Projects: Holding Tank Replacement

Removal of original Kracor holding tank and fiberglass bed, and installation of Ronco Plastics B126

Soon after we purchased Ariel, we discovered that she had an odor problem. We tried spraying the bilge with a bleach solution, replacing sanitation hoses, and generally cleaning her up to eliminate the odor, and yet it lingered. It was while replacing the sanitation hoses that we began to wonder if maybe the holding tank fittings were the culprit. We removed and resealed each fitting, liberally gooping them up with sealant, and hoped the smell would disappear. After a season or two of a still not-so-fresh smell down below, we decided that the time had come to take care of things.

Project Highlights: Ronco Plastics tank B126 (30 gal.) was the only tank that fit out of three separate mockups of Ronco tanks - B486, B115. B126 required removal of the original holding tank pan, and construction of a new support. Total expense for the project was approximately $400.00. Time involved, approximately 12 hrs. Materials included Schedule 40 1-1/2" PVC pipe, 1-1/2" barbed fitting, 1-1/2" combination elbow, 1/2" barbed fitting, hacksaw, epoxy, biaxial cloth, angle grinder w/ flapper wheel, furniture grade plywood (oak), expanding foam.

Removing the old holding tank is, as one would expect, a miserable task. Even though I had rinsed Ariel's tank several times before haulout, there was still enough residual nastiness to curl the old nose hairs. Note: Handle the old tank - and its contents - with caution. I was fortunate not to spill any, but getting the tank from the cabin and then down a 10ft ladder to the ground singlehanded was a bit tricky.

I was hoping to find a replacement tank that would be close enough to the original tank's dimensions to simply fit into the space without any modifications to the fiberglass pan bonded to the hull under the v-berth.

The original tank's dimensions (above) were very similar to those of tank B486 sold by Ronco. The dimensions were so close, in fact, that I was feeling pretty smug and imagined the whole job would be done far faster than I'd anticipated. I made a mockup of the Ronco tank and discovered that there was no way to get the tank into the forward compartment without removing interior trim pieces to make room. Although I debated going that route for a bit, I eventually decided that the approach was too much like cutting corners - no pun intended - and lacked professionalism.

It turns out that this tank (B486) was designed for the Cape Dory 30. Apparently, a few years ago several owners went in together on the mold for the holding tank to save production costs. Following are my comments about this from the blog:

"A recent post on the Cape Dory board by Scott MacCready seems to indicate that tank #B486 is a direct replacement for the CD30 ketch. Apparently the CD30 is a bit wider at the forward bulkhead! Seems like Cape Dory would have used the early 36 holding tank dimensions for the CD30 as well rather than go to the trouble of having a new mold built.

** 3.27.06 ** #B486 is a direct replacement for CD30s. A Ronco salesperson told me that several CD30 owners went in together a few years back on a run of holding tanks to defray the expense of having a mold made."

Once I discovered that none of the available tanks were going to fit with the original fiberglass pan in place, I began the process of removing it. I first used a cutoff wheel on my angle grinder to cut the pan loose from those parts of it that were bonded to the hull. With the pan out of the way, I peeled the remnants of the pan from the mastic, then began grinding the material flush with the hull. The whole process took approximately 2 hours and created an incredible amount of dust. In retrospect, I should have taken the extra time to cover everything in the forward cabin with polyethlene film.

Another CD36 owner, Randy Palmer, had replaced his holding tank with Ronco tank B115, a 25 gal. tank. According to Randy, the tank was a perfect fit. Following is a response I received from him:

It's a Ronco Plastics B115 H.D. 25 Gal. You can mention my name if you like. It sets about 4-5" forward of the "bulkhead" that supports the v-berth. It fit right in. I used an elbow for the input line (I had them put it on the center line) and the vent and suction lines are centered forward like the CD30's are. Because the boat tends to be a bit heavy on the stern I asked if the would run an internal suction line toward the aft end of the tank. They bent a PVC pipe to do the job (no charge) and it looks like it should work. Normally a suction line comes in from the top but there is only about an inch and a half clearance under the [V-berth] plywood to the top of the tank. If you have any questions you might look up the dimensions on their site and make some cut outs in cardboard. That's what I did and was confident that it would fit. It fit even better than I expected.

We used the tank for 10 days last summer when we went to Isle Royale and it worked great. Pump out seemed fine, too. It is like it was made for the boat (1978-82 models, I assume). The Ronco is heavier than the Kracors and cheaper. I give them two thumbs up.

Despite my attempt to fit the tank with and without the original fiberglass pan, there was no way this tank would work either. Why would it fit on one CD36 and not another? I have no idea. Even with the fiberglass pan removed, tank B115 sat too high and interfered with the v-berth bunkboards.

I finally made a mockup of Ronco tank B126, a 30 gal. tank that Ron Turner had used aboard his CD36, Salt Shaker, and used the mockup to get a rough idea of how the tank would need to be supported. When I was certain that the tank would work for our configuration, I created a schematic for Ronco Plastics indicating where I needed the inlet, outlet, vent, and inspection ports, as well as the pickup tube for waste removal. I waited for the tank to arrive before beginning work on the support to be certain that my measurements were correct.

I used two pieces of furniture grade 3/4" oak plywood that I had on hand to create the support for the tank. I installed the bottom support first, setting it in thickened epoxy, and then tabbed it to the hull with 17oz biaxial cloth. The forward support was installed the same way, and the joint between the two pieces covered with more biaxial cloth. The plywood was covered with a final coat of epoxy to seal it.

The gray areas on either side of the hull are the remnants of the mastic that had to be ground away.

The picture also shows the anchor locker drain in-progress.

The new tank is almost completely installed. The only piece remaining to be connected is the inlet elbow and hose - visible at the aft end of the tank. The original tank's pumpout hose was routed through the starboard side of the anchor locker bulkhead (the blue area). The specification on the new tank for the outlet port to be located along the centerline made it necessary to route the tank through the port side of the locker, so I filled the old hole with styrofoam and built up a couple layers of cloth over the hole on the inside of the locker. Once things had set up, I drilled a hole for the vent line and routed it through the starboard side.

The clear hose visible on the right, running alongside the tank, is the washdown pump supply.

No matter how hard I tried to get the Sealand Odorsafe sanitation hose to make the necessary bends through the bulkhead to line up with the tank's outlet fitting, I couldn't get a decent angle. The location of the new tank was such that the hose was placing too much lateral force on the fitting, a sure route to premature failure. I finally decided that the best way to solve the problem was to use 1 1/2" Schedule 40 PVC pipe. Prior to fitting the pipe, I used a heat gun to soften the pipe just enough to make the gentle sweep through the port side of the bulkhead. I quickly glued and fitted the pipe before it cooled enough to lose its flexibility. I then heated it again when the glue had set and I'd connected the sanitation hose to ensure that the pipe had a free run through the bulkhead and wasn't being tweaked or twisted by either the hose or the tank.

We immediately put the holding tank to use during our nearly month-long cruise during the summer of '06, and things have worked flawlessly. The odors have disappeared and the cabin is smelling pleasantly fresh - even after she's been closed up for awhile. The added capacity of the new tank - 30 gal. vs the original 24 gal - is a bonus.

back: projects