Centerplate Winch Modification...

[NormMessinger]

http://albums.photopoint.com/j/View?u=1229514&a=9072073&p=54676568&Sequence=0

One of these days I'll build a nice little mahogany cover box with rounded corners but in the mean time.... It takes more than a hundred turns to lower the plate. That's the easy part. Getting it up takes as many. So,...

My plea is for suggestions for putting a little 12 volt electric motor on there so if a fellow is single handing it wont be necessary to sit in the cabin for a few minutes at a critical time getting crankier and crankier.

Thanks.

--Norm

[G. Schollmeier]

Norm
Maybe something like this.
http://www.northerntool.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=25265&prmenbr=69 70 (http://www.northerntool.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=25265&prmenbr=6970)
Or this.
http://www.northerntool.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=806&prmenbr=6970
If not they have a lot of stuff for winchs.
Gary

[This message has been edited by G. Schollmeier (edited 09-30-2001).]

[imported_Conrad]

Go to the Northern site listed above and search for stock numbers 14116 and 14112- seems like the latter would be best; you're required to power in and out, no clutch to surprise those who aren't sure what to do next.... Also search for Harbor Freight Tools, a similar site.

[NormMessinger]

Um, I ask for suggestions then don't give enough information. I do not want to totally rely on power so the winches suggested above would put me in that bind. They are big, heavy dudes, too. What I wonder about is a small DC motor that will run about 50 or 60 rpms, maybe double that, and work forward as well as in reverse. It would be mounted just aft of the hand crank but not replace it. The crank would be stowed near by for use when the power fails or someone needs the exercise. Then we get to limit switches and all that. This may not be reasonably practical.

--Norm

[John B]

How about an experiment. just imagine you had a forked adapter/coupling which would go over that handle axle and was attached at the other end to a cordless 12v/18v or 24v drill/screwdriver.
What I mean is, hook up your cordless and see if it works.

[Will]

Free fiddleing around : If the photo is the All In possition there's significant excess capacity on the drum ,which figures with such a short lift .Could remove the wire ,pack out the drum with duct tape ,and reinstall .If you manage to increase the average diameter of the spooled wire by 25% , which lookes possible ,you'd only have to crank 75 times each way ,with 25% loss of power .

I can't guess the size of the hidden drum ,but you might be able to do even better , if you don't need the current mechanical advantage ,or can tolerate a longer handle .Bill

[capt jake]

That is on the same line as I was thinking. Norm, what kind of weight are you talking about exerting on the motor?

[Mirelle]

Norm,

Your plate can't be that heavy.

Block and tackle works fast; should you find you need more power, take the fall to an ordinary little rope winch like you use for headsail sheets.

An elegant approach is to lead the chain (you are using chain, not wire rope, onto the plate itself, are'nt you?) up through a pipe to a sheave on the coachroof, and fit the tackle up there, on deck.

[imported_Conrad]

OK, then how about www.grainger.com (http://www.grainger.com) where you will find 12 volt motors with built in speed reducers, should be able to find one that puts out 50-75 rpm. You'll also find couplers that you can adapt to your situation. Grainger is tops in industrial supply. Get yourself a double pole/double throw switch to reverse it while you're at it.

[NormMessinger]

Ah ha! Increasing the diameter of the drum would certainly reduce the number of turns. Good idea.

Yep, its that heavy. it is a piece of mild steel, 1 5/8" thick, about 4' long and 2' wide. I figured about 435 lbs prior to some drilling and shaping. The pull is in the top forward corner and the pivot is in the lower forward corner. Pretty near the entire weight of the plate is pulling on the cable when it is in the up position.

What worried me about a tackle and the lash up Oughtred drew was that if one were to let go accidentally the force of the plate dropping could do some real damage. Or so I think.

I'm on my way to Grangers. Thanks.

--Norm

[Wilson]

I like the cordless drill idea (12v of course).
Your present rig stays in place plus you get to go out and buy another toy, which as you already know is very handy to have aboard for other chores .

[Will]

Wow ! I thought such Plates were no longer among us . Attaching the pennant to the aft top corner would cut the load on the cable and the skipper in half . The load on the pin would be even more dramatically reduced .With the current rig fully raised , the load on the pin is about 600 lb.



[This message has been edited by Will (edited 10-01-2001).]

[Mirelle]

Yes, indeed; hoist should go from aft upper corner.

Furthermore, there should be a lug on the aft face of the plate which meeets a stop in the lower aft corner of the box; this is to stop the plate from falling right down if the lanyard parts or someone lets go inadvertently.

Very surprised and disappointed in Ian Oughtred; these points were well known to US designers early in the last century! Maurice Griffiths, then Editor of the "Yachting Monthly", crossed the Atlantic in the 30's to investigate what the Yanks were doing right and the British were doing wrong in centreplates and wrote a book ("Little Ships and Shoal Waters") about it.

[Mike Field]

My understanding is that it does go from the aft upper corner -- which becomes the forward upper corner when the c/b is up. But I don't have a proper drawing to work from.

Can you post a sketch, Norm, just in case anything else presents itself?

A stop would certainly help retain the board in the case if the pennant broke, but I don't think it would/can remove the likelihood of the damage you're worried about. The thing is not to let the pennant break, that's all -- then the stop is redundant.

[Mirelle]

I mean the aft upper corner when the plate is up! Dinghies and dayboats can have it from the forward corner when the plate is up, boats with lids should not, as the weight is so much greater.

[NormMessinger]

Hmm, to late to redesign now. McNulty built the first Farne Islander lifting the centerplate as Iain drew it bud judging from the article in "The Boatman" they did not use the same winch arrangement he drew. Anyway, here is part of the CAD drawing I made.

http://albums.photopoint.com/j/View?u=1229514&a=9072073&p=54730122&Sequence=0&res=high

I made the pivot pin much bigger (3/4" ss) than Iain specified, but as long as the lift cable does not have a downward vector how can there be more weight on the pin than the weight of the plate?

Interesting. Thank you.

--Norm

[Mirelle]

Yup, that's going to break, one of these days. Wire rope will corrode inside the case and the loading on it is much higher than if the point of attachment to the plate were at the aft upper corner with the plate raised.

Taking the wire round 180deg to get to the winch barrel does not commend itself either.

Of course, putting the lifting chain (chain, please, not wire!) where I recommend, at the aft end of the case and passing up to a tackle on the coachroof through a bronze or s/s tube, does cut into cabin space. On the other hand, it provides a hand hold.

[Alan D. Hyde]

ACB's comments make a lot of sense to me from an engineering perspective, speaking of course as a purely amateur engineer.

Any chapter and verse from the many engineers here?

Alan

[NormMessinger]

Another question: If the lifting rig were attached to the aft end of the plate per ACB's recommendation is there any problem with it, the chain, extending below the keel when the plate is down?

--Norm

[Mirelle]

Norm,

The answer is "no"; it's commonly done, and you will probably find that you don't need to lower the plate until it is vertical.

Another little centreplate detail; you have correctly put the pin outside the boat (far too many have it inside, guaranteeing a leak).

One more thing; if you are in an area (like the Thames Estuary on the east coast of the UK, or the Chesapeake in the USA, where shallow water and mud predominate, you may go aground on mud; in which case you need to clear the mud out of the slot before it dries solid and cakes the plate up; it's usual to carry a flat steel bar and to be able to unscrew the top of the case to get it down beside the plate to clear the mud out.

[Will]

Norm ,I think the single most important idea broached is ACB's of retrofitting some kind of stop .Thru crew error or material failure the board will one day drop , with bad result .

It's not too late to shift your lifting efforts to the aft end of the centerboard case .By cutting the forces involved in half ,everything will be easier and safer .If you look around you'll see this is standard procedure ,useing purpose made winches or tackles .I think the Catboat assoc. could suggest the right hardware.[Looks like the load would only be reduced about 1/3, now that I see the board ,still, not to be sniffed at .The other point is to have a rig that's operable from the cockpit , rather than the owner and crew being hunched up down below ,drearily cranking away while wondering where the boat's gotten to .]

Can't scan right now ,but we can think about the force on the pin by useing a simplified model of your board,a rectangle 2 ft. by 4 ft. with the pivot on the bottom righthand corner and the winch pulling horizontally from the top right corner .

Imagine the wieght of the plate concentrated at its centerpoint .Think about the moments around the pivot .The wieght(W) is pressing straight down ,2 ft. lateraly from the pivot , produceing a moment of 2W ft. lb. . The winch line, pulling horizontally, must be produceing an equal and opposite moment, or the plate would be rotating. It happens to be 2 vertical ft. from the pivot ,so the pull on the cable is the same as the plates wieght , as you estimated .

To find the resultant force on the pin you use a vector triangle .One leg is vertical and represents the wieght,length W .One leg is horizontal and represents the pull of the winch ,length W .The magnitude and direction of the load on the pin is represented by the hypotenuse of this triangle .It's an Isosceles triangle ,so the force on the pin is the wieght of the board times the sq. root of 2.That's 1.41W. or (435lb.)(1.41)=615 lb.

The same techniques can be applied to the actuall geometry of your plate to get an exact answer, but you get the idea .The pivot bolt is being pressed down ,and forward at an angle of (approx.)45 deg. How much, of what kind of wood , is resisting that ?If you rerig that force will drop to about .5W ,directed straight down.

If your boat is not going to sit in mud between tides you can get away with a simple hole in the top rear of the case for clearing . When the board jambs insert a short metal rod on top and bang it down with a 2 lb. hammer carried for the purpose .I think this would be worth fitting ,Norm,whatever else so you're not helpless when the inevitable happens :something jambing the board .Tho not in your league ,I have a swing keel on my 23 footer and have had to retrofit this ; stuff happens .I just use a wooden plug for the hole.




[This message has been edited by Will (edited 10-03-2001).]

[NormMessinger]

Ah, ha. I'm beginning to see the picture. The vectors are simple enough but I hadn't made the picture. Thanks Will.

You can make out the ballast bars in the drawing, pieces of mild steel 7' long on either side of the plate. The pivot is in the bars. The is a slot radiased in the plate with a bolt throught the trunk to prevent the plate from letting down to far but I doubt the trunk could take the force if the cable let go and it is below the water line. There is also a pin which can be inserted to hold the plate in the full up position or in the "survival" position were the plate can neither go up or down.

Knowing what I know now, the trunk would not taper down aft. While building it as drawn kept the intrusion into the cabin to a minimum, if I had made the top parallel to the water line one could sit on it without sliding off.

That would also have put the opening for an aft end lift mechanism above, rather than right at,the water line.

Much to think through.

Thanks all.

--Norm

[Dale Harvey]

Norm, I do not see a problem with your winch arrangement, other than that it should never be exposed to saltwater or the whole thing will quickly disintigrate. I assume there is a sheave in the front of the case to lead the cable to the winch. I do not see any indication of cable deformation, that would lead me to worry about excessive weights if present. If you simply move the winch further aft, so that the handel shaft is inside the cabin, and replace the handel with a pipe to a bearing block in the inside cabintop, make a plywood jam or "V" pully at the top, run a continuous drive rope (like on some old furling drums) thru pvc guidepipes thru the back of the cabin, you would have a slick rig.

[Mike Field]

Thanks for the sketch, Norm. I must say it does look a bit more primitive than I would have expected. Sorry, but I guess the comments already made cover what I might have said. (This is what is known as a cop-out.) Unless you want to design a whole new board and case of course -- I'd have a lot of ideas about that.

[Zane Lewis]

First, I don't understand why people are suggesting chain as in NZ it is unheard of? Over here most people in trailer yachts with ballasted boards used galvanised 1x19 wire rope which gives an indication of wear when it starts to sprag. More recently they are using spectra rope. The trailer yacht I race on has a 200kg (440 lb) dagger board which we raise with 4mm spectra to a winch idential to the set up shown. We have 110 turns.

6-8mm Spectra is commonly used here for trailer winch ropes.

Another idea an electrical friend has suggested is that a 12vt motor such as a windscreen wiper motor would have enough torque to do the job.

Your layout with the winch rope doing a 150 deg turn on to the winch is going to produce high loads. Is it possible for the rope to come up directly under the winch?

Another option is a 4:1 type block and tackel coming back to a small winch in the cockpit.

Another system I have come across is the use of a powered screw type arrangement. A threaded rod is attached to the center board and passes through a threaded gland on the top of the case. Either the rod or the gland can be rotated to rasie and lower the board. Personally I find this a bit complicated

Zane