How to maintain your craft with the environment in mind

Fitting a holding tank to a Nauticat 33

My Nauticat dates from 1971, when holding tanks were not even a twinkle in a green (or blue) person's eye: so retro-fitting one was not going to be easy.

What's the point, anyway? Waste regulations are currently very fluid and keep changing, but the indication is that more countries will implement a ban on discharging untreated toilet waste within 3 miles of the coast.

Well, of course you are a totally law-abiding citizen like me and never drive at even 1 mph more than the speed limit, but let's be practical about this. If you are 2 miles offshore and there is no estuary or river into which there might be a tidal flow, what is the environmental impact of you flushing the loo? If you really intend to stop all discharge of untreated sewage within 3 miles of the coast, then it is more important to tackle a far greater source of such sewage by fitting nappies to seagulls instead of holding tanks to yachts.

But things change once you are in an estuary or river or, worse, a marina: not only does your sewage then drift around with possibly little chance of being flushed right out to sea, but the number of boats per square inch increases, therefore so does the concentration of sewage. Consider also the poor swimmer or sail-boarder: just what are they swimming in or falling off into?

So there really is no doubt: in enclosed waters, don't flush. Especially in marinas with no through flow of water (most of them): there are some marinas where the smell is revolting, because the sewage just stays and stays.

This means that unless you have far greater bladder control than I (but that's just old age), you need something for when you mustn't flush.

 

Before you start

Step 1 Iinitial planning and tank location

The first question has to be: why bother with a holding tank? It is an immense amount of hassle, so do the advantages outweigh the problems?

The answer depends on your sailing. If you either sail from marina to marina and are happy to use the marina's toilet facilities, or do almost all of your sailing offshore, then there is no point in fitting a holding tank. Instead, carry a Porta-Potti for those few occasions when you are in a marina and its pelting down with rain and you can't be bothered to put on your oilies to have a pee. I carried one for 2 years and found it served its purpose very well: but do consider the disadvantages.

Firstly, where do you put it? It won't fit in the toilet because where do you put your legs when you are sitting on it. You may well find that there just is nowhere it will fit: you hardly want it in the cockpit all the time. Get the dimensions from a catalogue and make up a cardboard template: you will be surprised how big it is.

Secondly, it will need to be emptied. That means you have to carry it, full, to somewhere you can empty it: a full Porta-Potti is remarkably heavy, and where is there an emptying point? They are still few & far between, so you will often have to carry it into the marina toilet and empty it there. You will be amazingly unpopular, because the smell generated by emptying a Porta-Potti into a toilet is fearsome.

Third, the capacity is not huge: you will inevitably at some stage find that it is full and have to carry it out in the pouring rain to find that the nearest emptying point is a mile away.
Having said that, it is very much easier to install a Porta-Potti than a holding tank! But having used a Porta-Potti for 2 years it really became clear that it was not a long-term solution so installing a holding tank was the best option.  

Start off by looking at some web sites: for instance Tek-Tanks and Lee Sanitation www.leesan.com; they have a wealth of information for you to consider. Also perhaps look at suppliers such as Vetus www.Vetus.co.uk for odour-free hose, filters, diverter valves etc. Then start with the planning.

As with the Porta-Potti, the first thing is where to put it. The Westerly Centaur I had before the Nauticat had a totally useless space behind the toilet, which was ideal for a tank: I made a prototype out of plywood and resin to try out for a year and it was still going strong 6 years later. But few boats will have such an easy space.

The space should be:

• high enough so that the bottom is above the (heeled) water-line, to allow gravity emptying
  
• low down so the weight doesn't increase the boat's heeling moment

• large enough to have a sensible capacity
  
• not a convoluted shape: rectangular, for preference
  
• close to the toilet, to minimise pipe runs

• not already taken up by something else.

Well, there ain't no such animal, so compromises must be made. Take your time: this is the most crucial decision. Examine carefully all available (or could-be-made-to-be-available) spaces: measure the capacity of the space (just roughly will do) to find out how many flushes it will hold. A rough indication is that each flush will be 3 litres and a person needs 4 flushes per day, so 12 litres per person per day. Thus a 120 litre tank will do one person for 10 days, but 4 people for only 2½ days: and you will be amazed at how much space a 120 litre tank takes up. Measure the space in cm; multiply the width x depth x height; divide by 1000: that is the number of litres. Divide by 12 for the number of people-days that tank will hold (very roughly).

Remember that when in a marina, you can't empty your holding tank into the sea: the frequency of pump-out places is increasing, but is still very limited. So think of the worst case: you are stuck in a marina for a fortnight waiting for a gale to pass. How long will the holding tank hold out? If you walk to the marina loo when you can and only use the holding tank at night, you need perhaps 3 litres per person per day, so a 120 litre tank will last 4 people for 10 days. It is probably not worth fitting a tank less than 100 litres. A tank 50cm x 50cm x 50cm has a capacity of 125 litres, but if you can find an unused 50 cm cube on your boat, there's something wrong!

So you may well fall at the first hurdle: only pass Go if you have definitely identified a place which is large enough to be useful and the current contents of which you can stow elsewhere.

 

Step 2 Pipe location

Next stage: work out your pipe runs - can they actually run? Remember that 38mm diameter pipe is large and unwieldy: it won't bend round sharp corners. If necessary, buy a couple of metres and see how it bends (or doesn't). I found that Vetus "odour-free" pipe, although expensive, was about the most flexible.

The inlet runs from the toilet to the top of the holding tank. Don't be tempted to run it to the side of the tank near the top, because the contents will slosh, and will slosh back down a pipe unless it goes into the tank at the top. That usually means the top of the tank has to be lowered around 70mm below anything above it, eg the top of the locker it is in: you've just lost a lot of capacity! When specifying the inlet fitting on the holding tank, a good wheeze is to specify a pipe inside the tank with a bend in it, so that the incoming material is directed against the side of the tank, not straight down: that reduces the splashing noise considerably. In my case, the holding tank is under a bunk, so that is quite important!

The outlet can be to a pump-out fitting on the deck or to the sea: it is unwise to limit yourself to one or the other for obvious reasons, so you really need both. They can be from one pipe to a diverter valve, but a diverter valve is a much bigger thing than you think and has to be mounted where the handle is reasonably accessible. Usually far easier to have two separate outlet pipes.

 

Step 3 What type of tank?

Now you have done your initial planning and decided on the location for the tank and for the pipe runs, you must decide on the type of tank. A rigid plastic tank is the best possible answer. Don't go for stainless: raw sewage is amazingly corrosive - enough said. The tank can only be made straight lines: no curves. But you can have a number of edges. If the shape of the hole just will not permit a rigid tank, then you will have to go for a flexible tank: put lots of packing round the hole to eliminate chafing as far as possible, remembering that the tank plus contents will slosh about something rotten, when partially full. Also, there is no way of fitting a gauge. Be prepared to replace a flexible tank eg every 2 years: the alternative is to leave it until it does chafe through...

Assuming you think a rigid tank will fit, you now need a template. Don't think you can knock this up out of cardboard and sellotape: for suitable rigidity it needs 10mm plywood and wire to hold it together. My locker is an odd shape (but then what spaces on a boat are not?) and it took me and a mate a whole day to make a template. Measure the easiest side, cut it and offer it up. Measure the next easiest side, cut it, offer it up, then attach it to the first side with wire staples through holes. Continue... Taking the growing lump out each time to add the next bit is essential, as it will show you at what point you now just can't either get it into the locker, or can't get it through the boat up to the locker: at that point, you need to prune the shape, eg by cutting down a corner. I ended up with a shape made up of seven sides, with the bottom and the port sides being cut away to allow the tank to get into the boat and into the locker. Out of 30 corners, only 1 was exactly a right-angle (see picture).

You won't be able to send away your template to the tank maker: it's not strong enough. So you must measure the sides & angles and preferably make scale drawings of each side. Draw on where all the fittings will go, including the gauge sender and the inspection hatch. Remember that the fittings can't go where the baffles are: you will need one or two baffles to stop the contents sloshing about as the boat plunges. Allow for right-angle fittings to go somewhere: don't place them too close together. Allow sufficient room above the tank for the fittings plus a bit spare. My planning paid off (see picture): the fittings just fit all at one end, boxed in: the box is just the same height as the berth cushion, allowing for a cut-down cushion and a pillow on top.

 

Step 4 Getting to Work

Once the tank arrives, the fun begins. How long can it possibly take to fit a tank and some pipes? It took me a whole week: that's 7 days, 14 hours a day.

A good idea is to use expanding foam to line the locker: it prevents any movement and gives both sound and heat insulation. But you will need 3 or 4 tubes, since you squirt some in the bottom, then put the tank in place before it goes off, then you have to wait until it does go off before doing the next squirt: since the foam is moisture-curing, if you just fill up the whole gap, the foam at the bottom will take days, weeks or even months to go off since moisture can't get past the top bit which has gone off. That means it will continue to expand for ages, possibly crushing the tank. So squirt in 3 or 4 goes, sprinkling with water and waiting for half a day between goes (bracing the tank to avoid movement). When that bit has gone off, so has the foam in the delivery tube, so you need a new one...

Wrap the tank with plastic sheeting before putting it in place: that ensures it won't stick to the foam, so you will be able to get it out again. Plastic sheet is much easier than greasing the tank.

Don't worry about the wait between squirts of foam: you will have plenty to do! Even though you've planned it all carefully, it is incredible how long it takes to install a new toilet and new pipe runs and pumps. Mine was a bit more complex than usual, having both manual and electric pumps on the toilet and a separate electric pump for the pump-out, but it still took much longer than I anticipated. Label all the pipes: you won't remember which is which. The vent is often difficult to install because it must go high up; in my case inside a rather inaccessible space (see picture, left).

I like belt and braces, so as well as a Full gauge (a sender in the top of the tank which switches on when the contents are within about 20mm of the top), I have a contents gauge. Rather than a mechanical or electrical contraption inside the tank, which will eventually fail and need messy replacement, consider an exterior gauge (see picture left): this consists simply of two strips of aluminium stuck up the sides of the tank, with copper sensor plates stuck on top and some fancy electronics; it was about £130 from West Marine, but I gather they are now cheaper and available in the UK. I wish I knew how it works, but work it does: no moving parts and nothing inside the tank. That device has 4 possible inputs, so I can use it for the fresh water tank as well. Brilliant. Don't forget to fit the bits to the outside of the tank before fitting the tank in the locker!

All pipe connections need two Jubilee clips (put on in opposite directions) if they are below the water-line (at the normal angle of heel) or contain sewage: make sure they are stainless clips, with stainless screws. If they are magnetic, they are not stainless!

 

Step 5 Conclusion...

So was it worth it? Yes, definitely. It was a mammoth task (probably about 4-5 person-weeks in total, including extensive and essential planning), but it means I can do my bit towards keeping inland waters sewage-free and keeping on the right side of the regulations.

Have there been any problems? Very few. You have to remember to pump out while out at sea, before making land-fall. There are still few pump-out stations in inland waterways; but my view is that if people want you to pump out rather than empty into the canal or river, then they must provide enough pump-out stations: if they don't, then what alternative do you have?

The only problem I've found with the installation is my naive belief that odour-free hose is odour-free: how silly. Any flexible hose will smell if sewage is left sitting in it: use the best (most expensive) hose to reduce the smell and after emptying the tank, flush with water (flush the toilet about 10 times) and empty again, to leave freshish water in the hose.

So don't underestimate the amount of effort involved (and, of course, money: the whole installation cost around £2500 in parts, including a new super-duper electric toilet); plan in enormous detail before you start, checking that everything will fit and that (large) pipes will go round the corners required. Lay in a stock of rubber gloves for the removal of the old toilet and sell tickets for spectators - reduced price for downwind...