A few years ago I designed and built my own Composting Head for our 40ft Ketch “All the Stars” My wife (Di) and I had sailed on a number of yachts previously and Di hated the smell of boats with holding tanks. The final straw came when she was crewing on a yacht and one of the crew jammed up the on-board toilet, and in an attempt to clear it, a pressure effluent explosion resulted in turmoil, thus turning her off marine toilets on our future liveaboard.
After a lot of research we decided to build our own composting head and after 6 months living aboard we could not be happier with the resulting product.
We started by buying a Port a Poti 165 from a garage sale that had been used a couple of times. The main part we wanted was the top section with seat and lid. We removed all of the internals and cut the bowl at a slight forward angle (sloping from back to front) and made a trap door flap out of 3mm plywood with an indented urine collector and fitted a PVC 19mm hose barb outlet.
The trap door flap was then encased in epoxy and glassfibre. A stainless steel bracket was engineered and fitted to the bowl with the trap door handle exiting the housing on the right hand side. A piece of 19 mm PVC hose was then attached to the 19mm barb on the flap to a 19mm 90 deg elbow on the left hand side of the housing. This becomes the urine outlet.
A 12 volt computer fan was fitted to the right hand rear side with a thin foam filter to positively pressurise the unit. On the left rear a 45 degree 30mm PVC outlet was fitted this also has a thin foam filter fitted. The foam filters stop bugs/ flies from getting in to the compost. The vent is connected via a hose and is vented out side, on the odd occasion when the wind blows from it across the vent to cockpit you get an earthly ‘potting mix smell’
The lower half of the head was mad from sign fluted plastic board epoxy and glassed inside and out, with a lip fitted for the upper housing to slide over and is secure by small ‘Bungi cord’ closures. A Bungi cord was also fitted to secure the Trap door flap in the closed position.
The compost agitator is a simply a piece of stainless steel rod pre-bent that is threaded through the unit and sit in some nylon and rubber flanges pop riveted in to the base. The grove you can see on either side of the base unit side near the top are clearance holes for the urine outlet and the flap handle.
To make the unit semi air tight and bug resistant 5mm neoprene rubber was glued to the top of the base unit flange and the bowl of the unit where the flap closes. The units base volume is 30ltrs.
The urine outlet hose is fitted to a 10ltr container via a ‘Y valve’ to that can divert it over board when required.
The Process we use
We use a Coir brick from the local hardware store and place that in the required amount of water until it has expanded. The Coir is then placed in the base.
Before using the head, with the Flap secured in the closed position 2 pieces of toilet paper (or more recently we have used a coffee filter paper) is placed on the flap. We then take a seat and do 1’s and 2’s, the urine runs to the front of the sloped flap and into the collector along the hose and either overboard or into the collection container. Once finished, your toilet paper is then placed into the unit on top of the excrement and the Flap opened where the excrement and the paper fall into the base. The flap is then closed and secure by the Bungi cord. We then normally spray a watered down Citrus cleaner into bowl from an atomiser spray bottle, which again runs down the flap to the collector and the hose and leaves a pleasant smell. The seat lid is closed and the agitator is turned approximately 10 times. Job is done.
For the two of us the urine container is emptied every two or three days, the composter has been used for 3 months before being emptied. Total cost to build the unit, around A$200