"Well, you could get an idea b
"Well, you could get an idea by working backward again. If 1 horsepower is equal to 58 pounds of thrust, then to get the equavalent of 115 shp you would require 6670 pounds of thrust to move the object forward at the same speed over the specified length.
But that is in no way accurate, because it doesn't go from 0 to 115 horse instantly and the thrust calculation factors in the "speed over distance" with "x" pounds of force (energy) required to push the object in the direction of travel for a given distance in a specific amount of time.
Plus, initally, the torque band of the motor is significantly higher than the horsepower band, so I would suspect that "more" thrust is actually applied at lower rpms/lower horsepower (with greater stresses on the transom while it is trying to get to boat on plane) and it will drop off as momentum assists in moving the boat forward and the hull lifts from displacement, through semi-displacement up to full plane with minimal drag compared to the other conditions - which is where the torque curve which had been moving upwards starts falling and crosses the horsepower curve on it's way up to maximum.
To accurately determine "how much thrust is being applied against the transom", you would need to take numerous test measurements, figuring the time and distance covered from a dead stop in the water, over various fixed distances both into and away from the wind, waves etc. Going with the wind less horsepower would result in greater thrust and vice versa.
That would most likely lead to conclusions such as - with the wind 1 hp = 45 pounds of thrust - into the wind and waves 1 hp = 75 pounds of thrust.
And technically, a jet sitting on a taxi way with it's brakes locked whose engines are putting out 35,000 pounds of thrust in anticipation of take off, are producing "ZERO" horsepower because there is no movement over time to calculate.
I am currently working on a build of a glass over plywood boat that will have a 140 mounted on it. The best advice that I got for the transom was "build it twice as strong as the original spec, and if you think that's overbuilding it, make it even stronger, just to be sure"
Now my brain hurts so I'm going to leave this thread for a while
"