On Mon, 30 May 2005 11:49:12 -0400, ted williams wrote:

[bw]
There is in fact a formula which relates thrust to horse-power and
water speed.
Simply put: thrust in lb. =
( power in watts / speed through water in MPH )
X 0.1 scaling constant

[tw]
You are 100% correct in the theoretical thrust relative to speed.

///
Using your example, at a thrust which produces 37 lbs at 1 MPH could be
easily overcome by a modest breeze against the surface of the vessel that
produced more than the 37 lbs of force provided by the motor.

If the net effect of the breeze against the vessel surface produced 74 lbs,
the vessel would travel backward at 1 MPH.
Regards,
Ted

Hmmmm... the formula gives a value for thrust, given some water speed
and input power.

What it DOESN'T give, is a value for boat speed given thrust at a
given input power.
That would need knowledge of air drag and hull drag which do not
enter here.

However, if you could find the drag at given hull speeds, e.g by
towing the hull and measuring the force required, THEN you could
say how much thrust would be needed ( = drag) at that speed and hence
what power would be needed at that speed, ignoring the losses I
mentioned earlier.

Sincerely

Brian Whatcott