Thoughts on what seas are & aren't suitable for this hull?

Discussion in 'Stability' started by RSD, Nov 20, 2022.

  1. RSD
    Joined: Nov 2022
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    Location: Red Sea, Egypt

    RSD Junior Member

    The water around the pinnacle reefs (Panorama, Middle Reef etc) drops straight into 400 feet of depth - 15 miles offshore it is 800 feet deep but no pinnacles rising off the bottom so nobody is going to be diving out there. Also this boat isn't intended to head to the offshore reefs but instead head parallel to the coast heading further south sticking closer to the coast and going about 3-4 miles offshore at the most to get to the wreck of the MV Salem Express.

    Only if they go out to the offshore reefs where this vessel is not intended to go.
     
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  2. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Well, depth limiting certainly is a factor.

    But I still think you ought to decide the requirements. That is, the boat must be able to maintain a speed of x in a certain sea state of y. That way, rather than 'will it work'; you can get a more defined answer from experts or experienced boaters.

    In general terms, that boat is going to want to stay on top, and the sea state is what the passengers will feel.

    One thing you must understand about boats. They all have tradeoffs. These hulls are designed for massive loads (70 pax?), which is appealing to you, but perhaps too much and the tradeoff is poor economy and bad ride in rougher seas. If you hone the SOR; you should even be able to determine what loads you'll carry and whether this boat has more capacity than you need even.

    The SOR and the boat should be able to be compared objectively and side by side.

    All the best. Others need to speak.
     
  3. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    ....I associate to jumping and bouncing..... To be more precise in nautical terms, it's going to expose the crew and passengers to very high vertical accelerations and the hull structure to high impact loads, sc "slamming".

    The short, fat hulls will have a very high planing "hump" resistance, requiring high power to pass, and making the entire speed range around hump unpractical and even unsafe.
     
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  4. comfisherman
    Joined: Apr 2009
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    comfisherman Senior Member

    It's going to ride about like what a fairly heavy cat with a 17.5 foot beam would do... pound like a mofo in chop be a smidgen lively if the harmonics are off. Nothing worse than matching beam to average sea state and getting it just wrong.

    I'd guess the 36 knots is light ship. That seams a big optimistic but it's not a very heavy 32 footer especially given its beam and sponson displacements. I'd doubt 36 knots is possible with 70 passengers and 450 hp.

    I've been in on a couple specmar builds. They are OK, not quite the perfection of some but better thought out than others. They kinda run the balance of value, suited for the semi diy folks.



    As far as survivability.... about 10 years ago I had a mono 32 footer that would pound your fillings out in a chop with a 17'beam. But we put it through some storms that defied logic. I never found the limit of it, but often found the fear tolerance limit of myself and the crew.
     
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  5. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    These are divers, so add at least 75 lbs (35 Kg) of gear and supplies to the total weight of average 190 lbs (86 Kg) per passenger. 70 passengers plus a crew of 5 weighs about 20,000 lbs (8600 Kg).
     
  6. RSD
    Joined: Nov 2022
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    Location: Red Sea, Egypt

    RSD Junior Member

    I am working on 200 kg per diver with 8 divers@200 kg each and 2 non-diving crew@100 kg each giving a total of 1800 kg ( 3960 lbs).
     
  7. gonzo
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    gonzo Senior Member

    It is not 7 but 70 divers plus boat crew.
     
  8. RSD
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    Location: Red Sea, Egypt

    RSD Junior Member

    Local laws mean 8 (possibly 9) divers + 2 crew.
     
  9. gonzo
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    gonzo Senior Member

    OK, so you are only carrying 10 - 11 persons. Are you set on a catamaran?
     

  10. fallguy
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    fallguy Senior Member

    The issue here is your pax payload is 20% of what the specmar boat is 'marketed' as...so the specmar hulls would be running underweight and atop the seas if we lend credence to the specmar 70 pax business..

    And this is why honing the sor is so vital to your success. By recognizing the variation between your needs and the boats available displacement; you can choose a boat that'll ride better.

    But you also need to add something for the lifting equipment.

    I am assuming you want a cat for the wider hull, better stability as a platform and engines can be wider apart for dps. I don't feel wise enough to answer whether this is the best approach. But the displacement tradeoff needs to be understood.
     
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