Sunday, July 15, 2012

Yacht certified? Whats that mean?

When I read about the 34' Silverton with 27 souls on board that capsized, my initial reaction was "Clown car". I mean where could you put all of these people on a boat of this size, and what was the boat's rated capacity? It turns out there is no rated capacity for passengers on this vessel. It falls generically into the category of "Yacht Certified", if it was certified at all.


Power boats up to 20' in length are legally mandated to have a permanent label indicating maximum horse power, and passenger capacity. Larger recreational vessels, 26' and up typically fall into the "Yacht Certified" category, or not certified at all.

The "Yacht Certified" label is bestowed upon a vessel by the NMMA (National Marine Manufacturing Association) because it complies with all applicable ABYC (American Boat and Yacht Council) standards. This is an extensive list, but for vessels over 26' in length, but there are no standards related to capacity or stability, and I asked the NMMA to verify this. The USCG also has a lot regulations regarding passenger capacity, and stability, but recreational vessels over 26' in length are excluded from compliance. It seems to me there is a hole in the system that the 34' Silverton disappeared into.

Lets take a quick look at the numbers. 17 adults at 180 lbs equals 3060 lbs. 10 children at 90 lbs equals 900 lbs. 250 lbs of gasoline (full tanks) equals about 1500 lbs. 40 gallons of water (full tank) equal 340 lbs. The holding tank full weighs 150 lbs. The boat's dry weight is 12,500 lbs. If the tanks are full you have 1990 lbs at or near the waterline, and you have movable loads of 3960 lbs.

This is where it gets complicated. I think that the movable load, if properly distributed wouldn't have been as dangerous if properly placed. I think that a much smaller movable load improperly placed could be very dangerous. The question is what information does the captain have about the vessels actual passenger capacity, and stability? The answer is all too often close to zero. There are no rules that are usable, other than your instincts. If the tanks near the water line were nearly empty, does that mean you can increase the loads, or decrease the loads? If you have four people sitting on the flybridge, does that change the equation? The owners manual for most vessels is mute on the subject.

If you own a Cessna 182 aircraft, the manual tells you exactly what loads have to go where, and how much is load is allowed to insure proper balance and center of gravity in flight. Why is there so little information available to the owner of a powerboat? I'm pretty sure had the captain had some capacity/stability information available about this boat, it would have been followed. Some manufacturers do provide some general guidelines, but a lot don't.

In the end, I think manufacturers need to do a far better job of advising boat owners what the weight/load/placement limits are for their vessel. After all they design and build them. I'm not going to be an arm chair captain on what happened in this case. There are way too many variables here that are unknown. Was the boat taking on water? What were the sea conditions at the time? Were the actual loads too great, or in the wrong place? The list is endless, and in the end the experts will figure it out, and we will all learn something from it. But I don't like the fact that for most, there is no information available other than guessing, and this seems to be a shame. 


The photo I used is mine, and is not the vessel discussed.


3 comments:

  1. Has anyone determined if there was a capacity label for the flybridge and if it was exceeded? A much smaller movable load when extended away from the center of gravity will easily roll a vessel, especially if it becomes laterally destabilized (vessel abruptly changes direction, takes a wave abeam, etc.) Our Sea Ray 370 AC has a label that clearly states no more the 850 lbs total (people, gear, etc.) are to be on the flybridge when the vessel is underway.

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  2. Sam, to the best of my knowledge there was no capacity plate for the 1984 Silverton, or information in the owners manual either. In later years, the redesigned 34' Silverton version had a recommendation of not more than 15 persons, but no reference to bridge loading. Searay, Tiara, and a few others do provide capacity plates, and or information regarding capacity loading in the owners manual. I didn't want to analyse the reason for the accident, but instead used it as a focal point to talk about the lack of information about vessel capacity/stability that is available to most owners. You're right about bridge loading, and I talked a bit before about high center of gravity implications on boats, and moment loading. I just used simple calculations to illustrate the point, and did not included the considerable impact inertia can have. Thanks, Bill

    http://themarineinstallersrant.blogspot.com/2011/08/steps-and-second-steering-stations-on.html

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  3. If anything, it seems the USCG should have something on this. This overloading incident sounds like "lack proper vessel knowledge and operating skills" which ABYC and NMMA don't really deal with.

    Perhaps the "hole" is in the secondary education system. Anyone who completes high school physics should think twice about loading up a 34 foot boat with 27 people.

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