Installing a Composting Head on a Sailboat

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When we bought our Allied Seabreeze sloop several years ago, the head and attendant systems were, at best, adequate. Nothing smelled, everything worked, but clearly we would have to upgrade at some point. Over the years, we replaced the sea toilet, went through several repair kits and researched options to upgrade the full system, including bladder tanks, gravity-emptying tanks, macerators and various pump types—like everything else on a sailboat, options were myriad, as were the opinions.

I had always been intrigued by the apparent simplicity of composting toilets and began to look at them in more detail a couple of years ago. While listening in at a vendor booth at a boat show, I ran into an experienced voyaging friend who pointed to the composting head in front of us and said, “Best thing we ever put on the boat once we got back to Maine.” A bit more research, some more opinions, and we settled on the Air Head composting unit. The system was simple, had undergone several years of improvements and would easily fit into our vintage 1960s head compartment.

Installing the liquid collection bottle on the head unit

Installing the liquid collection bottle on the head unit

Waste Not, Want Not

A composting toilet works by separating the solid and liquid waste. The solids mix with a moist, peat-like “medium” in the solids container, are periodically agitated and break down over time in an aerobic process (oxygen-rich). Keeping the solids dry (by separating the liquid waste) eliminates smells and accelerates the composting process. While the liquid waste must be emptied periodically (follow your local regulations), the solid waste container can last a cruising couple an entire season without emptying.
The first job was to remove the existing head system. Because we were already in the water, I elected to leave the seacocks and through-hulls in place. But everything else came off the boat … lots of hoses, valves, tanks and the porcelain throne itself. I felt better already!

Because the Air Head sat a bit taller than our flushing head, I had to build a new platform to establish the correct height for the seat. Some scrap ¾in plywood sufficed, and after patterning and cutting, I coated the new platform in epoxy and painted it a gloss white. After some fiddling with a dry fit, we were good to go. The unit installed with a couple of stainless steel brackets—simple enough.

Proper operation of the Air Head requires a positive vent system to pull air through the solids container and out to the atmosphere. This keeps odors and bugs from collecting, and provides a continuous source of oxygen. A 12-volt computer fan is provided as part of the system and is inserted into one of the two vent options (straight or 90 degrees). Siting this vent prompted the most head scratching, but I eventually settled on placing it directly on the cabintop, where I had just enough space to set it next to (and behind) a dorade vent. Some cutting work with the Dremel, a bit of caulking to install the Nicro vent, and that was done. The site needs some prettying up, but that’s this year’s project.

The brick for composting solid material (left) and the brick broken up and the stirring device that helps the solid material decompose (right)

The brick for composting solid material (left) and the brick broken up and the stirring device that helps the solid material decompose (right)

The fan needed a 12-volt source of electricity, so I wired up a small (10 watt) solar panel directly to the battery, located it on the cabintop under the boom (enough sun to do the job) and things were humming. Over the summer, we found that this small panel kept the battery fully charged against the demands of the exhaust fan.

To set up the head, I had earlier placed a “brick” of the provided “Coco Peat” into a garbage bag, added water and over the course of the installation day it expanded by absorbing the water. This mass of moist peat was placed into the solids container, mixed up with the self-contained agitator handle, and we were ready to go, literally.

When using the Air Head, liquids are diverted forward into a separate container (sitting is recommended, a small price to pay for males), and a “trap door” opens via a flip handle to accept solids and toilet paper. The liquid container fills up every couple of days and must be emptied. Keeping liquids out of the solids container is key to proper operation (and odor control), and despite initial doubts we found it quite easy to keep things headed to the right place. After making a solids deposit, a couple of turns of the agitator crank handle built in to the container is all that is required to keep thing working properly.

The author secures the liquid collection bottle to brackets (left); the finished installation of the new head (right)

The author secures the liquid collection bottle to brackets (left); the finished installation of the new head (right)

We use the boat a lot during the season, but with only two of us on board for much of that time we found that the solids container did not need emptying until the end of the season, and could have lasted longer. A boat with a larger crew, or liveaboards, will find the need for more frequent emptying. At the end of the season, I simply detached the lower solids container, attached the supplied lid, and after the recommended minimum three months of “processing” time to complete the composting (sitting in a corner of our garage), disposed of a season’s worth of “deposits.”

In a world of no-discharge zones, pump-out stations, smelly hoses, suspect seals and valves, and head horror stories (we’ve all got ‘em), we couldn’t be happier with our choice. Indeed, compost does happen, even on board an almost 50-year-old sailboat!

August 2015

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