Seaworthiness concerns for excessively wide trawler

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

  1. makobuilders
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    makobuilders Member

    I'm flying to Istanbul next week to visit a designer/shipyard regarding construction of a steel trawler. Semi-custom, it would be an adaptation of his fishing boat design to my usage as a personal vessel for long distance cruising (ocean rating). The dimensions are as follows:
    • LOA 48-10
    • LWL 47-6
    • Beam 19/4
    • Midbody draft 5-0
    • Depth 8-2
    • Displacement at DWL 93,500 lbs
    • Construction is steel, round bottom with bulbous bow
    I'm concerned about the extremely wide beam of 19ft and perhaps the excessive stability that this would result in. I will ask to see the stability calculations and learn more about this design's roll amplitude, period, acceleration, stability curve, etc.

    I have told them that the vessel is to be designed and built to class rules, but I'm likely not going to pursue class certification.

    Am I right to be concerned about this design, or if properly designed, would it necessarily be as seaworthy and safe as any other ocean rated vessel of more moderate beam?
     
  2. fallguy
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    fallguy Senior Member

    This conversation is way outta my league, but doesn't fuel economy and hull speed enter the conversation here as well? I doubt you'll make 1.34 for SL, so I doubt you'll achieve 9 knots.

    I could be wrong, but in general the wider the craft; the more water to push.

    My bigger concern would be about meeting the SOR on vessel speed.

    ps ... I can't back my statement up, but someone wiser may tell me I am wrong or the SL calculation for real.
     
  3. makobuilders
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    makobuilders Member

    Certainly it is less efficient to push. But my required operational speed is 8.0 knots.
     
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  4. fallguy
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    fallguy Senior Member

    What did you use for SL? I am mostly just curious.

    Then it sounds like a no brainer, but it might be a bear to steer. How are you accomodating the steering of this wide body? Others more capable of helping might also want to know.
     
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  5. JamesG123
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    JamesG123 Senior Member

    The obvious question is, why? What requirement is driving this?

    The usual solution for "beamyness" is a catamaran configuration. Yes stability and steering is a concern, but your designer should be able to engineer a workable solution (corner rudders etc.) that is safe, or "seaworthy". What he won't be able to do is work a miracle. Either to take an unoptimum and unsuitable specification comfortable or efficient. The later being the important part. A draggy hull will not only be slow but will require more power to move it at any given speed, and this requires more fuel, which will cut into range. Also 8 knots is pretty marginal for a powerboat and can easily be eaten up by hull fouling, currents, and wind resistance leaving you with no maneuverability up wind/stream.
     
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  6. JosephT
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    JosephT Senior Member

    I agree with the others. Fuel efficiency & control issues with this extra wide beam would be the main concerns. Most other trawlers with a 19ft beam are over 60 ft long.

    Question: Are you insisting on a 19ft beam or is the builder just doing this on their own?

    It would help to have some pics of the vessel if you have them handy.
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    Wrong.
    A vessel of this nature will be and must be designed/built to Class rules. No exceptions.

    If you have concerns, seek independent advice and ask them to review the data to data and to engage into a dialogue with the shipyard to address your concerns.
     
  8. TANSL
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    TANSL Senior Member

    It is the same thing that the OP is saying who, therefore, is not wrong. A different thing is that the boat asks for/obtains the class certificate, which may not be mandatory.
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    An operator needs insurance for their work - without insurance they will not be able to get a PO from the Flag state.
    The banks providing the money for the build to the client and/or shipyard also requires insurance.
    Both are only possible if the vessel is built to a known standard.
    This is why vessel must be designed and built to Class - a known standard.

    This is common shipbuilding practice - everyone involved with commercial shipbuilding knows this!
     
  10. JamesG123
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    JamesG123 Senior Member

    This isn't a commercial vessel but a private yacht. OP might be an oil shiek and self-insuring and financing. Notionally.
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Contrary to how it is presented.

    So it is being built and thus classed, as a steel trawler - a commercial vessel.

    That is a variation order. And, banks etc still need assurance of a known standard of build.

    A vessel of this size, is still a Class design/build owing to aforementioned reasons. It is commercial build, regardless of its final usage.
     
  12. SamSam
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    SamSam Senior Member

    So it must be designed and built to class rules.
     
  13. TANSL
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    TANSL Senior Member

    Totally wrong.
    It must be designed and built to class rules, first and foremost because the shipowner asks for it. But the ship does not need "to be classed", neither for the administration of the flag country, nor for the banks, nor for the insurance companies. Do not confuse things and do not confuse the OP.
     
  14. Ad Hoc
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    Ad Hoc Naval Architect

    Yet again, incorrect.
    The client can ask for what ever he/she wants or doesn't want.

    The banks need guarantees for the build. These only come from being designed/built to Class.
    You clearly do not work in the commercial sector.

    Without being built/designed to Class, no bank will provide the funds for the project.
    Unless the client funds it themselves privately.
     

  15. makobuilders
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    makobuilders Member

    Good morning. Allow me to clarify... I'm not a rich oil sheik but just a normal working stiff :).

    Adapting the commercial trawler design for personal use wouldn't come with any requirement for classification other than my own peace of mind. I'm not seeking bank financing and the insurers I've asked offer only a couple of percent discount on their rates (which surprised me).

    Back to the technical stuff, I'm not a naval architect but as an engineer and having motored open ocean in my previous boats, I've become suspicious of extra-wide boats. The comments made above about fuel economy, steering, directional stability (tracking in heavy following or quartering seas) seem like real concerns. Also, I am not the one who specified the wide beam, that is the design they proposed to me.

    As they are the designers, and also have many designs built, I will approach them with a requirement for more moderate beam. Perhaps if kept to a max of 5m beam on the 15m length that would be a good guideline. What sort of L/B ratios would be "normal" or seaworthy, ocean-going vessels?
     

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