How to Select Prop for Alumaweld Blackhawk 202 with 115hp merc

[randydb]

Hi,
We recently purchased an Alumaweld Blackhawk 202 with a 2006 115 hp EFI 4 stroke merc.

Our old boat was 18ft and had 150hp on it so it got up fast and went well regardless of the prop pitch.

The Alumaweld came with a 15P prop on the motor and there is a 17P prop spare. The previous owner said something about not being able to get high enough rpm with the 17P prop with wide open throttle. Is it true that it is hard on the motor if it isn't able to rev high enough?

I also understand that the 17p prop won't get us out of the water quite as quick but will get us more speed. Right now with the boat running at 4800rpm the 15p prop pushes us at about 26 miles per hour.

So how do I know if the 17P prop is too much for the motor/boat? What rpm should the motor be at WOT with the 17?
I'm not even sure what questions I should be asking here. All input would be great.
Thanks.

 

[Scott Danforth]

Yes, lugging a motor will kill it

What is the WOT RPM listed for your motor?

 

[randydb]

https://www.kirschbaum.at/ki_prop/pdf/2015/RPM%20Chart.pdf

According to this chart 2006 Merc 115 hp EFI should run 5000-6000 rpm WOT.
So basically as long as I reach 5000 rpm or better WOT the prop is fine. Right?

 

[Scott Danforth]

I would shoot for 5500 myself

 

[randydb]

Scott, please explain why to shoot for 5500? Just to be on the safe side?

Our 2004 150hp merc had over 1700 hrs on it and was still running well when we sold the boat. It needed the odd repair over the years, but generally was a great reliable motor. We'd love this motor to do the same.