Whether it's an accumulation in the bilge or just a wet aft cabin mattress, in either case, the sources are almost endless. The obvious question is, when does it leak ? All the time, or only after some specific event.

Rain water, washing the boat, bath shower area moisture, hull and fitting leaks, engine leaks, condensation, beverage spills, holding tank leaks, sinks overflow, swimmers and water skiers, refrigerator and air conditioner condensate lines, fresh water system, etc. are all contributing factors on a regular basis.

A little detective work could easily locate the source in no time at all. Sometimes it isn't easy to find and or fix the problem, but it is less expensive to do the detective work yourself than to try and pay someone to find it for you.

Engine Sources
  • Engine coolers.
  • Wet Exhaust system manifold or block cracks.
  • Hot water heater hoses and or fittings (some hot water heaters use the cooling water from the engine to heat the water you drink).
  • Loose or missing engine block core plugs.
Thru-hull fittings
  • Prop shaft.
  • Rudder posts.
  • Back flow from bilge pump or shower discharge fittings.
  • Loose depth sounder thru-hull fittings.
  • Prop shaft strut bolts.
  • Speedometer tube between dash board and transom.
  • Water cooled air conditioner lines and fittings.
  • Air conditioner condensate pan drain.
  • Refrigerator condensate line.
  • Water tank and fitting leaks.
  • Condensation on the hull itself.
Topside Leaks
  • Rub rail.
  • Cleats.
  • Safety rail stanchion bases.
  • Windshield seam and fasteners to the deck.
  • External electric horn wiring under horn base.
  • Anchor locker hatches and or bins.
  • Cock pit drain fittings and hoses.
  • Spot light base.
  • Running light base.
  • Under wood, plastic or metal step pads.
  • Improperly located engine room vent covers.
Hull Delamination and Balsa Core Saturation

Although somewhat rare, the following two leak sources should be considered.

Some boat hulls and or decks, have a balsa core between two or more layers of fiberglass.

Thru hull fittings and holes drilled into and thru this type of structure are hard to seal and can water log large sections of the laminated balsa. Any fitting or hole run thru balsa laminates should be sealed and reseal every few years to reduce the chance of balsa saturation and subsequent deterioration.

Delamination on the other hand is a structural fault in the hull caused by impact or abuse that has separated the layers of fiberglass laminate. Delamination isn't usually a vertical crack. Think of it as being similar to corrugated or laminated cardboard, where the center of the laminate has been crushed or has disappeared. Water running between delaminated fiberglass panels can travel a long way before it emerges into the boat.

Testing for Leaks

Leaks caused by Rain and or Washing

Leaks caused by rain and or washing of the boat should be tested with a hose to simulate the event.

But don't just soak the whole boat. Isolate your testing to a small area at a time. Since water can flow a long way from where it enters the boat to the place you notice it. And don't be in a hurry. Give the water a chance to flow because sometimes dirt collects in cracks and holes and will repel water for a short time until the dirt gets saturated with water. Removing cushions, carpet and panels from the test area and the use of a screw driver and powerful flashlight are the only tools you will normally need.

Testing for Leaks in Sanitation Systems

One quick thought to get you started on this topic is that even if you smell an odor from the sanitation system, that doesn't mean it is leaking. Some sanitation hoses have a tendency to absorb the smell from its cargo and will have to be replaced to solve the problem. You could try flushing and soaking the system with chlorine to see if this is your problem, but usually this only lasts a short time. Over the years manufacturers have done a better job of solving this problem, so it might be a good idea to just replace the sanitation hoses.