I am just writing to ask if anyone has installed a composting toilet on their boat. I would be interested to hear which ones you considered or selected - and the practicalities of using one of these toilets on a boat, particularly while cruising. I have seen some older threads on this topic, but it has been a while so I thought it was worth asking again.

Regards,
Andy

Hello Andy - I installed a Natures Head in the forward head of our Whitby 42. It had many positive results. The Natures Head has a small exhaust fan so there was no issue with odor. The liquid collection and disposal was also relatively easy although it did need to be done daily with 2 people using it. The solids compartment was a bit more effort. The best bulking material to use is coconut coir because it is easy to store the dehydrated solid bricks. Hydrating the coir bricks is relatively easy once you work out a good method for this. The biggest chore is emptying the solids bin. We found that dumping the whole thing every 2 weeks was a big effort and seemed to create more waste. The easier method was the litter box approach. Every 4 or 5 days we would scoop out the lumps with a kitty litter scoop and toss these over the side or into shore side garbage. About once a month we would dump the whole bin and start over with fresh bulking material.

As for other models, I have looked closely at the C-head and it is not as well engineered. I can not really comment on any others.

I hope this helps.

Bill W

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bweigel2@gmail.com - 6 Feb 2024

Hello Andy - I installed a Natures Head in the forward head of our Whitby 42. It had many positive results. The Natures Head has a small exhaust fan so there was no issue with odor. The liquid collection and disposal was also relatively easy although it did need to be done daily with 2 people using it. The solids compartment was a bit more effort. The best bulking material to use is coconut coir because it is easy to store the dehydrated solid bricks. Hydrating the coir bricks is relatively easy once you work out a good method for this. The biggest chore is emptying the solids bin. We found that dumping the whole thing every 2 weeks was a big effort and seemed to create more waste. The easier method was the litter box approach. Every 4 or 5 days we would scoop out the lumps with a kitty litter scoop and toss these over the side or into shore side garbage. About once a month we would dump the whole bin and start over with fresh bulking material. As for other models, I have looked closely at the C-head and it is not as well engineered. I can not really comment on any others. I hope this helps. Bill W

Field report, composting toilet (more accurately described as a desiccating toilet)
Dick Stevenson, s/v Alchemy                        last edited, Feb, 2024

Composting Toilet, field report, season 2021
We were heading for the Great Lakes, USA, where there are plenty of pump out stations, but our holding tank was small and we like to spend long periods at anchor and we do not like tying to any docks and piers with any regularity as they are usually inconvenient at best and maneuvering around tight spaces near hard stuff is not my idea of fun.
So, we bought an Air Head composting toilet*.
ADVANTAGES:
1.  Legal in all areas of the world I am aware of.
2.  More important, we feel like we are doing the right thing. It has never felt good to pump overboard: clearly doing so in some areas is better than others.
3.  No more being in pristine clear waters and seeing the astoundingly clear evidence of pumping overboard. Especially if you or those around you are swimming in the area. For those of us who come from tinted water (clean, but with silt from rivers for ex. and usual in the US and Northern Europe), this is a visual revelation: and a far from pleasant one.
4.  The whole toilet is easily moved and/or removed, which, on my boat, makes access to some areas far easier.
5.  Two fewer through hulls: no chance of the toilet causing back-siphoning or one of the many joints giving way and causing a leak.
6.  We have lived aboard full time many years and a number of years 6 months on and 6 months off and it was a regular occurrence (every 2 years or so) that there was a major problem, even with vigilance. It was only the last few years that I felt confident in my set-up that we were not going to endure a problem necessitating an impressive period of time engaging in disagree-able work usually entailing much boat-yoga.
Ripping out all the conventional toilet installation was pure joy, although they had served us pretty well for decades: lots of hose and 2 anti-siphon vents jettisoned, 2 thru-hulls closed off, etc.
DISADVANTAGES:
1.  You are up close and personal with elements of everyday life that we, in the civilized world, have devised ways to not be closely acquainted with (see below). Once the learning curve has occurred this is far less pronounced and, possibly, even less so than conventional head toilets.
2.  Those vessels who entertain frequent guests will be challenged as each guest must engage the learning curve of proper use.
3.  We have not had to deal with long periods where the boat is amply heeled over and we are bouncing along. I anticipate there will be a new learning curve and some challenges when that occurs.
INSTALLATION:
Good directions and equipment for installation was provided.
Basically, installation was a no-brainer if ample time was given to work out the details ahead of actual execution.
The Airhead stood taller than the Raritan PHII that it replaced, but not so it was a big problem on my 40-foot boat. The biggest challenge is venting the solids reservoir (for drying out purposes more than for odors) which entails running some hose (1.25” if memory serves) to the vent area. I vented mine to an aft machinery area where, over a couple of months of full-time cruising, there did not appear to be any moisture build up or odor. Air is moved continually by a small computer fan. Other options have venting through the hull or deck to open air. You are supplied with a corrugated hose (for flexibility), but for a long straight run I used PVC pipe as it is smooth bore and not crushable.
Learning curve, operator error/forgetfulness took precedence in this area:
1st liquids and solids are stored separately for good reason and the Airhead makes this fairly easy to accomplish.
2nd There is a manually operated flap opening a hole allowing a human deposit of solids to drop straight into their storage area. Neglecting to flip that flap before delivery makes for a cleaning challenge.
3rd One will need to learn to position one’s posterior so that your natural drop zone aligns with the hole revealed when opening the flap; there is motivation to accurate position-learning as “missing” demands cleaning up solids that do not find their way cleanly down the hole to the storage area.
Once learned (a few “mistakes”) using the toilet is very straightforward and, in most ways, quite a bit easier: no pumping for an obvious one.
IN USE:
1.  There are a number of recommended mediums (peat moss, coconut mass, wood chips) which often needs moistening ahead of time and preparation (breaking up for example). This medium resides in the solid’s container and is agitated (stirred remotely) after every solids deposit.
2.  The learning curve has been described.
3.  Liquid deposit for 2 adults is surprising in volume: probably a daily emptying of the reservoir even if you get the larger one.
4.  We get 2-3 weeks before needing to empty the solids collection tank and suspect we will extend that time as we get better acquainted with the unit. The agitating arms are limited in their reach and after 2 weeks, one can improve the mix and extend the time before emptying by removing the top and stirring/agitate by hand with a stirrer of some sort. This is far less disagree-able than imagination would dictate.
DISPOSAL:
1.  The liquid reservoir unfastens easily from its base and has a cap for enclosure and a handle for carrying.
2.  The “seat” of the toilet comes off the container for the solids, which in turn comes easily off its base attached to the boat. It has a sealed top if transport is planned.
3.  Emptying the liquid reservoir presents with multiple possibilities. Land based toilets are always recommended. Saving for land-based deposit in the form of some sort of auxiliary reservoir is possibly. Pouring overboard is discouraged in some writing because of a high concentration of (I think) nitrogen.
4.  Solids disposal again has a number of options. The solids will remind many of cat litter: not disagree-able, and it can be dumped into a plastic garbage bag easily and without mess. From there it can be disposed of with regular garbage (think of the number of doggy disposal bags that get deposited in garbage or also know that diapers/nappies compose 10-15% of landfill). We double bag. Another option when more in the wild is to dig a hole. It is great fertilizer (reportedly), but not for growth that might find its way to human consumption.
*Composting is a bit of a hype/exaggeration: solids are not left long enough to actually compost and liquids are disposed of frequently: 2 people, well hydrated, generate a lot of liquid. It is better described as a desiccating toilet. For more please see an excellent article in Practical Sailor, probably sometime in 2021.

Having got fed up with cleaning lime scale out of the Henderson Mk V pump, pipework and holding tank attached to the Lavac,  I installed an Airhead in Tystie in 2007, in Hawai'i, and it remained in service until I sold her in 2016. The Airhead and the Nature's Head are more complicated than necessary, in my opinion (but certainly an improvement on a water-flushed head). With all the fiddly little bits that go along with the churning mechanism and closing flap, I found it difficult to keep clean, and once you have a fly infestation in the tropics, you really cannot get all the eggs and larvae out of the crevices. And however much you try, back they come again, those pesky flies.

KISS. For my final cruising boat, a 23ft David Thomas Duette, I made a DIY head which was fully successful. Basically you need to buy a urine separator such as one of these: https://my-composting-toilet.com/blogs/composting-toilet/how-to-find-the-right-separation-insert-for-your-composting-toilet (this website also gives you all the how-to info you need) and a domestic toilet seat and lid. The urine is diverted into a bottle, which can be anything, but a 10 litre/2 gallon jug is convenient. The solid waste goes into a rectangular plastic box or crate, preferable with handles. Then you do some work with  plywood and epoxy to house them all, and some Formica/Arborite or similar on the surfaces helps to keep everything clean. Next to the head, you need a box for the medium, which can also be built in, and then the plan is to drop in about three handfuls of medium after each deposit, enough to cover it. Here are the basic components:

 I found cat litter to be the easiest medium to buy, store and use - compacted wood-based pellets that will swell up and break down into pleasantly scented pine sawdust when lightly rehydrated. No churning required, so no fancy mechanism. The top is hinged up for access to the bottle and crate, which are emptied as necessary, either at sea or into shoreside facilities. If the crate is lined with a plastic bag, that can be tied shut and put into the trash. You can add a 12volt computer fan and some ducting if you like, but I didn't find it necessary.

And that was a complete success for the remainder of my sailing career. Or at least, let's put it like this: it was the "least worst" marine head that I've been shipmates with. 

Or, if the thought of DIY doesn't appeal, and if they would fit into the available space, there are now some ready made examples of this KISS type, such as:
https://mytrelino.com/collections/composting-toilets/products/trelino-evo-m-portable-composting-toilet

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David Tyler - 12 Feb 2024

Having got fed up with cleaning lime scale out of the Henderson Mk V pump, pipework and holding tank attached to the Lavac,  I installed an Airhead in Tystie in 2007, in Hawai'i, and it remained in service until I sold her in 2016. The Airhead and the Nature's Head are more complicated than necessary, in my opinion (but certainly an improvement on a water-flushed head). With all the fiddly little bits that go along with the churning mechanism and closing flap, I found it difficult to keep clean, and once you have a fly infestation in the tropics, you really cannot get all the eggs and larvae out of the crevices. And however much you try, back they come again, those pesky flies.

KISS. For my final cruising boat, a 23ft David Thomas Duette, I made a DIY head which was fully successful. Basically you need to buy a urine separator such as one of these: https://my-composting-toilet.com/blogs/composting-toilet/how-to-find-the-right-separation-insert-for-your-composting-toilet (this website also gives you all the how-to info you need) and a domestic toilet seat and lid. The urine is diverted into a bottle, which can be anything, but a 10 litre/2 gallon jug is convenient. The solid waste goes into a rectangular plastic box or crate, preferable with handles. Then you do some work with  plywood and epoxy to house them all, and some Formica/Arborite or similar on the surfaces helps to keep everything clean. Next to the head, you need a box for the medium, which can also be built in, and then the plan is to drop in about three handfuls of medium after each deposit, enough to cover it. Here are the basic components:

 I found cat litter to be the easiest medium to buy, store and use - compacted wood-based pellets that will swell up and break down into pleasantly scented pine sawdust when lightly rehydrated. No churning required, so no fancy mechanism. The top is hinged up for access to the bottle and crate, which are emptied as necessary, either at sea or into shoreside facilities. If the crate is lined with a plastic bag, that can be tied shut and put into the trash. You can add a 12volt computer fan and some ducting if you like, but I didn't find it necessary.

And that was a complete success for the remainder of my sailing career. Or at least, let's put it like this: it was the "least worst" marine head that I've been shipmates with. 

Or, if the thought of DIY doesn't appeal, and if they would fit into the available space, there are now some ready made examples of this KISS type, such as:
https://mytrelino.com/collections/composting-toilets/products/trelino-evo-m-portable-composting-toilet

Hi David,
Nice report, and you are completely correct to point out that a DIY sanitation system may work better for many crews/boats, especially those that vessels that are smaller. And, I suspect some will really appreciate the URLs you gave for further research.
Your report also underlines the fact that these are more desiccating toilets than composting toilets, but that they are mis-named does not matter as the use does not change.
A couple of comments:
I wonder whether designs have evolved: we have not had troubles with nooks and crannies that are hard to clean. The structure is basically molded plastic. But we have not had bug infestations, thank goodness.
I might suggest a fan vented to an area where smells do not matter: perhaps a usage profile of a single-hander may not lead to smells, but other profiles might. Besides, a computer type fan will go a long way towards desiccating the solids and make disposal more pleasant.
Also, guests (and especially children) need educating as to usage. Some can be squeamish and the Air Head and others) have the advantage of “looking” more like conventional toilets.
My best, Dick Stevenson, s/v Alchemy