Stopping a centreboard from clonking

Kelpie

Kelpie

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Our boat has a bronze centreboard housed in a lead stub keel. Unless you are hard on the wind in fairly flat water, or alternatively you have wound the keel very tightly up, it is liable to clonk from side to side. Most of the time this hasn't been a bit problem, but certain sea states make it quite irritating. I also assume that this causes some wear on the pivot pin.
I'm thinking of addressing this problem by adding some sort of packing. There is a small gap, say 5-10mm from memory, at either side of the keel, so any packing would have to fit within that. Considering using a hard plastic type material, e.g. PTFE sheet. Possibly two thin layers, one bonded to the centreboard, the other on the inside face of the slot.
Just wondering if anybody has done something similar, and lessons learned, etc?
 
The clonking may well be due to worn pivot holes in the plate, or the bolt / pin; apart from the pain of drying her out - I'm assuming it's your Deb 33 we're talking about - and a pit or something to drop the centreplate, first question is how easily can you get at the pivot ends to release the plate for inspection / work ?

These plates wear oval holes quite quickly, wave action can do it even when the plate is raised on a mooring etc with the boat static.

So a rounded out pivot hole with bushes pressed in and probably a new pin would help if that's the case.

I don't know your keel set-up, but some boats fit thin sheets of PTFE or similar inside the keelcase - a thinly sliced plastic ' hygenic ' type breadboard comes to mind as a good source !

If doing this with the plate removed, a thick strip of this stuff or tufnol etc in the trailing and upper keelcase edges might be an idea, if not already fitted; I didn't know my boat had this ' crash bumper ' in case of hitting something nasty before I fitted a new lift keel, but it seems worthwhile.
 
Fortunately I can access the pin quite easily- it is in the stub keel, outside of the hull. The previous owner had it checked and said that it was OK, but I don't think he dropped the plate itself. I'll need to man up and do that. It's a heavy beast though!

Perhaps the simplest packing to use would be four layers of thin sheet material, two either side, cut into a washer shape, and lined up so that the pin goes through the middle. Can imagine it being a right faff to get lined up. But on the plus side, I wouldn't have to worry about how to fix in place.
 
Kelpie said:
Fortunately I can access the pin quite easily- it is in the stub keel, outside of the hull. The previous owner had it checked and said that it was OK, but I don't think he dropped the plate itself. I'll need to man up and do that. It's a heavy beast though!

Perhaps the simplest packing to use would be four layers of thin sheet material, two either side, cut into a washer shape, and lined up so that the pin goes through the middle. Can imagine it being a right faff to get lined up. But on the plus side, I wouldn't have to worry about how to fix in place.
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Kelpie,

I'd strongly suggest you check the keelplate hole & pin wear, other people with much smaller boats than yours have reported frighteningly rapid wear, ie elongation of holes in plates primarily & wear on pivot pins secondly.

' Tha last owner said it was OK '...need one say more ?!

Yes it will be hassle and probably expense but it's a rather primary bit of kit.

Re the lift keelers I run the Owner's Association for, I always say re new keels ( which I don't profit a penny by ) ' the real test is when clawing off a lee shore on a dark night against a F6 +, with family on board, how worried do you feel ? ...'
 
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I'm hoping to do at least a partial drop of the plate to inspect the hole this winter. The pin is located close to the leading edge of the plate, which means that with the plate up I'd only have to drop it a few inches. The boat will only need to be blocked up on a couple of sleepers to get the clearance for that- no need to dig pits etc.
The downside of that, though, is that the idea of using packing washers around the pin might still let the board flop from side to side, as the pin is quite far from being in the middle. If that makes sense?
 
Kelpie,

as wear is pretty much a foregone conclusion and drying out is a real PITA, would it be possible to look at her plans and have a bush & side washer etc repair scheme ready, maybe the bump stops I described too or if you have the whole winter with her ashore you be should able to take time and fix it; I'd take careful notes of the symptoms when afloat though as it all seems different on a cold windy boatyard !
 
What's the recommended way of repairing a worn hole in the plate? A bush made from something super tough I presume?
 
I'd suggest bronze as it's a traditional material for this sort of application, minimal corrosion and to a small extent self lubricating, but no doubt others will disagree and suggest coagulated pixie droppings, squirrel's tears or similar...:)
 
Well that would make sense, what with the centreboard being bronze and all!
Would i need to machine out the oval hole, or just fit the biggest bush that fits and epoxy it in?
 
Kelpie said:
Well that would make sense, what with the centreboard being bronze and all!
Would i need to machine out the oval hole, or just fit the biggest bush that fits and epoxy it in?
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The easiest solution if it is possible would be to have the hole machined back to circular and use a larger pin made to fit. Is that doable?

If not, then a bush. The best way would be a press fit, but that might be expensive and not DIY. There are immersible adhesives for bronze and non-ferrous metals, but it's a specialist application, so a call to someone like West after the hols would get the proper advice.
 
Seajet said:
A bronze bush would be better than wearing away the plate
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It depends on the degree of wear and how much metal remains. If the hole is only 1mm enlarged and 50mm from the nearest edge then making the hole a bit bigger is entirely feasible - if a bigger pin can be used. I suspect the OP won't know until it is dropped and examined.
 
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As usual Angus is just being contrary to anything I say, apparnently because I once remarked accurrately that his trimaran has a very limited window of opportunity to sail well & safely - by his published figures - and as a designer chum put it, " only really stable when it's upside down ! "

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Back in the real world a bronze bush might very well be the way to go, the wear on centreplates even at rest just from the joggling about on moorings or berths can be quite alarming, there have been a few threads about this; the Finesse 24 springs to mind as one example.
 
Seajet said:
As usual Angus is just being contrary to anything I say, apparnently because I once remarked accurrately that his trimaran has a very limited window of opportunity to sail well & safely - by his published figures - and as a designer chum put it, " only really stable when it's upside down ! "

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Back in the real world a bronze bush might very well be the way to go, the wear on centreplates even at rest just from the joggling about on moorings or berths can be quite alarming, there have been a few threads about this; the Finesse 24 springs to mind as one example.
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On the contrary (:)), I agree a bronze bush is an option, but it's just that, an option, and there may be other easier solutions, as I suggested, given that the plate is already bronze. Why put a bronze bush in bronze if there is no need?
 
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Seajet said:
Because a bronze bush is very different material to a bronze plate ? ! :rolleyes:
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There's a possibility that it is already bushed I agree, but I would not be surprised if it's been pivoting in the bronze of the plate for many years already. Even if it is already bushed, there is still the possibility that there is enough metal left in the bush relative to the apparent wear for the hole to be machined rather than the bush pressed out and replaced.

We won't know until it the plate is dropped and a piccie can be posted.
 
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