single vs twin

[Mike_g]

Hi Guys,

Just a theoretical question:

If I have single engine set up, let say 23 ft monohull boat with 200hp engine and 22 inch prop and I would like to swap it into twin 200hp engines.

Should I put bigger proppellers?? Cause if I undestanding wright if I put two 22 inch props I will not go any faster.

Thanks for help and sorry if there was a topic like this

Mike

[Mark75H]

A light 23 ft mono should be able to go faster with double the power. It will go slightly faster with the same pitch because there will be more thrust even though it is possibly the same thrust velocity from the pitch - and the rpm of the motors will probably be able to be higher. To bring the motor rpm down to normal and take full advantage of the power increase you would need to use props with more pitch.

[Jeff_G]

In addition to what Sam said with two engines they are pushing half the weight and trying to overcome half the resistance. So all things being equal you would be able to turn much more pitch and possibly diameter as the engines are not working as hard as in a single.
But keep in mind the loss of efficiency, the additional weight etc, so in some boats the end result may be a wash.

[donmac]

I usually go up about 4''s of pitch as a starting point.