Best location for fuel tanks

Discussion in 'Stability' started by Big H Buck, Jan 13, 2014.

  1. Big H Buck
    Joined: Jan 2008
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    Big H Buck Junior Member

    Hi Folks

    We need some advice as to the best location for fuel tanks on a
    steel boat (13'6" x 46' - LOW) we are re-building from the hull up.

    My questions are:

    Which would be a better location for two 200 gal steel tanks 24"x24"x80:

    1. Centered over the keel, or longitudinally Tight to the Chines ???

    2. Which location would afford Greater Stability ???

    3. Which location would afford Better Righting Moment in Heavy Seas ???

    Thanks in advance for your help

    Big H Buck
     
  2. rasorinc
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    rasorinc Senior Member

    There are others on this forum that know all the formulas for this but my 2 bits is line them up over the keel as low as you can with the length going fore and aft with the line between the two tanks centered on the balance point (center) of the fully equipted, and provisioned boat. Putting them out by the chines means you would have to draw down the two tanks equally. Ventilate the area well.
     
  3. JSL
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    JSL Senior Member

    Where were they before? If the trim works, put them over the LCF so full or empty the boat stays at the same trim.
    You might want to hire someone who can help: 46 feet warrants good guidance. Or, you can just 'wing it' and hope everything works.
     
  4. PAR
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    PAR Yacht Designer/Builder

    It would be rare to get lucky enough to place the tanks directly over the CB, particularly since the most desirable living spaces share this location.

    Frankly, you'll need to hire a professional to work out the "moments" for you, so the boat will trim properly. The obvious questions would be; what design are you building - why aren't you placing them where the plans suggest they should be placed - if redoing the boat, why aren't the previous locations being considered - have these "modifications" been worked through by an NA or qualified designer, etc., etc., etc.

    A 46' vessel will require sizable tankage, so their placement can dramatically affect the handling, stability and other important issues concerning the boat, in general. If you just take a guess, place them a little aft of midship and hope for the best.
     
  5. Kailani
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    Kailani Senior Member

    If [large if] both side-to-side options can be the same fore-and-aft, would a pair of side tanks ever give more stability than a belly tank down low??

    I vote belly tank as low.
     
  6. Kailani
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    Kailani Senior Member

    P.S. pay attention to those above. I don't have their knowledge.
     
  7. Kailani
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    Kailani Senior Member

    P.P.S. what's the beam and the distance between your keel and chine at the best fore-and-aft location for the tanks?
     
  8. shanehand
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    shanehand New Member

    I think this issue is a very interesting one where all the calculations meet the real world. I am a Naval Architect and there are some key issues here. If the distance from the center of gravity to the metacentre is relatively low for the boat then wing tanks would be more comfortable as it would slow the roll of the vessel, but raise your CG. If a bilge tank were used it would save space in the vessel and lower the CG but that might make the motion of the boat more uncomfortable and you would have to consider its interaction with the structure of the boat, is it transversely framed or longitudinally frames, can the fuel flow between each frame, would cutting a mousehole in the frame (to allow the fuel to flow) impact the structural rigidity of the vessel? There are hundreds of questions to be asked that a more experienced mind can answer with more information on the vessel. Best of luck with your project
     
  9. michael pierzga
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    michael pierzga Senior Member

    Two wing tanks are easier to live with.

    A single tank sloshes fuel from side to side and is very shallow. On port tack all fuel is on starboard. A single tank greatly complicates all fore and aft plumbing runs.

    Fuel Tanks must function...ballast and trim location are secondary. First design functioning tanks with a full size manhole covers for inspection and cleaning...then locate.

    Only the black water , waste water tanks need to be deep and on centreline.
     
  10. shanehand
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    shanehand New Member

    That is assuming it is a sailing boat to begin with, but I do agree with what you say about wing tanks being easier
     
  11. michael pierzga
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    michael pierzga Senior Member

    The problem with cruising boats is that every problem has two best answers. Always compromise.

    The beauty of a gran prix race boat is that It only has one answer..
     
  12. TANSL
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    TANSL Senior Member

    Big H Buck, in the order of your questions I will tell you the following:
    1.- Unaware General Arrangement of the boat is impossible to answer. For example, is there a shaft line passing through the tanks if they are placed centered on the keel?
    2.- the lower the better.
    3.- Weight can not provide righting moment (so, no righting arm). The righting moment is produced by boat's hull shapes. The weights always produce heeling moment.
    I hope I have helped. If you have further questions, I will gladly try to answer.
     
  13. athvas
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    athvas Senior Member

    It is a good practice to locate a large tank as possible to close to the midship so that the consumption of fluids does not lead very large variations in the trim. For the ships with the large beam it is good practice to have one centre tank and two wing tanks so that the list can be kept in check and it is also advisable to divide the tanks athward ships to reduce the free surface effect.
     

  14. TANSL
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    TANSL Senior Member

    I almost agree with what Athvas says. Just to clarify that you'd try to locate the center of gravity of the tanks with consumables (its longitudinal position) as close to the centroid of the float as possible, not amidship.
     
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