One Good Turn

One Good Turn — Maintenance April 2001
One Good Turn
Don’t let a faulty through-hull fitting sink your boat.

By George L. Petrie
 More of this Feature
• Part 1: Through-Hull Fittings
• Part 2: Through-Hull Fittings continued
 Related Resources
• Maintenance Editorial Index
 Elsewhere on the Web

For want of a nail, the kingdom was lost. The devil is in the details. It's the little things that count. Folk wisdom abounds, warning us not to overlook seemingly minor things, the stuff we often take for granted. With that thought in mind, ask yourself how long it's been since you inspected the seacocks and through-hull fittings on your floating palace.

Hidden in the bilge, seacocks are often hard to reach. Out of sight and out of mind, they're all too easy to forget about. But failure to properly maintain your seacocks and through-hull fittings could one day cost you your boat or even your life. So before you put to sea, give these vital components a thorough once-over. Here's how.

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 drain. Its function is simply to let water flow in or out and to provide a point of attachment for internal piping. Through-hull fittings may be metal or plastic, and each material has its pros and cons.

Metal through-hulls, especially those 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 have some susceptibility 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 ultraviolet (UV) light. Most plastic through-hull connections are made of Marelon, an impact-resistant, noncombustible, glass-reinforced material with UV inhibitors, formulated for marine applications.

The outboard side of all through-hull fittings should be inspected and cleaned at least once a year or each time the vessel is hauled. Remove accumulations of barnacles or marine growth, and inspect the fitting itself to ensure that water can flow freely in and out. If your bronze fittings appear bright and shiny, that may be an indication that galvanic corrosion is occurring.

While the hull is out of the water, note the location of all through-hull fittings, and make sure you know how to access and inspect each of them from inside the hull. Several times a season, check to make sure all fittings are tight. Don't ignore the possibility that impact with a piling or even a floating object may have loosened something. Look for corrosion and stains that could indicate a slow leak or a leak that occurs only while underway.

When purchasing a new or used boat, check that all through-hull fittings are well secured and have backing plates inside the hull to reinforce them at the point of connection. Care taken with the installation of through-hull fittings may be indicative of a vessel's overall quality of construction.

Next page > One Good Turn continued > Page 1, 2

This article originally appeared in the May 2003 issue of Power & Motoryacht magazine.

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