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Old 29-08-2012, 10:07   #1
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New Swing Keel Idea ?

I have an old John Alden44 with a swing keel that has never really functioned properly. (I can force it up for the bahamas or lock it down off shore).
Im thinking of a radical new design and would welcome some comments.
The original keel (Please note: there are no ballast issues) was just a ply/epoxy fin with a single pivot point. It was designed to be winched up and gravity lowered.
I'm thinking about designing a 'boomerang' shaped keel with the pivot point on the outside 90degree elbow. this will allow for winch up AND winch down attachments at the end of the lever arm which will always remain in the keel housing.

Winch the lever arm up and the keel will lift and (via opposing pulley) the keel can be winched down.

Im also guessing that the lever arm element will provide addition fin stability in the down position.

Is this a stupid idea?

anyone ever tried this?

john
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Old 29-08-2012, 10:38   #2
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Re: new swing keel idea?

Don't know much about design so I won't comment there, but might it not be easier to drill out the trailing edge of your current board (board up) and pour in some lead to increase the weight?
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Old 29-08-2012, 10:55   #3
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Re: New Swing Keel Idea?

I never liked the thought of a gravity keel. In the water when the boat is moving up and down, gravity no longer is an effective stabiliser.

I saw a picture of one boat that looked like a worm gear lowered the keel, if true that would provide some measure of proterction from a keel coming back up unexpectantly if the boat rolled.

Another design of locking keel I saw was a clutch bolt that could be tightened against pivot. Or a stop bolt that pinned it down.

The boomarang sounds good, but where will you put the extra leg when up?
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Old 29-08-2012, 10:55   #4
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Re: New Swing Keel Idea?

The board is old and needs replacing anyway. I was thinking about using coated steel and a hydraulic ram, but I dont like the idea of anything (neither ram or line) being in the water. Having a lever keeps everything except the fin out of the water, but Ive never seen such a design.

thanks for your thoughts.
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Old 29-08-2012, 10:59   #5
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Re: New Swing Keel Idea?

There is room withing the keel housing for the 'up' lever, which would be at 90 degrees to the waterline when the keel was up. I looked at the idea of a worm drive, but there is no fail safe for striking. Hydraulics would be better, but I like simple most of all..

thanks
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Old 29-08-2012, 11:18   #6
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Re: New Swing Keel Idea?

You've got a center board not a swing keel. Swing keels are heavily ballasted and act like a fixed keel increasing stability when down. Center boards are usually just heavy enough to fall down and provide resistance to leeway but little, if any, increase in stability.

Most centerboards are winched up and deployed by gravity. The reason for not physically lowering them and locking them down is to prevent damage in a grounding. Some centerboard designs are mechanically lowered but that means way more complicated gear and the threat of damage when lowered. You say yours is lowered by gravity but locked in place. How is it locked in place?? Do you have to insert a pin, some kind of lever arrangement or what??

Usually gravity is enough to deploy the board but they may hang up because of side loading as you are trying to lower it. Momentarily heading up to remove side loadings will often allow the board to drop. Boards can get jammed in the well by marine growth or small rocks after a grounding. If gravity is not dropping the board reliably, adding some additional ballast to the bottom of the board might help. Also check the winch and cable to be sure that's not causing the problem.

Your idea might work but would require elongating the C/B well or moving the axle pin aft to allow room for the lever arm you are creating. Moving the pin is probably going to cause big problems as that would move the board aft and change the center of effort of the underbody. I'd definitely want to talk with a Naval Architect before I'd go any further. Elongating the well is probably going to be a major job.

What is the problem with the centerboard?? What is the mechanism for locking it down?? Why do you lock it down when going offshore?? Usually the board is only deployed for going to windward. As soon as you ease the sheets, the board is typically retracted to reduce resistance and increase sailing speed. On some boats, they can ease pressure on the helm if partially deployed on other points of sail though the designers usually reccomend either full up or full down.
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Old 29-08-2012, 12:17   #7
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Lightbulb Re: New Swing Keel Idea?

Hi everybody, I just install my own 3/8" scissor type 304 SS with a 12V off road 4x4 winch with remote. I've been sailing hard for about 6 months In what feels like a new boat. OK, it's a Rob Roy 23. BTW, the winch raises and lowers the mast. The drawings are a bit confusing, as both pieces have tabs on the rear end that are stopped by a ss plate in the hull I could go on further, but I'll let you ask questions, if you wish.
Capt.Fred. See attached photos and ask.
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Old 29-08-2012, 12:36   #8
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Re: New Swing Keel Idea?

thanks Capt.fred for the pics.. thats what Ive got in mind, but I have room for a longer lever which I think will make it easier to maneuver.

I cant quite make out the pulley system - can you winch it up AND down.. this seems important to me as everytime Ive cleaned my 'DAGGER BOARD', it soon gets fouled again and quickly sticks.

To Roverhi: I should have used the term STUCK rather than LOCKED...
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Old 29-08-2012, 16:38   #9
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Re: New Swing Keel Idea?

Quote:
Originally Posted by captainblue View Post
I looked at the idea of a worm drive, but there is no fail safe for striking.
thanks

No fail safe on a fixed keel either.....just saying.
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Old 29-08-2012, 17:19   #10
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Re: New Swing Keel Idea?

captainblue, The draft on my RR23 is 20" with the CB up. I usually sail with the Dbl CB at the limit of the smaller unit, which adds about 15 more inches, to a total of 35" and I find that adequate for my boat. I can lower the "L" shaped unit to a total of 53", but I feel vulnerable with the single piece exposed to under water hazards. The two pieces weigh over 250# and have contributed to the stiffness and speed substantially. The electric winch lifts and lets it down. I move the center boards up and down every couple days to prevent them from sticking. It has worked for me. I also soaked the 304 in muriatic acid to dissolve the surface iron molecules. (Very dangerous, especially lungs or any body part.) When the 304 ss was dry, I coated it with a two part under coat epoxy. Then I bottom paint it. At almost 80 years old I still wear a scuba tank end scrub the bottom. It is a pleasure as the white sandy bottom and the smooth, clear warm water cannot be matched. Our sand is white quartz from the Appalachian Mountain Chain. BTW, I made a mistake in my last thread. My 304 ss CB are 2 pieces of 7/16, my total slot is . In rough weather, I hammer two starboard wedges on each side of the CB trunk, squeezing the slot to firmly secure the center boards in any position.
Happy days,
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Old 02-09-2012, 22:31   #11
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Re: New Swing Keel Idea?

If you lock down your board, you are going to do serious damage to your boat one day. No offense, but I doubt that you have the design experience of the designer (Alden). Find a set of plans, or find an owner of another boat like yours and repair the board to design specs. It makes all the difference in the world sometimes.
I love our board & use it daily, even at anchor.
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Old 03-09-2012, 08:27   #12
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Re: New Swing Keel Idea?

Quote:
Originally Posted by capta View Post
If you lock down your board, you are going to do serious damage to your boat one day. No offense, but I doubt that you have the design experience of the designer (Alden). Find a set of plans, or find an owner of another boat like yours and repair the board to design specs. It makes all the difference in the world sometimes.
I love our board & use it daily, even at anchor.
Dear Capta, No desrespect to John Alden, or you, but the CB design on the RR23 is not a the best functional design. True, I have not devoted my life exclusively to boat design, but I don't think Mr. Alden actually owned a tender, slow and very beautiful RR23. As a lic. architect that has designed many structures including the cutter rigged yawl Daedalus, (before I knew how to sail) I suspect my RR23 is stiffer and faster than any other RR23. I say that without modesty. If you go to my albums #2 & #3 you will see a small portion of my work. Now as far as locking the CB in heavy weather; have you ever been in heavy weather in a tiny boat? BTW, the lock down sequeezes the upper broad portion of the CB trunk 1/32" on each side. No problemo. It's the same trunk that supports the CB in all conditions.
Warm regards, Capt.Fred
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Old 03-09-2012, 18:15   #13
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Re: New Swing Keel Idea?

I think there is a huge difference between a 23 foot boat and a 44 footer.
Center board trunks do not do well if the board is locked down and you hit bottom.
At any rate I know nothing of your RR23, I was trying to help the OP with his Alden 44.
I can't speak highly enough about a properly functioning center board. Any amount of trouble restoring the board on the Alden 44 will be rewarded many times over with better sailing and more comfortable living aboard at anchor.
As I said above, we use our board underway AND at anchor. Since we never use marinas, that's pretty much every day.
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Old 03-09-2012, 18:52   #14
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Re: New Swing Keel Idea?

Tony Smith's design of the centerboard for the Gemini is winch up and down. Releases on impact too.

Same design as on the Telstar too.

Telstar 28 - Centerboard Assembly and Replacement on Vimeo



Centerboards
The centerboards are located within a case in each
hull. A winch handle in the socket lowers and raises
the centerboard. The centerboard is locked into position
with a wing nut going over the 3/4" nut.
Releasing the wing nut and turning the socket approximately
two turns counterclockwise will fully
lower the centerboard (it should not be lowered too
much). Tightening the wing nut will lock the board
down.
Raising the board is simply reversing the procedure.
Turn clockwise two turns until the board comes in
contact with the top of the case. Be careful when
unlocking the board from the down position as the
board is very buoyant and will begin to lift up quickly.
The board will float if left unlocked in the up position
but the back of the board will still be hanging 9"
down out of the hull if not locked up. Therefore,
after raising the board, be sure to tighten the wing
nut with the board fully raised.
The boards are designed to push up if run aground.
The boards are only necessary for windward work or
when close maneuvering in a marina. Only the leeward
board is necessary but it is acceptable if both

are used. If traversing a narrow area, put both down 1
1/4 turns.


Caution
: The boards are designed to only be in the

down position when necessary. Do not leave the
boards in the down position for an extended period as
there is a small tolerance between the board and the
centerboard case. If barnacles and growth build up
on a board left in the down position, it will be difficult
to impossible to raise the board without first

scraping it clean.

The manual is online and page 27 has a nice picture also.


http://www.gemcats.net/static/Gemini...nual_105Mc.pdf
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