USCG Stability Test for Power Trimaran

Discussion in 'Stability' started by mike w. schultz, Feb 10, 2020.

  1. mike w. schultz
    Joined: Dec 2018
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    Location: South Mississippi

    mike w. schultz Junior Member

    IMG_0570.jpeg 50% thru build on power 64' trimaran, was hoping to get Coast Guard approval (COI) for 12 passengers and wondered how a stability test on a Tri hull would differ than a mono or cat????

    Your thoughts and input would be appreciated.
    Mike S.
     
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    That is certainly a very interesting trimaran - who is the designer (or did you design her yourself)?
    Do you have a side profile photo that you can post please? And maybe a photo from the bow or stern showing the widths of the hulls?
    Where do you expect her load waterline to be? I am guessing with the outriggers immersed about 8" perhaps?
    Re stability, I would think that she would heel fairly easily up until the underside of the bridgedeck between the main hull and the outrigger makes contact with the water surface, and then her stability should stiffen up significantly (?)
    I would guess that a 'standard' inclining test would be carried out, in similar fashion to how it would be done on a catamaran or monohull (?).
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Maybe this should have been addressed at the design stage. At first appearance, it certainly does not seem to be getting much help from the outriggers, that remind me of T-Rex's tiny little "arms". but appearances may be deceptive ! :D
     
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  4. mike w. schultz
    Joined: Dec 2018
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    mike w. schultz Junior Member

    Will upload more photos shortly, yes we anticipate the Amas to be submerged around 10" at rest, I just brought her out of the barn on Sunday when this photo was taken, she weighed 4009kg, no power, no interior, strictly Nida Core honeycomb panels, resin and cloth The design and co-builder is Jon Coats, he has built numerous boats over the last 50+ years. He builds card board model, then makes all the parts on table with vacuum bagging technique. He normally works by himself 6 hours a day 6 days a week, never sits down and has design vision that is eerie! He permits me to grind glass on occasions. IMG_0488 (1).jpeg IMG_0569.jpeg IMG_0578.jpeg
     
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  5. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Nice building.
    I do not believe there is a special procedure for trimaran. It will probably be the same as for a monohull but what will be different are the conditions to be met in the different loading conditions. In any case, I think it is best that you consult that with the USCG agent in your area.
     
  6. mike w. schultz
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    Location: South Mississippi

    mike w. schultz Junior Member

    Thanks for info!
     
  7. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Just a thought re the 12 passengers approval by the USCG - whereabouts on the boat are you planning on 'parking' these folk?
    The long thin foredeck looks a bit risky....
    Is there a large 'cockpit' (for want of a better word) between the two sponsons?
    What is your proposed propulsion method?
     
  8. mike w. schultz
    Joined: Dec 2018
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    mike w. schultz Junior Member

    I have uploaded a photo of interior space looking aft, the floor goes from ama to ama. There is ample room forward in mail hull for 50" wide bed, genset, battery bank, diesel and freshwater tanks along with bow thruster and windlass. We pulled her out of the barn as we had no more head room to build the fly bridge, ample space up top for 8 quest. Power is to be a pair of Yamaha 115 4 stroke, they reside in the aft hatch, 4 feet forward of the swim platform, With E.L.A.N. effect we have calculated 75% throttle to push her finished weight of 9 tons at 12 to 15 knots, assuming we can obtain the proper pitch props. Built transom today, will move .5 miles this week to "New Building". Launch date projected to be Fall of 2020. interior.jpeg
     
  9. fallguy
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    fallguy Senior Member

    What is the range of the vessel and why a tri versus a big cat?

    Are you at all worried about slamming at the abrupt hull change for'd?

    looks great; curious about the cockpit aft; looks big

    where out of?
     
  10. mike w. schultz
    Joined: Dec 2018
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    Location: South Mississippi

    mike w. schultz Junior Member

    Range is based on calculation of 2.3 mpg x (2) 95 gallon tanks (190 gal)= 437 miles (running both engines 75% throttle)
    Will not know until after sea trials what can be achieved with one motor running.
    Money (lack of) and curiosity pushed me to the Tri, it was a 50% reduction versus a cat of similar length and better fuel economy.
    Repeatability to duplicate this build is simple and cheap and easily shipped in 40ft. container. IMG_0578.jpeg
     
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  11. Ike
    Joined: Apr 2006
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    Ike Senior Member

    what Tansl said. In fact you should have submitted plans to the Coast Guard before you started building it. You may have to make significant changes. Contact the Marine Safety Center and they will put you in contact with the nearest Marine Inspection Office. Marine Safety Center (MSC) https://www.dco.uscg.mil/Our-Organization/Assistant-Commandant-for-Prevention-Policy-CG-5P/Commercial-Regulations-standards-CG-5PS/Marine-Safety-Center-MSC/

    As far as I know the 12 passenger category is currently only permitted in the US Virgins. As for the stability test it is probably the simplified stability test. See the following USCG--Simplified Stability website https://www.dco.uscg.mil/Our-Organization/Assistant-Commandant-for-Prevention-Policy-CG-5P/Commercial-Regulations-standards-CG-5PS/Design-Engineering-Standards/Naval-Architecture-Division-ENG-2/Simplified-Stability/
     
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  12. mike w. schultz
    Joined: Dec 2018
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    Location: South Mississippi

    mike w. schultz Junior Member

    Thanks Ike
     
  13. mike w. schultz
    Joined: Dec 2018
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    Location: South Mississippi

    mike w. schultz Junior Member

    Long Beach, MS boat construction site, Seeing that she won't plane, any slamming should be minimum, this area has been beefed up in the event of... Of course sea trial and time will tell. Try to get a cockpit photo up loaded.
     
  14. mike w. schultz
    Joined: Dec 2018
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    Location: South Mississippi

    mike w. schultz Junior Member

    Swim platform with mold on the plug, should remove in 48 hours. IMG_0583.jpeg
     

  15. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Thank you for all of these excellent photos Mike.
    Re the swim platform above, is the underside of the bottom step just kissing the water surface, or is it immersed?
    I am intrigued by how you have arranged the well for the outboard motors forward of the swim platform - could you also post a photo of this area as well please?

    Edit - another question - have you calculated how much buoyancy you have in one of the outrigger floats at say 10" immersion?
     
    Last edited: Feb 12, 2020
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