Breather Line Forced Seawater into Diesel TankProfessional Skipper Magazine Issue 38 Mar/Apr 2004
Well, I've just got back to my office after drawing oil samples from another vessel. Standard issue, twin engines in a tightly confined space - as usual! However, as I normally do, so that I can bring it to the operators/owners attention if need be, I had a look at the fuel/water separator sight glasses. To my amazement there were two very different defined layers of colour. The top 2/3rds of both were a nice light yellowish colour, which is quite standard for diesel but the lower layer in both was a deep brown colour. This vessel had only just completed a trip down from the Bay of Islands and had arrived in Auckland no more than a couple of hours before. When I informed the skipper as to the condition of his sight glasses he too was amazed. He said he had only just cleaned them out the day before he left to come down from up north and that they weren't noticeably that bad.
I normally carry clean glass lab sample bottles for just such occasions so I was able to draw a good 300ml sample from the starboard sight glass. The lower layer was obviously water or what we call 'Free Water', however the deep brown colour was partly the result of sediment and unfortunately a large amount of it. When the sample was given a good shake and then left to stand for a short while, the water just fell out of the fuel and settled on the bottom, leaving a residue in the top of the glass bottle. This tends to indicate that the water is the result of seawater entering the fuel tanks. However, without lab testing this cannot be confirmed. The lab is able to tell us whether the Free Water is all saltwater or a mix with fresh water i.e. condensate from inside the tank or wash down water that may have entered somehow.
Another reason for the dark colour of the water is after-market additives i.e. biocides and fuel conditioners. When large amounts of water are present these tend to faze or drop out of the fuel into the water. This is because they dissolve easier in water than in the fuel. The skipper confirmed the use of a fuel conditioner, which contains a biocide. As a result it was decided not to have the sample tested for Diesel Bug, as if there were any they were more than likely dead, but instead have the sample tested to confirm what the water was and where the sediment and colour may have come from.
Unfortunately when large amounts for water, particularly saltwater, enter the fuel system it can cause some dramatic results. The worst one I've seen to-date was a brand new yacht put in the water just before the Coastal Classic to Opua a few years back.
The weather was particularly bad so the crew pulled out of the race and started the engine and made their way into Opua. The following morning when they checked the oil in the engine before starting they found the level was half way up the stick, some three inches above the full mark. They called a local engineer whose quick assessment was that when the engine was installed they must have put in too much oil and he then proceeded to pump some out, leaving the level about right.
The crew then headed back to Auckland mostly under sail, but also using the engine when needed. On their return to port they checked the oil level again. To their amazement the level was again half way up the stick, this time they called the company that supplied and installed the engine. I was immediately called in, as the company wanted an oil sample done to see what was going on. Once we got the engine started, albeit after it turned over a few times, we let it warm up then took the oil sample.
The oil was very obviously affected by diesel dilution. When the engineer and myself started to look around, we noticed that the fuel sight glass was more than half fill of water. We drew a small amount out and a quick taste told us it was saltwater, yuk! We then started to investigate how the water may have got into the tank. What we found blew us away.
The breather line, which came off the top of the tank came up through the deck into the base of a stanchion and exited forward through a small 1 cm hole just above the deck. What would have happened was that when the rail went under while sailing, water would have been force fed down the breather and into the tank. With that amount of water in the fuel tank the fuel/water separator would not have been able to keep up, thus the water would have got through to the pump and injectors. What had happen was that the injector nozzles were destroyed and diesel was pouring straight in, past the rings and down into the sump. What was remarkable was that the engine was still able to run, if only just. While the initial damage was repairable the resulting damage caused by corrosion would more than certainly have been ongoing and costly to resolve.
The reason these two vessels had seawater in their fuel was that the breather outlets were in the wrong place. The vessel with the multi-coloured sight glasses had breather outlets no more than half a meter above the water line and towards the stern. While the vessel's breathers had water traps in the lines it would not have taken long for them to fill or for water to be forced down into the tanks at high speed or during rough weather.
If you have any noticeable signs of water in your fuel/water separators don't hesitate to get it checked out. By testing the free water you will be able to establish its source, thus making it easier to ascertain its method of entry.
Written By Kelvin Hieatt
Managing Director
Marine Diagnostics Ltd
