Installing a Composting Head
What's wrong with a conventional holding tank retention head aboard a sailboat?
- It requires at least one, generally two, through hulls below the waterline, with their attendant seacocks and hoses. Through hulls are holes in the bottom of your boat. Seacocks should be maintained, or at least examined, annually, though few people do it. The seacocks and hoses leading from them are all that is holding the water back from flooding in and sinking your boat.
- It requires maintenance. While I have no experience with it myself, I have been told that clearing blockages, rebuilding flapper valves and replacing hoses on the raw sewage side of a holding tank head are among the most unpleasant jobs you can do on a sailboat.
- It is complicated to use. Operation comprises a series of valve openings and closings, interspersed with pumping. Sailors quickly learn how to use their own systems, but what about guests and visitors? It can be a daunting process, and what if they accidentally pump with a valve in the wrong position?
- It requires a tank. For a cruising boat with two people aboard, a 40 gallon tank may last a week to ten days between pumpouts. That means weekly trips to the pumpout dock, or a trip offshore to discharge directly. That tank, when full, is going to weigh around three hundred pounds, which comes out of the capacity of the boat to carry supplies and amenities. And what, heaven help us, if the tank springs a leak? It will probably happen along a seam at the bottom, hidden deep inside the cabinetry, and it may ooze for some time before the boat owner comes out of denial and decides something must be done. At this point, the tank has to be pumped as dry as possible (and it will be far from dry) and probably cut out in place, as the builder no doubt inserted it and added bulkheads and cabinetry around it. Then a new tank will have to be fashioned and somehow inserted. Some sailors replace their leaky tanks with bladders, an easier replacement job, but bladders are subject to chafe and wear as the boat moves on the water. Bladders are generally not a good idea.
- It smells bad. Most holding tank setups exude anything from a faint odor to a nauseating reek of sewage. If you haven't noticed it on your boat, it's because you are used to it. The peculiarly foul odor produced by the holding tank is due to the anaerobic decomposition of sewage.
- And finally, you may want to read this at Rod Collin's Marine How To website. It's not explicitly about retention heads, but it starts with an amusing story that shows why you don't really want to sail around with 40 gallons worth of sewage in your boat.
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In the olden days, sailors used a bucket of seawater and dumped it overboard. That's not considered good form anymore. So some kind of head is standard equipment on all boats larger than a daysailor. It may be a retention head that has to be pumped out, or it may be a chemical head that treats the sewage on the spot and spews it out into the water (even these require some kind of retention tank for no-discharge zones). A relatively new option that is gaining adherants is a composting head, which stores waste in a bin mixed with peat moss or coconut fiber. This provides for aerobic decomposition, which doesn't create the noxious gases of anaerobic decomposition. I will refer to this type as a composting head, or composter, and the older anaerobic type type as a retention head.
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I have crossed paths with a number of sailors who have retrofitted their boats with composting heads. The first I saw was aboard Calypso, the Westsail 32 of Jeff and Wendy Gower. They told me their daughter had a history of allergic reactions when she came aboard the boat, but on her first visit after the composter was installed she commented on entering the cabin that something was pleasantly different about the air. She has had no problems with her allergies since. My Matthews Point friends Scott and Yvonne put a composter aboard their Pearson and had nothing but praise for it. Daniel and Angela on Teasa had a homebuilt composter that was every bit as good as the commercial ones. My own experience with one came in the worst of conditions, cold weather when there is very little composting action to dehydrate and compact the waste. I was crewing for a friend from Edenton to St. Augustine in December. We made the trip on short notice, and the captain neglected to empty his half-full bin before we left. By the time we reached St. Augustine, it was well nigh overflowing. But it worked fine, I couldn't complain. He could, though, so I offered to buy it from him. He was willing, but wanted full list. I decided to buy a new one from the factory.
Probably the oldest commercial builder of composters is Air Head. They got their start in 2001 building for boats, but since have expanded into the RV and cabin markets. In these days of Covid, the demand for their units is so strong that as of November 2020 there is an eight-week lead time in getting one. Air Heads are the most common ones to see on boats, but Nature's Head is another established manufacturer whose units are seen frequently. Like Air Head, they have a major backlog in November 2020. A third maker is C-Head. I visited their small facility in central Florida a few years ago. I was impressed with the quality, low cost and innovative design features of their unit. They will also customize if a unit is needed to fit a difficult location.
After taking a lot of measurements I determined that I could fit a composter from either Air Head or Nature's Head in the space on my boat. Long deliberation led me to conclude that the two options were essentially equivalent, so I ordered a Nature's Head since it was a few dollars cheaper. If there had been issues with fitting the unit, I would have considered one of the C-Head models since they are a little smaller.
It took a week to receive my Nature's Head (expect six to eight in November 2020). At Edenton a few weeks later, I started work. First step was to remove the old head.That was fairly simple. The bolts holding it in place came out easily, and I cut the hoses free. A bronze adapter between one of the seacocks and a hose stuck up a couple of inches above the seacock, and rather than risk wrenching the seacock off the through-hull, I cut the adapter off with a hacksaw. One issue that I had expected was that the seacocks stuck up into the space for the head. The square base of the composter took a greater amount of floor space than the original head. I had made a platform for the composter, to lift it above the seacocks, before I left Winston-Salem. The platform lifted the head an extra seven inches above the level of the old head, to clear the seacocks. This was a temporary measure until I could have the boat hauled and the two through-hulls and associated seacocks removed.
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The extra lift, combined with the slightly greater height of the composter, made it something of a trick to get on top of, so I brought a step-stool we made in the shop at home for a booster. Later, with the seacocks removed and through-hulls glassed over, I could dispense with that, but my friend and sailing partner Taylor said for a while the composter was an authentic throne, with the commanding height and step-stool to mount it.
It was touch and go getting the head into the space available. The dimensional drawings at the Nature's Head website, I'm sure through oversight and not through guile, neglected to include the complete width of the lever on the side that opens and closes the bin cover. That extra half inch required me to slightly angle the installation to allow the exhaust hose on the opposite side to slide over its flange. It also meant that the head had to be mounted slightly forward to clear a diagonal structural member at the back of the space. Fortunately, once I was able to lower the platform after the seacocks were removed, I had a little more room to work with.
All that was left to finish the installation was to connect the vent on the side of the head to an external vent. The Nature's Head installation literature warned that this would probably be the hardest part, but for me it was trivially easy. Terry Ann has twin dorade vents in the head compartment. I routed the exhaust hose out the starboard dorade. When I am in port, I try to keep the port dorade pointed into the wind. This puts a slight overpressure in the head compartment, which forces airflow through the head bin and out through the starboard dorade. There is a low amperage fan built into the head which can be run to increase the airflow through the bin, but I rarely use it.
With that, the head installation was complete. I taped a sheet of paper and hung a pencil beside it and started logging uses. Currently I am at 70, and am not close to filling it up. I'd guess I will get at least 40 more uses before the time comes to empty it. Like many composter owners, I do not put paper in my head. Used paper is carefully folded, clean side out, and put into a lidded container lined with an empty 5 pound flour bag. This can go in the trash at any shore visit. We also don't use the urine container. I keep a P-Jar for each person aboard, to be discretely emptied overboard as needed.
I am quite satisfied with my composting head installation. On a recent visit to the boatyard, I had the two now-extraneous through-hulls glassed over, which allowed me to drop the platform by several inches. A few things remain to be done. The tank for the old retention setup can be removed to free up storage space. It's a shame that I will probably have to cut up this perfectly good tank to get it out of the locker. Pearson evidently installed it before the cabinetry in the forepeak was finished, and it won't come out in one piece. The wiring for the chemical treatment apparatus can also be removed. Yes, Terry Ann was built in 1964 with a primitive chemical head. The Whale Gusher that once moved seawater and sewage can be removed, rebuilt and put into stores.
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So what are the downsides? None, as far as I can see. Oh yes, just one. They are ridiculously expensive - not as expensive as a new retention system, but way more expensive than they should be.
The only thing I would do differently if I were to install a composter on another boat - I would build one myself rather than buying a commercial one. After seeing how the design principles are put into play, I'm sure that my shop partner Joe and I could construct one from marine plywood, fiberglass and epoxy that would be just as good as anything I could buy, at a small fraction of the cost.
Text and Photographs by Paul Clayton. Posted 11/10/20.
Copyright © 2020 Paul M. Clayton