More Drips and Plastic Welding

On our trip to the Bahamas, we encountered some sloppy seas, which helped us diagnose the remaining port engine fuel problems, but also generated new problems with the water system. This time it was with the water tanks. We filled the water tanks in St. Augustine, FL, and noticed the sound of running water after we were through. We checked the tank and found that the weld that we had made to the starboard tank had split. (See my post Drip, Drip, Drip for the description of the welding.) We hadn't brought any of the tank welding materials with us. We have a low-powered heat gun and a SailRite Weller soldering-iron-hot-knife, so we have the basic tools. We lacked the proper plastic to use to effect a new weld. So I assembled one of our folding bicycles and headed off to find a store to buy something that was made with the right material.
I had noticed in Annapolis that when doing the welding with the Low Density Polyethylene (LDPE) that it seemed much more flexible and less dense than the original material of the tanks. I thought about this on my bike ride to Target. I wandered around the store, looking at all sorts of containers. The recycle label on the bottom has a set of letters under it, indicating the type of plastic. Most of the storage containers in the store are PP (Polypropylene). On a chance, I picked up a bottle of carpet washing soap and its container was labeled HDPE (High Density Polyethylene). I called Mike and we discussed the material that we previously used versus what is used to make the tanks and decided that HDPE might actually be the right material. The bottles I found seem to have the same consistency and stiffness as our water tanks.
While on the phone, Mike found a gallon jug that had previously contained pink (potable) antifreeze. So I head back to LUX without buying anything.

We cut the bottle into strips about 1/8 to 1/4 inch wide to use as our welding rod. We added an aluminum shield to our light-duty heat gun to focus the heat and the Weller hot-knife was heated up.

The old LDPE was removed with the Dremel tool using a sanding drum. (The Dremel tool is an essential boat working tool - don't leave home without it and a good supply of bits, cutoff wheels, and sanding drums.) The HDPE was added to the seam and it bonded well. The new material is white, but when heated it all turns translucent. That's how you know that the material is bonding to the tank. Try to minimize the area being heated. The tank tends to buckle when it is heated. Also don't overheat the tank or it may sag and open a really big hole that will be very difficult to close. The hot knife was used to melt and shape the plastic while the heat gun is used to keep the plastic in the area hot. The combination tends to work suitably well. We used a wood board on the hot plastic to force it flat again while it cooled.

We later found that the repair that we made in Annapolis had a small leak. Doing the same repair process, we found that there was a small path that water could follow through the weld, which hadn't been done very well, due to our inexperience in plastic welding.
The result is a reasonable weld. The white is the new material and the black marks are where material that adhered to the hot knife burned and then came off as I was working the plastic. We'll have to see how well it holds over time. It allows us to continue using both water tanks and we don't have to get new tanks made and shipped to the Bahamas - certainly an expensive proposition.


We have a couple of thoughts for the future. We want to add a generator to LUX and know that if we have to remove the water tank after the generator is installed, we'll need to cut the tank in half. We will then need to replace it with two smaller tanks that can be installed separately.

  -Terry