Well-maintained through-hulls and seacocks could one day save your yacht—or your life.

By Capt. Ken Kreisler — April 2003

More of this Feature • Part 1: Hull Care • Part 2: Hull Care • Part 3: Hull Care
Related Resources • Maintenance Index

Pop quiz: How many holes are there in your boat’s bottom? There are several, for sure, and probably more than you think. Raw-water inlets for engines, gensets, heat exchangers, plumbing, and other systems riddle the underside of your hull. Next time your yacht is hauled (or before you recommission her this spring), inspect the bottom and take inventory of your through-hull fittings. Necessary as they are for the systems they serve, each penetration is also a hole that could one day sink your boat. That’s why it’s vitally important to keep these fittings in tiptop condition.

But even if all your through-hull connections are sound, what if a hose, pipe, or fitting inside the hull fails? If the failure is below the waterline, water may still enter and could ultimately sink your boat. Your best defense against that dire possibility is to ensure that every through-hull penetration is fitted with a proper seacock.

Here’s what you need to know about through-hull fittings and seacocks, plus a regimen for inspection and maintenance. It’s one area where an ounce of prevention is worth a ton of cure.

Through-Hull Fittings
As the name implies, a through-hull fitting is a fixture installed in way of a hull penetration, such as for a water inlet or a drain. It is a passive device whose function is simply to let water flow in or out and to provide a point of attachment for the internal piping. Through-hull fittings may be fabricated of metal or plastic, each material having its pros and cons.

Metal through-hulls, especially for fittings that protrude beyond the surface of the hull, are more resistant to damage caused by scraping against a piling or a submerged object. The downside is that virtually all metals are susceptibile to corrosion or galvanic action. Bronze is the most commonly used metal for through-hull connections because of its relatively high resistance to corrosion.

Plastics, on the other hand, are inherently noncorrosive and nonconductive but may degrade after long-term exposure to ultra-violet (UV) light. Most plastic through-hull connections are made of Marelon, an impact-resistant, noncombustible, fiberglass-reinforced material with UV inhibitors, formulated for marine applications.

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