Steel trawler building

Discussion in 'Boatbuilding' started by janesci, Apr 28, 2013.

  1. janesci
    Joined: Dec 2012
    Posts: 30
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    Location: KOREA

    janesci Junior Member

    Hi everyone,

    I was just wondering if someone advise us for the following queries.

    To build a 55ft steel trawler that is for commercial fishing purpose.
    (L55ft/B24.6ft/D7.8ft) that will runs by 500HP @ 1800 RPM.
    ** Dispc abt 90tons.

    What size of the pitched prop would be optimized to use? and blades..

    Another question is have you guys anythoughts of building times for the hull to be fully welded with 4welders? after steel plate nesting?

    Thanks for your comments in advances.
     
  2. Eric Sponberg
    Joined: Dec 2001
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    Location: On board Corroboree

    Eric Sponberg Senior Member

    Janesci,

    You don't have enough information to specify a propeller at this stage. You'll need to know more about the hullform shape, the engine selected, the reduction gear, and the intended speed.

    On my Moloka'i Strait 65, LOA = 65', B = 19', D = 6', displacement = 81 L. Tons, the installed power was a CAT3406C at 440 HP at 2100 RPM with a 2.43/1 reduction. The propeller was a 4-blade Hundestadt controllable pitch prop DxP = 38.5" x 23". This worked for this yacht, but your requirements would likely be different. You should be expecting a propeller diameter in the neighborhood of 48" dia. for that weight of boat and installed horsepower. Everything depends on the reduction gear--the deeper the reduction, the slower the propeller will turn and the bigger the diameter will be. The most efficient propeller for this application would be 3-blade, but that might not be able to absorb all the power. Therefore, 4-blade may be better. Vibrations will be important, so you may have to go to 5 blade. With each additional blade, efficiency and diameter will both drop slightly, but that's not really a problem--you just have to account for it in the propeller calculations.

    As for building time, we had the Moloka'i Strait hulls fabricated at Custom Steel Boats in North Carolina. So this was a professional yard with many workers building a round-bottom hull at 65'. The metal fabrication took a year, from the summer of 2001 to the summer of 2002. The deck house was built in aluminum and welded to the deck using a Deta Couple (or the equivalent, actually I think it was TriClad). The deck house was built contemporaneously along side the hull and it had its own crew of workers.

    You can read more about the MS 65 and the other Moloka'i Strait designs on my website: http://www.sponbergyachtdesign.com/Molokai65.htm.

    For your boat, if it is a chined hullform, it won't take as long. On the other hand with only 4 welders, it may take longer.

    Eric
     
  3. janesci
    Joined: Dec 2012
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    Location: KOREA

    janesci Junior Member

    Eric,

    Once again, thank you very much for your thoughts and advise.
     
  4. Decisive
    Joined: Apr 2013
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    Location: United States

    Decisive New Member

    Janesci

    Well when it comes to the work boat that you are talking about ultimate average size for the length would be 44" with a 3 to 1 ratio and max for 55' work boat would be 64 " with a 4 to 1 ratio for what I have seen so if you are not after the max pulling power I would go for 54" with a 3.5 to 1 reduction just in cause you have a draft requirement .

    This is out of reference from the past projects I`ve been threw with customer and I have built 70 boats over the past 7 years and these are all thinking 9 knots at the 90 tons you gave.

    Cory boat builder
     

  5. Decisive
    Joined: Apr 2013
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    Location: United States

    Decisive New Member

    Janesci

    44x36 bollard pull 9032 lbs
    54x34 bollard pull 10349 lbs
    64x33 bollard pull 11267 lbs

    Cory Boat builder
     
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