Centerboard problems

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Re: Centerboard problems

Postby mark48 on Wed Sep 06, 2017 7:56 pm

This isn't a problem yet, but I'm posting to ask advice about the centerboard pivot installation to prevent one:

Page 26 of the PS manual advises leaving the "epoxy-filled" (pivot) holes in the forward end of the developing centerboard trunk "until much later." Page 223 notes that we've "located and drilled out the pivot hole" for impending installation of the centerboard. At this point of course, the centerboard trunk is a completed, integral part of the hull - and it seems that the "port" and "starboard" pivot holes must be at right angles to the keel and perfectly lined up with each other to allow installation of the pivot rod and appropriate CB pivoting. Also, as we drill the pivot holes on each side of the trunk, we must avoid penetrating the thickened epoxy in the holes which would defeat the protection of the trunk from future water damage.

#1 - I'm wishing I'd drilled those holes before I'd built the trunk when I could position the two trunk sides exactly together, one over the other. (See #2 below for why.) I also wish I'd drilled the holes a bit oversized so I'd have more diameter through which to now drill the two holes for the pivot rod. (And in fact, were I to build another PS, I'd make a number of the "drill-fill-drill" holes a bit bigger. John Harris has endorsed that with respect to the companionway hood drain holes and the holes draining the footwell through the transom.) But penetrating the hardened epoxy and inadvertently touching centerboard trunk wood is a disaster to be avoided; if it were to happen, it's critical to recognize it at the time and re-seal the spot with epoxy, even if it means re-filling the hole with thickened epoxy, without leaving slag on the inner trunk surfaces.

But #2 - How are builders ensuring the pivot, when installed, is indeed at right angles to the keel (so the CB is free to drop)? It seems that some filing of one or the other hole will be required to get the pin to fit through the CB trunk opening.

And #3 - Don't I want the 3/8" stainless steel pivot rod itself to be motionless once it's sealed into the trunk with thickened epoxy, while the pivot hole in the CB is just slightly over 3/8" in diameter to allow the CB to swing freely on the pivot? It seems I wouldn't want the rod to "work" at all as the CB was lowered and raised over time. Maybe I'm worrying too much, but other PS Forum posts about water damage in the CB trunk have made me properly scared.

Thanks for any advice,

ps - Maybe "Were I to build another Pocketship..." deserves its own subject line in the PS Forum.
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Re: Centerboard problems

Postby Bflat on Thu Sep 07, 2017 10:31 am

I followed the manual for installing the CB pivot and had no problems although, like you, at the time I wondered why I couldn't have drilled and filled the holes earlier (one could, it seems). Anyway, It was quite easy. Although care should be taken, extreme precision isn't necessary since a tiny bit of slop in the fit is desirable for the board to pivot freely. To fill the large holes I wrapped waxed paper around a 1" thick scrap wood and inserted it in the CB slot. Then I easily filled the holes with thickened epoxy. When that cured I removed the scrap. The next step was of great importance - locating precisely where the final hole should be drilled. I made a "fake" centerboard from cardboard that matched the profile of my actual board including its pivot hole. When inserted in the slot this greatly aided locating the best spot to drill the hole. Another aid was to start with a small pilot hole first. With that hole in place I could check that the fake CB had proper clearance. A small round file made short work of "creeping up" on the final hole location. It turned out really well.

Getting the hole to be at a right angle to the trunk was not difficult. Drilling the small pilot hole first and using a round file to get it to final fit was the key on that point. After the pilot hole is "tuned" a bit with a file I used increasingly larger drill bits to bring it to it's final size. Also, since the pivot hole of the CB itself is slightly bigger than the pivot rod (it shouldn't be a really tight fit) aerospace precision isn't needed.

Once the pin is finally inserted, the thickened epoxy used to cover it up will keep it from moving.

Before permanently installing the pin, I checked the final fit with the actual centerboard to be sure it could move freely.

I agree with you about filling holes. I gradually learned to make filled holes generous in size to avoid problems. I can't remember, but I don't think I deviated much in that regard when it came to the CB pin.

I've finally launched my boat. Raising and dropping the board has been problem free (so far).

I hope this helps.

The photo won't be of much help, but just shows the CB being held temporarily with a screwdriver as pivot pin. I wish I'd taken some photos of the hole filling and drilling process (much before the attached photo was taken).
P1060068.JPG (132.28 KiB) Viewed 2168 times
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Re: Centerboard problems

Postby mark48 on Fri Sep 08, 2017 6:15 am

Bflat, thanks for your advice and suggestions.

My biggest concern is that I'll inadvertently penetrate the hardened epoxy somehow, during drilling or filing the hole to allow the pivot to fit, and not recognize it - allowing water penetration to a "hidden" part of the hull which will ultimately cause a disaster. Most of the rest of the hull I'm able to inspect for adequacy of epoxy coverage; the CB trunk assembly is another issue. And if I'm not sure, I'll re-drill the hole to a larger diameter and refill the holes with thickened epoxy. I just wish I'd done that in the beginning.

All the best,
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Joined: Fri Jun 28, 2013 9:55 pm

Re: Centerboard problems

Postby Wayne G on Sun Nov 26, 2017 5:32 pm

Wayne G wrote:I had a similar issue where the centerboard dropped into place during assembly but would gently stop after about two thirds of travel when stationary in water. I figured that I probably introduced a slight inward bow to the centerboard box during the box glue up ( should not have put weights on the center of the box when curing). I have resolved the issue by drilling a hole and installing a drain port in the cockpit above the centerboard void and using a 1/4" aluminum push rod with rubber tape on the contact end (I call it a podger). This works really well and the center board fully drops with nothing more than a nudge from the podger. Even after raising and lowering the centerboard quite a few times it does not fully drop without this aid, but it is no big deal as the operation is quick and simple.

After one year of sailing Janey Mack the sticking CB suddenly resolved itself.
This change seems to be due to my putting an additional 100 lbs of ballast in the bilge as I found the boat to be somewhat "twitchy" when sailing solo (now have a full 300 lbs in the hold!). I presume that the additional loading on the hull has pushed or stretched the CB box down and so reduced the slight inward bow in the box side walls.

The additional ballast does not seem to have harmed the boat's performance; she is noticeably more stable and the freely dropping CB is a great bonus.
Wayne Gray
Orlando Florida
Wayne G
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Re: Centerboard problems

Postby on Wed Aug 04, 2021 10:42 am

I just installed my centerboard, and I tried checking the pendant length by pulling the board up out of the slot (the boat is still upside-down). With the knot 28" from the bushing (as specified in the manual) it extended too far, about the same as in John's photo below. I re-tied the knot at 23", and it looked OK. And measuring off sheet 4 of the plans, 23" seems to be the correct length.

Has anyone else checked the position of the board when down, and verified what pendant length actually works for them?


John in CC wrote:Image

Another thing I noticed was the board when it did go down went a bit too far (as seen in the closeup picture) I raised the board to the correct position and took the slack out of the pendant and then marked where the knot should be. The old knot was carefully measured when it was first tied but I guess as the knots (the one on the board and the one up top) tightened and seated in moved (stretched or whatever) and got a little long. I have retied the knot and the travel is now perfect. I have not measured it but I would be will to bet it is the exact measurement John Harris recommends.
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