If you ever get the chance to design your own narrowboat, let me give you a suggestion about where to start the design. In the toilet. Once you have this topic pinned down, the rest gets easier.
Much has been said about toilets and boats, and the pros and cons of different types of loo. As experienced hirers we had two particular events to reflect upon.
One boat we hired had a macerating toilet which, just one day out of the marina, failed to do the macerating thing. The "engineer" was called out and he asked if we had run the engine when pressing the flush button. Foolishly, as it turned out, we had not. His explanation was that the battery was a bit iffy, and the wiring none too good either so to be sure of a good strong churn we should always run the engine to get the alternator boosting the electricity at the time. Brilliant. Late in the evening you feel like doing a No.2 and have to wake the neighbourhood to announce what is about to pass...
Another boat we hired developed an intermittent fault on the macerator switch, so that going to the toilet became a lottery. Would it go or would it stay? This time the "engineer" announced that the switch was behind the tiled wall and to get at it he would have to remove half the wall, and this might make matters worse. Fortunately we had a second toilet on that boat, so we pressed on with just that one in service. The conclusion we drew from these experiences was that we would not be reliant upon a single macerating toilet.
We wanted Perseverance to be suitable to entertain family groups, including current and future teenage girls and boys. Our experience of teenage boys (we raised two) is that they can take an age in the shower, so it had to be possible to operate the boat with the shower room occupied. This led to (a) a decision to have a corridor bathroom, so that we could get to the bow while the shower was in use, and (b) a decision to have a separate toilet so that we could go to the loo while the shower had been in use but something else was happening (shaving? hair straightening?? toenail painting???).
The first design therefore had one macerating toilet and one cassette toilet. We lined ourselves up for alternating visits to pump-outs and Elsan points, knowing that both often stank but this was the best we knew.
Then our builders, Ortomarine, suggested Compoost toilets. "Look at the Foxes Afloat vlog" they said, and we dutifully chuckled our way through 14 minutes of toilet jokes. Further more, Ortomarine had fitted pump-out, cassette, incinerating (both gas and electric) and Compoost toilets and said this was the best thing they had found by far. We decided to pencil one in for the design, and undertake a formal trials programme of our own. After all, I'm an Engineer (not "engineer") with a test and measure background.
For those not familiar with this toilet, it is similar to other composting toilets in that solids and liquids are kept separate, which avoids most of the smell. The urine goes into a large bottle and this is periodically emptied either pouring it down an Elsan point, or onto fields well clear of the waterways as wee is a good fertilizer. Poo falls into a bucket which is prefilled with some compost. A stirring paddle mixes the compost and poo which forms neat compost covered balls. A small fan draws air out of the toilet, both drying the compost mixture and removing what little smell there is.
So much for theory. To test one, we bought a toilet and set it up in our garden shed, with a car battery to run the little fan. On the boat we will vent overboard, but as I didn't want to drill a hole in my shed, we used a carbon filter during the test, and vented the toilet inside the shed. The test configuration included copies of both Canal Boat and Waterways World, for a balanced evaluation, and we trialled biodegradable and standard toilet papers.
The most fascinating thing was that there was very little smell. Indeed, after a couple of weeks of use, a visitor confirmed that the shed smelt of - shed !
When emptying the bucket into plastic bags (double bagged, this can go into the dustbin) there was a gentle compost fragrance , and there was a more noticeable whiff of urine when emptying the bottle onto our compost heap. However, neither was anything like as bad as the smell of a badly kept pump-out station, or some of the Elsan points we have visited around the system, or our last hire boat.
The trial was so successul that we decided to fit two Compoost toilets on our boat. This has some consequences for the boat design. We won't have a cassette toilet, so there will be no need to access and manage the cassettes. More signicantly, we won't have to fit a sewage tank and sewage pipes (I know they are often given more polite names, but that's what the macerating loo waste tank is). This means that there will be more storage space on board, and our travelling plans will not be dictated by the availability of pump-out facilities. OK, we'll have to keep a bag of compost on board, but that is easy to do.
With the hardest decision made, it was (relatively) easy to design the rest of the boat, of which more later...
2022 Update
Having used these Compoost loos for some time now, and with a number of different guests, I can say that we made a right decision. Tipping some pee into the hedgerow of an evening has become matter of course, and we haven't found too much trouble finding bins to put the poo bags into. At Crick we gave the CRT representative an earfull about why our funds pay for Elsan disposal, but they plan to do nothing about recycling disposal. Their answer was "a third party will come along if it is profitable". Quite astonishing.
And now onto some lavatorial detail. We have found some guests use vast amounts of toilet paper. Not only do they get through a roll a day, but they barely fold or crease the sheets. The end result is a bucket of tumbling origami and cries of "it's overflowing!" after just a couple of days. With a feeling that this must be what it's like to run a hotel, we recycle the loo and supply another roll.
For convenience (love the pun) we have a third wee pot, so that if the "nearly full" alarm goes off in the evening, we can replace the pot and empty the full one in the morning. Saves wandering down the towpath in the rain at night wearing slippers.