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Sussing Out the Sneaky Ones

Leaks you can see on your boat are one thing. Tracing the source of ones you cannot see require some creative thinking.

Water leaks often require sleuth work. Water is ever present above and below the waterline. Rain, washdown water and spray look for ways to seep in through the topsides. Beneath the waterline, water is pumped in through the engine and other machinery for cooling, and can find countless holes for thru-hull fittings, transducers and underwater lights. Hoses and clamps are critical for watertight integrity, as water patiently waits for any chance to sneak in and cause problems.

For instance, while prepping my boat for a trip to Nantucket, Massachusetts, one summer day years ago, I replaced a raw-water pump impeller. When I shut down the diesel after checking my work for leaks, I heard a drip. I traced the sound to a pipe behind the engine that was weeping a drop every few minutes from a welded joint. There was no way to change out the pipe before I was scheduled to leave the next morning.

I wiped the weld area with a clean rag and acetone, and cut and sliced a piece of hose that would wrap around the pipe a few inches on either side of the weld. I mixed up a batch of Marine-Tex epoxy, took another pass with the acetone-soaked rag, lathered the epoxy over the weld, and wiped the inside of the hose with a thin layer of epoxy as well. Wrapping the hose around the pipe with a pair of stainless-steel hose clamps at each end did the trick. The drip was arrested until I replaced the pipe at the end of the summer.

Visible leaks like that one are easy to access and simple to address. Not so with leaks that appear out of nowhere and then come and go.

I recall the case of a friend who returned to the marina after a hard ride offshore and spent the rest of the afternoon putting his boat back together. He had a wet carpet in the middle of the stateroom and couldn’t figure out where the moisture was coming from, since there were no portlights or overhead hatches in the stateroom.

Old caulk can be affected by mildew, allowing water to seep beneath it

Old caulk can be affected by mildew, allowing water to seep beneath it

When I lifted the mattress, I saw the source immediately. The evaporator pan designed to collect and drain the condensate from the air conditioner was overflowing. Lint and other debris had clogged the drain tube, causing the condensate to spill onto the sole beneath the berth. It eventually wicked out onto the carpet.

Because this was a new boat, I cautioned my friend to check his air conditioning pans and the drain tubes monthly, and to clean the filter screens as well.

One of the most confounding and memorable leaks I ever encountered occurred in the lower forward bunk aboard a 45-foot cruiser I ran. Apparently, the leak had been a problem for a while, although what I noticed first was a subtle scent of dampness in the stateroom whenever the air conditioning was off. It was not until I lifted the bunk cushion and felt the weight and wetness that I realized I had a perplexing problem: As with my friend’s boat, there were no hullside opening portlights.

I was able to dry out the cushion while I searched for wherever the water was entering. Originally, I assumed that there were unbedded holes where the screws attached the stainless--steel bang strip to the rub rail because I removed a few fasteners in the bow area and did not see much caulk on the screw threads. Recaulking the screws and adding more caulk in the holes was the solution—or so I thought until I noticed a wet bunk again a week or two later.

So, I dried the bunk cushion one more time and then placed a plastic sheet under it to protect it from the dampness. And, I scheduled a haul out. When the boat was on land, I was able to better inspect underneath the rub rail, and noticed a void where the bang strip, hull and foredeck assembly came together. Globs of caulk would have been the solution at the time of the boat’s manufacture, but out on the ocean, pushing the bow into head seas apparently worried away enough caulk to provide an opening.

The few inches of void were several feet forward of where the water eventually leaked into the boat to wet the bunk, but I was able correct the flaw by cleaning out the void and repacking it with an adhesive sealant. The bunk remained dry, and the boat was sold a year later. The new owner never said a word, and I assume the cure remains successful to this day.

While the leak on this boat was due to a manufacturing flub, poor boat handling also can open the door to leaks. I recently took a boat out on a sea trial for a broker on a particularly rainy day. The buyer was aboard, and the broker asked me to look at an obvious leak near a porthole in the forward stateroom. Water had stained the valance, and it looked bad.

Marine stores carry various types of caulk and adhesive sealants, and good results can occur when instructions are followed for surface preparations. 

Marine stores carry various types of caulk and adhesive sealants, and good results can occur when instructions are followed for surface preparations. 

The porthole was a new replacement for one that was damaged during a docking maneuver before the boat went up for sale. From the dock, the porthole looked acceptable, but on closer inspection, it was slightly angled compared to the midship porthole. I finally realized that it was securely installed, but that fiberglass damage to the hull was causing it to appear out of alignment. The repair worker had relied on caulk instead of new fiberglass laminates and putty to mount the porthole. Rainwater running down the hull found an easy way to come aboard and damage the valance.

By the end of the sea trial, the buyer was happy with the boat, but insisted that the porthole be removed, the surrounding fiberglass repaired, and the porthole made watertight before completing the sales contract.

Marine stores carry various types of caulk and adhesive sealants, and good results can occur when instructions are followed for surface preparations. However, I have experienced issues with good installations suddenly going sour. Although caulks are sold in sealed, fresh tubes, they do age on the shelf, even if unopened. Caulk that sits around a couple of years and goes through changes in air temperatures may prove problematic, causing a leak or other premature failure. Before buying any caulk, check its date of manufacture.

Old caulk also can be affected by mildew, allowing water to seep beneath it. A wise, old skipper told me that caulk is used to keep water out, but that it also can trap water in. If you see any caulked hardware, fittings or fasteners aboard your boat with rust stains, it is a sure sign that water is getting between the caulk and the metal. It is a firm warning that the caulk has lost its prime and that leaks may soon follow.

They always find a way.