I used Motocalc many years ago – about 2005 ish. It's primarily designed to calculate electrics/power/thrust etc for model airframes, but I managed to fudge it a bit to calculate thrust for model hovercraft. I didn't find it very useful for model boats. As Charles states, the list of equipment in the database is extensive. Users can input their own data, if their specific equipment isn't included in the Motocalc database.