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Find a Leak 101

Questions and Improvements on Key West Boats Hulls, Parts, Hardware and Structural Components

Find a Leak 101

PostPosted by Tom Marlowe » Mon Jul 29, 2013 3:08 pm

How to find a leak:

Most leaks in boats can be attributed to plumbing or through hull fittings. Boats with live wells may also have leaks associated with the live well itself or the associated plumbing. It’s almost inevitable that a small amount of water will occasionally get into the bilge but enough to cause the bilge pump to cycle on and off while in the water is reason to find the leak. The source can be evasive but here are a few tips to help in that process.

Since live wells are the most common cause I suggest starting there. Find the outlet on the hull where the live well drain exits the boat and plug that hole. Since water can pass through the live well pump you should also plug the inlet to the live well pump. If you are not sure of the drain simply run some water in the well and notice where it comes out. Once the drain is plugged fill the live well to the top and see if water starts to accumulate in the bilge. If it does it’s most likely coming from the live well tank to deck joint. It’s usually simple enough to seal this joint with a bead of sealer around the top edge on the inside of the live well. I like to use 3M 4200 sealant for that purpose. It is also possible for the hoses or fittings in the well to leak. If you’ve plugged the drain on the outside the hose will fill with water and you should then be able to see the hose leak or at least see that water is coming from that direction. Water will also fill the hose and fittings from the live well pump and the pump itself allowing you to check the pump and plumbing for leaks at this time as well.

Testing through hull fittings in the hull not associated with the live wells is similar. Install the drain plug and run water into the bilge until it is high enough to cover the fittings. If water is getting in it will also come out at the same spot. The most common source of a leak in the hull found during this type test is the drain plug. Through hulls as used in floor drains seldom leak unless they are broken. The hoses going to those through hulls are high quality, double clamped, and sealed with caulk. No procedure is fool proof though.

Other possible sources of leaks include items such as fasteners used in the installation of accessories. Examples would be trim tabs, transducers, even engine mounting bolts. In boats with wash down pumps it’s also possible for some of that plumbing to leak. If other sources have been eliminated and still no leak is found it may be time to check that. Since the intake for that pump is usually on the bottom of the hull you may need an adaptor to feed water to it, or if it’s convenient you can back the boat into the water. It’s not necessary to take the boat off the trailer to test a wash down.

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Tom Marlowe
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