I have untarped the top of my boat and had the mast lifted to the ground so I can rewire it. On Tuesday I was showing a friend the work on the boat and it was raining while we were inside. That showed a couple of leaks I needed to deal with really soon. One more serious leak was under the port rope clutch. I hadn't planned on any work on the deck until the next time the boat was out of the water, but Too Many Holes changed my mind about that, at least for the top rear of the cabin top.

When I pulled the backing plate off from the clutch I was stunned to see not only some serious soggy balsa, but missing glass, missing balsa and a backing plate that had some serious corrosion. This area had become so weak that I think it could have easily failed under load. The starboard side was better. What I think had happened over the years is that these clutches had been moved from one spot to another because under load they would pull hard enough on the structure to elongate the holes and the leaking would begin when the sealant failed. The winches have been moved along with these clutches, so lots of poorly filled holes left behind too.

My brother had given me some scraps of really high density foam material and my plan is to use it underneath the clutches and the winches. I will start by cutting the top of the cabin away and work from above for a change. So I have pieced together the high strength foam with some regular Divinicel, such that the high strength stuff will be directly below these devices. I will also use a fairly heavy layup above this core and then get after the underside once I have something to draw vacuum against. I am not looking forward to fairing this all out, but for sure when I am done this area will not leak and while drilling oversized holes in this material and refilling with CS might be overkill, I am not a fan of leaks on my head when using these births.

I was thinking about this problem a little more and it occurs to me that an installation using one of these captured nut types (I'm not sure what the official name of this kind of nut is) would always be challenged. The hole you drill for the nut end is much larger than is needed for the screw end, if you drill only one sized hole. In the case of this rope clutch the screws are 5/16" and the threaded capture nut is 1/2". So when this device is under load on the topside the clutch is going to creep forward until the screw can bear against the top surface skin, and/or the tension in the screw becomes high enough to stop the forward movement of the clutch. The better way would be to drill two different sized holes, one that matches better the screw diameter and one that matches the captured nut. Otherwise over time and loading the loaded device will creep and encourage the sealant to fail.

Dave - better that the interface on the fastener not be beveled. Those type inserts are available in stainless with standard round heads from McMaster Carr.

Bill,
I am not sure I follow you. These beveled inserts match the bevel in the large machined aluminum backing plate (that was nicely corroded from contact with water and the stainless insert). The image above is of the side contacting the overhead. The opposite side has the mating bevels for the nut inserts. If there is any advantage to this arrangement with this backing plate it is that it makes for a little less chance of braining yourself on something protruding from the overhead because it is essentially flush.

I think the original hardware arrangement can be made to work OK, but with dual sized holes through the core and some Duralac on the insert to stop the corrosion. For sure the high strength core I will use would likely solve much of this problem anyway. I'm not sure what the compressive strength of this core is, but you could hit it with a hammer and not dent it. I would also expect it to be more thermally stable making the sealant work much better and longer.

After completing the core and skin work my plan would be to use the aluminum backing plate as the drill guide, but only letting the 1/2" bit penetrate about 5/8". Then use the center of that hole to drill the rest of the way through with the 5/16" bit. I may do some testing with a small scrap piece of this core to see if it would be even helpful to oversize drill and then refill with CS. I suspect that It wouldn't make much difference. This core already has glass layers bonded to it on both sides, so with the added layers in the repair glass (inner and outer skins) I have to believe the screw will have much more solid glass to bear against under the shear loading.

It is a good thing to have a brother in the high end boat building business, so you can mooch crazy expensive scraps like this core. It also makes you aware that as much as I am spending rebuilding this old boat, it pales in comparison to new boats.

Aspen Power Catamarans

I had the same thought as Bill, but now that you explain the countersunk backing plate, that sounds perfectly fine, so you are on the right track.

Going through these things before they become a problem is so much better than people getting hurt trying to save the port side halyard winch from going overboard just before a douse - just sayin! ;-)

The backing plate for a clutch is considered by many to be overkill as long as the area of the holes has some non-compressible material added in there such as what you describe. A small countersink on the top to create a seal with non-silicone based caulk is advisable as well.

You are spot on about two different sized holes in the deck to handle the increased diameter of the nuts as well. Alternatively, Barrel Nuts with thick stainless fender washers serve well in lieu of the backing plate as long as the structure has a combination of CS and G10 tube or something like G10 plate.

Cheers!

Here is a beauty shot of the topside of this plate. I suspect that someone had it made to deal with the compromised cabin top. I think it is a good thing to have even with a solid and sound core.

I will have to inspect the primary winches before we put this beast back in the water. I had been thinking this stuff was fine for the time being.

It isn't raining right now so I am going to go up and cut this skin away and then cover it up. Hopefully the core next to the portlights (below this area) hasn't gotten wet too and this is just a localized problem, but so far that just hasn't been the case on this boat. If that has gotten wet it may just have to stay that way.

As a side note what I have seen so far with all of my core work is that on some areas that were under my temporary cradle until last fall when I removed it, the core has dried out. My guess is that the moisture just moved to the areas around that had been fully dried out. Then in one area that had been fully dried out, but was next to the wet core about 5 to 7 inches away from where the cradle was the moisture level has gone back up. So I tried to use the high vacuum and heat again to improve that with some limited success. I am not going back into the repaired areas so I am hoping that as this last area of core is dried and/or replaced where the cradle was that the moisture level equalizes out. The weather is slowly improving here so I can get after this glass work again.

Here is why that plate was needed (see first image). I suspect that however this clutch was originally attached catastrophically failed and the fasteners pulled through. The inner skin had been torn and pulled upward into the balsa core. So a plate was likely added to reinforce this area. It wasn't enough.

I also got lucky today. The core was only destroyed in a fairly local area around this clutch. A few inches away it was fine, with the exception that it was full of old holes. So the plan to replace this entire area will take care of this problem.

The remaining inner skin is so thin after peeling the balsa that I will have to glass it first before doing any core replacement. The area that was damaged in the original failure is also going to have to be ground away to just make a flat surface. This decayed balsa was almost as bad as the area around the exhaust.

Now I just need some days of dry weather.

The weather was great today so after lunch I got everything sorted out and staged. One other bit of prep work was getting a seal on the inside of the cabin and supporting the old thin layer of glass so it is at least sort of flat. Then started by laying in 10 oz. cloth on top of the inner skin. Followed by a thick layer of CS epoxy resin and assembling the puzzle pieces of new core. Topped that all off with a little bit a peel ply and breather cloth (I didn't want the breather to get bonded to the core when the CS extruded around) and then sealer plastic. Used the sink drain as a vacuum port and turned on the Infamous Bad Mistake that has gone so right the Glast R1 vacuum pump. The beauty of this pump is its ability to work in a far less than perfect vacuum and run day and night until the epoxy fully cures. Using blue painters tape to seal the work saves time and a ton of expense too. This pump pulls an even 25" of H2o (not Hg) over the surface and IMHO is perfect for core work.

Tomorrow looks to be another good day so I plan to fill this top surface and get some glass on. After looking closer at the starboard side I think I can just cut the sections out for the high density core and leave the rest of the balsa core in place making for a smaller repair. I will still sand and cover these sections with new glass layers. On the port side I counted 32 holes through the cabin top in this one section.

That's an awesome vacuum bag setup!

Dave- i don't mean to second guess, especially after you have this all together. But, why use the aluminum plate again? Wouldn't stainless be better so it wouldn't corrode. Seems a 1/8" would be plenty. you could get them laser cut at a local shop and they would probably even do the countersinks for you it you wanted. Or you could fab yourself.

Second, instead of drilling different size holes, use a piece of stainless tubing that would make the outer dia of the bolt and t-nut the same. After you overdrill, fill and then drill to size, It's all going to be in a cylinder of epoxy anyway, right? so, it will be bearing against the hole all the way through, not just the skin.

just wondering if these ideas are viable.

joe