What size prop should I be using on a Mercury 200 2 stroke?

[93Robalo]

I currently have 21p's on my twin Mercury 200's (they came with the motors) however I only get around 2100 RPM's at full throttle under load and boat will NOT get on plane. Are props too big? Any suggestions? Boat is 2320 Robalo. Thanks

 

[steelespike]

Re: What size prop should I be using on a Mercury 200 2 stroke?

I would think that 400 hp would produce planing speeds on a 23 ft boat.
In fact I think it would plane on one motor.
We need the info requested in "read this first" at the top of the forum.
I would try one motor at a time.I wonder if some component that affects both motors
is defective or set wrong.