Fexas P.I. Page 2
Spectator — December 2002
By Tom Fexas
|Part 2: The Case of the Flapping Hull Sides|
I soon learned that the boat had been undergoing major engine work while in protected winter storage in the water and that the exhausts had been disconnected at the engines. I immediately suspected foul play (or at least a foul mechanic). It is rather common for boats afloat with exhausts disconnected at the engines to sink when water backflows through the exhaust penetrations in the transom and into the bilge through open, unplugged pipes, especially when there is little rise between the transom penetrations and exhaust manifolds. This boat's exhaust pipes, however, penetrated the transom well above the water--four inches or so above the waterline--so how could water have gotten into the bilges? The vessel was fitted with a winter cover, which, instead of being peaked for snow and rain runoff, was virtually flat on top. Knowing the date the boat sank, I checked with the local weather bureau. Sure enough, on the night of the sinking there was a heavy snowstorm. Knowing the depth of the snowfall, the weight of snow, the area of the canvas, and the pounds-per-inch immersion figure for the hull (which I calculated), I had my answer. Elementary, my dear reader. I was able to prove mathematically that the weight of the snow on the canvas was sufficient to immerse the boat to a point that the transom exhausts became immersed, allowing water to flow into the boat. The insurance company was off the hook.
Case of the Flapping Hull Sides
How could such a catastrophic failure have occurred? My investigation revealed that during the refit the gelcoat had been peeled from the bottom for antiosmosis treatment using a hand-operated gelcoat-peeling machine. After chipping away some fairing compound, close inspection showed the eight or nine plies made the transition around the hard corner from the bottom to the topsides at the chine, where the failure occurred. What happened was simple and obvious: The gelcoat-peeler operator had gotten a little too frisky at the chine and cut diagonally through all but one ply of fiberglass. This left fiberglass "end grain" from the hull sides exposed to the water. When the boat was at high speed, hydraulic pressure at the point of impact pumped water up between the plies, causing each to delaminate. We recommended rebuilding the area, and today the boat is happily cruising South Florida waters as good as new.
Boats that only turn to starboard (Republican boats?), hulls that porpoise, weird vibrations, and strange structural failures--I love this stuff! If, however, you suspect your wife is diddling or you lost your Yorkie, call someone else. This P.I. only does marine work.
Tom Fexas is a marine engineer and designer of powerboats. His Web site is www.tomfexas.com.
This article originally appeared in the January 2003 issue of Power & Motoryacht magazine.