[Alberg30] Sally Ship

[Robert Kirk]

Amy & David Swanson wrote:

>I wraote a paper for a history a couple of years ago about a 17th century
>Swedish warship called the Vasa, which sank on its maiden voyage.  The ship
>was top heavy, and when the first gust of wind hit her, over she went.
>
>Anway, one interesting thing I learned was that the standard test for
>stability back then was to have 100 men run back and fourth across theship
>three times.  The test was cancelled after one round on the Vasa because it
>appeared it would capsize.  I am amazed to hear that modern warships undergo
>testing thesame way.

Sorry if I gave the impression that sallying ship was a standard operation 
with modern warships. It's a perfectly legitimate way of estimating your 
metacentric height (stability) with a straightforward equation, but as far 
as I know, it's not generally done anymore. I did it more for 
the  challenge and with the blessing of an impish skipper.

The usual stability measurement is called an "inclining experiment" and 
generally done only on the first ship of a class to get a baseline. 
Sometimes it's done after an extensive overhaul with lots of gear replaced, 
but not always, if time & money are short. Naval ships are held to a pretty 
strict "class rule" where you can't make alterations without the direction 
of the Bureau of Ships (called a SHIPALT) and you have to report back to 
them when it's done. There's a little lady in the basement of the Bureau 
who keeps a spreadsheet on each ship and records the changes and calculates 
its new stability values after each change and warns the Admiral if a ship 
is approaching its minimum stability.

The inclining experiment is done much like Gordon's description about HMS 
Tecumseth. In the Navy's case  they substitute massive multi-ton weights 
instead of weighing a bunch of sailors, but the principle's the 
same.  Which makes me wonder how or if they do an inclining experiment with 
an aircraft carrier. They'd need a couple of thousand tons of weights. 
Maybe they do something else?

Bob Kirk
Isobar #181


 +---------------------------------------------------------------+
 |                This Old Boat by Don Casey                     |
 | http://www.amazon.com/exec/obidos/ASIN/0071579931/alberg30-20 |
 +---------------------------------------------------------------+

Public-list mailing list -- Public-list at alberg30.org
http://www.alberg30.org/mailman/listinfo/public-list
To unsubscribe: email to Public-list-request at alberg30.org
Include command "unsubscribe <password>" in subject or body.
Use command "help" for more options.

 1055182841.0