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Smart Through-Hull Management

Keep the Water on the Outside

Checking these items now can prevent wet feet—and worse—later.

Through-Hull Fitting

Spring and fall are the yin and yang of a northern boater’s world. Fall’s the low point, when we’re facing a winter without our favorite toys while spring is the high, as we see the new boating season in the offing. At both times we’re faced with a plethora of chores, but especially in spring.

Regular readers of this column know that at both times I usually avoid offering the typical list-of-things-to-do column. Power & Motoryacht readers, being seasoned boaters, already know those drills, and besides, many of you will hire someone to do them for you. Instead, I prefer to use these columns as opportunities to draw your attention to maintenance areas that you might otherwise neglect, tasks that don’t appear on your typical list of things to do.

I’m devoting this column to two items that you’ll pass over many times as you do your spring check-out and to which, until now, you may have never given a thought. Yet failure to do either could have devastating consequences. I’m talking about through-hull fittings and raw-water hoses, which I’ll bet you haven’t looked at in a while. And understandably so, as they’re famously durable and designed to withstand considerable abuse and neglect—but only up to a point.

For reasons of simplicity and safety boatbuilders try to minimize the number of through-hulls in their boats but they can only go so far. Even a boat with a sea chest will probably have a half-dozen of them. Through-hulls can be made of bronze alloy or composite; each material has its place and advantages. Bronze is usually the material of choice for large through-hulls like those for engine cooling; it’s more durable and tolerant of abuse but is subject to oxidation that can result in seizure. Composites, not prone to oxidation, are typically seen in smaller applications like air conditioning and raw-water washdowns.

Despite what you may have heard, through-hulls of either variety are not maintenance-free, although the amount of attention they require is minimal. Simply opening and closing them every couple of months will usually preclude the accumulation of internal corrosion, ensuring smooth operation and a tight seal. But of course most boaters don’t do that, especially where hard-to-reach fittings are concerned. So spring’s a fine time to locate all your through-hulls (you do know how many you have and where they are, right?) and exercise them. When you do this the first time you may be surprised at how difficult some are to reach, a sobering thought considering that you might need to close one quickly to keep your boat from sinking. I have a friend who’s painted the handle of each of his through-hulls Day-Glo orange so he can quickly spot them—not terribly aesthetic but undeniably effective. He’s also recorded their locations in his log.

Sadly, easy access is not always the prime criterion when a boatbuilder positions a through-hull, which is why you might find one under an engine or generator or beneath a flooring panel. There’s usually no practical way to relocate a though-hull—it pretty much needs to go near the hole in the hull—which is why knowing the location of each is important.

Some bronze through-hulls can be disassembled for cleaning and have zerk fittings, so you can grease them. Disassembly is typically not necessary unless there’s a problem but greasing you should do annually. The only other maintenance is ensuring internal passages are clear of obstructions like marine growth. Don’t expect your boatyard to do this when they paint the hull. Do it yourself, but of course only with the boat out of the water. All you’ll need is a flashlight and a scraper or screwdriver to remove the growth.

If you encounter a jammed through-hull be wary of how much force you apply to it. Pipe wrenches and handle extensions are no-nos. Bronze can break, and even if you do free the fitting by applying extraordinary force, you may also break its seal with the hull. And never try to free a frozen through-hull when your boat is in the water. If you break it or induce a leak your options will be limited to say the least.

Hoses need attention too. Those below the waterline must be double-clamped for safety. Those clamps can loosen over time due to vibration, so tighten them annually. And hoses deteriorate, especially those connected to mains; squeeze them along their length to make sure they’re firm. The diesel shop I used to work at recommended changing engine and genset coolant hoses every five years. When we did it we found a shocking percentage of the old hoses were about to fail.

An annual once-over that includes attention to often-neglected items like through-hulls and hoses is a good idea regardless of where your boat lives. If you inhabit the higher latitudes, however, spring launch provides a perfect opportunity for a checkup. But even if you live where winter layup is unnecessary, it’s still the best insurance for a carefree boating season.

This article originally appeared in the April 2016 issue of Power & Motoryacht magazine.