Force Created By Propeller

[DUCKHTNR]

I need to know how to calculate how much force is created by a given propeller/engine size, so I can figure out how much force will be put on the transom.

[nemo]

You should get the open water diagrams of your propeller. On the x-axis you have J=V/ND, where V is the speed (not exactly the speed of the boat, but near that), N is the rpm of the propeller, D is the diameter of the propeller. On the y-axis you can find the Kt curve, with Kt=T/pN^2D^4, where p(rho) is the water density, and T is the thrust given by the propeller. You can enter the diagram with the design speed. The only problem could be the N, but maybe you can get it if you know the gear reduction ratio. This is just an approximated method, but I think it coulb be enough to calculate the stresses on the transom.

[chares-haske]

When designing a transom, do you consider the twisting force (moment produced by prop distance from transom mount) or is sizing the transom for the forward thrust (based on the hp of the engine) enough?

[Stephen Ditmore]

To clarify - we're talking outboard engines?

[nemo]

Well I think DUCKHTNR was talking about outboards.. I've always done the inverse process, finding the optimal propeller and engine given the Resistance->Thrust, but I suppose what I said before could fit if all the data are available.
You should consider the moment produced by prop distance, I think that's what could lead the transom to failure.