Actually the finger in my thought experiment was designed to simulate the propeller. I was visualizing the boat while motoring. Sorry I wasn't explicit.
The force while motoring is at the prop.
While sailing it is at the mast.
It is easier to visualize how tender the helm will be while motoring as the propulsive force is at the stern.
Less easy to visualize is when motoring with a fast current. Again the helm becomes very sloppy. But instead of tender it becomes sluggish.
I have experience this when running with the current through hell gate in nyc for example.
Last edited by davidpm; 05-20-2011 at 01:19 AM.