Rear Water Tank Leak - WARNING

[pablosgirl]

I have finally  chased down a mysterious intermittent leak in the aft cabin of our 88' MKI.  It was coming from the aft water tank.  It turns out that the two bottom screws on either end of the fiberglass cover for the steering gear had penetrated into the water tank within 3/4 of an inch from the top edge of the tank.  I discovered the leak by chance when I had filled the tank to overflowing and then a few minutes latter went into the aft cabin to get something.  I saw water leaking out below the steering gear cover and from the bottom of the aft wood panel.  I removed the cover, the port panel, and the aft panel to investigate.  If found two spots where the screws had penetrated the tank and over time had elongated the holes from the tank shifting port and starboard by about a quarter of an inch each way.   It turns out that all the screws were 1 inch long. The bottom outer screws need to be 3/4 inch to avoid penetrating the water tank. There is a recess in the middle top of the tank so the middle bottom screw does not come in contact with the tank.

I would recommend checking your aft water tank to see if your boat has a similar situation.

The water tank is manufactured by Ronco Plastics.  I called them for advice on how to repair the tank. 866-973-0597.  They said that the only way to properly repair the tank was to heat weld it and that an epoxy based repair product would not bond properly to the poly tank. They also said if I would bring the tank by or ship it to them they could repair it for about $20.  However the shipping cost to California and back to Texas was prohibitive.  Instead I had them ship some repair material and I heat welded the tank myself.  I would recommend watching some of the poly tank repair videos on heat welding on youtube.  It helped me get an idea of the technique to use in my repair. 

It was relatively easy and I did it with the tank in place using a heat gun and the thinner strips they sent me.  You want to use thinner repair strips so that you don't over heat the tank and deform it's shape while trying to melt the repair material into the hole.  I started by heating the strip end and then applied the strip to the tank while applying heat to the strip and the tank together. once the material gets hot enough it becomes pliable and "sticky" and you work the repair material into the hole until full.  I added a little more material beyond filling the hole to make sure I had a good bond to the surface of the tank.  Think rivet head.  I let the repairs cool and filled the tank to over flowing to check for leaks. No more leak.  I purchased two 3/4" long SS screws and ground the tips off to insure that they would not scratch through the tank again.
Paul & Cyndi

[Ron Hill]

Paul : It's too bad that you didn't pick/read an old 1990s Mainsheet tech note that I published and passed on the "heads up" on making sure that you don't mix up the screws from that "Steering Dog House" cover because the longer screws will penetrate the aft water tank!!!!
The longer screws are for the portion that is attached to the cockpit underside and the shorter screw are for the aft teak panel.

I even recommended that you glue a nickel (coin) on the water tank just so someone couldn't do what happened to you!!

Great tips and information in those Mainsheet tech notes.

A thought

[pablosgirl]

Ron,
Good idea on glueing a nickel to the tank.  I have had the "dog house"  cover off only once in the 7 years we have owned the boat and ALL the screws are the same length.  I don't know if that is something the PO or the factory did?  This is the first time that i have taken down the aft panel to expose the water tank.  Just wanted to give everyone a headsup on the potential issue with the water tank.
Paul & Cyndi