Nature's Head built its toilet with boats in mind: its user guide says the toilet was designed to withstand the rigors of the boating environment, and its marine page pitches it as a way to skip holding tanks and pump-outs. This guide covers what changes on a boat: the Marine Kit, deck venting, power from the house bank, the liquids bottle in a seaway, and laying up for winter. All specs come from Nature's Head's own pages and manual, and from our listings.
What the Marine Kit includes
The Nature's Head Marine Kit is the standard composting toilet plus the parts a boat needs:
- The toilet: 21" high, 20" wide and 19" deep, 23 lbs, with a 2.2-gallon liquids bottle and the 12V fan already mounted
- A Portos-1 mushroom ventilator made by Vetus, the outside vent for a deck or cabin top
- A 9L bag of coco coir
- From the toilet box: the inside vent flange, 5 feet of 1-1/2" vent hose, a fuse and fuse holder, and two mounting brackets with knobs
The kit comes with a Spider or Foot Spider handle. Nature's Head's marine page says the compact Spider handle saves space, which matters in a tight head compartment. The same page says the toilet meets USCG requirements for a Type III marine head, and lists sailboats, motor cruisers and trawlers as the boats it's meant for.
Will it fit your head compartment?
Measure against Nature's Head's drawing, not just the outside box:
- Behind: at least 1.5 inches from the bulkhead so the bowl can tilt back
- Left side: 2 inches so the bowl can slide off its slip hinge for emptying
- Above: enough height for the lid to open fully and the bowl to tilt so the bottle comes out
- Front: the bottle sits 6 inches ahead of the 13-inch base
The fan housing and the handle can both be moved to the other side. Nature's Head also suggests offsetting or angling the toilet slightly where space is tight. If even that is too much, its manual says that in severely confined spaces you can remove the mounting knobs and slide the toilet out to service it.
The Weekender is lower and narrower (16.75" x 18" x 18", 19 lbs). Nature's Head lists boats among its uses, but there's no Weekender Marine Kit, so you'd add the mushroom vent separately. Our Nature's Head buying guide compares the two in more detail.
Mounting on a boat
The toilet is held down by two L-brackets that sit in recesses under the base and are fixed with the knobs. The supplied screws are for wood or plywood: drill a 1/8" pilot hole for each. For other surfaces Nature's Head says a different fastener may be needed. Its brackets take #12 countersunk screws or bolts.
On a sole that gets wet, Nature's Head says to put a little sealant in the holes before the screws. Check what's below before drilling, and don't overtighten the knobs, because they can strip the threads in the base. The Mounting Hardware Kit has spare brackets, knobs, washers and screws.
Venting through the deck or cabin side
Nature's Head's manual says the unit must be vented outside. The outside end needs a cover so wind doesn't blow back against the fan, and a screen against insects.
Our listing gives these sizes for the Portos-1:
- Cut-out: about 3-3/8 in (85 mm)
- Deck thickness: about 1.1 to 1.6 in (27 to 41 mm)
- Height above deck: about 1.2 to 1.8 in
- Overall diameter: about 4-5/8 in
Nature's Head's FAQ notes the mushroom vent is useful where you may want to close the vent for a period. Check your deck thickness at the spot you choose before you cut.
Through the cabin side or coachroof: Nature's Head's manual says the Shell Vent can be used on a boat's cabin side or roof. It needs a 1-3/4" hole. On a thin single-skin cabin side, the toilet's inside vent flange goes on the inside to meet the vent. Nature's Head's FAQ points to the flange for single-walled installs such as boats.
The hose run: keep it as short and direct as you can. Nature's Head doesn't recommend more than 20 feet. Attach the hose to the housing that holds the fan (the right side as you face the toilet, unless you've moved it), and make sure the fan blows out. Extra 1-1/2" hose is sold by the foot.
Power from the house bank
Nature's Head's figures for the fan:
- 0.07 A while running
- 1.68 Ah per day
- 20.16 Wh per day
The fan is meant to run continuously. Its manual says a deep cycle marine battery can power it off-grid. On a battery or any circuit without its own protection, use the supplied fuse holder. Nature's Head specifies a fuse between 2 A and 5 A.
For a neat connection in a damp head, the 12V Wall Power Port Kit has a panel port with a waterproof plug and a 6 ft cable. The 12V socket panel uses tinned copper wire, an inline fuse and a waterproof rubber cap. Keep a spare fuse aboard. Nature's Head's troubleshooting starts with the fuse and the single-pin connection when the fan stops. Full wiring steps are in our installation guide.
Living with it aboard
- The liquids bottle. Two people full-time might empty the 2.2-gallon bottle every 3 to 4 days, per Nature's Head. Empty it at three-quarters full, and cap it before lifting it out. If the bottle overflows a little, Nature's Head says the liquid stays in the container base as long as the overflow isn't excessive. Don't count on that in a seaway; empty early before a passage.
- Solids. About every 3 weeks for two full-time users. The bag method suits boats: stretch a 13-gallon kitchen bag over the base, invert it and empty without taking the toilet ashore. Nature's Head notes this is especially useful on boats.
- Spares and supplies. A spare 2.2-gallon bottle, the Bag of Replacement Parts and 35L coco coir cover most needs between ports. Our 35L coir is a hydrated bag and needs no soaking; a dehydrated coir brick is more compact but needs up to 12 hours in water.
- Cleaning. Use 1:1 vinegar and water down the urine holes after each use. No bleach or abrasives.
The full routine is in our coco coir and emptying guide.
Laying up for winter
Nature's Head's FAQ says many boaters leave the solids in the toilet over the winter and empty it in the spring. The longer it sits, the more it breaks down. The exception is a boat that will sit in sub-zero temperatures (below).
Empty the urine bottle before freezing weather. Frozen urine can expand and crack it. Composting stops below about 55°F and goes dormant at freezing. Frozen compost can lock the handle, and Nature's Head says not to force it. If the boat will sit through sub-zero temperatures, its suggestion is to empty both and start fresh in spring.
Also, unplug the fan if the toilet won't be used for a week or more, so the medium doesn't dry hard.
Disposal
Nature's Head recommends a proper compost bin for the solids. When traveling, its manual says the contents may go in a conventional dumpster. It says to check with the local municipality on how and where to dispose of the waste. Urine can be emptied into a toilet or other appropriate facility. Don't empty the bottle or the bin overboard: federal and state rules restrict discharging human waste, including urine, from boats (see the EPA's vessel sewage page). Empty ashore, and check the local rules where you cruise before you go.
FAQ
Is a Nature's Head legal on a boat?
Nature's Head's marine page says it meets USCG requirements for a Type III marine head. It doesn't make overboard emptying legal: federal and state rules restrict discharging human waste, including urine, so empty ashore and check local rules with the harbor or municipality.
What size hole does the mushroom vent need?
About 3-3/8 inches (85 mm), in a deck about 1.1 to 1.6 inches thick, per our Portos-1 listing.
Can I run it off my house battery?
Yes. Nature's Head rates the fan at 0.07 A, or 1.68 Ah a day, and says a deep cycle marine battery can power it. Fuse it at 2 to 5 A.
What do I do with it over winter?
Empty the urine bottle so it can't freeze and crack. Many boaters leave the solids until spring, but if the boat will sit in sub-zero temperatures, Nature's Head suggests emptying both and starting fresh. Unplug the fan while the boat sits.
See the Marine Kit and every spare in our Nature's Head collection. For a quick list of vent parts, see how to power and vent a Nature's Head.