Issue 18: May/June 2001
I received an urgent call from an old friend with a Pearson Commander. The boat is his pride and joy, and he has kept it beautifully. The under-deck reinforcement of the on-deck mast step was weeping water. He told me he thought he knew what it was but really did not want to confirm it: osmosis.
I was immediately able to assure him it was not osmosis, but it could be other problems such as a saturated balsa core. Osmosis usually occurs where the hull is immersed in water and, while the problem may migrate within the hull laminate into the topsides, I have never seen osmosis above the hull-to-deck joint.
The next day we met at the boat. The bolts holding the deckstep for the mast and the compression post underneath it in the cabin, were dripping water onto the cabin sole. I sounded the deck area around the mast. All sounded solid; no wet balsa. My analysis was that the mast itself had filled up with rain water to a height that created enough water pressure to force water down around the threads of the bolts, past the caulking under the bolts and onto the sole.
I cut out the caulking around the VHF coax cable where it entered the mast, about six inches above the deck. Bingo! Water — and a lot of it. I was kneeling on the cabintop next to the mast as I worked and so much water flowed out of the mast that my pants, socks, and shoes, were immediately soaked.
We still had more than 5 inches of water inside the mast, so the next step was to drill two 1⁄4-inch holes, port and starboard, in the mast wall just above the inside base of the mast. Again, lots of water. By heeling the boat to port, we assured ourselves there was no water left trapped in the mast.
Going below, we removed the nuts, washers, and caulking from the mast reinforcement bolts. The area was damp, but there was no running water. I recaulked the VHF coax cable hole but left the drain holes open to permit any water that entered the mast at the masthead to drain out at the mast base.
After a week of letting the bolt area dry, I reinstalled the washers and nuts on the bolts. Problem solved. There has been no migration of water down the bolts and over the cabin sole.
Naturally, the next time he has his mast down, he will want to recaulk the mast step and mounting bolts.
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