Wednesday, March 1, 2017

A Desiccating Head Part One

The idea of a 'composting' head on a boat - even one as big as Autarkia - is a little misleading.  The composting process usually takes a period of years under the right conditions, where the resulting material has been truly composted into harmless and fertile soil.

Marine composting heads such as the Natures Head and Air Head should really be called desiccating heads. They keep the liquid and solid wastes separate, but mix the solid wastes with a drying agent such as peat moss, sawdust or a mix of both, and further dry it out thereby reducing the volume thereof.  The resulting substance winds up being dry, relatively odour free and easy to dispose of.  But as it is not 'compost',  it may be reconstituted with water to a disgusting semblance of its former self.  Composted properly, the addition of water would just make it wet soil.

But from a practical standpoint after all said and done, on a boat it does not really matter if the poop is composted or not, as long as it is kept dry and consequently odour free.

In past posts where I have discussed having a composting head, we had made a decision to buy a Natures Head as seen below.

It is arguably one of the better products out there, well regarded by those who have them.  Apart from it being a good product that does what the makers promise, there was a secondary reason we were considering:,  and that was the 'social acceptability' - if you will - of a 'store bought' device, costing a lot of money thereby making it all right in the minds of friends and relatives.

You might wonder why that would ever be a consideration for a couple such as us, building a completely unorthodox boat to begin with, and who in other aspects of our lives often reject the values, trappings, and behaviours of mainstream society, but it was.  Go figure.

What really changed our minds though was when we looked into actually ordering one, as Autarkia is now ready for it.  What we though might be an investment of around $1000 all in, turns out to be really about $2000 Canadian with the required accessories (ventilation kit) and after taxes and shipping.  "No way!" we said,  "we're going to make one!".

It has been done before and it is not rocket science.  The key things that are of utmost importance are:

1) Urine separation and collection to keep the poop dry.

2) Ventilation - preferably with a fan that keeps a negative pressure inside the toilet (sealing must be considered here) and that assists the drying process.  A screen over the outlet to keep the bugs out (this advice from RLW of BoatBits fame, who has been using a DIY unit for a decade now).

3) A desiccating medium such as sawdust, peat or a mix of both, to be sprinkled over each deposit.

As long as the above things are considered, a successful desiccating toilet can be built.

Let's look at the first item - urine separation:

For most guys an effective but inelegant way of dealing with this is using a plain old pee bottle.  You can buy these at marine outlets - they are made of red plastic, and have one flat side (I assume because it is also a medical product that can be used in bed).  An attachment is also available for female use as well, and it works.  Not so good though for getting up in the night.  So a means of being able to sit down (for either sex) and pee while groggy or still half asleep has its advantages.  And fellows, we don't go out and hang it overboard in the middle of the night.  Unsafe.

So it becomes an anatomical and ergonomic issue to design such a collector that does a proper job of separation.  That is, to be able to collect a urine stream from either sex, directed or not.  Furthermore, the urine collection receptacle must not interfere with other biological workings further aft!  A fine line must be drawn.

So here is the problem with a factory made device:  The designers must make assumptions about the user's anatomy and design something that satisfies the needs of the many but may not meet the needs of the few.

However, if we are building our own, we can mock up, experiment, mock up some more, experiment some more and come up with something that will work perfectly for us as individuals.

Without going into too many details here is what we came up with geometry wise.  The toilet seat was supported on either side with two chairs, so that one could sit down, reach in under and explore said geometry, as well as one's own geometry in a tactile manner.  Sorry, I tried to be more delicate...

I bought the toilet seat.  The SS bowl was stolen from the kitchen.  When sitting, there is some contact on the aft edge of the bowl, confirming that both guns are on target.  The other thing that has apparent advantage is the opening is quite a bit larger than what the Natures Head provides.  When researching the Natures Head, I contacted the company and asked about 'aiming accidents' in the aft area, and was reassured that cleanup was easy with a spray bottle filled with a water/vinegar solution.  I thought that if the opening were large enough that cleaning up would not be necessary.  This looks good so far.

I used epoxy putty to put the fitting on the bowl for the urine collection hose.  The reason for this was that any kind of fitting that attached mechanically would have a lip that would dam the urine, and not allow the bowl to empty completely.  With the fitting stuck on in this manner there is no lip.  Nonetheless, after each use I think that giving the bowl a spray of water/vinegar is a good idea in this instance.

Further along in the mockup and design phase of the project we are considering the tub to use.  Many designs out there use an orange Home Depot bucket of about 5 gallons capacity.  RLW tells me that the two of them are good for a month of use with one of these, but since I had this 'muck tub' from the farm store, I thought we would use it.  It should provide many months of capacity but there are other advantages too.  The extra space makes it easier to plumb in the urine tube, and the exhaust ventilation tube (probably will be 1-1/2" PVC) can go right down one side to draw air right across the growing pile.

To line the tub, I used a heavy plastic 'contractor' bag.  It is large enough to fit this tub.  At the bottom I put a circle of cardboard.

I then cut a piece of 1/2 inch plywood to fit very snugly inside the rim.

The top deck for the toilet is glued and screwed to the round insert.  The SS bowl was installed with PL Premium glue - very solid.

This is as far as I've gotten.

The top deck is over-sized, but I left the extra material so I can fit it nicely into the boat with a suitable surround for the sides.  I still need to decide how the lid will seal.  I may put the seat itself down with silicone sealant so it can be removed if I have to replace it.  I may have to make a gasketed cover to go over the hole.  I don't think that the toilet seat lid will seal well enough, even with weatherstripping foam.

To be continued....


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  3. I must say I'm delighted to see you go this route. You might recall my earlier comment a couple of months back?

    "confirming that both guns are on target" has been my first laugh of the day, thank you for the laugh, and the image.

    I think you'll find that people (friends and relatives) will quickly accept and adapt and I for one think you've made an excellent decision.

    You'll know of course that Bob at BoatBits only recently did an updated post about urine seperators ( but making your own out of stainless mixing bowl is even better!

    Looking forward to seeing the Completed Job. (so to speak)

    Anticipating update Number Two?

    1. Thank-you Jon! I will be continuing work on the toilet today, and anticipate having it mostly installed by the weekend. So I should have a 'Part Two' by then.

  4. Al,

    Looking good, I second the opinion from Jon about being glad you went this way instead of Nature's Head. Regardless how wonderful that non-composting, composting toilet is,I morally object to paying $1,000 for something to poop in.

    I'm watching your design with a lot of interest because something like this is in my near future. I have two comments.

    First, it seems that it might be better to leave the toilet seat installed in the standard way so it can be lifted. Probably not for normal male urination purposes, but for the simple purpose of cleaning underneath it. Second, you might consider abandoning the normal toilet seat cover and simply building a shallow box that fits over the entire toilet seat area. IT could easily be sealed. Plus, you could put hinges on the back and a simple handle on the front of that little box to allow you to lift it up out of the way. And because it's a box, when you lift it, it can rest on its own back side. ;-)

    No matter what you do, I'll be looking forward to it eagerly, both in terms of design and then later, feedback from actually usage.

    I always admire your willingness to be a pathfinder. We all benefit from it. More power to you.


    1. Hi Yoda! Thanks for the compliments, and for the idea of the box-cover. I am going to use it, firstly because it solves all of the sealing problems. I only need to weatherstrip the lower edge all around. That way, I only use the seat portion of the toilet-seat (can discard the cover), and I can hinge it up for cleaning as you say. But the second reason is that the toilet is going in under my forward hatch/companionway, and will serve as a step for egress/ingress. The box cover will do well for that, serving as a step, and hiding the toilet entirely. Great idea, Yoda!

  5. I like the top sealing box idea too, luckily I have not finished the install on the toilet yet. I am not sure how you are handling the liquid, but with my design it was what caused the most odours if not promptly emptied and rinsed at least every second day. I am using 1 gallon windshield washer fluid bottles, so I can just cap and dispose if required. Another note, Red Wiggler composting worms did very well in the main bucket, and the worm castings were mush closer to "dirt", see if a local worm guy will let you have some for a trial.

    1. Thanks Dennis. I think that keeping the urine system clean with a little rinse of water/vinegar after each use may be a good idea - not much - just a spritz or two from a spray bottle and a wipe of the steel bowl with a tissue. I like the washer fluid bottle idea - if I can make it fit inside my enclosure so much the better. I can put a little access door in the front panel.

      Lorri and I have a bit of experience with worm composting and I kicked that idea around. The problem with it is keeping a certain moisture content to keep the worms happy. I think it will be far easier to just dry it out with the desiccant and ventilation and not have to worry about the pets :-)

  6. Looking good, Alan. I have been saving all my table saw sawdust in feed sacks for its dessicating properties when I go amsimilar route.