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How To

Change Those Old Thru-Hulls

By Randall Litchfield

If some of your thru-hulls look like an old pipe peened over a copper washer, it's because that is exactly what they are. And you should change them on your next haul out because they have been known to sink Albergs.

What happens is that the solder joint holding the pipe and washer together eventually corrodes and fails. The pipe part of the thru-hall literally falls inside your hull, followed by a furious half inch stream of water. Hopefully you're on board at the time and have an emergency wooden plug ready to hammer in. If not, the next time you visit your boat it will be sitting on bottom.

Upgrading these substandard thru-hulls is an easy procedure requiring just a few simple tools and steps:

1: Visual Inspection - If your thru-hull looks like the one pictured at far right, with the outlines of a half-inch pipe and washer visible, it's time to change. You can see where the joint between pipe and washer has disintegrated. Proper thru-hulls have a gently rounded, smooth surface.

2. Remove the hoses and valve/seacock - Start by removing whatever hoses are connected to the inside valve or seacock fastened to the thru-hull. Then take a wrench and unscrew the valve. This was easy on my boat Impromptu, because it has always been in fresh water. Otherwise the procedure may require generous amounts of WD-40 and time. If it is the original gate valve (looks like your backyard hose faucet) it's advisable to replace it with a bronze seacock, because gate valves are also known to seize and fail.

3. Extract the thru-hull from the outside - Although the original sealant will have largely disappeared (no 5200 back then), it will still be a tight fit and difficult to extract. Pounding with a hammer from the inside doesn't seem to work. You may have to do what I did and fabricate Ye Olde Thru-Hull Puller (right). Drop a six inch bolt down the thru-hull from the inside with a big washer on it to grab that end. On the outside I ran it through a four inch square piece of scrap aluminum, wide enough to span a couple of wooden spacers. Then simply thread the nut and tighten and this will pull out the thru-hull.

4. Enlarge the holes to ¾ inch - The originals were half inch, but its very hard to find replacements (probably why Whitby made their own). Better to enlarge the hole with a grinder on the end of a drill and replace with a ¾ inch thrull-hull. Your engine would probably prefer a ¾ inch water intake anyway

5. Dry fit and clean the hole with acetone - On the inside you will need to fashion a wooden plate to conform with the curvature of the hull. As my old plates seemed in good shape, I simply reused them.

6. Install the new thru-hull - First, apply generous amounts of 5200 sealant around the thru-hull flange and then insert in the hole, making sure it's snug fit. Next, you need to tighten the bronze locking ring on the inside - a two-person operation as you will need someone on the outside preventing the thru-hull from spinning as you tighten. They will need a tool to hold it still, and for this I constructed a special-purpose wrench from a short piece of half-inch copper pipe (my old thru-hull!) You cut two small notches in the end to lock onto two small bumps on the inside of the new thru-hull, put there for this purpose.

7. Wipe off the excess 5200 sealant with varsol - It cleans up easily provided you don't wait too long. Let the sealant dry for 24 hours and then tighten the ring some more. Now you're ready to install the seacock and reconnect the hoses.

8. When you launch, take extra care to check these thru-hull for leakage while your still in the slings!