I completely understand. An out house is an open septic tank complete with smelly chemicals and floating Baby Ruth bars...gross. I would not want that on my boat either.
Composting toilets are not open. And, while Jeff is right about the humid environment being counter productive to the composting process, they actually benifit from a topsy, turvey, tumpling motion. Ever turn your compost pile?
Here is a short description of how they work from
FAQ - Composting Toilet World
How do they work?
They work by providing a
enclosed environment for the natural process of aerobic decomposition. The same type of environment on forest floors which decomposes wildlife droppings and converts them into valuable nutrients for the vegetation to use.
There are many different designs of composting toilets, but all carry out this basic process of aerobic decomposition. Design variations enhance this process and they include:
• air baffles for distribution of air into the pile
• heating units to keep the compost at the best temperature
• injected air for increased decomposition
• mixing tongs to ensure full decomposition throughout the pile
• the addition of composting worms and macro-organisms
Sunmar appear to be the pioneer in this particular industry. Here is an excerpt from thier website on marine use,
Composting Toilets By Sun-Mar - The Environmental Solution
The First Composting Toilet Designed Specifically for Mobile Use
The SUN-MAR Mobile, introduced in1994 was the first waterless, self-contained composting toilet designed for use in marine and RV markets, and for that matter, for use in anything that moves. The key feature of the mobile unit was that at only 19" wide it could be installed virtually anywhere.
Other than the width, what was new in this composting toilet was the 3" vent stack with a special fan/filter box which scrubbed the vented air so as to avoid any inconvenience on deck. In addition the finishing drawer was gasketed in place so that liquid could not escape even during violent motion, and the footrest folded back into the unit which is only 23" deep.
In addition a shore based waterless composting toilet was introduced with a 2" vent with a special fan assembly, and a 160 watt heater in the base compartment. This unit, the Spacesaver, is ideally suited for installation in cupboards or small corners where a toilet is needed but space is a problem