Rusty the Junk - Plumbing

It is surprising how many tanks you need in a boat. We have tanks for water, diesel, paraffin and a holding tank (sewage). Both the water and the diesel are split systems, so that if we get water or diesel that we are not sure of, we can separate the tanks and just fill one, until we have checked the quality in use. In addition both the heating and the generator require gravity fed diesel so the addition of a smaller day tank, comparatively high is required.

Contents	Number of Tanks	Total Capacity
Diesel	3	350
Water	2	300
Paraffin	Not fitted yet
Holding	1	100

None of our tanks are simple shapes. Their bases follow the hull, so though we made them planes, not curves, the bases slope both front to back and side to side. We modelled them on our 3-D design package, Rhinoceros. This meant we could check out the design, check the model against our model of the boat, automatically calculate the volume and extra dimensions, and print out 2-D plans. Big pluses, and easier than making a real space model.

The first tank we had made was our holding tank, simply because that had to go in before the engine did. This also means that it can’t come out again without moving the engine too. Not ideal, but you have to compromise somewhere. We took a lot of careful measurements of the tank beds, and the height from the roof to the bed at all the corners, so that we could get a horizontal top. Our fabricator was impressed with the plans, which made it much easier for him to cut out, but he did have a couple of points. Firstly that it would have been easier to cut straight edges for the limber holes. Curves are as easy as straight lines on modelling software, and we hadn’t thought about the real life difference there. We also made another, more serious, basic mistake. The drawings and dimensions had been so spot on for the rest of the sides that he just cut out the bottoms from the drawing dimensions, and they were too small! Nick made a mistake when he did the fuel tank plans. He’d taken the dimensions off a perspective view, not in the same plane as the sloping bottom. Since the bottom isn’t in the horizontal plane, perspective made it appear slightly smaller.

Pip measured the filler pipes wrong, they’re only 2”, not 2½”. Not a problem to taper down, but it would be much easier to fit in 2” valves, and the pipe between the tanks should have valves each side, in case the connecting pipe gets a leak – from old age, if nothing else. 2½” valves are more difficult to find, and lots more expensive, as is 2½”fuel pipe. We also have 2 connectors next to each other, which makes it more difficult to fix valves. And they should have been inside threads, which would have made them shorter.

We were surprised to discover that mild steel is preferable to stainless for diesel tanks. Apparently diesel can attack stainless [unfortunately we can find a source for this any longer]. Presumably this is not a huge problem, as it wasn’t well known among the fishermen in our area. But we needed very heavy diesel tanks, as we would be walking on one and storing heavy batteries on the other, so mild steel would save us quite a lot of money. We had them blasted after they were built and tested, and painted them with some of the left-over epoxy primer. Our first go was with a brush, which was a mistake. A roller finish is much faster and smoother, with a brush to get into the corners around the pipe fittings. Do we care how they look when they’re out of sight in the engine room? Well actually, yes we do. And if you want justification, it’s better for the fit of the gasket if the two surfaces are reasonably smooth.

The gaskets were cut for us by a local plastics firm. Seems to be a standard procedure – I took along the inspection hatch cover (to give the size and spacing of the studs) and measured the diameter of the hatch hole (this assumes the hole is central to the cover, of course), and they made it while I waited. I was given the choice of having the whole circle, or cutting the hole area out of it. The price was the same, and not having the hole means one would have to take the gasket off, as well as the cover, to access the tank. In retrospect I wish I’d asked to keep the centres – it would come in handy for something. For fuel tanks the gasket material must be diesel resistant, nitrile being most common. While I was there I also got some nitrile foam strips to glue along the fuel tank beds, anti-chafe for the tanks. Nitrile is a lot more expensive than ordinary foam, so we only used it on the fuel tank. The foam we used is closed cell, so that it does not absorb and hold any liquid.

The water tanks are stainless steel on the grounds of purity and cleanliness, although we do have filters fitted on all water outlets.

Our water tanks and diesel tanks can be filled from either side of the boat. This obviates any problems with coming alongside. The fillers are mounted in the side decks under covers, with a drain hole that can be blocked going over the side. The actual fillers and caps came from a second hand piece of farm equipment, probably used in a milking shed, that had comparatively short stainless steel pipes with screw on caps welded into a stainless steel plate. We cut up the mounting plate to give ourselves two large fillers for diesel, and two slightly smaller ones for water, then welded them in place, with the bottoms of the pipes sticking through the side deck into. On the port side, they emerge in the wet locker in the wheelhouse, and on the starboard side they emerge directly into the engine room. We fitted balance pipes to the tanks so that we could fill from either side. An extra filler was put in on the port side for a paraffin tank. We don’t have one yet, but we intend to one day, as we cook by paraffin. In addition, on the starboard side, allowance has been made for pump out of the holding tank.

Diesel piping was done with black rubber pipes, of an appropriate material and quality. Water piping was done with red rubber food grade pipes (actually brewery distribution piping).

The diesel system has filters on the take off from each tank, together with isolation valves, so that we can change a diesel filter while the engine is running. After that there is a further filter at the engine and a water separator. The diesel day tank has two take-offs each with its own filter, for the heating and the generator.