by 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.
~ green ~ lake ~ ~