Seaworthiness concerns for excessively wide trawler

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

  1. makobuilders
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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
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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
  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
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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...
     
  12. comfisherman
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    comfisherman Junior Member

    It was a kvichak built pilot boat designed for the Columbia river pilot. Failed due to fire extinguisher falling from a unsecured braket when the crane took it half way over. Was a big yellow thing, lots of press there for the show.

    My first bay boat had a 2:1 length to beam ratio. It rode pretty solid, took it in weather most on here would not believe. Some of the shallower versions had a funky snap and pounded in a headsea, the all points out of Marysville could pound your fillings out....
    Look up some of the commercial novi boats, beam ratios out of this world. Have spoken to many owners who love them. For a pleasure boat, my preference would be long skinny with a gyro.
     
  13. makobuilders
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    makobuilders Member

    So it would seem that my boat is the Turkish version of a Novi :) with an 18' beam on a 45' waterline. Luckily it has a good displacement at 42 tons, a nice 5' midbody hull draft and the bulbous bow which the designer states softens the pitching. My rough estimate for roll period is a bit quick at 4 seconds, but I'm awaiting the designer's calculations to confirm.

    The interesting thing is that he reports about a 30% reduction in roll with the large bilge keels (rolling chocks) that are employed. I've always read that you're lucky to get 10%, but he swears otherwise based on the many boats they've designed and built. Admittedly most of the chocks I see on various boats are perhaps 6 inches wide, so perhaps that is why the low performance usually seen.
     
  14. goodwilltoall
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    goodwilltoall Senior Member

    Novi's look like typ. lobster boats with about 3/1
    L/B
     

  15. comfisherman
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    comfisherman Junior Member

    I was thinking the wedgeport and aylward grizzly type. They are 39.4 feet long and 25-29 feet wide. I think they aren't likely to stop till they get to 1:1.

    Back on subject. Fishing boats are simply that, for fishing. Usually that means exorbitant weight carrying on a length dictated by permits. Deep draft, big beam, excessive horsepower. Notice few of those requirements cross over to pleasure boats or trawlers.
     
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