Most efficient waterline length?

Discussion in 'Boat Design' started by OceanLinerFan, Feb 17, 2013.

  1. OceanLinerFan
    Joined: Jan 2012
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    OceanLinerFan Junior Member

    As far as designing ships go, how do you go about finding the most efficient waterline length for a ship, for a particular speed?

    I have been looking at warships, ocean liners, cruise ships, etc. and the SLRs (speed-length ratios) vary widely from one ship type to another. I would think it would be wiser to use the shortest possible hull length for maximum speed. But I think it depends more on the type of ship and what the speed requirements are, and then finding a hull that gives the most optimal result across all speeds.

    Capital ship (warships) formula for top speed: 1.20 x square root (waterline length)

    Merchant ship formula for top speed: 1.23 x square root (waterline length)

    Here are a three examples I have looked into in depth:

    Iowa Class Battleships:

    Design max. speed: 33 knots (SLR = 1.125)
    Maximum speed by formula: 34.9 knots
    Waterline length: 860 ft

    SS United States Ocean Liner:

    Design max. speed: 37.3 knots (SLR = 1.216)
    Maximum speed by formula: 37.7 knots
    Waterline length: 940 ft

    and this is my ship derived by looking at the trend above...

    MS Canada - my own ship

    Design max. speed: 32 knots (SLR = 1.156)
    Maximum speed by formula: 34 knots
    Waterline length: 765 ft
  2. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    The design of any boat is dictated far more than just its length. This is even more so of warships.

    There is terms of seakeeping and statical/damage stability to consider. Then there is the powering..and the amount of fuel it must carry...and then the crew, the accommodation and the weaponry, the stores the am munitions etc etc.

    There is no one size fits all. The design must satisfy the SOR. The result, is..well, what it is...that which satisfies the SOR, cross the board from speed to length to capital costs to maintenance and through life costings.
  3. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    There is not a more efficient waterline length. They are however, efficient speeds for every hull. These speeds are usually even multiples of the square root of the waterline is knots or close to it.
  4. Yobarnacle
    Joined: Nov 2011
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    Yobarnacle Senior Member holding true course

    All coeffcient ratios are multiplied by sq root of wl length. Ergo, n all cases, greater wl length will result in greater hull speed. longer is better, but other factors like cost, locks and docks, ect, determine max length

  5. 805gregg
    Joined: Apr 2010
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    805gregg Junior Member

    One that will get you on a plane so waterline length goes out the door
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