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fit and vent a fuel tank

John de Frayssinet (editor of Yachting Life)

'there lurks within the inaccessible bowels of a boat an item of equipment that can kill you.....'

Fuel tanks are often forgotten by those fitting out until the boats are nearly finished. By that time, your initial enthusiasm for the work is wearing pretty thin, and the tank can easily be thrown in as an afterthought. Petrol(gasoline) is obviously the most dangerous fuel used on craft, and if it is at all possible, I would always prefer a diesel installation, but given the right conditions, even diesel fuel can catch fire very easily.

In a new installation, the first consideration must be the siting of the tank. Very often the designer of the hull will be able to advise you. Weight distribution can be very important, and the performance of a boat may be marred by a fuel tank in the wrong place. If you are fitting out a standard hull it would be well to follow the practice of the builders.

Many boats have tanks installed where it is virtually impossible to inspect them. It is important to be able to examine fuel outlets and breathers, and check for corrosion at very regular intervals. A tank failure at sea will mean a bilge-full of foul smelling highly inflammable liquid, If it is at all possible, site your tank below an easy to open hatch, or where it can be examined through, say a locker.

To maintain the centre of gravity as low as possible, it is preferable to place tanks low in the boat. This will enable a fire-retarding bulkhead to be placed on either side. Often, the bilge will have to run through the tank compartment, and in the event of failure, fuel will rush through the bilge into the engine compartment, battery or galley.

In high speed planing craft, where tanks are subjected to the most severe conditions, it might be advisable to fabricate plates that can blank off the bilge run. These should be easily fitted, and used only during rough or high speed passages, and removed once in port to allow for ventilation. In this way, fuel spilt after a tank failure will be contained for the most part in the tank compartment.

Choice of material for constructing the tank is very important. I am very suspicious of steel tanks, even when. galvanized. Steel tanks are quite often used for gas-oil, but must not be galvanised if so. On any steel tank constant scrutiny is required for signs of rust. In particular beware of straps and braces, that might rub against the tank and wear off any galvanizing. Often, heavy corrosion is found under retaining straps.

Much better to install a stainless steel or marine alloy tank, supplied by a reputable maker. Such companies will be able to construct a special tank for your requirements. that will fit the space you have available, allowing the maximum fuel capacity. Always be sure to tell the manufacturers exactly what you intend to do with the boat. If you are keen on power-boat racing, then the tank will have to be much stronger and contain more baffles. Always insist that the tank is pressure tested before delivery, and if possible obtain a signed note to that effect.

Often forgotten, is the correct location of the tank filler. Should fuel be spilt, where will it run to? If it should find its way into a locker, then you have an explosive situation on your hands. Some builders favour placing the filler at the bottom of a self-draining cockpit, but fuel vapour could remain on the cockpit floor or in the drain pipes for quite some time. All you have to do is to light one cigarette, and ...

In my opinion the ideal location on most boats is on deck, outside the coamings. in a position where excess fuel will run directly to the scuppers.

The choice of pipe from the filler to the tank can be difficult. many yachts use reinforced plastic, such as that found on toilet installations. Over a period of time, such plastic may become brittle, and in any case they are not totally resistant to fuel, so get expert advice.

Care must be taken to ensure that the tank is adequately vented. If this is not the case. blowback will occur when filling, throwing fuel all over the place. The vent pipe should have a minimum of 1/4ins. ID. be of fuel resistant materials, such as nylon hose, and be led out through the side of the hull in a flame proof skin fitting.

The fuel outlet should leave the tank at the top, or high on the tank side. This will prevent fuel spillage should the piping fracture. All outlets that enable fuel to run out under gravity or siphon, must be fitted with an on/off tap, directly on the tank. Often, fuel outlets block, usually at the most embarrassing moment. It is not a bad idea to have a second outlet plumbed to the fuel line with a change-over tap.

Fuel gauge sender units are a source of leaks. Every care must be taken to ensure that this does not occur. some tanks are fitted with a drain plug below, to remove sediment. This is another source of failure, and if possible should be omitted. Consider fitting an in-line fuel computer instead.

Fitting the tank into the hull can cause problems. Remember, it will be extremely heavy when filled. Under no circumstances can a tank be able to break loose in heavy weather. Fixings should not be absolutely rigid. When in a seaway, the hull of a boat is constantly working, and if the tank was rigidly fixed, this might cause undue stress, resulting in a fracture. For the same reason, all plumbing to and from the tank must be capable of flexing. The filler pipe must not put strain on the tank filter flange, and if metal fuel piping is used, bend in a coil close by.

Some tanks are provided with fixing flanges that are bolted to the hull. I am against such designs, as too much strain will be taken on only a small part of the unit. It is far better to spread the fixing load over as great an area as possible. Metal straps wrapping around the tank and bolted to the hull are often the ideal arrangement. Always make sure that a rubber packing is placed between the tank and the strap. On craft capable of planing at high speed, the tank must be better insulated from shock. One effective method is to house the tank in a compartment lined with several inches of closed cell fuel resistant foam. This method will spread load evenly over the tank.

The United States Coastguard and several European countries have laid down strict requirements for tank installations. Having studied them, I. am doubtful whether all the requirements are possible to include in most boat designs, in fact in many cases they are virtually impossible. However, there is no question that much more effort should be made to ensure maximum safety of small craft. Check that your boat is fitted out safely. It could be your last chance!


Sail Craft
  1. Explosion proof vent skin fitting. Normally on outer hull for craft that do not heel.
  2. 3/4" minimum ID fuel resistant vent pipe.
  3. Outlet to engine.
  4. inspection hatch.
  5. Screw top filler. outside coamings and marked ‘fuel’.
  6. Flexible fuel resistant pipe.
  7. Double hose clips.
  8. Retaining straps over rubber packing.

 


Vee hull planing craft

   9.  Fuel vent. Explosion proof fitting.
  10.  Fuel vent. Esplosion proof fitting.
  11.  Bulkhead.
  12.  Removable plate for high speed or
rough weather cruising to contain fuel in case of leak.
  13.  Bilge run
  14.  Flexion coil in fuel pipe is in solid material such as copper
  15.  Fuel resistant pipe
  16.  Filler cap...screw type

 


TEN TIPS
  • Make sure that the fuel tank is sited so that it can be easily inspected from time to time.
     
  • By positioning a fire retarding bulkhead either side of the tank your safety margin is increased.
     
  • Blanking plates should be fitted to prevent any fuel spillage from reaching bilges while under way.
     
  • Material for the tank is important — we recommend either stainless steel or suitable marine alloy.
     
  • For high speed craft your tank will need to be stronger and fitted with more baffles.
     
  • Try to site the filler on the deck of your craft to reduce cockpit spillage risks.
     
  • The tank must be well vented to prevent blowback when filling.
     
  • Outlet for fuel should leave the tank at the top or high on the side.
     
  • Gravity feed systems must incorporate a tap in-line and as part of the tank.
     
  • All piping must be capable of flexing.