This is the biggest '**?**' for me, and I suspect many others.

Assuming the propellor size is in keeping with a scale displacement model, is there a **rough** guide to (brushed) watts per kilo displacement to attain a scale speed?

When I've tried to calculate it, I get weird numbers. More experienced builders might just chuck in a motor(s) knowing they'll be 'enough'.

Andy

When doing a scale model, it helps to know the real things horsepower. Converting to watts and dividing by the cube of the scale, then doubling the result to allow for the difference between power out (real) and power in (model) works well. Once you know the power, since you know the battery voltage, you can get the amps for the ESC.*

There can't be a formula linking weight to power required because all boats doing different jobs have different requirements. The differing hull shapes in the water don't help, either.

*e.g. a 1/350 battleship, 100000 horsepower. 100000*745 = 74500000 watts. 350 cubed = 42875000. power/scale cubed = 1.74 watts. Double that, 3.6 watts. 2S Lipo, divide watts by volts, 7.4/3.6 gives 2 and a bit amps. Provided it has a reasonable prop, the battleship will look right when going along. Any extra power is a valuable "get out of jail" card.