Post
There has been a debate onboard regarding when to use the drop down keel on our 32 ft shoal draft cruiser.

Position A is always. For lack of the correct descriptive physics it seems to me that the counter forces of the sail and keel enable the sail plan.

Position B is that the keel may provide too much drag/resistant foce in light air thereby slowing the boats progress, and to only use it during heavy wind and or large wave action.
06-17-2008 10:33 PM
arbarnhart I have a little swing keel boat. On a beam it will limit leeway but cost me speed. Going windward even a little bit it helps, especially for tacking. Running downwind it does nothing but slow the boat and makes gybing harder.
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