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Converting To A Composting Toilet/Head on a Gemini 3200 Sailboat

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How to install a composting toilet?

Our Gemini 3200 is a 32 foot sailing catamaran named Ariel. Ariel had a normal, smelly, boat toilet/head that stored all the 'stuff' in a holding tank. After a month of owning her, we began to look for alternatives. What we settled on was a composting toilet from Natures Head. Below are the blog entries that walk through the process as we progressed.

Benefits of a Composting Toilet


When you go with a composting toilet, there is no smell, no water, and no holding tank. The other benefits of a composting toilet include less maintenance, no seacocks, and a lot less weight.

Maintenance for the sanitation system will be reduced to disposal and cleaning. Under the current system, we have to pump-out the tank (disposal), cleaning the toilet, lubricate the internal workings of the toilet, and check to hoses on a regular basis.

The composting toilet will eliminate the need for 2 seacocks. Seacocks are holes in the hull. Seacocks can either be intake (which allow water in) or outtake (which allow water to go out). But don't let the designation fool you, all holes allow water in. The foremost concern of any boat owner is unwanted water coming into the boat. The more seacocks you have the more opportunities unwanted water has to get inside.

Weight on a boat is another concern of any boat owner. You can have too much weight and it can lead to the boat sinking. By removing the current sanitation system, we calculated that we would be eliminating approximately 150lbs or more of potential weight in favor of a system that will weigh approximately 35lbs at the heaviest. This gives us the ability to store another 115lbs of supplies.

Again the composting toilet is a no brainier. The only reason, I can think of, that boat builders don't install composting toilets on their boats to begin with is because of the cost. A composting toilet can run anywhere from $800 to $2,000. But I believe it will be worth every penny!

Air Head or Nature's Head Composting Toilet?


After review all of our options, which included constructing our own composting toilet, we are down to two worthy products, Air Head and Nature's Head. Both toilets are made from a molded polymer and at first glance look very much like the toilet we have in our apartment. Both toilets separate the solid waste and liquid waste into their own containers that have to be emptied at some point. The toilets are very much alike, except in two ways.

First, the Nature's Head toilet has a normal size (like found in your home) molded toilet seat, while the Air Head's seat is a little more compact. The compact seat wouldn't bother our girls, but it could get a little uncomfortable for Bill and I.

Second and most importantly, Air Head's basic unit cost $969 + shipping, while the Nature's Head unit cost $850 + shipping. Additional components for the toilets, such as additional liquid waste containers, are similar in cost.

So which toilet, Air Head or Nature's Head? Well the choice for us is oblivious. Nature's Head. I'm planning on purchasing the toilet on Friday. We hope to have it by November 25th so that we can install it over the Thanksgiving Holiday.

If you want to learn more about these two composting toilets, I've provided links below.
Air Head:
Nature's Head:

Composting Marine Toilet Conversion - Step 1


In late November 2009, once our Natures Head compositing toilet arrived, Val began the process of converting our traditional wet marine head to a dry composting one. This odyssey would be the largest modification we've made to the boat to date. The photo here is of the original marine head in all its stinky glory.

Step one in the process was motoring the boat over to the sewage pump out station and emptying the holding tanks of all the stuff.

Tanks as dry as possible, with chest high and nose pinched shut, Val attacks the project by removing the first hose. Our boldness and conviction would be tested as we faced obstacle after obstacle. Enjoy the smelly journey!

Composting Marine Toilet Conversion - Step 2


Oh my! Talk about STINKY! When we entered the boat, with the hoses disconnected, the putrid smell knocked you back. We elected to eat lunch out this day.

With the original toilet removed, Val started with a small exploratory cut with her Dremel tool so we could gauge the dimensions of the holding tank on our Gemini 3200. The exploratory cut is the small cut out section you see at the bottom of the photo. With this cut made, it was time to open up enough of the wall to pull out the poopy tank. Using her cutting tool, this took about 2 hours total. This was spread over 2 different days since her battery powered Dremel ran out of charge.

Once the holding tank was pulled free, we found an outstanding space that we will re-purpose storage location for the Peat Moss and extra toilet paper. Proudly, and very carefully, the offending holding tank was extracted from the boat and placed on the dock cart for removal. This was a proud moment indeed, and one could almost hear the trumpets as it was paraded up the dock.

Time to create new coverings for the holes we've created.

Composting Marine Toilet Conversion - Step 3


Upon arriving at the boat, the smell wasn't bad at all. In fact, it smelled better than it has since we've owned the boat. There was a slight hint of stink, but we believe the odor is due to the few hoses that we still have connected to the seacocks. Those will be removed post haste.

We now have 2 holes, or open spaces, that we need to fill. The first one is towards the top where the holding tank was previously, and then at the base where we are going to install our Natures Head composting toilet. We made patterns for both.

For the upper backing, we used Luan 1/8th inch board. We picked Luan because it was light, cheap, and once painted sealed. It can tolerate light splashes of water quite easily.

For the bottom flooring, we used a standard piece of 3/8th inch plywood. We will drill holes right into the flooring where the original toilets holes were drilled.

Composting Marine Toilet Conversion - Step 4


The flooring is now being painted and sealed. You can see the 2 holes drilled into the board where the brackets to the Natures Head composting toilet will be screwed in.

The Natures Head toilet does not come with any bolts, so we had to acquire some. They were Stainless Steel, the only way to go in a sea water environment. We've dry fitted everything and it goes together nicely. One issue, however, is that the throne is very high now and we will need a step up for the kids.

Once the paint is dry, we will put everything together, and bolt it down nice and tight.

You will notice that one of the bolts is shorter than the rest. This is because of where we elected to seat the toilet. We pushed it off center so that the cranking arm of the compost agitator and the exhaust port/hose could clear the sides.

When drilling off center, I ended up in a thin part of the fiberglass flooring, and this necessitated the shorter bolt.

Almost time to put it all in, and then we will have to attack the ventilation part of the system.

Composting Marine Toilet Conversion - Step 5


All bolted in! Wahoo! A dry run, literally, was done with plenty of simulated rocking and rolling. The new commode is secure!

Running the bolts all the way through the fiberglass base of the original toilet was the way to go. It was tricky, though, holding them from underneath and putting the bolts on. The bend of my elbow had to be exactly right. There were a few nut drops along the way resulting in colorful words and starting over.

The hose off to the left side is the vent hose, and it runs up the back behind the new false wall, to the old pump out hole. The next phase of this project involves installing the solar powered vent system at the top that will run 24x7.

With the lid open, you can see inside the NaturesHead with the drop shoot opened. This is for working in number 2 mode, as it were. Another picture shows the NaturesHead operating mode when taking care of number 1. According to the literature, a female can use the system in number 2 mode and the appropriate stuff will for 1 or 2 will make the correct journey. A man, on the other hand, must keep things, well, aligned and its recommended he chose a singular mode and use the system accordingly.

Whew! I think I said all that needed to be said, without saying it!

Nicro Day/Night Plus Solar Vents Installed - Step 6


Sail Harbor Marina and Boatyard installed the 3 Nicro Day/Night Plus Solar Vents (2-4" vents and 1- 3" vent) that we had previously purchased.

We had the two 4" vents installed in the hatches at the galley and the head. The galley vent is an intake vent, while the vent located in the head is exhaust. Each of the 4" vents moves 1000 cubic feet of air per hour, which should be more than sufficient in keeping the air moving on our Gemini 3200. When we reviewed the installation of the vents, we noticed that the vent in the head was not working. After a little trouble-shooting, it was determined that the battery that came with the unit was bad. A replace battery is now on our "Need To Purchase" list.

The 3" vent was installed as an exhaust vent for our Nature's Head Composting Toilet, where the old pump out fitting was located (This is the 6th of 7 steps).

Composting Marine Toilet Conversion - Step 7 - Completed!


Once the 3" Nicro Day/Night Plus Solar Vent was installed by Sail Harbor Marina and Boatyard, all that was left to do was to connect the hose to the vent and add the peat moss. Sounds simple right? It was simple after I noodled how to get the 1 1/2" hose to fit the 3" opening on the solar vent. I went out to Nature's Head's web site to see if they had an adapter or instructions that would help. They showed an adapter that came with my unit, but in it's original state would not work with our vent since the vent protruded below the ceiling. Using the "Contact Us" function on Nature's Head's web site, I sent an email asking for assistance. Within 24 hours I received an email from Larry at Nature's Head asking for my phone number so that we could talk. I sent Larry my phone number on Friday afternoon and didn't expect to he from him until after the Memorial Day holiday. To my astonishment, I receive a call from Larry on Saturday. We discussed the situation and come up with a solution together.

The solution was to trim the adapter that came with the unit down to fit the vent's opening. The Nicro Day/Night Plus Solar Vent has tabs on the inside, of the vent, for an insect screen. I trimmed the adapter down to size and notched out two notches for the tabs. After some tedious machining (trimming) using my Dremel, the adapter fit. I removed the adapter, connected the hose, place the adapter back on the vent, and checked if I could feel air being pulled out via the hose. SUCCESS!!

The last step was adding the peat moss. I added peat moss until the agitator could just barely touch it. Then I added water until the peat moss was a little moist.

Approximately, 6 months after starting this project it is complete!! YEAH!!!! (The only reason that we didn't complete this project earlier was we had more pressing projects, like getting the boat transported,etc.)