How important is a slight list on a small boat? by Jim Cross
The client called me after the dealership he purchased the (New) boat from four years earlier and his local mechanic could not determine the cause of a starboard list that seemed to be increasing each year. He mentioned that the list was almost imperceptible after the second year, but was very noticeable after this, the forth year of his ownership. He actually picked up on the problem while he was painting the bottom the second year and noticed the scum line at the transom on the starboard side was just about an inch above the water line. He let it go for a while because he thought the full tanks or other gear stored on one side may have been the cause. He also thought there was a possibility that the factory may have improperly installed the water line. So, he painted up to the scum line the third year and all seemed well. The season passed by and his boat was hauled and prepared for winter storage by the yard. When he arrived to remove his personal gear for the winter he noticed that the scum line had gained a further foothold on the starboard side, aft. The starboard side scum line was about an inch higher that the previous year. About another inch had been added to the starboard side while the scum line on the port side also increased about about a half inch. Now he knew he had a problem because about half way through the season he managed to keep the fuel, water, and waste tanks close to empty and only added fuel or water when he was going out for the weekend. He also kept track of all extraneous gear aboard and kept it to a minimum.
Typically, with a fairly new 24 foot boat my first thought would be that there was a balance issue regarding fuel, water, waste, or possibly an inoperative bilge pump. However, after hearing this mans story, I knew that was not the case. As this boat was fitted with trim planes, a stern drive and two other hull penetrations at the transom, I thought it possible that water could infiltrate to the core through these ports if they were not sealed properly. On this boat, as with many others, the transom is about two inches thick and about three fourths of that thickness is plywood. How could that small amount of wood hold enough water, even if completely saturated, to offset the balance of this fifty five hundred pound boat? (Not likely)
The bottom of this boat is solid fiberglass laminate. Molded into the structures are various stiffeners and supports which provide for effective structural tabbing of other members. There is also an inner liner which prohibits complete inspection of the inside surface of the laminate. (What to check next?)
A second thorough inspection from the inside, just to be sure, turned up nothing new. We percussion sounded the hull again and did notice that the sound from the starboard side was not quite as crisp as the sound from the port. I also used a Barcol hardness meter on both sides and there was not a substantial variation in the results.
Because this boat was stored at the original selling facility there were several similar boats in the water ready to go for the season. I scouted around and noticed that each of four other boats had no list and the water lines were actually above the scum line in each case. So, with my trusty helper in tow we got permission from one of the owners to go aboard his boat to determine if our weight would cause a similar list to that of the problem boat. I climbed aboard (I weigh about 240 pounds) and positioned myself all the way to starboard and all the way aft. My helper measured the list and noticed that while the boat did list almost two inches to starboard that the port water line was now above the water by about an inch. At this point it became obvious that there was much more than 240 pounds of something, somewhere it did not belong, and it was growing.
Our next inspection included the transom and bottom. Because the bottom paint defeated the moisture meter, we scraped and sanded several small areas to the gel coat on both port and starboard sides. We cleaned areas in a symmetrical fashion in hopes of making a comparison of the approximate percentages of moisture content of the areas. The results from this effort were gratifying, in that we determined the port side (areas of the bottom laminate) contained less than ten percent moisture and the comparable areas on the starboard were totally saturated, right off the scale. We also found that the transom was totally saturated. We all know that any moisture meter can only be a guide and is not one hundred percent conclusive, but a core sample is. Using a half inch hole saw, a sample was taken from about ten feet forward of the transom. As soon as we got the sample it was obvious where the water was as water began dripping from the laminate. The sample I withdrew from the hole saw dripped liquid into the small plastic vial I was using to transport it. I poked around the edges of the hole with an awl to find that the laminate was coming apart and was no longer solid. I tried to pull the plug apart and with very little effort I was able to separate the inner surface from the plug. The inner surface was epoxy coated and very solid. The outer surface had the original gel coat intact and felt solid, but there was a thickness of about one eighth of an inch where the laminate failed. It appeared that there was no resin in the area, just matt. Failure to wet out the glass during the laminating schedule with the proper amount of resin at the factory and failure to seal the areas that would allow water infiltration to the core were the causes of this failure.