What parameters make a good seaworthy hull?

Discussion in 'Boat Design' started by JTS, Dec 10, 2018.

  1. JTS
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    JTS Junior Member

    If you could design a 75m motor yacht with a 13m beam, optimized for passenger comfort, what principle dimensions would you aim for?

    GM, Roll Period, LCG, LCF, location of max draught, CB, CP, Draught, Displacement etc...

    Any hull designs that people would take from the offshore commercial industry and use in Super Yacht design?
     
  2. TANSL
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    TANSL Senior Member

    I am not sure that your question has a clear and unique answer. To give just one example, you can design a hull that allows you to reach a high speed with reasonable power. However the hull, from the point of view of rolling, will be very uncomfortable, obviously. But you can solve that problem with dynamic stabilizers.
     
  3. JTS
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    JTS Junior Member

    Thanks TANSL, I agree, no such thing as a perfect solution and I can understand that you can optimize for head seas, beam seas, wave height, wave period etc... However assuming speed would be relatively low (16kts max, cruising at 14kts) and efficiency not a big concern, what factors differentiate those "good seaboats" from the "green machines"?
     
  4. BlueBell
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    BlueBell Ahhhhh...

    "What factors"... all of them, and then some.

    A catamaran. But I'd go a lot wider than 13m for 75m LOA.
     
  5. TANSL
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    TANSL Senior Member

    As has already been said many times in this forum, it is about getting a hull that gets the least bad possible to combine the various requirements of a SOR, many of them opposed. Therefore, without knowing exactly what you want to optimize or what is for you "optimized for passenger comfort", it is not possible, in my opinion, to give a valid answer. There are many aspects that contribute to the comfort of the passage. Do you mean the period of balance or the temperature and humidity in the accommodation spaces ?. Many aspects of comfort for the passage will not depend so much on the part of the hull submerged underwater as on the superstructure of the vessel.
     
  6. JTS
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    JTS Junior Member

    I wonder if anyone with some design experience has any useful comments to add...?
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    In order to do that, YOU must define what YOU mean by - passenger comfort.
     
  8. JTS
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    JTS Junior Member

    Hi Ad Hoc, I am considering Passenger Comfort to be related to the ship motions. I know that smell, humidity etc also effect comfort, but these are irrelevant in the hull form design.

    From doing some quick research into the COMPASS project, they defined the "multi-axis equivalent frequency weighted acceleration" to be one of the main contributing factors... I'm curious to know what hull types would give minimum accelerations in rotational and lateral movements...

    upload_2018-12-10_21-37-37.png
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    Good.
    That's an excellent place to start. Thus you need to establish how this is measured and then what is the PASS and FAIL criteria that is considered 'acceptable'.

    Such as:
    upload_2018-12-11_11-57-6.png

    This defines acceptable limits and shows the variation for different ship types.

    Then you can begin to introduce the actual motions further still, this case roll/Acg limits:

    upload_2018-12-11_11-57-56.png

    Which then starts to lead in to performance levels. The activity that is the dominant activity on the vessel. This lead to MII or Motion Induced Interruption. This is is defined as an incident where ship motions become sufficiently large to cause a person to slide or lose balance unless they temporarily abandon their allotted task to pay attention to keeping upright.

    And on it goes...

    Aaahh..that is a totally different question altogether. It is the basis of seakeeping. Seakeeping is a terribly complex subject and has many many inputs that there is no one single simple answer.
    Since the most obvious one liner reply is...well, make it big! Look at the seakeeping of the QM2 passenger liner, fro example.

    But if you are only after a vessel that is just 25% of its length...how is this going to influence the seakeeping which of course influences the motions. Thus, Seakeeping and Motions whilst being directly related, the causes of which have a multifaceted input and there is no 'one shape/length/size' is best. Thus, you need to establish what is your SOR for the vessel. Then design it to ensure you obtain the best, of all the possible options that you have, possibly seakeeping??. Since the best seakeeping will not be the lightest or fastest and cheapest or easiest to build etc etc. as all these are inputs no matter what the SOR ends up being. Thus having Seakeeping at the dminatant SOR dictates how the design is shaped, and all other factors becoming secondary - merely to ensure the seakeeping/comfort meets the objective that YOU decide upon.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    And never forget that vital component, the nut behind the wheel !
     

  11. JTS
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    JTS Junior Member

    Thanks Ad Hoc, some great advice there.
     
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