Secondary Fuel Tank

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    Czarina Blue

    I have just cleaned out my port side secondary fuel tank in order to use it to increase my range, with an extra 114 litres of diesel.

    I wonder if one can just open its wheel valve when you want to use it, and leave it open, letting it fill the main tank by gravity (it is positioned higher), or whether one should open the wheel valve for a period until the main tank is full-ish, then close it again, ie use it in stages in order not to overfill the main tank?

    Does anyone have any experience of using it?





    Hi Duncan,

    I have watched this carefully on Conche.

    My opinion is that is to  close the wheel valve and  fill the wing tank on the filler plug on top of this wing tank.

    And independently to fill the main keel tank on the filler plug located on the port side deck.

    This way you are not creating an additional  column pressure on any piping joints in between the two diesel tanks.

    Check if your wheel valve is functioning properly. On Conche I will need to replace it.

    This you are able check just listening to. With the wing tank filled and with the valve closed you then may open the plug of the visit box of the keel tank and listen if you hear any diesel dripping on to the keel tank.

    Hope this can help.

    Greetings from Lisboa Portugal,



    Czarina Blue

    Thanks that makes sense Joao. Duncan

    Erik Theunissen

    Thanx for the tip. wasn’t even aware we had a secondary fuel tank. Still lots to discover 🙂



    The breather on the main tank will put diesel into the bilge if you fill it fuller than 38 imp galls. I don’t think this breather is higher than the top of the wing tank, so if you just leave the wing tank valve open, I think you will fill the bilge!  For sure, once you remove the dipstick plug in the main tank, you will get an eye-full!


    Not all Nic 38’s were fitted with a secondary fuel tank – it was an option to have it added under the lazarette seat(s).

    For example, our Rainshadow (hull #126) does not have these wing tanks, which leaves us very deep storage instead.

    Marilyn the Moderator

    Erik Theunissen

    Hi Marilyn

    Thanks for explaining, have been searching and searching everywhere for those tanks.Thought i was going crazy but happy to hear we just don’t have them 🙂


    Czarina Blue

    In regard to Voltair’s post above about getting it in the eye, and breather heights, that sounds feasible. But what about the breather on the port side deck on the outside coaming adjacent to the main tank filler plug, if you overfill the main tank it bubbles and flows out of there onto the deck before it overflows from the filler neck itself.  Is that not therefore the main tank’s breather ( which is then higher than the wing tank)? Anyway, it sounds like important to use any wing tank with great care.

    Jean Clair

    Hi Duncan

    We have a reserve fuel tank on Jean Clair and have used it for the

    eight years we have owned her.  The two tanks are connected, not only by the 1 inch feed pipe with the wheel valve but also by a 15mm breather pipe which obviously exits from the top of both tanks.  This 15mm pipe goes from the main tank to a position just under deck level before descending into the reserve tank. We always ensure there is enough space in the main tank so that we can empty the reserve into it without worrying about overfilling.  We always close the wheel valve after transfer to ensure we do not fill the main tank through the reserve. Hope that helps



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