Seaworthiness concerns for excessively wide trawler

Discussion in 'Stability' started by makobuilders, Oct 4, 2018.

  1. makobuilders
    Joined: Feb 2009
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    makobuilders Member

    I've always understood that very wide beam boats would always have a lower ultimate stability because of their higher initial/form stability. If I decide to build this boat then I'll just have to accept this compromise but ensure absolute watertightness of the structure. So in extreme conditions the pilothouse on top of the deckhouse would provide a good righting arm/buoyancy if inverted.

    My estimate is about 22-24 tons of steel in the structure, +1 for engine/running gear, etc. Honestly I was hoping for a heavier boat, and would try to ensure the vessel is at highest displacement whenever possible.

    Thank you for reminding me. I only sent them a brief summary previously, but will spend today/tomorrow creating a more detailed SOR so we can discuss in person on Friday.

    Cheers!
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    It would be an unusual type of vessel, that would hold true for.
     
  3. TANSL
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    TANSL Senior Member

    Normally pilot house can not be taken into account as a buoyancy reserve. To do this, it should have watertight closures in all its openings (doors, windows, vents, ...) and always navigate with everything closed.
    Regarding the value of the AVS, in addition to being higher or lower, you should measure the area limited by the GZ curve (dynamic stability) to see if your ship is more or less safe: that is, the work needed to carry the boat to that AVS.
     
  4. makobuilders
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    makobuilders Member

    On a different note, I notice that neither Gerr nor Wyman powering formulas take into account beam. Obviously a boat with a L/B ratio of 2.6 requires more power than a slimmer hull which Gerr/Wyman must be assuming. As a rough estimate, how much more power would one expect?
     
  5. rxcomposite
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    rxcomposite Senior Member

    Gerr and Wyman is a very general equation and won't give you accurate result. Yours has a bulbous bow and Holtrop/Mennen resistance and Power prediction is better suited. Not sure if your parameter suits the equation as it has a certain range that the formula fits. Several H/M in Excell form has been posted in this forum.
     
  6. goodwilltoall
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    goodwilltoall Senior Member

    These are 9.95 LOA 8.40 LWL × 4.8O Beam x 3.20 Draft. Eyemouth fishing boat 2 length to 1 beam
     

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  7. makobuilders
    Joined: Feb 2009
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    makobuilders Member

    Wow that Eyemouth is funky looking. Very functional, but not exactly a stylish yacht!

    I've returned from Istanbul. The final dimensions of the proposed design are:
    • LOA 14.2m = 46/7
    • LBP 12.94m = 42/5
    • LWL 13.74m = 45/0
    • Beam 5.5m = 18/0
    • Draft 1.5m = 4/11
    • Draft keel = 6/4
    • Depth 2.5m = 8/2
    • Freeboard 1.0m = 3/3
    • Displacement 42.6tons = 93,720lbs
    • D/L = 459
     
    Last edited: Oct 18, 2018 at 11:10 AM
  8. SamSam
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    SamSam Senior Member

    A number of years ago there was a short video of one of our Coast Guard vessels undergoing self righting tests. It failed badly when a fire extinguisher came off it's mounting bracket and broke out a window. There are some weak links when the pilot house is depended upon for buoyancy.
     
  9. TANSL
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    TANSL Senior Member

    At the moment, although I think that for many, many years now, the pilot house glasses must be, at least, of secured glass and of a thickness that avoids accidents like the one you describe. The windows glasses must withstand the impact of an extinguisher and the impact of the waves, which can be much greater. It is strange that the Coast Guard did not take it into account.
     
  10. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    Actually, it might not have been a Coast Guard boat yet, but was being tested by the manufacture before the Coast Guard accepted it. I tried looking for the article years ago but it seemed to have been scrubbed from the internet.
     

  11. JamesG123
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    JamesG123 Senior Member

    Not to mention doing a great impersonation of a submerged submarine...
     
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