Michael Daly wrote:
On 4-Jun-2004, Peter wrote:


A study done by David Jones (The Stability Of The Bicycle; Physics Today,
April 1970, 34-40) used a variety of modified bicycle designs to
determine the key elements in stability.


An earlier analysis of this stuff is in Timoshenko's book on Dynamics.
It is indeed centripetal and (D'Alembert) centrifugal forces that
provide stability to a bike. The degrees of freedom in a bike are
coupled - if you turn the front wheel to the left or right, the
bike leans a bit accordingly. This changes its direction which
generates a counteracting centrifugal righting force.

Sure, there are plenty of references that make the theoretical claim
that gyroscopic forces result in bicycle stability. But Jones tested
those claims with an experimental arrangement where the gyroscopic
effects were canceled out by using a second counter-rotating wheel next
to the regular wheel. The resulting bicycle was found to still be very
stable and easy to ride whether the second wheel was turning backwards
(no gyroscopic effects), forwards (double the effect), or stationary.
Bicycles are still stable even in the absence of gyroscopic effects.

The steering geometry was found to be more significant, especially the
amount of trail between where the steering axis hits the ground compared
to the position of the contact patch of the tire.


But I would expect the
movement to help rather than hinder stability. The upper part of the
bow curves outward and if this surface is brought into contact with the
water by leaning the boat then the forward movement of this curved
surface should tend to produce an additional righting force.


OTOH, the water flowing over the surface may generate a normal force.
Water flowing over the surface results in less pressure on that surface.
hat that does in the end depends on the orientation of that force
relative to other forces.

I've been told that longitudinal stability is enhanced with motion, but
I have no idea what it would do to rolling stability of a heeled craft.
It seems to be below my threshhold of awareness, regardless.

As I wrote before, I expect the effect to be small at the relatively low
speed of kayaks. But the heeled-over surface of the upper part of the
bow has the leading edge higher than the trailing edge and when pushed
forward through the water it will tend to push the water downwards which
requires a corresponding upward push on that part of the boat. This
force will provide a net torque helping to keep the boat upright.