Monday, September 10, 2012

Drip, drip, drip... Water Tank Repair

After our trip to the Chesapeake, we found that both forward cabin mattresses were wet on the bottom inboard corners and that the storage lockers under the bunks had collected a small puddle of water. It had not rained in a while so it must be from the water system. The plumbing looked ok. The forward lockers where the water tanks are located showed water at the aft end of the tanks. Draining the tanks and removing them was the next step.
We found that the fiberglass module that supports the water tanks had not been completely fiberglassed into the hull at the forward and aft ends. Any water that collected under the tanks drained into these holes. It didn't look structural, so we filled the gaps with 5200 caulk. That took care of the leaks into the cabins.
These tanks carry a big load. A full tank is almost 100 gallons at 8.3 lb per gallon, or about 800 lbs. We found that the tank support module is two strips, with no support down the middle of the tank. We added a narrow piece of plastic in the gap between the two existing strips to provide better support to the tank bottom.
Next, we examined the tanks. Why is water leaking from them? We had been told of a repair to the bottom of the port tank. The repair looked ok, but seemed to be silicon caulk covered by a piece of duct tape. It came right off. It was a long crack in the plastic tank - about 4-6 inches long. The other tank developed its leak from a crack that was about 2 inches long, located at the bottom of what I'll call "the donut hole" internal brace.
Plastic can be welded if the matching 'welding rod' material is heated along with heating the tank itself so that they melt together. Mike did the research and found that the tanks are made of low density polyethylene (LDPE) and that Rubbermaid makes several products from the same plastic. He found a Rubbermaid trash can that has the letters "LDPE" in the recycle symbol on the bottom. He cut a some strips from the trash can to use as welding rods. We bought a plastic welder from Harbor Freight Tools. The first plastic welder died while making the repair so we used a heat gun with the concentrator adapter (a metal cone to concentrate the heat and air flow) to complete the weld of the first crack.

The easiest prep was to use a rotary tool (Dremel tool) with a cutoff wheel, held diagonally, to grind open the crack in a nice U shape of the desired width and depth. Then we used the heat gun/welder to heat the plastic strip (welding rod) and the tank along the crack. We were careful to not get the tank too hot and burn through it. We applied just enough heat to get the plastic tank and the rod to turn glossy. As the rod melts, we swirled it in a circular motion along the crack, to get it to bond with the tank material. It is important to keep the welder far enough from the puddle that the stream of air doesn't blow the material out of the crack. The result was a very nice weld.
The plastic welding was a new and interesting experience that saved us from having to buy new tanks at $400 each, plus shipping. We now have dry bunks and our water stays in the tanks.

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