Issue: December 2007

Here are some tips to help you track down the source of seepage.

by Frank Lanier

It's a shame that leaks aren't as good at fixing themselves as they are at inventing themselves. But alas they are not. In fact, they're not even particularly good at revealing themselves in some cases--at least not until a good deal of damage already has been done. So fixing leaks--or at least discovering them so that someone else can--is up to you.

Patience and careful observation are virtues, and a good sense of smell doesn't hurt in cases of fuel- or sanitation-system leaks. The color and consistency of the leaked fluid itself can point to likely sources, too (coolant and transmission-fluid leaks are good examples). While hunting for leaks, you'll need good lighting, such as a small, bright flashlight or drop light. Depending on the type of leak, other necessities may include paper towels, a wet/dry vacuum, a small inspection mirror, washable felt-tip markers or sidewalk chalk, and a can of Soft & Dri spray deodorant (we will discuss this trick in a moment).

Water in the Bilge
Water in the bilge is never a good thing, particularly in large and increasing quantities. If you are faced with a leak of clear water, it's helpful to know whether it is salt water or fresh, but we know of only one quick and simple way of determining that--your tongue--and we'll leave it to you to decide whether the situation is urgent enough to require a taste test. If it is fresh water, and the boat is in salt or brackish water, your search can be narrowed down because the likely sources are either rainwater or the potable-water system. That is, it's not coming from outside the boat.

If it's salt water and you haven't run aground or otherwise damaged the hull, the likely suspects are through-hull fittings, seacocks (including the hoses), through-hull transducers, strut fasteners and any other hull penetrations below the waterline. Sailboats can also have issues with leaking keel bolts, while powerboats can leak around trim tabs, swim platform mounts or U-joints and bellows (for those with stern drives).

If the leak only occurs while under way, the engine raw-water cooling system may be the problem, or it could be a stuffing box for a driveshaft or rudder. Even driveshaft stuffing boxes in good working order typically leak three to four drops per minute while under way, because water is needed to lubricate their packing, but they shouldn't leak at all at the dock. Rudder posts may not leak a drop while in the static position, but gush water while under way; look for telltale signs of corrosion, rust or, in the case of bronze hardware, the greenish compound known as verdigris that is caused by contact with moisture. These typically signify a leak. If a stuffing box is the source of a serious leak, it probably needs to be repacked with square flax rope specially impregnated with wax and lubricants.

For sailboats, leaks under way when heeled could indicate anything from loose keel bolts to back-siphoning through the leeward bilge-pump discharge--often caused by a fitting with an inadequate (or missing) riser loop.

Tracing Leaks Back
Unless you spot a steady stream of water, you'll likely have to do a little investigative work to find the source of the leak. The water may drip or become noticeable a boatlength away from where the actual leak is. 

The first step in locating a non-obvious bilge leak is to pump or vacuum the section of the bilge where the leak seems to be coming in, dry it as much as possible, then place folded paper towels fore and aft of the area. Wait a bit, then check the towels to see if any are damp. If one of the end towels is wet, then the adjacent bilge area is suspect, meaning you simply move to that area and repeat the process. Work through as many compartments as the boat has and you should locate the one where the water is actually entering.

Once you've narrowed it down to one section of the bilge, there are a couple of ways to determine where the water is coming from. One option is drying the bilge and covering it with paper towels, then simply watching to see which ones get wet. Another is drawing a few lines along both sides of the bilge with a water-washable felt-tip pen or sidewalk chalk; check back after a bit, look for runs in the ink or chalk, then work your way up the hull till you find the leak.

Finally, if all else fails, you may want to haul the boat and check the exterior for damage. Once the hull is dry, you can also run some fresh water into the bilge and look for wet areas on the outside.

Exhaust Leaks
Engine exhaust-system leaks are serious, not only because of the potentially catastrophic engine failure they can herald but because they can introduce carbon monoxide into the interior of the vessel, with potentially deadly consequences. 

Dry leaks (gases escaping between manifold and block, for example) can often be found by feeling around for escaping exhaust or holding tissue paper near the suspected area and watching it for movement.

Wet leaks in manifolds, exhaust risers or mufflers are normally accompanied by corrosion, stains or "running rust" that originates at the leak itself. Lacking these signs, you can clean the area completely (nonflammable aerosol disk-brake cleaner works well), then spray on Soft & Dri deodorant and let it dry (this could take 5 or 6 hours on a cold engine). Once dry, the deodorant leaves a uniform coating of white powder that not only makes a leak easy to spot but also is easily removed.

The American Boat & Yacht Council (ABYC) recommends installing a carbon monoxide (CO) detection system on all boats with enclosed accommodation compartments and either an inboard gasoline propulsion engine or a gasoline generator. CO gas can come from incomplete combustion in either of these--but it can also be drawn into a vessel (through its ventilation system) from nearby boats running engines or generators. If your vessel already has a CO alarm, test it often, keeping in mind that the batteries have a fixed life-span. Units should be professionally inspected or replaced on a regular basis as recommended in the manufacturer's instructions. If your boat doesn't have a CO detector, get one; they are available in marine supply stores and can be easily mounted on a bulkhead or overhead.

Fuel Leaks
Lastly we'll tackle fuel-system leaks, which common sense says must be found and fixed sooner rather than later. For suspected fuel leaks at the engine (and this applies also to oil, antifreeze or any other engine fluid), clean and dry the area beneath the engine, then cover with paper towels or oil pads and check for wet areas, bearing in mind that the engine may have to be running to generate the leak. 

If you suspect fuel fittings, clean the connections with alcohol and tie a little wad of toilet paper or paper towel on each fitting. Go grab a cup of coffee, then come back and look for evidence of leaking.

Tracking down leaks is likely the closest thing to detective work most of us will do, and while it may not have the excitement of solving a cold case, finding a persistent leak does have its own rewards. Just don't let the other boaters at the dock know how good you've gotten in sniffing out leaks--they likely have a few of their own.