Seaworthiness concerns for excessively wide trawler

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

  1. fallguy
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    fallguy Senior Member

    Rule of thumb google calculations of 4.3M are not advisable.

    Too many other factors...

    The fact you are asking here means you ought to disqualify and bring in a third party. Sometimes the most professional thing to do is find a better professional.

    http://www.brayyachtdesign.bc.ca/Stability.pdf

    Way outta my ballpark; I am just curious and generally good about avoiding these architectural matters.

    I was onboard a charter vessel last year and she had been refitted with a third deck. The well known boat was no longer allowed to leave the harbor with passengers as she was no longer stable at sea. Her l/b had NOTHING to do with the issue. It was all about raising centers of mass and failing to meet USCG minimums for stability.

    Hire an expert. You'll be glad you did versus finding out the seakeeping is horrid later.
     
  2. makobuilders
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    makobuilders Member

    fallguy and AdHoc I hear your comments about hiring a third party to check the design. I very well may if I decide to move forward with this shipyard but still have doubts about the design. First step is to visit them next week and see how open they are meeting my needs as opposed to those of the local market they serve.
     
  3. rxcomposite
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    rxcomposite Senior Member

    Trawlers and tugs are special types of ships of high Froude numbers and low L/D ratios. It is designed to push or pull hard and driven uphill of the friction line. Don't expect any economy on the operation as it will be in the Fn of 0.38, above the economical point of 0.35.

    Typical design have L/B ratio of 4.0 to 5.5, thus with the widest (at 4.0 ratio) you get 11.5 feet breadth. Your concern is valid why it is 19 feet.

    To find how much power you need for cruising at 8 knots with 19 foot beam, you have to run it with a suitable powering software/powering formula to see what your penalty is for running such a beamy boat. Van Oortmensen might be a good tool to start with as it is suited for tugs, trawlers and workboats.
     
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  4. baeckmo
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    baeckmo Hydrodynamics

    One concern regarding seaworthiness that comes to mind is the tiring, vomit-inducing corcscrewing motion that has been noted in cases where the transverse stiffness comes closer to the longitudinal stiffness. Or, in other terms the longitudinal and transverse resonance frequencies are too close. With the proportions of the vessel here, I'd say there is an increased risk.
     
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  5. fallguy
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    fallguy Senior Member

    It is great to be named with Ad Hoc, but I am definitely not worthy and I never ought to have posted this thread.

    What I find interesting is you sought out a yard rather than first a design.

    For a purchase of this magnitude, I would have sought a proven design or at least a wise designer and then found a builder.

    My gut hunch tells me the hull is ready to be finished and you are the unwary buyer or that we are not getting the whole story.

    Even people buying production speedboats and pleasurecraft have been later miserably disappointed in the way the boat handled or fuel economy, etc.

    I find the tack odd. No disrespect.

    Years ago I bought a design and looked at it for three months and had second thoughts and bought a different design now building.

    The design is what you need to like first. My last post on this thread. Best of luck.
     
  6. SamSam
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    SamSam Senior Member

    I'm guessing that shape is ok as long as you are pulling nets and sometimes have large deck loads and/or want a large capacity, or pull nets over the sides etc to the detriment of comfort and efficiency. There are at least three of these boats with the ERGIN KARDESLER name. If you search the name you can find out their location, there might be one in port where you could ask the Captain or crew how they ride or how suitable they might be for your use.
    There's also a criminal with the same name that is in the Turkish news, so you might specify it's a SHIP you're looking for when making inquiries as the Turkish police look kind of serious.
    Here's a deck picture of one boat...
    [​IMG]
    [​IMG]
     
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  7. SamSam
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    SamSam Senior Member

    They also might be that shape to take advantage of a loophole in fishing regulations. There are some Alaskan fish boats of extreme width to length ratio to take advantage of restrictions on length , but not width.
     
  8. makobuilders
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    makobuilders Member

    I suppose I was unclear, but this is the designer who I am in contact with. His company is invested in several shipyards. So it’s a design-build relationship. They apparently are quite successful with their boat designs to meet their market needs. Whether or not they are open to meeting my particular needs, is yet to be seen. But I am hopeful. Also need to assess the quality of workmanship at the yards.
     
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  9. Milehog
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    Milehog Clever Quip

    I'm suspect of a designer that would steer you toward a burdensome tub rather than an efficient hull with better proportions for a cruiser.
    Keep looking.
     
  10. waikikin
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    waikikin Senior Member

    SamSam, That was my thought when I saw the pics... contorted to exploit a size rule, seen some similar but different stuff in past.
    Jeff.
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Don't put yourself down, don't forget, everyone is entitled to an opinion :)

    The only difference between an opinion and a reasoned argument is that one is a personal view and the other is a personal view based upon knowledge and experience and can be quantitatively explained beyond a just a subjective reply. That's all. ....:D

    Keep on plugging away everyone is worthy....otherwise creativity and debate will cease!
     
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  12. makobuilders
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    makobuilders Member

    I have received the stability curves (hydrostatic and GZ) for this vessel, in preparation for my trip there in two days. I would greatly appreciate any naval architects' interpretations of these graphs, which are attached. Once again, the vessel's dimensions are as follows (feet-inches):
    • LOA 48-10
    • LWL 47-6
    • Beam 19-4
    • Midbody draft 5-0
    • Depth 8-2
    • Displacement lightship 60,500 lbs
    • Displacement at DWL 93,500 lbs
    • Steel, round bottom, bulbous bow
     

    Attached Files:

  13. TANSL
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    TANSL Senior Member

    I enclose a summary of the loading conditions of a ship of dimensions similar to yours.
     

    Attached Files:

  14. makobuilders
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    makobuilders Member

    So this very wide design has a capsize angle of 72 degrees, versus the 80 degrees of your 1380 boat, versus 90 degrees for Diesel Ducks or Nordhavns. Is this more limited angle a major concern for ocean cruising?
     

  15. TANSL
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    TANSL Senior Member

    It does not have to be a problem but it is curious that a ship with a low value of the L/B ratio has a lower AVS than its counterparts. In any case, what should be studied are all the parameters, not just one, of your ship under its actual load conditions.
    Another curious thing is the high value of the leight ship weight.
    Again I repeat that studying one or two items can not draw serious conclusions about the suitability of the hull for the purposes you intend it. You should write an SOR for your vessel and have the shipyard prove whether the hull they propose meets or not. If, for example, they offer you a hull that is much heavier than normal, with the consequent increase in fuel consumption and / or decrease in speed, they should explain how they compensate you for this inconvenience.
     
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