This a continuation of a series of articles arising from problems we find repeatedly in our work as marine surveyors, referencing a specific boat problem and discussing our experience and involvement with the problem. Water accumulates in bilges. The first thing to determine is whether it is fresh or seawater (assuming the vessel is in the ocean). For healthy options to determine if your bilge water is fresh or salt, read this (https://themarinesurveyors.com/dont-drink-the-water/).
The specific boat problem in this case is unique and interesting (to us boat nerds). Seawater accumulation in bilges is not. Before we get into the details of the interesting case, lets discuss some of the more usual suspects.
Seawater can come from any source on the exterior of the vessel which is below the waterline, or where the ocean reaches underway. There are common sources such as shaft and rudder seals.
All the items that supply seawater or discharge or drain seawater can be the source along with fixtures below the waterline such as swim platforms, trim tabs, underwater lights, transducers, spray rails, etc. can be the source. Some of these leaks will be apparent and accessible, however we have encountered leaks into areas which are not accessible or apparent, but eventually drain into the bilge.
In addition to looking at the source of the water from the intake side or failure of a seal from some underwater fitting, the discharging drain side also must be inspected. We have been involved with numerous incidents where the water intrusion was from the engine exhaust. These incidents can be more stressful and urgent. If the bilge water is warm, examine the exhaust system. Do not immediately shut off your engine unless you have determined there is no potential for it not to restart. It is much better to have a flooding boat and the ability to run it aground than to have a flooding boat which is immobile.
The specific boat for this article is a 1987 44’ powerboat. The vessel was well maintained and the owner was active in the maintenance process. He owned the vessel for some time and had replaced cast iron exhaust elbows twice. He decided to have stainless steel elbows fabricated, as he had found water accumulating below the starboard engine. As he began the disassembly process he discovered that his assumption of the source of water was inaccurate.
He found water trickling into the starboard engine’s drip pan from a source outboard and aft of the fuel tank, located outboard of the engine.
The owner then suspected a failure in the engine’s exhaust muffler. He put dye and water into the muffler and filled the muffler, but there were no leaks.
Prior to our inspection he had removed the fiberglass water lift muffler which was mounted on a shelf to starboard aft in the engine room, aft of the fuel tank. This made the job of determining the general location of the source of water easy. We inspected the area, noted a small trickle of water below the plywood shelf and confirmed the leak was in this area with scope cameras. The plywood shelf was mounted on a fiberglass athwartship support, which began at the chine and continued to the outboard stringer. Forward of this athwartship component was wet, aft of the athwartship component was dry and there was no moisture above the shelf.
The owner’s diver inspected the hull bottom in the area of the leak. We had suggested releasing sawdust, as it will float and accumulate at the water intrusion point/suction. The diver apparently chose to use milk as a similar test. The test was not productive.
The next step in the process of discovery was to remove the plywood shelf. To our surprise we found the water coming into the bilge through a circular hole. This hole was not wear and tear, it was clearly a hole caused by a circular component such as a drill bit or a screw. We probed the hole and it did not penetrate through the exterior of the hull.
A seawater leak through the bottom of the vessel will continue until the water inside the vessel reaches the water level externally. If the water on the interior is not pumped out, this will happen every time. Sometimes, this will result in a more significant leak from a secondary source and a catastrophic submersion. In this case there was a small trickle, it was finding its way into the drip pan below the starboard engine, eventually into the bilge and was easily removed as nuisance water by the automatic bilge pump. We had no immediate concern for submersion but we had a nuisance leak with an unknown cause. The vessel was hauled for further inspection.
Upon hauling the vessel there was no obvious external problem found on the hull bottom, in the area of the internal leak. Air pressure was applied to the hole which was found leaking on the interior of the vessel and the source of the leak was determined. The air pressure exited (and bubbled) above the chine several feet away from the hole in the bilge.
The exterior coatings on the fiberglass were ground away in the area of the apparent source of the water above the chine to starboard aft. Initially a crack became apparent at the radius between an externally attached rolling chock and the hull side. Logically this rolling chock was a component which was attached after the hull was removed from the mold, and there should be no communication into the hull. In this case the crack clearly was a path for water intrusion and communication to the interior of the hull and probing of the crack showed that it was deep into the laminates.