In Norway, engine has to be less than 10 HP or else the children won't be allowed to use it. So we have a 9.9 HK engine (in reality it's a 15 HK engine).

Oh, the rules also states that the boat should not be able to go faster than 10 knots. I think ordinary march speed on the dhingy is 20 knots. Details, details ...

Our david is dimensioned for lifting a simple rubber boat without engine. I believe it's physically possible to lift up the RIB with it, but some few small waves and the whole thing will be destroyed, hence we always tow the RIB.