Wednesday, December 28, 2011

About that Assumed Average Weight Per Person thing

Updated below ...

There has been a lot of mirth about the US Coast Guard regulation requiring passenger vessels to alter stability calculations in relation to the "Assumed Average Weight Per Person".

Effective 1 December 2011, the Assumed Average Weight Per Person was increased from 160 lbs. to 185 lbs. The impact on US flagged passenger vessels is significant, particularly smaller types. In Washington State the ferry system declared that (rather than weigh every passenger) they would be reducing their passenger capacity to stay within the stability criteria established for each ship. (I'm not sure about the heeling moment that would occur in a ship like the Puyallup if everyone ran to one side).

It's not just Americans

In fact, during the notification phase the USCG received several submissions. At least two recommended that the AAWPP be increased to 187 lbs., the actual average weight of American adults.

Before anyone starts pointing too quickly at the population of the US there should be some heed paid to decisions by the International Maritime Organization's Maritime Safety Committee. The MSC made amendments to the International Life Saving Appliances code taking effect in October 2010 and then again to take effect 1 January 2012.

Under international rules the former average assumed weight of occupants of lifeboats, liferafts and rescue boats was 75 kg (165 lbs). Effective Oct 2010 the new assumed average weight of all persons, worldwide, getting into a lifeboat became 82.5 kg (182 lbs). As of 1 January 2012 the new mass of 82.5 kg per person applies to all survival craft, worldwide.

Looks like we're all getting fatter.

Good question:  From Christina, in comments, about life jackets and whether there have been any changes to match the changes in survival craft. The answer is, YES. Go here for details.

New requirements for the carriage of additional equipment, also effective July 1, 2010,
have been introduced under the SOLAS Convention, as follows:

•     On all ships where adult lifejackets are not designed to fit persons weighing up to 140 kg with a chest girth of up to 1,750 mm, suitable accessories are to be provided that allow the lifejacket to be secured to such persons.
•     All passenger ships are to be provided with lifejackets for “infants”.
Update 30/12: The infant lifejacket requirement noted above prompted an offline question: How many?
The answer is as follows:
1. For vessels on voyages under 24 hours: 2.5 percent of the total passengers.
2. For vessels on voyages of 24 hours or greater: An approved "infant" lifejacket for every infant onboard.
Infant lifejackets should be marked INFANT.


Christina Montgomery said...

So if it's all lifesaving appliances, and they've downsized the capacity of lifeboats in sone places as a response, has there been any consideration of lifejackets? I'm assuming that things like chutes are built to carry bigger people already, and that you still go down them one at a time, so that doesn't matter.
I'm just off to look up the info on lifejackets, but I thought maybe you would know something about whether they've changed at all, regulation-wise, as average weights go up. Does the Newton rating requirement change, or do the jackets have to be physically bigger, longer crotch straps, stuff like?

Christina Montgomery said...

Sorry, I meant in "some" places. Poor typing.

tidalstation said...

Good question, Christina, (as I would expect).

I've answered it in the update above. Many thanks for bringing it forward.

Christina Montgomery said...

Thanks, Mr. Station (Ms Station? Station Nation?)
That's pretty interesting then, the idea of a jacket that has to fit a chest of up to 1750 mm -- that's almost 69 inches.
I wonder what the "accessories" you use for people past that look like, and if you keep some jackets ready with them pre-attached, or if you try to do all that as the emergency or evacuation is under way.
Wow. Interesting times.
I've been searching around trying to find out if there's a weight limit on people you can toss into an emergency chute. Can't find anything yet.

tidalstation said...

Hmmm... Mr. Station, I suppose. Well seasoned master mariner, still running 56,000 tons of passenger vessel from time to time.

"Attachments" can be anything from a custom designed device to a piece of line and a picture of sheet bends. That's the problem with MSC resolutions - you could drive a VLCC through the loopholes.