You'll find this problems in places where deck hardware and fittings are through-bolted (or if there's a crack in the surface). It's caused by water infiltrating the balsa core layer where the seal was inadequate or the fitting loosened up and caused a breach. You can tap around suspected areas with the handle of a screw driver and hear the difference between a dry area and one that's soaked in water. Thud vs tap I guess you'd call it. Someone may correct me, but I believe the cored areas are limited to horizontal surfaces--deck and house top only maybe? t On Thu, Jun 5, 2008 at 10:59 AM, Andrei Caldararu <andreic@math.wisc.edu> wrote:

Dear all,

as I explained in my earlier messages, I am looking at buying an older, 1975 M-17. Some people here have expressed concern about deck core rot. How does one tell? What does it look like? Where to look for it? Since now I have a Compac 16, I never had to contend with the issue.

Thanks,

Andrei.

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The cabin roof, fore and side decks were built with balsa core. Essentially, a thick outer skin of fiberglass (the part you see on the outside), then a layer of balsa core (small squares) is laid over that, and then covered by an inner skin of fiberglass. The resulting sandwich works like an "I" beam and is very strong for it's thickness and weight. But if any deck hardware is mounted, it means the builder had to punch a hole through the core to install screws with backing plates and nuts, including the sides of the cabin top where the side chain plates are mounted. Unless the holes were drilled out oversized and backfilled with resin (they were not at the factory), any leaks past the fitting caulk and screw goes into the balsa core. There it may stay, soaking into the core like a sponge. Eventually, it rots out. You can tell by tapping on the cabin top with a hammer or hard plastic end of a large screw driver. Sounding for damage. You want to hear a sharp, loud report vs. a dull "thunk" sound. You are tapping....not hitting hard enough to really damage anything. You can also tell by pulling a fitting and digging around in the hole with an ice pick or some other small, skinny probe. If it's wet, brown gunk will be evident. If it's good probably nothing will come out of the hole. Another good reason to hire a surveyor if you have any doubts about the boat. They sound but also use moisture meters. Rotted core can be fixed, but it's not a job for beginners. To anyone else who has not done it, I'd advise fixing all the holes if your core is still sound. It's not that big of a deal. Drill your holes out a little oversized (about 3/8") from the inside, then tape over the hole from the inside (blue masking tape), then backfill the hole from the outside (outside hole is not drilled out...it's the small, original sized hole). Backfill with thickened epoxy. Use a syringe of about 3 cc. The epoxy will spread into the core, so backfill at least twice. Once the epoxy sets up, drill holes out again. Once you have sealed the hole up, any moisture that gets by the caulk goes right on by and the core stays dry. Pulling all the deck hardware, cleaning up, fixing holes, and rebedding is a weekend job at most (unless you have rot). The big time is waiting for the epoxy to cure (overnight). Howard On Jun 5, 2008, at 12:59 PM, Andrei Caldararu wrote:

Dear all,

as I explained in my earlier messages, I am looking at buying an older, 1975 M-17. Some people here have expressed concern about deck core rot. How does one tell? What does it look like? Where to look for it? Since now I have a Compac 16, I never had to contend with the issue.

Thanks,

Andrei.

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