Fuel in the Bilge and Fuel Tank Tests

Wanderlusts cruising the canals in Frnace

Wanderlusts cruising the canals in Frnace

Why does Wanderlust have fuel coming into her forward cabin bilge?

It’s a good question. If we knew the reason why, it would be easier to resolve.

It is not impossible for a new boat to have a fuel leak. Indeed, we know of a fuel leak identified at launch on one of our builder’s boats. In this case, the leak was spotted and welded closed before the owners arrived.

Did Wanderlust also have fuel leaks at launch? We will never know for certain. Access to the bilge is minimal at best. Neither the builder’s personnel nor we had anyway of seeing what was happening below the hardwood floors. Short of ripping up brand new floors, there is no way to tell what’s happening in the bilge, at launch or years later.

Diesel fuel in the bilge access in the saloon...

Diesel fuel coming up on the starboard side of the bilge access in the saloon…

...and on the port side near the engine compartment bulkhead.

…and on the port side near the engine compartment bulkhead five meters away.

Part of the concern stems from the method of construction. Wanderlust’s fuel tanks are constructed integral to her hull. This means is that the hull of the barge is the bottom of the tank and the tank is built up with the sides and top welded on to form a box. It is an acceptable method to construct a diesel tank and has numerous advantages. A downside is that each tank is necessarily custom. Every integral tank needs to be properly tested to assure that it does not leak.

Fuel systems, including the tank, should be, by rule, tested using air pressure. To do this the fuel system is sealed and a low pressure of air is applied. If the pressure holds, the tank is to a high level of certainty leak free.

Wanderlust's red diesel tank under construction

Wanderlust’s red diesel tank under construction

Pressure testing is a regulatory requirement for good reason. According to a marine engineer we spoke to, leaks from properly pressure tested fuel system are extremely rare. If a tanks holds air pressure during the test it is very unlikely to leak fuel. That being said, the regulations aren’t always adhered to. Marine surveyors have told us that it is not unheard of to find out that a UK barge builder has skipped the pressure-testing step altogether. The test procedure is time consuming. And from the perspective of the builder, a carefully constructed tank is unlikely to leak, so why bother with the test?

The white diesel tank is labeled as required by the build standards. “20Kpa” is the maximum pressure for a tank test.

So was Wanderlust’s fuel system constructed and pressure tested as legally required? It’s a good question. Indeed, if we knew with high confidence that Wanderlust’s fuel tanks were built and tested per the regulatory rules, our search for the source of the diesel appearing in her bilges might take a different course. Consequentially we have asked our builder, through our solicitor, for the supporting information for fuel tank tests. We expected that this information would be provided without issue as the sales brochure, current at the time of the signing of Wanderlust’s build contract stated, “Copies of notified body reports are available for inspection at our works.” As we understand things, the notified body report should have included at least a declaration that the fuel tanks were tested. Surely there would be some information relevant to Wanderlust’s fuel system in these reports. Yet despite repeated requests, the builder has steadfastly refused to provide any documentation relevant to Wanderlust’s build and certification.

This bilge flood, a consequence of a faulty plumbing connection in the sewer system, led us to discover that Wanderlust had diesel fuel in the bilge in multiple locations.

This bilge flood, a consequence of a faulty plumbing connection in the sewer system, led us to discover that Wanderlust had diesel fuel in the bilge in multiple locations.

As we have learned, a UK boat builder evidently has the right to withhold the certification files for a customer’s barge. It is a strange system. Shouldn’t a customer be able to see the documentation for a boat that he or she is buying? And why would a builder want to withhold this type of information? If you were an ethical boat builder faced with a customer’s request for certification documentation wouldn’t you want to clear up all possibilities that there was anything amiss about the build? What is the value of withholding the certification information that by rule must be in a file somewhere? What is the value of adding suspicion?


13 thoughts on “Fuel in the Bilge and Fuel Tank Tests

  1. All Pipe work should have pressure testing , including plumbing…… soil water included . This was a standard taught when one did proper five years apprenticeships and a National Trade test in Southern Africa forty years ago…. The test was always set up over the week end ….. and checked by the Plumber and Government inspector before the sign off…… it sure kept a standard……. how have standards slipped with the Namby pamby apprenticeships and resultant standards on offer to day….

    • It would seem sensible as unlike a house the plumbing on a boat can’t be practically tested before the walls go up. That being said, I’ve been unable to locate any standards relevant to boats that apply to the interior domestic plumbing fit out. By and large the governing RCD standards are mostly concerned with safety.

      • Another thing to check , is the fuel tank venting pipe, (pipes). Are they venting over board or to a point high up inside.
        Diesel engine Fuel pumps draw more fuel than is required, so what is not used is returned to the tank. This should go back to the tank it has been drawn from. If not , it will fill the other tank up , until it overflows.
        This happened to us on a new 53ft Motor Yacht . In this case it was being pumped over board. All the time the generator was running. Same goes for main engine, s.
        This could be your problem, very easy for the builder (technician) to get it wrong.

  2. You mention pressure testing the fuel tank using compressed air. This is not correct. Testing with compressed air (or any other gas) may not indicate a small or even a moderate leak or weakness in the tank structure, and can be dangerous. Pressure testing if done at all should always be done using a liquid. Liquids are non compressible therefore even a small a leak will show as a drop in pressure almost instantly. Furthermore, tests should be carried out at 150% (strength test) and 110% (leak test) of the design pressure. In the case of your tank the strength test would be at 30 kpa and the system leak test at 22kpa. The initial strength test (150% design pressure) is carried on the tank alone to prove the structural integrity and strength of the tank. Once the fuel system is fully built and connected the whole system, or as much of it as can be isolated, should then be tested at 110% of design pressure for leaks. Again, both tests to be carried out with liquid (diesel) and with all air bled from the system. By excluding all air (this is important) there is no compressible pressure reservoir and any leak will show almost instantaneously as a pressure drop . Consequently when done correctly such tests need only take five minutes each.

    • I’m certainly no expert on this subject so let me provide my sources:

      –My primary consultant in this area is an active marine engineer who participates in the construction of ocean going vessels. He is very familiar with the tank pressure testing process and cites the IACS test procedures document.
      –I read EN ISO 21487:2012 as stating that air pressure may be used as an alternative to hydraulic pressure for this [the leakage] test. The test methods described within the ISO standard are consistent with what my advisor has told me.
      –The ISO standard also describes the hydraulic pressure/strength test consistent with what you have mentioned, so both methods seem acceptable.

      It would seem to me that either the tank should be tested with air or filled completely. In practice, for Wanderlust’s build, it is extremely unlikely that a pressure test was done with a completely full diesel tank as 1000 L of diesel was added to each the 1200 L tanks. This would leave a considerable volume of compressible air in each tank. Even if an attempt were made to completely fill the tank with diesel, the design of the tank with a flat top and a raised inspection port would make it very difficult to remove all of the air.

      • I can’t see any reference to pressure testing with air and this is certainly not normal industry practice. The source of the required pressure can be compressed air ( or a pump) but this does to mean that the test itself is carried out with air i.e. it is a hydrostatic test, not a pneumatic test for the reasons given. The ISO standard in this case is derived directly from ASME safety standard for pressure vessels which by the way specifically forbids pressure testing with compressed gas.
        (There may be some confusion with ‘hydropneumatic’ tests which are allowed in certain circumstances in some ships tanks where this would reflect the actual loading conditions in use e.g. an oil tanker’s cargo tanks where there is always gas on top of the crude oil. This is not applicable to a stand alone diesel tank such as yours.)
        If your fuel tank was provided by a third party i.e. a fuel tank manufacturer, it should have come complete with a hydraulic strength test certificate.A hydraulic test on a small tank is a perfectly routine and simple process although a little more inconvenient once the tank is installed. Did your boatbuilder state anywhere that Wanderlust would be built to ISO standards?

      • Perhaps there is some confusion. Wanderlust’s tanks are integral to the hull. They were constructed by the boat manufacturer as the hull was built up. There is not possibility to test it separately. Indeed, without a bottom drain, removing any test fluid would be very difficult.

        The builder did state that the boat is CE certified, cites the relevant ISO standards, and signs off on a Declaration of Conformity.

        The marine engineer I referred to did say an empty air test. He saw the set-up.

        Does any of that clarify things?

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  5. Mate, no one in there right mind uses air to pressure test a container. Just imagine the stored energy in a 1000 litre container pressurised to test. The volume of air that would have to be pumped in to get to test pressure would be huge, probably 20 times the volume. Just imagine the consequences if the tank ruptured there would be bits flying everywhere. No its always hydrostatically tested, probably filled with water, which is not compressible and then pressurised hydraulically. The leaks are easy to see and the risk is low. I see on one of your photos what looks too be a large “threaded bung” at the top corner of a tank, that maybe the test point.
    If this tank form part of the hull how then do you drain out any sediment. Perhaps poke a pipe in down through the big bung and suck up and gunk.
    Good luck, I have had a similar experience with our brand new catamaran, that is waking up with thee smell of diesel in the bilge.
    Take care,
    Tony C

    • The EN ISO limit for the air pressure test is 20 Kpa or one-fifth of an atomosphere. The volume of air added is 1/5 of the volume of the tank, not 20 times the volume. At test like this can only work because the viscosity of air is much lower than that of a liquid. The tanks themselves are structural and are made of 8 mm steel.

      In any event the post was speculation about how the pressure testing was done, if it was done. I’ve heard back that water testing is preferred but the problem is that, as you have noted, it would be very difficult to dry the tank after the test. It would seem unlikely that was done. Given the timing, it couldn’t have been done when the tank was filled with diesel either. So that leaves air.

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