The speed thingy is quite easily explained. It's basicly vector velocity.
Assuming the true straight ahead course is the Y-axis, and LHS is the negetive X-axis, and the RHS is positive X-axis.
As the boat is travelling at the direction (dictated) by the ob (in this case slightly to the right, say 10 degree). The boat is travelling at 100% (presuming no energy lose to friction etc) of the output, in the direction of 10 degree. Say
However, if Jim wants to stay on the [true] course, he has to compensate it with a counter balancing force along the -ve X-axis. Resulting with a slightly less the 100% of output, probably around 92%. Hence the drop in speed.