Re-coring the Chainplate Areas–Refit Time, Part two…

Dreadnought 32 Idle Queen
Mast off. Ready to remove chainplates.

What follows is a description of a repair that I did not want to get involved in… After removing the damaged parts of the hull and seeing how well-bonded everything still was, I am pretty sure that Idle Queen would have survived another circumnavigation without issues from this area if I had just replaced the chainplates and continued sailing her. But, even if I had stopped new water from getting into the hull, the water that was already inside would have continued to cause further damage by rotting the core, slowly prying the skins from the core with each freeze cycle, and causing hydraulic damage when impacts from waves against the outer skin pushed the water into new areas. Ignoring the problem would have eventually meant the end of the boat because the hull would have weakened and the required repair would have just continued to grow.

Dreadnought 32 Idle Queen Chainplate area
Chainplates removed. Note water draining from hull…
Dreadnought 32 Idle Queen Core repair
Drilling holes to determine the extent of the saturated core- Note water draining out…

I received a lot of advice from passers-by as I was contemplating what needed to be done after I removed the chainplates and saw water draining from the resulting holes. Mostly, the suggestions were to try injecting products like epoxy, or Git-Rot into the problem area. That would have been little better than just leaving the whole thing alone, as there is no good way to remove the water without completely taking off one skin. Leaving moisture in the core leaves the original worries, and by talking to people who have made these sorts of repairs before, I learned that trying to inject anything into the area is very close to useless.

The first steps of the repair, as already mentioned in the last post, were to find the extent of the moisture penetration, and then remove the outer skin. It was tough to drill those first few holes, but once I got past that psychological hurdle, the work went quickly. I could immediately tell where the core was wet or not when the drill bit brought forth either a stream of water (from the plywood area), damp, but still solid balsa, or dry balsa dust. As an interesting aside, a moisture meter passed over the hull from the outside did not register the extent of the moisture hidden inside. The outer skin on this Dreadnought 32 is between 1/4″ and 3/8″ thick. Maybe a moisture meter works better on thinner-skinned laminates.

Dreadnought 32 Idle Queen core repair
Attempting to keep some of the fiberglass dust off of me while cutting and prying. Note the shredded fiberglass due to a tenaciously bonded core…

I taped off the edges of the area that I intended to cut out and then picked up my oscillating multi-tool (a knock-off Fein multi-master) with a metal/fiberglass blade and began to cut the outline. Work slowed down a few minutes after getting started as the glass fibers dulled the metal teeth of the blade. Partway through this step of the project, a friend loaned me a Dremel high-speed circular saw with a diamond-tipped blade. I was able to set the depth of the cut to just more than the thickness of the outer skin and zip relatively quickly along each planned cut. At this point, I was thinking that this project was going pretty well and I was only taking about as long as I planned. Of course, that meant something unexpected had to come up soon!

Dreadnought 32 Idle Queen balsa core repair
Removing the outer skin, port side. First section off!
Dreadnought 32 Idle Queen core repair
Once the skin was off I still had to chisel out all the wood.

That problem came in the form of a good bond between the balsa and the skins. I had built model airplanes when I was a teenager and was pretty familiar with the soft, easily-cut wood from hours of shaping it into wings and fuselages. I hadn’t expected that it would be difficult to get the outer skin off, and actually had visions of popping it off intact and re-using it. Ha! An hour after I began trying to pry the outer skin off one side of the hull it was totally obvious that the balsa core was going to force me not only to destroy the outer skin, but also spend a couple of days doing it. I began with a hammer and a very large screwdriver but only succeeded in tearing the outer laminations of the skin off. Lots of mat remained stubbornly glued to the balsa. After experiments that involved using every prying tool I had access to, including an air-powered chisel, the method I settled on was to cut the skin into two-inch square chunks and then pop each one of the little squares off. That meant a lot of lines to cut! I am amazed at how well the diamond-tipped blade held up, but towards the end it was more burning through the fiberglass instead of cutting…

Dreadnought 32 Idle Queen core repair
Removing old wood core from port side.
Dreadnought 32 Idle Queen stitched plywood
Interesting stitching in the plywood reinforcement of the chainplate area. Lots of people tell me this was to hold it in place, but the stitches don’t go through all the laminations, as you can see in this picture. The plywood reinforcement in this part of this boat was simply pushed into a bed of thickened resin as the hull was laid up, and then glassed over.

Once the skin was removed, I had to chisel all the rest of the core material out. This was complicated, again, by the excellent bond between the fiberglass skin and the balsa wood, and also by the fact that the plywood part of the core extended beyond my cut-out area. It was very effective (and dusty) to take a high-speed grinder and 24-grit sanding discs to remove the balsa. A sharp chisel also did the job, but was slower and I had to be careful not to go into the inner skin. The plywood was a pain because I wanted to remove it from between the skins at the upper edge of the repair. I didn’t cut the outer skin all the way to the rubrail (which is un-cored) because that wouldn’t have left enough room to get a 12-1 taper for a strong repair of the outer skin. I slowly cut it out with the oscillating multi-tool.

Dreadnought 32 Idle Queen balsa core repair
Starboard side all cleaned out and ground down– almost ready for new core, but I still have to build up the depression in the top part of the repair area where there used to by plywood.

Once that was finished, it was simple to finish grinding a 12-1 bevel into the surrounding outer skin, and finish grinding all of the inner skin with 36-grit in preparation for bedding in new core material, which is 1/2″ end-grain balsa. Instead of putting plywood back where it had existed before, I built the area up with layers of “1708”, which is a biaxial, non-woven fiberglass material which consists of two layers of continuous fiberglass strands (weighing 17 ounces per square yard) running 45 degrees each side of vertical (biaxial) stitched to a layer of 8 ounce mat. Layers of this material were laminated until the surface was level with the surrounding area where balsa was to be placed. The balsa was cut to fit the repair area, and then bedded in a thick mash of resin, chopped strand, milled fibers, and fumed silica (Cabosil).

Dreadnought 32 Idle Queen balsa core repair
Vacuum-bagging the new balsa core in place

Next order of business was to cut plastic to use as a “bag” to hold the balsa in place. I put an old through-hull mushroom in the middle of it. The through-hull was scored so it could suck air in even if flat against a surface. Once everything was cut to fit, and the filler mixed, I rolled resin onto the balsa to saturate it. It took a few heavy coats before it stopped sucking resin in like a sponge. I catalyzed the thickened mash mixture and spread it over the whole area with a heavily v-notched spreader, working quickly. The balsa was all pushed into place until mash squeezed out around all the edges. The ”bag” was taped over the area and a shop-vac used to apply pressure to the area. This does not apply the same pressure as a specialized high-vacuum pump, but it still applies a lot of force to hold the core tightly against the inner skin while the mash cures. It applied more pressure than I could by hand, as more mash squeezed out from behind the balsa.

Dreadnought 32 Idle Queen hull repair
Adding fiberglass to the re-cored area.

After the core had cured in place, all of the scores in the balsa were filled with thickened resin. This prevents water migration in case there is ever a break in one of the skins. The balsa was cut out where the chainplates mount so they mount over solid glass. Then, all of the new balsa core was sealed with resin until it stopped soaking it in. Additional ayers of 1708 cloth were built up to make up for the difference of thickness between the core and where plywood had been used originally. There are as many as 15 layers of 1708 in the area of the chainplates.

Dreadnought 32 Idle Queen hull repair
New skin lamination complete. Next step is fairing

I made templates of the repair area and used them to cut layers of 1708 biaxial mat for the new outer skin. Using a 3/8″ nap roller, I wet the area with resin and saturated the glass. Each layer was carefully laid in place and the extra resin squeezed out with a fiberglass laminating, or consolidating roller. It was hot work, with the sun making sure that I was soaked no more than 10 minutes after beginning work each day. After the final layer of 1708 was laminated, I covered the whole repair with a layer of “peel ply”, which is basically a fabric like nylon coat liner that doesn’t stick to the surface. When removed, it provides a fresh, textured surface that is perfect for adding more laminations, or fairing material. Saturated with resin, and then painted, it protected the repair areas while I went away for the summer to work.

To be continued…

 

2 thoughts on “Re-coring the Chainplate Areas–Refit Time, Part two…

  1. Hi, My name is Tony. I meet you in Oriental a couple of years ago. I was looking at the boat “BOUNTY” that was for sale nearby. I am the guy that was a retired “Fiberglass Man” from up North. I just came across your site. YOU DID AN EXCELLENT REPAIR !!! Hope to meet you again some time………. Tony and Pam

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