Tuesday, March 25, 2008

More on launching instability

Oh, man. The idiot with the needle gun is out there on the rusty old Ranger again today, futilely hammering away. "Idiot! Idiot! You are accomplishing nothing except to drive me nuts!"
I'm going to go outside and scream at him.

(...three minutes later) Well, he couldn't hear me yelling, but I feel much anyway.

As I wrote yesterday, Cangarda's (ex Magedoma, ex Cangarda) near capsize is not unique in ship launching history, especially for long slender vessels like steam yachts. Here's an illustration from the London News in 1883 showing the capsize and sinking of the S/Y Daphne:

Not quite the same thing happened to the American S/Y Norma in 1884 as you can see from the Times archive:


It simply had too many passengers on deck. It wasn't a launching instability.

Back to Cangarda. Here is a the picture of forward moving dolly:

Note how it only supports the vessel at a single point on the bar keel. And wow, check out the tires:

Even more amazing, those were the good "road wheels", the mover changed them for even more threadbare launching wheels right before the launch.

To retrun to yesterday's theme, what does its launching instability say about Cangarda's ultimate seaworthiness? Basically, nothing. Here is a graph of its righting arm in its most adverse loading condition:

Cangarda has a great range of positive stability (> 90 degrees) but, compared to a modern motor yacht, a very little initial form stability. This means that it will be very subject to roll motion and have large roll response to relatively small waves, but is also pretty immune to full capsize due to the low center of gravity. The roll stabilizers (obviously, not original to the vessel), should give it a better ride.

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