Maximum Capacity Calculations

Discussion in 'Class Societies' started by Willallison, Jun 21, 2010.

  1. Willallison
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    Willallison Senior Member

    Trying to locate a recognised method of calculating load capacity (people) for larger recreational vessels - 20m LOA.
    Unfortunately, I have little information available other than the vessels basic specifications....
     
  2. Paul Kotzebue

    Paul Kotzebue Previous Member

    The applicable standards for a 20m recreational vessel would be ISO 12217-1 or 12217-2, where the maximum load capacity is the maximum number of people you can put on the boat and still meet the standard.

    Of course, you'll need much more than the basic specifications.
     
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  3. Willallison
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    Willallison Senior Member

    Yes - Thanks Paul... I may have to get in touch with the manufacturer and see if they've done the calcs, or if they're prepared to give the required info (not holding much hope on the latter).
     
  4. Landlubber
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    Landlubber Senior Member

  5. Paul Kotzebue

    Paul Kotzebue Previous Member

  6. Landlubber
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    Landlubber Senior Member

  7. Ike
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    Ike Senior Member

    The USCG uses a stability test to determine the number of passengers for small passenger vessels under 100gross tons but carrying more than 6 passengers.

    46 C.F.R. § 171.050 Intact stability requirements for a mechanically propelled or a nonself-propelled vessel.
    Title 46 - Shipping

    Title 46: Shipping
    PART 171—SPECIAL RULES PERTAINING TO VESSELS CARRYING PASSENGERS
    Subpart C—Large Vessels

    § 171.050 Intact stability requirements for a mechanically propelled or a nonself-propelled vessel.
    Each vessel must be shown by design calculations to have a metacentric height (GM) in feet (meters) in each condition of loading and operation, that is not less than the value given by the following equation:

    where—

    N=number of passengers.

    W=displacement of the vessel in long (metric) tons.

    T=14 degrees or the angle of heel at which the deck edge is first submerged, whichever is less.

    b=distance in feet (meters) from the centerline of the vessel to the geometric center of the passenger deck on one side of the centerline.

    K=24 passengers/long ton (23.6 passengers/metric ton).
     
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  8. Paul Kotzebue

    Paul Kotzebue Previous Member

    Using 171.050 by itself is risky. The USCG is requiring virtually all inspected vessels to meet 170.173. It is possible that a vessel will easily pass 171.050 and not pass 170.173. Also, the USCG standards generally apply to vessels over 65 ft (20 m).

    The original post asked for recognized standards that apply to a recreational vessel 20 m LOA and we digress by suggesting commercial boat standards.
     
  9. Ike
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    Ike Senior Member

    I offered this up because there is no USCG standard for number of passengers for recreational vessels 20 feet (6 m) and over. The only USCG standard for vessels 20 feet and up is the commercial standard. And the amount of weight per passenger has been significantly increased. It was 160 lbs but due to the Ethan Allen accident in New York and the pontoon boat accident in Baltimore, it has been realized that 160 lbs is way too low. The last I heard 184 lbs was being discussed. But since I rarely deal with commercial vessels I am not sure. I did see a NVIC that said 174. Lbs so it needs some clarification.

    As far as other standards go, ABYC does not have a capacity standard for vessels 20 feet (6m) and up, and as far as I know neither does ABS. As far as I know all loading for larger vesselsis based on stability. If the the vessel can still pass a stabiltiy (actually an inclining experiment) test with a given load then it is ok.

    Citing only 170.50 was my feeble attempt to break it down to a simple formula that he could use without him having to read the entire CFR. As usual that makes it too simplistic.
     
  10. Ike
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    Ike Senior Member

    Oh yes, just an addendum; They do use a rather simplistic inclining test for those small vessels. They simply place weights to represent the passenger weight, on one side of the vessel. If it heels too far it fails. That is exactly what happened in the Ethan Allen case. All the passengers moved to one side and the boat capsized.
     
  11. Alik
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    Alik Senior Member

    I would use few approaches:

    - number of seats/standing place for passengers;

    - weight/freeboard considerations

    - stability considerations (offset load test); ISO12217-1 or maximim value of heel is 10 degrees (for passenger craft);
     

  12. Willallison
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    Willallison Senior Member

    Thanks guys
    The Australian Standard (that Landlubber referred to) uses the simple inclining experiment - in this case the maximum heel angle is 14 degrees, same as CFR that Ike kindly offered up, upon which it is no doubt based. The AS's scope is for vessels up to 15 metres long. Hence the original question.

    No doubt the (newer) ISO standards have more detailed and possibly more applicable information, but I don't have ready access to them yet, and was under the impression (confirmed by Paul, thanks) that the calculations would require far more information than I have available to me.

    In the first instance, I'll get some numbers based on the AS methods. In the end, I may have to contact the manufacturer and see what data they have...

    Thanks again to all....
     
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