Centerboard modification

[Tim Bentley]

Several people have asked how I did my center board stabilization modification, so here it is.

Of all the modifications that I have made on Gray Lady, my Bayraider 20, the most rewarding has been stabilizing the center board - don’t have to listen to the clunk clunk of the board going side-to-side, she turns smoother, and points higher into the wind.

To accomplish this I put two large slabs  of plastic on either side of the board using this procedure:
Put the boat in the water and the center board all the way down. Measure the inside width of the centerboard trunk at the narrowest area directly behind the board. Outside calipers work well for doing this but you can also do it with a tape measure. Next measure the thickness of the center board at the back edge. Subtract that measurement from the trunk width measurement and divide that result in half to get the approximate thickness of the plastic that you need to put on each side of the board.

On my boat that measurement came out to exactly 1 inch. This may be the same on all Bay Raiders, don’t know how consistent the construction is. The plastic slabs I  used were 21” long and 11” from top to bottom and 1 inch thick. I got my plastic in the recycle bin of a local plastic store, but there are also several kinds of plastic slabs available on Amazon. You may have to combine two pieces to get the thickness that you want. You don’t want the plastic slabs pushing tightly against the board, just close is good enough for stabilization

To install the plastic pieces, put the boat in the water and the board down. I screwed a small half round bracket to  the top center  of each slab and used a piece of parachute cord (later removed) to lower the plastic in place, Be careful not to drop it through the bottom of the boat. Slide each slab forward as far as it will go along side of the board. The plastic slabs are anchored in place with two stainless steel machine screws through the outside of the centerboard truck and into the plastic. The screws are well above the waterline so you don’t need to worry about leaks. 

I think you will be amazed how much this improves the boat's handling.

[Sea Simon]

Thanks for that TB. Very interesting, and food for thought while my board box is open....

Do you have photos, by any chance?

[Peter Cockerton]

Tim

Very detailed post on your centreboard case modification and fairly easy to visualise the implementation, what I cant fully grasp is the physical improvement to the board with the lateral “packing out” of the case which results in the improved windward pointing capability of the boat.
The lateral movement of the board and the resultant “clunking” is a standard “feature” on the boats but I wasn’t aware that the board has any lateral flexing over its length under close hauled conditions and I’m not suggesting that you have inferred this, so the mod reduces the lateral movement scope of the board and that over several feet of the board results in the improved windward performance do you think.

Peter C

[Graham W]

On a BR20 sailing to windward, the top of the centreboard can exert considerable lateral force on the slot through the top of the wooden centreboard capping.  This may allow the centreboard to flex to windward, probably not helped by being mounted on a fairly small pivot pin.  I know about this lateral force because my wooden capping popped off its screws one day off Corfu.  Admittedly a contributory factor was my crew heaving on the centreboard downhaul when they shouldn’t have.

So if you pack the case with plastic either side, that ought to distribute the lateral forces over a greater depth of the centreboard case, including the more rigid parts lower down - where the ballast tank roof meets the case, for example.  That probably ought to reduce flexing and movement of the centreboard on its pivot pin.  And that in turn should help you to sail closer to the wind.  It might also help reduce clunking off the wind and gurgling and occasional fountains of water coming through the centreboard slot.

The question is, which plastic could be used?  Amazon UK don’t sell anything like the range available on the US Amazon site.  I’ve looked at the properties and prices of the materials available on other internet sites in the UK and HDPE appears as if it might be suitable, at not too extortionate a price.  See for example https://www.directplastics.co.uk/hdpe-sheet.  Teflon/PTFE would probably be better still because of its low friction characteristics but the cost would be prohibitive.  Epoxy-coated marine ply with a thin sheet of PTFE fixed to one face?

Who’s volunteering to go first?  Or as Tim has already pioneered it, second?  They should be called Bentley boards.

[Sea Simon]

I too looked at materials prices and availability, and I'm afraid...stopped there! At least for now.

I have in the past used plastic chopping boards for similar packing/spacer applications but 10mm Thickness is about the most I have seen. Butchers tools/supplies?

Perhaps some hardwoods (oak, elm?) Might be appropriate? Heavy? Probably even more expensive, and harder to find?
 Neither my wood stocks nor my skills are really up to that option I suspect.

I'll concentrate on sorting my board up/down haul systems for now. That also not as easy as hoped!

[Graham W]

Apparently most plastic chopping boards are made from HDPE.

A 25mm thick HDPE sheet of 500 x 500mm, which could be cut in two to give two sheets a bit smaller than Tim’s recommendation, would cost about £95 from Direct Plastics, above.  PTFE sheet from the same supplier would be more than £1,000.