plywood fuel tank

Discussion in 'Boat Design' started by whitepointer23, Feb 1, 2014.

  1. NavalSArtichoke
    Joined: Oct 2013
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    NavalSArtichoke Senior Member

    Ethanol content is not mandated so that each gallon sold has to have a certain percentage of ethanol in it. What the EPA does is mandate that so much of the corn crop be converted to ethanol and blended into the gasoline supply every year. Currently, 37% of the corn crop is required to be converted to ethanol, and don't send any sob stories about children starving in Africa, because the EPA don't care. As with any government program, there is a byzantine maze of regulations, waivers, kick-backs, logrolling, idiocy, and black-glove thuggishness occurring, but it is still possible to find ethanol-free gasoline at certain stations across the US, because the EPA has yet to repeal the laws of chemistry.
     
  2. tom28571
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    tom28571 Senior Member

    There may be another issue on installation of plastic tanks. Previous Moeller tanks needed an additional 2% of space around the tank for expansion although I did not know the reason for expansion. Don't know if that applies to the new ones but you should check.
     
  3. SukiSolo
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    SukiSolo Senior Member

    The 2% additional space will be because of roto moulded tolerances. The standard tolerance with no jigs is +/- 10mm per meter! So all the roto moulded boats (an example would be the Laser Bahia) are held in cooling jigs to get the movement and end shape to sensible tolerances.

    BTW if the shape of the tank is simple, you can in fact make a mould yourself in sheet steel, then (the fun bit) try and get someone to mould it.

    I've designed a few things for roto moulding including a range of professional speakers for public performance. Primarily high end acoustic/classical/jazz music, fortunately the tolerances were OK for this application. There are specific tricks of the trade when designing for this mode of manufacture, so be careful if you go this route.
     
  4. erik818
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    erik818 Senior Member

    The problems and danger with petrol make a good case for diesel, if that is an option.
    Erik
     
  5. Westfield 11
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    Westfield 11 Senior Member

    Please post a link to a diesel outboard. For many, diesel is not an option.
     
  6. Westfield 11
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    Westfield 11 Senior Member

    If one is able to make a mold in sheet steel wouldn't it be cheaper and easier to just make a tank instead? Perhaps using stainless steel?
     
  7. tom28571
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    tom28571 Senior Member

    This is what I read from Moeller's website.

    "NMMA OMT Service Announcement - Portable Tank Swelling
    Tank swelling will occur and is associated with a New “Low Permeation Compliant” Portable Outboard Marine Fuel Tank!!"

    Whether this applies to the tanks made for interior use I have no idea. Still, I would check with Moeller tech guys before assuming that there is no swelling on these tanks.
     
  8. Joris
    Joined: Mar 2013
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    Joris Junior Member

    http://www.klaxondieseloutboards.com/ has diesels.

    If your making your own fueltank i think aluminium would be a better choice than stainless steel.
     
  9. Westfield 11
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    Westfield 11 Senior Member

    I agree, but steel was mentioned and one can weld steels using cheaper equipment than alloy. A simple buzz box with the right rods will do a fine job on CRES for a fraction of the cost of a MIG welding system for alloy.

    Your link only has low power motors, 40hp maximum. Nothing in the more useful 100 to 200 HP range. I suppose one could use several of them, but then weight and transom space becomes an issue.
     
  10. SukiSolo
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    SukiSolo Senior Member

    Could well be Tom, there are quite a few materials used in roto moulding (not just PP or PE) and then there are subtelty altered variations. However the 2% would probably cover the diurnal temperature range on swelling/shrinkage too. We have the same problem (in EU) with added % of variations of fuel affecting car fuel lines but not heard of any old tanks leaking yet. Evaporation/porosity through skin is a bit different though.
    The newer tanks may well be more than one skin thick, ie a two part mould with the outer for mechanical shape, wear and tear etc and a less permable inner (thin) skin. The roto boats are 3 skins in one so to speak. The first foaming core ones date from around '96.

    BTW most moulds for roto moulding are steel (braced sheet) or aluminium castings bolted together.
     
  11. peterAustralia
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    peterAustralia Senior Member

    if your woodenboat has steel fittings (bolts, screws, etc etc), is it wise to add another metal, issue could be electrolysis. When I built figerglass boats they had plastic tanks under the floor (dont forget the earthing wire to the petrol inlet, sparks and petrol dont mix), however for a yacht maybe a deep narrow tank is best, because it sloshes around a lot, a flat wide tank can allow air to get into the fuel line, much less likely to happen with a deep narrow tank. Please dont ask me how I know this (bleeding an engine at sea aint fun)
     
  12. Westfield 11
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    Westfield 11 Senior Member

    I think you can get the same effect by installing baffles in the tanks, something that is not an option for molded tanks. That and the limited number of shapes available for reasonable prices makes me think that welded metal is the better materiel despite the expense. Having a fabricator make a custom tank is expensive, but relative to the total cost of the project, not THAT expensive. And there are other benefits too, like not having to worry or allow for plastic tank expansion after the first fill, no odor due to vapor porosity of the plastic, larger capacity for a given location due to the custom nature of the metal tank, the aforementioned issue with sloshing fuel, etc. Plastic tanks are cheap and convenient, but for gasoline that are not ideal by any means.
     

  13. pdwiley
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    pdwiley Senior Member

    Cost a friend of mine ~$4000 for his diesel tanks in stainless steel. Cost me $500 for mine, about the same capacity.

    Difference was, I welded mine, he had to pay a welder for his.

    Either way, not that great an expense. It was a great PITA though. I farmed out the holding tank, not being set up to weld plastics. Ditto water tanks as soon as I make up the patterns.

    Dave Gerr's book on boat mechanical systems has a bit to say about ply/epoxy tanks. IIRC he also says there are issues with ethanol in the fuel so perhaps not the best idea for other than diesel.

    PDW
     
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