This is a series of posts which details the work which was required to outfit our boat with a holding tank for toilet waste. The project grew over time to include a refit and reconfiguration of the entire bathroom space.

The law, is the law

As you may know, our boat was designed and built in the 1970’s. This means that many of the modernities and standard gear you would find on a modern boat wasn’t even conceived when she was launched.

One of these features is the holding tank. A holding tank provides the ability to store all your toilet waste onboard and later empty it in a designated shore facility. In 2015, a law was passed in Sweden stating that all pleasure vessels had to have the ability to store toilet waste onboard. Emptying your tank while at sea was also made illegal.

For most, this law meant that you had to drill a hole in the deck and run a hose to your existing holding tank. For us, this law has bigger consequences. It would require rearranging the entire bathroom/toilet area.

For reference, the image on the right shows how the space was configured before work started.

The toilet, before the refit.

The elephant in the room

This project has been lurking on our list for quite some time. We knew from the day we bought our OE36 that we would have to take it on at some point in time. This would be the winter to do it.

As with any project, the hardest part is getting started. For us, many projects start on a Sunday, just when we’ve finished a previous project. This was no different.

Just as I had finished putting the galley back together after our sanding + varnishing project, I thought to myself: “why don’t I just quickly check if I can dismantle the bathroom?”. An hour later, all cabinetry and panels had been removed.

Revealed to me was a blank, albeit dirty, canvas to start working from. On the wall towards the hull, our boat was equipped with a large cabinet with two big doors. The cabinetry held three shelves and had space for tonnes of stuff. This has been one of the least efficiently used spaces onboard.

I carried on by cleaning up the surface and sanding away most of the old hull paint.

Then it was time to measure the area and start to sketch out how a tank could be mounted in the space, while still having room for a cabinet for storage of toiletries and cleaning supplies etc.

I thought to divide the space into three sections essentially. The leftmost two-thirds of the space, where the hull is beamiest, could be dedicated to the tank. And the third to the right could provide space for a new cabinet. We had made the decision a long time ago not to buy a tank off the shelf but rather have one custom-made. This would provide the neatest solution.

This would require some careful thinking and measurement. It would mean we needed to install an additional partial bulkhead to provide support for mounting the tank, as it cannot be attached directly to the hull. Complicating the matter slightly was the fact that on the left bulkhead, which makes up the left wall of the bathroom, are mounted the chainplates. These are an essential component of the rig and mast support, and I could not under any circumstance prevent access to them by putting a tank in the way.

To make sure we were thinking in the right lines, we decided to make a template of a tank of roughly the intended dimensions. For this, we used cardboard, sticks of wood and hot glue. The initial template made the tank unnecessarily wide, so we decided to cut about ten centimetres off the width.

Measure three times, make two drawings, cut once...

With these considerations in mind, I started to measure the space and to make a sketch in Sketchup. This meant learning the basics of CAD-drawing, which might come handy in future projects. After a couple of days of work, adjusting, thinking and further adjustments to the drawing, the tank had taken shape. It came out at 70 litres which feels like a lot, but it will provide us with the ability for extended cruising in remote places without having to drain waste overboard. The generous volume is further reassuring when you have guests onboard.

With the drawing completed, I asked for quotes from a few local firms and got a very good quote from a welding company about an hour north of our location. They asked for 550 EUR to build and pressure-test the tank. We thought that was a great offer, considering an off-the-shelf tank (obviously cubic) comes in at around 300 EUR for a comparable volume.

The build-up

As the tank was placed on order, we started installing the new bulkhead. This meant sanding and prepping the underlying hull and interior ceiling surfaces.

To capture the shape of the hull for the bulkhead, we used a technique I picked up from a Youtube channel. Using hot glue and tiny strips of plywood, we made a template which closely matched the curvature of the hull, in the exact location where the bulkhead would go. We cut a 10 mm sheet of marine grade plywood into the new shape, and to our relief, it fit perfectly in the intended location.

The board was held in place by a rig, manufactured of scraps of wood and two holding clamps. We then applied a fillet of Epoxy mixed with a microsphere additive to the gap between the board and the hull. After curing, we then re-prepped the surface and laminated the board with three layers of chopped strand matting glass fibre mat.

After some additional sanding and prepping of the surface, we then proceeded to paint the entire space with three layers of Hempels Multicoat – a paint we have truly learned to love.

This whole prep process took place over about four to five weekends and involved many trips back and forth between the boat and our workshop. But after these steps, we were prepared to start planning for mounting the new tank and associated hosing.

More on that in an upcoming post!