[Paddlewise] turning

PeterO wrote:

>
> But its not at all clear or intuitive why different boats may turn in one
> direction or another when edged on one side only? And I doubt that I'm
alone
> in not understanding this even qualitatively.
>
> I'ld be very appreciative of an explanation or a reference! Are there any
> standard texts that treat this subject?
>

This has to do with the  unbalanced forces around the center of gravity. As
the boat heels the under water hull changes shape. How it changes shape
determines the direction of turning. I know of no easy and simple way to
predetermine this since it involves many variables. For example, lifting
forces, drag forces, and shifts in the center of gravity. The math gets
pretty complex. If you are really keen on this kind of thing I suggest
starting with Principles of Naval Architecture published by the Society of
Naval Architects and Marine Engineers. You need only purchase the volume on
Controllability (Vol #2 I think. I am at work and do not have it handy to
check that) It has a list of technical papers dealing with specific
problems. You will have to do some mental gymnastics with all of this since
the research focussed on ships and sailboats. The principles remain
consistent though so if you can manage the math you should find the rest
understandable.

I found the sailboat stuff most valuable since controllability when heeled
means so much in sailing. Many theories about this have surfaced over the
years. One famous one, the Metacentric Shelf Theory actually produced boats
with excellent course stability over a wide range of conditions. The Colin
Archer type cruising boats were designed using this theory I think. Later
research proved that they worked for other reasons so it looks like you can
do the right thing for the wrong reasons. :)

It also turned out you could produce boats with poor directional stability
using the
Metacentric Shelf Theory.

You can test this kind of thing best in a tank where you can easily measure
the forces involved in a controlled setting. Not sure you can do it reliably
in real life.

Cheers,

John Winters


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