TO HAVE AND HOLD?
The Straight Poop on Composting Toilets
There are many delightful aspects of cruising. Holding tanks are not among them. Like it or not, the periodic pump out is the price paid for freedom from shoreside utilities. So too is the realization that some day, things could go wrong in a very smelly fashion, requiring the repair or replacement of odiferous fittings.
During some early brainstorming sessions on the TT35, we wondered if there might be an alternative solution to onboard waste management. That's when we started looking at composting toilets. Self contained, self-composting marine heads have been around for a number of years, and they have caught on with a subset of cruising sailors. Reports and reviews from online forums and chat rooms seemed largely positive, and when we put out an online survey on design options for the TT35, nearly half of the 600-plus respondents indicated potential interest in a composting system. Encouraged but still unconvinced, we wanted more verification from cruisers who had actually used similar systems in powerboats. This lead us to a pair of cruisers who own MC 30 power catamarans. These Polish-built pocket cruisers are trailerable, and were originally equipped with conventional marine heads. Both Tom Rogers and Bob Cantell replaced these systems with composting heads.
“I had an electric head and a 22 gallon holding tank,” Bob recalls, “There were a lot of causes for failure, and it wouldn't work when the boat was on a trailer. With people living aboard the tank would fill in four days. No more island sitting for us, we needed to find a marina to pump out.”
Manufacturer's literature states that a composting head will provide a month's capacity for two people before the need to empty the composted solids. Bob's real-world experiences are similar. “There is no stink, and the composting toilet has a capacity that really negates concerns about when we empty,” he says, “By eliminating the holding tank, we gained a lot of storage space.”
Tom Rogers replaced his conventional marine head some ten years ago, and has cruised the Great Lakes and Florida with a composting system ever since. “We cruise for up to ten months a year, but are intermittent users,” he says. “We spend a good portion of our time at marinas because we cruise with a dog, and we take advantage of shore facilities whenever possible. But having the composting system is a real convenience for those times when it is needed.”
While some composting systems incinerate solid wastes, Tom opted for a simpler system with minimal power demands. “It has a small ventilation fan with a milliamp draw, but even at times when the fan became disconnected, we didn't notice an odor.” One key to odor-free operation, both men feel, is the separation of liquids and solids. “The chemistry experiment of mixing seems to be the cause of the stink in a conventional system,” Bob says.
The three primary manufacturers of marine composting toilets all incorporate designs that divert urine to a separate receptacle from the sold waste chamber. Urine chambers are removable for emptying. Tom says the addition of a dishwasher rinse additive keeps urine containers free of buildup and odors. Bob equates the periodic emptying of the solids chamber to changing a cat litter box.
“We just tip the solids into a trash bag and dispose of it ashore.” Tom says, “If you leave the solids in the chamber long enough, it actually becomes garden-ready compost. We usually empty the chamber sooner than that, but what we're removing is definitely not just a bucket of s**t, and is appropriate for municipal trash and land fills.”
The system needs less cleaning that one might initially expect, Tom says. He spritzes the bowl after use with a commercially available biodegrading enzyme solution to keep things tidy, while also giving a boost to the digestion process. Decomposition typically takes three to five days in climates above 60 degrees says he says. “The one thing that will really increase capacity and speed digestion is excluding paper from the chamber, he says. Some cruisers already do this with their holding tanks, but it's the biggest change those who don't might want to make.”
Aside from the periodic emptying, there is little to no maintenance involved in a composting system, Tom says. “And if something did fail, you could remove the entire unit and have it on deck in five minutes with no plumbing parts to deal with.”
Based on feedback such as this, we're taking a serious look at composting systems as a viable solution aboard the TT35. Of course, we will also offer the highly-reliable traditional marine heads that been a feature of our GH and N series models for nearly two decades. This will give owners the option to hold and pump or compost and dump, based on their personal sensibilities and cruising habits.
10/7/2016 09:33:33 pm
This is encouraging news! We've had a Purasan system for several years and when it's working correctly it's great but as time goes by working correctly is an issue. The composting system with less moving parts seems like the way to go. Now, to find the best system for two live aboards?
10/23/2016 08:34:10 am
We have had an "Airhead" composting toilet on our Albin 30 Family cruiser for about five years. I can echo the simplicity and no odor comments from the blog. A composting head for the TT35 would definitely be on my list.
8/25/2022 10:59:12 pm
Great readinng your post
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By Ken Fickett
Ken is the founder of Mirage Manufacturing,