Huge anchor on the shore & a big spring balance?
Putting my serious hat back on, the hull weight is irrelevant to THRUST
- the thrust is entirely down to the blades interacting with the water. So you would need to know the shape of the blades, engine torque & power at a given RPM as a minimum to get a meaningful number.
Whether that thrust goes into moving the boat or water is a whole other set of equilibrium calcs.
You still get thrust if tied to the pontoon at the marina- the only difference between that & the boat zipping along at 20 odd knots is that when tied to a pier the warps are taking the strain & you are moving water with the available energy rather than the boat.
Hence my bollard & spring balance comment.