[Paddlewise] Radius of Gyration

The radius of gyration is the distance k from the axis of rotation at which
a single point mass equal to the object's mass M would be put to have the
same moment of inertia I as the object.
Found this definition at http://www.unb.ca/web/physics/1040/torque.htm
I have just looked at a lot of warship pictures on the web and they range is
from reverse rake on some early 1900's battleships to near 45 degrees of
rake on some modern U.S. anti aircraft missile cruisers and over 45 degrees
of rake on some Russian ships. Way more rake still on one Russian aircraft
carrier. The majority had modest rakes of 75 to 60 degrees. Looks to me that
the ship designers haven't reached agreement on this issue yet either.
Couldn't find the Gerritsma research though (in less it was in one of his
research papers that SNAME's website wanted $30 for). I'm still betting that
he moved weight around to change the gyradius of the sailboat rather than
testing various rakes. I don't know but I'll bet he found that the lower the
gyradius for a given hull the faster it was through the waves. If I am right
it may be evidence to support the lift over the wave advocates rather than
the punch through the wave advocates as to which is faster into seas. I'm
betting on the "pitch as little as possible but at the same time don't let
water wash over the deck" compromise school of though on this one. So far I
have lacked much beyond subjective evidence and Sea Kayakers 1986 very
limited wave tank towing tests to back up my theoretical speculations. Even
if I'm proved wrong I have a lot of subjective personal evidence that a
compromise between the extremes is the most comfortable for me the paddler.


Matt Broze
http://www.marinerkayaks.com

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