Preventing another Poonami

The toilet on Vestlandskyss is generally well behaved, but while on passage to Eden, we experienced several strange incidents. On one occasion, we opened the head door to discover that the shower tray was swilling inches deep in what appeared to be effluent. On other days, the toilet bowl appeared to have filled with clean sea water and then spilled into the bilge. After each event, we cleaned up, but couldn’t see where the water – dirty or clean – was coming from.

Both of those incidents occurred during several days of continuous 30 degree heel on a port tack. All of our through-hulls are to starboard, so we assumed that something odd was happening with the increased pressure on those fittings. Once we arrived at our berth in Hobart, the system was well-behaved but the toilet bowl would occasionally slowly fill, usually with clean water but a couple of times with oily black liquid.

I couldn’t see a pattern, so I was experimenting with leaving her overnight with different combinations of valves open and shut. One evening I left just the inlet cock open, which hadn’t caused a problem on previous tests, but on the following morning I discovered that every bilge was filled with seawater, to just below the level of the floorboards. Hundreds and hundreds of gallons of it, slowly spilling from the toilet bowl and overflowing into the boat. It was time to bump the task up the priority list.

First up, I needed to get rid of the water. We have four bilge pumps, two electric and two manual, and they made short work of it, but the process revealed some shortcomings with our existing plumbing system. At some point, some hero has reduced the aperture of the galley sink pipes to something like 12mm just before the through-hull, and then plumbed the two midships bilge pumps into the same line. There was no way that the volume of fluid from those pumps could pass through the restriction, so it bubbled up into the kitchen sink and overflowed back into the bilge. Marvellous.

The other two pumps – one aft and one forward – handled the load, and soon the bilge was clean and dry. No lasting damage appeared to have been done.

Clean sea water was presumably syphoning in from the inlet seacock, but where was the black oil coming from? We do have a black-water holding tank which is the obvious suspect, but we had never seen it and had no idea where it was. The pipes run under the sink and then vanish behind a load of posh panelling. There were some clues, in new water stains running down behind the sink from above. The tank must be somewhere behind the mirrored cabinets… but where?

I hesitated and put it off, but in the end gritted my teeth and grabbed a drill and a saw and made a few exploratory holes. I found that the black-water tank is sandwiched between the hull and the left-hand bathroom cabinet, to which it is inextricably bonded. There is no way of getting to the tank without destroying the cabinet, but by cutting an inspection port through from the right-hand cabinet, I was able to (just) get sight of the overflow tube.

Figuring it out

To cut a long and grubby story short, I finally worked out that we had been hit by a perfect storm of unfortunate incidents.

1 – The toilet had been installed exactly on the waterline (thus, sometimes above and sometimes below, depending on the angle of heel). In this situation, any toilet should always be fitted with some mechanism to break an accidental siphon, but for some reason Vestlandskyss didn’t have any vented loops.

2 – The black-water tank sits higher than the toilet, and is protected from surge by an overflow which leads out to sea by means of a dedicated through-hull which mysteriously does not have a stop-cock. Both overflow pipe and through-hull were however blocked with debris.

3 – The black-water tank has a bypass valve, which in combination with the effluent through-hull valve, can allow us to divert the contents of the toilet either up into the tank, or down into the sea. Although apparently closed, the bypass valve is either faulty or had been knocked, and remained partially open.

4 – While heeled over at 30 degrees or more, beating through swell at hull speed with maximum hydraulic pressure on the effluent outlet, one of us had gone to the toilet and opened the outlet valve to flush (correct behaviour). Sea water entered under pressure, could not find its way into the toilet (correct design of the toilet mechanism), and instead squirted up into the black water tank through the partially open bypass valve.

5 – The resulting pressure in the tank should have been relieved by the stainless steel overflow pipe, but it was blocked and had rusted through, so the junction ruptured, allowing the now dirty sea water to escape the tank, swill behind and through the bathroom cabinets, down behind the sink, and into the shower tray and bilge.

6 – I believed at the time that the black water tank was empty. However, at our angle of heel and given the leaky valve, it was probably almost full of sea water mixed with whatever was stuck to the insides of the 26-year old effluent tank. Next time we achieved an even keel, any fluid that hadn’t already escaped into the bilge through the broken overflow, slowly drained past the faulty bypass valve into the toilet, filling the bowl with black oil.

7 – Because of the lack of vented loops, leaving the salt water intake open at certain heel angles (or if there was an unlucky wind gust at anchor), sometimes set up a slow syphon of clean sea water into the toilet bowl (which eventually spilled out into the boat).

Fixing the Problem

I thought long and hard about different ways of repairing the stainless steel overflow pipe, but in the end I decided that I didn’t trust the integrity of the black water tank, and so isolated it from the system as a problem for another day. I used epoxy to seal the broken vent pipe, and taped a plastic bag to the inlet port to prevent any remaining fluids from entering the bilge. I also removed the broken and blocked tank overflow pipe, which meant that the unrestricted through-hull was now open to water ingress. It’s slightly above the water line, but would definitely be underwater on a port tack, so I blocked it with epoxy until such time as I can take the boat out of the water and work on it properly.

Although I hadn’t seen any syphoning effects in the black water pipes, I thought it would be prudent to add a vented loop anyway. This sits between the toilet bowl and the through-hull, at the top of a long loop that will run up the inside of the hull to the highest heeled water line. I have fabricated the loop, but haven’t fitted it yet, because I’m going to need all the room that I can get in that little crawl space when I work on the through-hull.

Since I had the toilet fittings disassembled, I fitted a raw-water strainer to the inlet hose. I wondered if the air gap at the top of the strainer would prevent syphoning (it didn’t), but it will be good to prevent odiferous seaweed and debris from being flushed into the toilet bowl. On my previous boat Cheval de Mer, I twice had to extricate whole fish which had been sucked somewhat messily into the toilet pump mechanism.

In order to fit a vented loop to the toilet’s salt water inlet hose, I needed to insert a long pipe downstream of the pump, in place of the short tube that currently connects the pump to the rear of the toilet bowl. The new pipe needs to loop up above the highest possible waterline, pass through a vented loop, and then back down to the toilet. This means drilling holes in the fancy bathroom fittings, so I fitted a shorter temporary pipe to make sure that it was all working first.

The temporary pipe will remain in place until I can get the yacht out of the water, because I’m going to need all the elbow-room that I can get to work on the through-hulls inside the little cupboard under the sink.

The strainer and temporary vented loop have been in place for a couple of weeks now, and everything is working just fine. The next poonami has been averted.