Center board screws

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Center board screws

Postby bwilldoit2 » Sat May 27, 2023 9:33 pm

I could use some help. My Son bought a 1984 O Day Day Sailer 2 and we, Son and I were attempting to remove the center board for some line replacement. We were just getting started and we got two screws out on one side. The two on the other side just spin, don’t one out or tighten. What would be the fix for this problem? I’m pretty mechanical, I just don’t want to make things worse or more expensive than it has to be
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Re: Center board screws

Postby GreenLake » Sun May 28, 2023 1:34 am

I have the same problem with one of the stemhead fasteners on my DS. (I don't plan to remove that fitting, but it's a bit disconcerting that some of the bolts are in a state that is neither fast nor loose).

I believe in both cases, there's a backing plate that is tapped to receive the bolt. In my understanding, these should be large enough (or even a single plate for both bolts), so that there should be no conceivable way that the backing plate itself can spin inside the fiberglass.

However, you write "screws". Are the two that you removed actually screws, or did you just use that term loosely, and they are in fact bolts that go into a tapped backing plate?

If they are bolts, and if the backing plate can't spin, then the threads must have a damaged section that allows the bolt to turn, but beyond that,there's enough thread left to both hold the bolt in place and perhaps damaged in a way that does not allow it to engage.

In my case, I tried to wedge the bolt while turning to see whether I could get that remaining thread to engage, but failed. And, of course, you can't really drill out the bolt, as it will turn. I haven't tried to look elsewhere for suggestions; this seems like a problem that must occur in other settings, and perhaps there are some hints for extraction. (If you find any, would love a pointer posted here). As a lark, I asked one of the AI chat-based searches this question and nothing practical emerged from that.

Now, specific to your case, there is a slightly extreme solution that you could try, which is to cut out the entire section that contains the glassed in backing plate(s). The good news is that rebuilding fiberglass is eminently feasible without weakening the boat. The bad news is that the spot is a bit awkward to get to and you may need to cut an inspection port into the cockpit sole. Also, it's not a simple flat section, but an angle, with a receptacle for the CB pin and of course, contains embedded backing plates... doable, but finicky.

What can you tell from the "screws" that you removed? (And the holes they come from?). Is there a chance that the bolts extend far enough beyond whatever backing plate that it might be possible to grip the end from the inside? (Even if that means removing a bit of fiberglass covering that same end). If that looks feasible, you would need an inspection port, but then only dig out the ends of the bolts, clamp them to stop their spinning and then drill out the heads.

If because of the gap for the CB pin, there are two backing plates, one for each bolt, then it may be possible to free them from the fiberglass from the inside and perhaps even drill out the bolt from the inside (while keeping it from spinning from the outside). If the plates can be chiseled out, so that the outer skin of fiberglass is untouched they can be replaced by new ones without the need to recreate complicated shapes and once positioned, they can be glassed over. (If the end of the bolt is waxed, they can be glassed over withe the bolts in place).

One of the methods found by my searches suggested heating the bolts so they get stuck. I'm not sure how feasible or risky that is, esp. given the presence of fiberglass....

I'm sorry I don't have a magic wand solution, but perhaps this gives you some ideas. Circular inspection ports are available (usually called deck plates) and installing one in the place from which you can access the inside of the CB fittings should be relatively straight forward. Pick the largest diameter, or pick two that are positioned a bit apart on either side to give access with both hands.
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Re: Center board screws

Postby Alan » Sun May 28, 2023 1:42 pm

On my 1980 DSII, the centerboard retaining plates are attached to the bottom of the hull with flathead Phillips machine screws, like so:

centerboard retaining plate screws resized.JPG
centerboard retaining plate screws resized.JPG (62.75 KiB) Viewed 5310 times


I believe the 1984 DSII is the same.

The upper ends of the screws are visible through the inspection ports in the cockpit floor just aft of the cuddy bulkhead. (I've got photos somewhere; if I find them I'll post them.) It looks to me like they thread directly into built-up fiberglass, and there's no visible backing plate.

It may be possible to reach in to the ports with a long flat screwdriver or similar and have one person apply downward pressure on the upper end of a screw while another person turns it counterclockwise from below.

By the way, the goop that looks like auto body filler was applied by a previous owner. My best guess is that he was trying to stop water leaking into the bilge. The water was actually coming from the centerboard uphaul line fitting (lots of posts about that problem on the forum).
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Re: Center board screws

Postby GreenLake » Sun May 28, 2023 6:09 pm

duh, "machine screws", of course.

However, I don't think these are screwed into bare fiberglass, even if it may look that way. The reason is that that the loads on the CB pin are not trivial, and the screws are loaded in tension not shear. Anything short of metal in metal would pull out. The other reason is that tapped backing plates embedded in fiberglass are definitely used in other places on these boats. For example to hold the mainsheet swivel.

Wood screws or sheet metal screws with their coarser threads might have reasonable holding power in fiberglass, especially if placed before the laminate has fully cured. But again, that's not something you would do for holding a CB pin.
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Re: Center board screws

Postby Dirtybug » Mon May 29, 2023 6:06 pm

Here's a view through the inspection port on my dsII.
3075
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Re: Center board screws

Postby GreenLake » Mon May 29, 2023 8:46 pm

Nice. To me it still looks like some backing plates might be there, but if so they would be glassed in (so you can't see them from the inside) with the machine screws extending all the way through. It looks like the screws were placed while the resin was wet, but someone found a leak and tried to fix it with the blob of filler.

The way to be sure about plates or not, would be to look into the holes for the screws that came out. Failing that, if the inside rise above the hull laminate is more than the depth of the channel outside, that would argue for a layer of something buried in the layup.

However, with the ends exposed, if pushing on the ends makes the remaining threads grip so the screws can be extracted (as suggested by Alan), that would be the easiest. If not, the ends could be gripped with anything that keeps them from rotating, and the screws could be drilled out.
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Re: Center board screws

Postby Alan » Wed May 31, 2023 2:52 pm

Found one of my photos, and you know, GL, it looks like you're right. Here's a view of the upper ends of the screws through the port-side inspection port:

centerboard retaining plate screws fom above resized.JPG
centerboard retaining plate screws fom above resized.JPG (44.28 KiB) Viewed 5262 times

centerboard retaining plate screws fom above resized (2).jpg
centerboard retaining plate screws fom above resized (2).jpg (88.78 KiB) Viewed 5262 times


The blue arrows in the second photo point to the screws. The red arrow points to one corner of what looks like a glassed-in backing plate.

If the backing plate is stripped out, I think you could install a nut and washer on the upper end of each screw. Working conditions would be a bit awkward, but it does look doable.
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Re: Center board screws

Postby GreenLake » Wed May 31, 2023 8:03 pm

Good point about being able to place a nut given the exposed ends. Perhaps a nut would also work on screws that won't come out, basically to hold them while the head can be drilled out for removal.
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Re: Center board screws

Postby bilbo » Thu Jun 01, 2023 8:29 am

If there is a stripped backing plate, could you drill and tap the next thread size up once you've extracted the original screws? The countersunk holes would need some work too. I've had to do this on other applications and was quite successful.
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Re: Center board screws

Postby Alan » Thu Jun 01, 2023 11:52 am

Bilbo,

It would be easy enough to drill and tap the holes in the boat. Where it might get tricky is enlarging the countersunk holes in the retaining plate. They're made of stainless steel, which is notoriously hard to drill. Maybe grind them larger with a tapered grinding stone mounted in a drill or Dremel?
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Re: Center board screws

Postby GreenLake » Thu Jun 01, 2023 6:55 pm

The few times I've had to drill SS it worked fine. Cobalt bit and moderate but steady pressure. However, an alternative would be to take them to a machine shop.
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