Sunday, June 14, 2009

Project: Replace the Holding Tank

(Project from 2003)

Now here is a project you never want to do.

This is an uncomfortable subject, but then living aboard forces you to come face to face with most of the aspects of your existence, many of which are "out of sight, out of mind" on shore.

I don't know how long it has been illegal to discharge sewage into Puget Sound, but it has been a long, long time. Accordingly, boats are required to retain sewage and carry it around in a holding tank. I want to invite the folks on shore who are always saying that people who live on boats are polluting the Sound with raw sewage to my next "Replace the Holding Tank Party".

Our holding tank was made of aluminum and was 20 years old. It had begun to seep, especially where someone screwed a bronze fitting into it, causing galvanic corrosion. It needed to be replaced.

First: accessibility. The holding tank is in a small bilge compartment amidships. There are two hatches into this compartment, but neither is very large. Initially, I carefully measured up the space and the hatches and sent the measurements to Adam, who put them into a fancy CAD program. I then gave him a tank catalog (Ronco Plastics has a great catalog!) which he then used to determine which tank(s) might be able to fit thru the hatch, and could then be rotated into position. As it turned out, only very small tanks (less than 20 gallons) would work. So we bit the bullet and cut out the section of floor between the hatches and removed the supporting 4x4 teak beams underneath (the aft beam is still in place in the picture). Now the opening is large enough to accommodate a tank of realistic size: 45 gallons, the same as the existing tank.

Thankfully, there are no pictures of the next step. As preparation, we pumped and rinsed the tank repeatedly, then dumped a gallon of bleach into it and filled it again and left it to steep. Then another pump out to get rid of the bleach solution.

Now the steps were these:
  • rent a SawzAll (not gonna use any of MY tools for this...)
  • put on old clothes
  • climb down in the hole
  • cut the tank up
  • hand the pieces to Jane
Now mind you, there was only a little smell initially, but after the coating on the inside walls was disturbed, and after the 2" of sludge in the bottom started sloshing around, it was a totally disgusting job. After all the pieces were out, I sloshed bleach over everything and then scooped up the remainder into a bucket. Yes, there was a lot of misc. "stuff" around, behind and under the tank. Then hose out the area after the bleach swab-down. Then shower. Shower. Shower again.

There is a lot more room down there now...

When the custom-manufactured tank arrived (only a week after ordering - Ronco is great!), it barely fit into the back seat of the Fox. It is a rotationally molded polyethylene tank, with 3/8" wall thickness.

The new tank goes on the port side of the compartment instead of the aft bulkhead. In order to keep the tank in place, a substantial framework had to be built and fiberglassed to the hull. One should remember that when full, it will weigh over 400 lb, and will attempt to jump around down there in a seaway. A loose, full holding tank is a thought I really don't want to contemplate.

As the construction proceeded, lots of trial fittings were required, each a fairly major ordeal. For the final fitting, the plumbing was attached (it couldn't be done when the tank was in place), and the tank was installed.

For completion, 2x4 keepers were screwed in place trapping the tank. You can also see that we gave the entire bilge compartment a couple of coats of white paint, which improved appearances immensely.

Final steps: I cut thin (less than 1/8") teak strips and attached them to the raw edges where the floor panel had been cut out. I reinstalled the floor panel, plugged the screw holes, and applied varnish to the unfinished wood. And then finally, sand/refinish the entire floor in the office area to incorporate the newly finished areas.

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