If you have a left hand and a right hand propeller
then you will need to reverse one of the motors.
As for propellers
I think that at the and of the day you will have to experiment to find out what suits your needs as you must remember that you are dealing with scale models
and that the water it is on is not at the same scale.
A 2-blade propeller
produces two pressure pulses per revolution, whereas a 3-blade propeller
will produce three smaller pulses per revolution for the same amount of total thrust. As a result, the 3-blade prop will be inherently smoother and therefore quieter.
A 4-blade propeller
can improve all those characteristics that make for practical, all-around boat performance.
Four-blade props usually have a lower pitch to keep the rpms the same as a 3-blade.
But are 4-Blades Slow?
So, why might a 4-blade generally be slower than its 3-blade counterpart? To be honest, many 3-blade/4-blade speed comparisons are simply not fair. That’s because the respective propellers
in question are simply different styles, designed with different purposes in mind—different diameters, rakes, cupping, and blade shapes.
If however, for comparison purposes, we take two propellers
, identical in design (blade shape, diameter, rake, cup, etc.) that are appropriate for a given application, and simply add a propeller
blade, we get a truer representation of just where the difference lies.
The addition of the extra blade causes increased drag, which, in turn, requires more horsepower, in order to achieve the same rpm. Since the horsepower is limited, the rpms drop, and the speed will tend to drop with it. This is why, when going from a 3-blade to a 4-blade, the pitch is dropped an inch, or more, in order to keep rpm parity. It is this difference in pitch that causes any potential speed differentials between the 3-blade and the 4.
I don't know if this will help you but this is a complex subject and you could get your self totally bogged down with all of the theory.