[Alberg30] Sally Ship

[Robert Kirk]

George Dinwiddie wrote:
>Gordon LACO wrote:
>>Okay boys - here we go...
>>"Careening" a vessel is heaving it down on its side by use of tackle to the
>>mast(s) or by beaching it and letting it lay down on its side as the tide
>>goes out.   The various gear shown in the picture is preventing careening.
>
>OK, Gord.  Well what do you call this?

Well, it ain't exactly careening, but related in a way is the old nautical 
term, Sallying Ship. Every ship, aircraft carrier or Alberg, has its own 
natural period like a pendulum. The period doesn't change unless you add 
weight aloft -  like lengthening a pendulum. Anyway, the period can be 
related to the ship's metacentric height and thus it's stability. When a 
warship is built they go to great lengths to calculate its stability, but 
of course that changes over the years as new gear is added.

One time when I was damage control officer on a destroyer I persuaded the 
skipper to let us "sally ship". While at a mooring the crew all stood on 
one side of the ship. We blew a whistle and everyone ran to the other side. 
We kept doing this back & forth, getting the whistle timing in sync with 
the tiny roll we generated. Like a kid on a swing. The roll became pretty 
noticeable after a while. Everyone had a great time and you could hear the 
cheering all over the San Diego anchorage. (See the related term, "Chinese 
Fire Drill.")

As I recall, the period was 13 seconds which translated to the old girl 
still having pretty good stability. The longer (slower) the period, the 
more unstable a given ship is for its size. (Obviously, if it doesn't come 
back up the period is infinite. But that's another problem.)

I wonder what an Alberg's period is? Much shorter, of course. Maybe at the 
next raftup we can have a contest. The shortest period boat has the least 
weight aloft.

Bob Kirk
Isobar #181


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