View Full Version : bolt for centerboard
07-06-2001, 08:52 AM
Okay, here is a question that will really show my ignorance. I need a bolt for my centerboard pivot. The board is white oak and the logs on the case are B. Mahog. The plans call for a 3/8" bolt, but doesn't specify the material or the type of head, etc. Also, should there be any kind of bushing through the holes or should the bolt bear directly on the wood? There isn't much edge distance on either part. How should I seat the bolt so it doesn't leak? Any advice would be appreciated. In fact, if somebody wants to go to the defender or Jamestown distributors web sites and show me exactly what to get, THAT would be appreciated.
The boat is a 15' plywood Whilly boat.
I guess it all depends on how the cb trunk is constructed. If you can get your hands on a copy of How to Build the Catspay Dingy, available from WB, it shows a very detailed drawing of how to install the pivot pin, and associated construction. I would suggest a broze pin.
07-06-2001, 10:43 AM
I'm using 3/8" bronze rod inside 1/2" OD copper tubing bushings. To seal the holes in the logs I am using small pieces of 1/4" plywood sealed and screwed in place.
As a real basic alternative, a really old banks dory I used to have used a 3/4" dowel that was wedged on both sides. It never leaked a drop.
07-06-2001, 11:33 AM
Don, do you mean you're countersinking the bolt head and nut and screwing the ply on the outside of the case? Copper bushings through the board, the logs, or both? Also, should there be anything between the bolt/bushings and the wood? I'm worried about water seeping in, and all I know how to use is epoxy, which I suppose would be too permanant. Incidentily, the bolt is below the waterline.
[This message has been edited by casem (edited 07-06-2001).]
07-07-2001, 10:55 PM
I'm not using a bolt. Just a piece of 3/8" bronze rod as long as the centerboard case and logs are wide. In my case I have a 7/8" ID on the centerboard case. The case is made of 6mm ply and the logs are 3/4" thick, so the total length of the pin is 2-7/8". There is a section of copper tubing epoxied in a 1/2" hole on both sides of the centercase and through the logs. There is also a piece of copper tubing epoxied through a hole in the centerboard. I enlarge the holes and use a liberal amount of epoxy to make sure the joint is not starved and there is a good seal all around. The plywood covers are about 1" x 2" and cover the holes in each log. It is sealed with caulking around the edge and screwed in place with small wood screws for insurance.
07-08-2001, 10:42 AM
Don that sounds like a great idea. I am getting ready to build a center case for a Penobscot 14. Thanks
07-08-2001, 11:39 AM
My favorite method entails drilling a hole with plenty of clearance clear through the log, centerboard and log on other side. Seal the inside of the holes. Trim the pin so that it is slightly shorter than the distance between the outside of the logs. Slip the pin through the holes. Cover the outside of the holes with a gasgeted disk screwed to the log. For 3/8 bronze I would use a 1" dia 1/16" thick piece of sheet bronze with three # 6 screws. A piece of wood will also work. A neoprene rubber gasket works best for me but silicone sealant will also work fine. Don't use anything that can stick (adhesive or glue).
The 3/8 rod needed for this method is available from marine stores, including Defender (I think). I have also been known to buy a long bolt and cut off the head and threaded portions. But this sure is a waste of a good bolt
The sheet bronze is harder to find. I once bought some from McMaster Carr catolog sales (search the web for them).
I have never had problems with bronze bearing on hardwood as long as the bearing area is adequate. 3/8" rod for a 14 foot boat is reasonable. The limit to bearing strength is from the wood not the bolt so you don't even need to use a rod. A piece of thick wall pipe is fine for larger centerboards.
I once substituted copper pipe (thick wall) and sheet copper for a centerboard pin assembly on a small boat. It worked fine for as long as I owned the boat.
07-08-2001, 11:50 AM
An additional tip I'd like to pass along.
I remove my CB each season and after maintenamce and painting it's sometimes difficult to align all holes in the case and CB.
Use a large mirror angled to see thru when the alignment is correct for the pin to be inserted.
07-08-2001, 06:36 PM
On my 24' half decker I moved the bolt to the keel outside and below the planking - the problem of a leaking case does not exist. The bolt is 1" monel going through an oak keel and a steel centerboard and is perfect after many years use.
07-09-2001, 08:34 AM
I used 1/2" threaded PVC end plugs in my centerboard case. Point your browser to
and go to the bottom of the page for an explanation. No screw holes, everything sealed with epoxy, and the caps are readily available. I also used bronze bushings in the centerboard case logs.
07-09-2001, 08:50 AM
Lots of good ideas here. Thanks everyone. Of course, I'm still not sure what I'm going to do, but at least I have some ideas. I wonder why more people don't put the pin thru the keel, ala Smacksman. That seems to be the easiest thing to do, but you'd have to design the board for it.
07-09-2001, 01:01 PM
In building the Ness Yawl, I did as Don Mauer describes above, except that the bolt is 3/8 brass and instead of copper tubing, I used 1/2" OD bronze bushings, one in each log and one in the centerboard. I glued small pieces of plywood over the logs. To keep the glue out of the bushings, I cut a circle out of packing tape and stuck it on the outside of the log over the bushing before gluing down the ply. Hasn't leaked. I guess I'll put a few small screws into the ply just in case.
The problem I have with the centerboard is trying to figure out how to rig the lanyard so that I can control the board while underway. When the board is fully down (upright) it rests against the center thwart. The lanyard is about 1" above the center thwart. I can't lead it straight back because it would foul the main sheet cam cleat which sits on the back of the centerboard trunk. I can't lead the lanyard forward because there is no lead in the board. It floats like a cork. Which is kind of neat, as opposed to the usual tremendous thud of the board slamming down everytime somone pops the wrong control line and you think the whole bottom is about to fall out and you stare in amazement at the rigging vibrating like crazy.
If I just cleat it to the side of the CB trunk, the lanyard will chafe on the trunk and the thwart.
Right now, I just tie it round the thwart--which looks kind of lubberly if you know what I mean.
07-10-2001, 12:59 PM
Ian didn't show how?
Run a lanyard forward to pull it up. Use a pin through something (the case? a fitting of some sort? two plastic fairleads?) to hold it down. Of course hitting something would cause a lot of strain on the board, the pin, etc.
I saw a trick setup at one of the old Newport boat shows where a guy adapted a snow-ski boot quick release to hold the board down. If he hit something, the release let the board float up. It looked like something only an engineer would love but it seemed to work http://media5.hypernet.com/~dick/ubb/biggrin.gif
[This message has been edited by TomRobb (edited 07-10-2001).]
07-10-2001, 07:05 PM
Don, when your board is down I presume you have a lug/ear of the board showing above the case? Fit a strop of thick bungy to your thwart and stretch it over the ear to hold the board down. If you hit something the bungy [elastic] will give. If you make the strop in a figure of 8, the top loop acts as a lanyard for a handhold to work the bottom loop over the lug of the board. A rubber buffer fitted inside the case acts as a stop to a zealous dropping of the plate.
An endless uphaul/downhaul rope works well. Fit the block at the fore end of the case on some bungy along side of a longer piece of rope. This will give you some slack when hauling and then the bungy will self stow neatly when finished.
07-10-2001, 07:08 PM
How about adding a bit of lead to the board, just enough to make it sink.
She sure is pretty, how does she sail?
07-11-2001, 10:42 AM
Thanks for the suggestions. For now, I'll go with a bungee cord type arrangement that will allow the board to give way.
What about lead in the board? Iain O. and others say that the amount of lead you can put in a board is often not enough to really overcome buoyancy. A 3" diameter hole cut in the bottom of the board will allow a little less than 3lbs of lead according to my guestimate. (4+ cubic inches of lead at .61lb a cubic inch). Is this really enough to overcome the buoyancy of four or five feet of 1" thick ash--especially combined with the pressure on the board resulting from forward motion through the water?
If I can get the board to sink, a control line can lead forward to a micro block on the bottom of the forward thwart. The line can then head aft to a small cam cleat on the side of the trunk.
The Ness Yawl was launched in May 11, a date I'm sure the Harbormaster will remember for a long time. It was a sunny day with a light, steady wind. She does indeed sail like a witch. I have been meaning to post about the launch, but I wanted to wait until I had photos to accompany and that is another story all by itself. I'll try to post about the launch separately later this week or over the weekend. I certainly have some questions.
Compute the volume of the board (or measure it) and you know how much weight of lead you need.
Measure? Archimedes. Fill the bath (the kid's wading pool, tarp suspended by 2x4s on edge, poly cement mixing tub, fishpond, aquarium, whatever) to overflowing, let the surface settle. Entirely submerge the daggerboard, let the water slop out. Measure the amount of water needed to return the pool to just about to overflow; that's the volume of the entire board. Now submerge the part that's not in the water, refill, subtract the volume of the non-immersed part from the volume of the total. 231 cubic inches in a gallon, 231/16 for a cup (American). If your pool is sufficiently deep you can do it directly by only submerging the wetted part of the board; maybe an empty poly garbage can?
07-11-2001, 09:49 PM
The lazy way would be to tie a baggie and a ten pound weight onto the bottom of the board, then dribble lead shot into the baggie until it balances. 1x12x60 inches should be about 25 pounds, less if it's tapered (a pair of diamonds would cut the volume to half, foil shape maybe 2/3.)
I'm at the same point in the Shearwater construction so the timing here is perfect and the solusions are ingenious. Correct me if I'm wrong: the greater the over all diameter of the pivoting pin (pipe) the stronger and more laterally stable the center board, ie: a piece of 1" od pipe would maker a better "pin" than a pc of 1/2"?
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