Aluminium Boat Tank Advice

Discussion in 'Boat Design' started by MMMarkyMark, Jan 13, 2019.

  1. MMMarkyMark
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    MMMarkyMark Junior Member

    Hey guys,

    I’m currently building my own designed aluminium mon hull 5.7m.

    The fuel tank is the first one I have ever built and I have have two questions I would appreciate some feedback on.

    Q: What PSI should I test my tank for leaks. 20PSI?

    Q:I have attached a couple of photos of my fuel pick up line. Can someone confirm it will be adequate, if not what should I do?

    tank1 — Postimage.org https://i.postimg.cc/mgJwkGY7/tank1.jpg
    tank2 — Postimage.org https://i.postimg.cc/4dZpH4mH/tank2.jpg
    tank3 — Postimage.org https://i.postimg.cc/1XXnD8PX/tank3.jpg
    Cheers in advance gents!
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Pick-up should be OK, though might have been better nearer the side that is closest to the stern of the boat. As for pressure testing , just a gentle overpressure will be enough, it isn't a pressure vessel as such, and if it holds a few PSI (2-3 maybe) for a couple of hours, all good. 20 PSI would deform and/or destroy it. Any pics of the boat ?
     
  3. MMMarkyMark
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    MMMarkyMark Junior Member

  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Your own design ? What plate thickness ?
     
  5. MMMarkyMark
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    MMMarkyMark Junior Member

    Yeah my design I based the internal layout on the Allison Fisherman 5.
    Increased the beam and changed the hull design. 4mm 5083 plate
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Looks OK to my eye, I hope it proves up to your expectations. Has this proven to be as much, or more work, than expected ?
     
  7. MMMarkyMark
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    MMMarkyMark Junior Member

    If anything less work than expected. Probably only 50 hours in it so far.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    Are you a welder ?
     
  9. MMMarkyMark
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    MMMarkyMark Junior Member

    By trade I’m a carpenter but I do own a fabrication business. Hence the ability to build aluminium with ease.
     
  10. JSL
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    JSL Senior Member

    You should check with your government regulations. They may have their own regs or adopt standards of ISO , ABYC, etc
     
  11. Barry
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    Barry Senior Member

    H24 of the ABYC standards book, Gasoline Fuel Systems comprises 17 pages of requirements
    I will try to hit some of the high points but realize that not all requirements are included
    1) Valves located on the bottom of the tank, for drawing fuel from the system are not allowed
    ( ie you cannot rely on a closed valve at the bottom of the tank to hold back the fuel. A tapered plug fitting is fine
    2) Hoses will comply with SAE J1527 Marine fuel hose
    3) Cork gaskets are not allowed, ( sending unit)
    4) Tank connections shall be accessible through a port or hatch of the deck or boat floor
    5) Tanks shall be restrained so they do not move more than 1/4 inch (6.4mm)
    I would recommend straps over top of a material, non metallic, non moisture absorbing, not abrasive, that is glued to the tank
    6) All non integral tank supports, chocks, or hangers shall be separated from metallic tank surfaces by a non-metallic, non-moisture absorbing, and non-abrasive suitable for the purpose (eg neoprene, Teflon, high density plastics) permanently bonded to the tank surface with an impermeable, non-hydroscopic adhesive (poly urethane adhesive)



    7) Metallic tanks must be installed above flat surfaces shall be separated from the surface by at least 1/4 inch air space when filled with fuel and the flat surface shall be self draining

    8) Metal tanks shall be installed where they cannot be reached by normal accumulation of bilge water in the static position

    9) the filler hose requires 2 hose clamps and they must be stainless 300 series. Note many automotive clamps have a stainless band and a galvanized metal worm. They would not meet the code.

    10) Fuel fill lines shall be self draining, ie no dips, Same for the vent, there should be an inverted U so the that fuel will drain down and any water egress into the line will go out the vent

    11) minimum inside diameter of the vent line shall be 7/16 inch

    12) Flexible fuel line in the engine compartment will meet the local requirements for your country (USCG TYPE A1 OR A1 -15) (some USCG A hoses are not designed to be clamped)

    13) 15 inches of clearance required between the vent fitting on the hull to any engine or other compartment inlets

    14) There should be an anti siphon fitting on the draw line

    15) The tank and any other metal components that are filled with fuel shall be grounded so that its resistance to the boat ground is less than one ohm (includes metal deck fill)

    16) Due to galvanic corrosion, you can not have any copper fittings, screws, bolts etc in contact with the tank, aluminum fittings or stainless 316 series are allowed

    17) I could not find the clause, but I do not believe that you can have the fuel draw off the bottom of the tank. You need a dip tube, non copper, so that in case of a fire, and the hose burns through, you will not have fuel continuing to feed the fire



    Again, this is a shortened version of the US regulations and it may not be applicable to your area.

    The above post was from an earlier thread that I responded to

    Re your installation.

    How are you intending to hold the tank down to the bottom of the boat? What will support the tank? I would strongly recommend NOT bolting the tank to the bottom of the tank but the tank should rest on plastic, glued to the tank as above. Then a strap, aluminum would be fine, but it too has to have plastic glued to the interface, uhmw or equivalent. The hull will flex during use and if you use the 4 holes on the tabs to bolt them down, you will in time crack the welds in that area.
    What is the purpose of the 4 tabs with holes in them?
    Are you cutting plug weld holes in the top sheet of the tank?
    What is the ID of the draw line? How are you dealing with the vents, I think that they have to be 7/16 inch minimum but 5/8 preferred thought buy the exterior vent ie to the hull, first to make sure they match ID's
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    He won't be needing to comply to any such schedule of specifications, unless under survey for commercial use.
     
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  13. Ad Hoc
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    Ad Hoc Naval Architect

    For every 2foot of head test at 1 PSI.
    Thus if the head is 4 feet, = 2PSI...etc.

    Then pressure test for 12 hours at said PSI....this is our standard.
    Min PSI = 2.
     
  14. Barry
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    Barry Senior Member

    Agreed that for a home built he may not have to meet these requirements but for an insurance policy, often at least in North America, a survey is often required. A competent surveyor would notice pretty much all of the above and note deficiencies on the survey. Particularly for home built registration.

    Regarding meeting the specifications, most of these noted above are ABYC requirements are established to ensure that constructions standards are met which
    are recognized as being safe.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    For sure, better to comply with all measures that ensure safety. Most problems with alloy tanks seem to arise from corrosion.
     
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