June 27, 2013

Tracing the source of leaks

IF THERE WERE any justice, a fiberglass boat wouldn’t leak. After all it’s built like an eggshell. How could water get in?

All too easily, apparently, because there IS no justice. The trouble is that fiberglass hulls have holes in them. In most cases, the number of holes is comparatively small — dozens or scores — but in others it can be in the hundreds.

Most boats have large fittings that let fluids pass right through the hull, in and out. The engine cooling water comes in that way, for example, and water for flushing the head goes out that way when the Coasties aren’t watching. The galley sink drains that way, too.

The through-hull fittings are bedded in compounds to prevent leaks, but as boats age, the compound shifts, oozes out, or becomes more brittle, allowing water to enter. Old seacocks often leak, too.

All boats have holes through the deck and cabintop for various fittings, and some have hundreds of holes for screws holding down strips of teak decking. In theory, all these holes are sealed. In practice, many will leak when it rains or when spray hits the deck. And if you have a cabin liner, or ceiling boards on the cabin sides, tracing the source of a leak is notoriously difficult.

This may sound a bit whacky, but the best way to find where the water’s coming from is to seal the boat and pump in air at low pressure. Brush soapy water over the superstructure and watch for bubbles.

You can use duct tape and butyl putty to seal the hatches and ventilation holes temporarily, and the air pressure doesn’t have to be high. A few pounds per square inch will do it.

Today’s Thought
Where least expected, water breaks forth.
— Italian proverb

I want to know
How fireflies glow.
Do they carry
Little Exides
Slung beneath
Their tiny bexides?

(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)


KevinH said...

The reason that boats have really heavy keels is to make sure that they float with the topsides above the water. Otherwise, as we have all seen,the moment it begins to rain, - water pours into the boat from above from an infinite number of locations. So make sure your boat floats the right way up, otherwise it will sink in a flash. !

The Unlikely Boatbuilder said...

I have a wooden boat with an impossible-to-find leak in the deck. I never heard of the air pressure method, but it sound like it might just work! Thanks for the tip.

FrankO said...

An ultrasound leak detector is the best method, but the instruments are pricy; $100 and up, way up. Smoke generating leak kits can be had for $25 or so. Or if you have a point and shoot electronic thermometer, warm up the inside of the boat and scan the thermometer over the outside of the suspect area. Any holes where the warmer inside air leaks out will show up as a warm spot on the thermometer.