Diesel Fuel Tank - Fiberglass

Discussion in 'Fiberglass and Composite Boat Building' started by savagescout, Apr 18, 2012.

  1. savagescout
    Joined: Jun 2009
    Posts: 37
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: australia

    savagescout Junior Member

    Hey Guys,

    I am in the process of restoring my 25 foot half cabin cruiser and am looking at fuel tank options.

    I am installing a 220hp turbo diesel mercruiser and am thinking about fabricating some fuel tanks myself using GRP. I would plan to use Vinylester resin for all of the layups but was wondering what people think of my proposed method.

    1) Make up a box type mould but leave the top panel off (much like a bathtub).
    2) Layup the mould to whatever thickness is required (any input) and incorporate large fillets in corners with extra fiberglass reinforcement in these areas.
    3) incorporate a 2 inch lip on the top edge of the mould to allow the top panel bed down onto.
    4) Install all filler points, outlets, breathers into top panel including large inspection/clean out hatch.
    5) Bed down top panel onto flange using thickened resin (with cabosil). Apply layers of glass over seams to complete fabrication.

    Does this method sound ok? How would a GRP tank compare with an aluminium/plastic variety?

    my main concern is how you fully seal all of the fittings/filler tubes/sender units... How does this normally work?

    Looking forward to hearing from you.

    Nick.
     
  2. tunnels

    tunnels Previous Member

    Ok couple of things missing Baffles that are strong and wont come loose and a way of getting into the tank to clean and inspect sometime in the future .
    Thw inspection top is a good place to put all your fittings and the like can be a aluminium so fittings can be welded into the tip !! I aluminium ring on the inside of the tank that can be drilled and threaded and bolted down together and sanwich the glass and a gasket to seal when you finished . Reall at the end of the day is one hell of a lot of work and if you get it wrong have a protentual disaster on your hands!!
    Proffesional boat builder magezine had a whole chapter on Glass tanks quite some time ago !! how and what etc etc !!. In really big boats they can be built in as a part of the hull but the materials and proceedures are basicly the same .
    check it out and read and read again . they have to be presure tested and the US coat guard had a whole lot of info to read about testing differant types of tanks !! so you just scratched the surface !!. :D:p:p
     
  3. tunnels

    tunnels Previous Member

    Well any more thoughts about glass tanks ????
    :confused:
     
  4. Frosty

    Frosty Previous Member

    I think its a great idea. Make a box as you say and glass inside it, I would super glue some ply wood baffles in and glass over them in a one hit operation with a white tin to the resin so dirt can be seen.

    The top should have a lip and bolt on the top to the tank with a ring of bolts. This could be alluminium so fittings could go in that.
     
  5. pescaloco
    Joined: Feb 2006
    Posts: 301
    Likes: 10, Points: 18, Legacy Rep: 81
    Location: so. california

    pescaloco Senior Member

    I might mention you should only use Vinyl-ester resin - No poly or epoxy

    And yes fiberglass tanks properly made are a good alternative for a Diesel fuel system
     
  6. tunnels

    tunnels Previous Member

    :pTotally agree Vinylester of the right type for everything and to line all the inside and special coatings for everything inside . Check and double check that you get the correct resin to do the job and the correct paint for the inside and dont miss any where !!. :confused:

    Baffles are best made from ALUMINUUM sheet ,egg crated to slide together and need to be a tight neat fit and a foot sticking out each side against the side to glass over and bond to the tanks surface .
    A 2/3 or 1/2 tank of Liquid moving from the motion of the boat has enormous force when its sloshing in every direction you can think of!, so baffles have to be strong and well fixed in or you will have a noisy tank if they become unattached because they havent been glassed properly !!.
    All fittings need to be mounted in a aluminium plate that serves as the inspection cover in the top of the tank so look at what has to go in there and make sure its big enough to take everything and not bunched together and cant get a spanner to do up the fittings or slide a hose on !
    The return from the motor , fuel gauge sender , breather , and not forgetting the all important filler plus a grounding wire possibly !!!!
    Dont forget a drain in the lowest corner to get shot of the rubbish and sludge at some point in the future !!Makesure the fitting is a decent size and easy to get to !, not in a place you cant see or reach !! :p
     
  7. iceboater
    Joined: Jan 2011
    Posts: 67
    Likes: 11, Points: 0, Legacy Rep: 116
    Location: Iceland

    iceboater Junior Member


    I am doing my tanks in very similar way you are thinking. The "box type mold" I make out of 15mm
    airex foam panels and I put 450 gr. strand mat on them before I fit them in. The thickness of the tank
    is from 5 to 9 mm on the inside. The whole tank is glassed in 2 turns, with the flange. The tank on the photo is 900 liters.To bed down the top
    panel I would not use thickened resin, I would use Scott badder 1152 or approved fiberglass bonding paste.
    Here
    is a link to photos of my tank and I hope that you find them useful to look at.

    Axel
     

    Attached Files:

  8. Frosty

    Frosty Previous Member

    Fuel bladders,--- big rubber tanks that can fit any size hole you want to stuff it in --or hang it up. I know boats that only have bladders.
     
  9. savagescout
    Joined: Jun 2009
    Posts: 37
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: australia

    savagescout Junior Member

    Sorry for not replying till now - i dont get on here as much as i would like.

    i really do appreciate some of this feedback and confirm i definitely plan to pursue the use of GRP tanks.

    I plan to incorporate a port and starboard tank in the outermost stringer compartment of my deck area. I dont want to utilise the existing hull structure as an integrated tank and as such i will be making a separate tank structure that i can drop into the subfloor compartment.

    The dimensions of the tank are as per the image below and will be 3600mm long (or approximately 12 feet).

    [​IMG]

    I have also included an image showing the two tanks with top panel removed showing the internal baffles. I have spaced these baffles at 450mm (or 1.5 feet) created 8 compartments of approximately 25 litres each. Will this be enough baffling?

    [​IMG]

    I was planning to layup the tanks so they are approximately 6 mm thick (more in corners) using vinylester and 450gram CSM. i will most likely incorporate a single layer of woven rovings to stiffen the sides. Will this be ok?

    Top panel will also be fibreglass but area with the fittings will have a glassed in piece of aluminium so fittings can be thread fitted on. The top panel will first be bedded in place and then fully glassed to the tank. i will incorporate a couple of access hatches in areas but trying to limit the number of penetrations.

    Also, should my fuel picked be at the stern of the tank, middle of the tank or front of the tank? i would have thought the stern as the boat is likely to sit stern heavy and therefore as tank empties, will be more full at the stern..

    What are peoples thoughts?

    Thanks again!
     
  10. savagescout
    Joined: Jun 2009
    Posts: 37
    Likes: 0, Points: 6, Legacy Rep: 10
    Location: australia

    savagescout Junior Member

    Any thoughts on number of baffles as above? and length of tank against its depth?

    Cheers guys.

    Nick
     

  11. tunnels

    tunnels Previous Member

    The more baffles , less splash !! :D:D
    Pick ups at the aft end as the boat is always with its nose pointed up when under way !!:p
     
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