Help with propeller choice?
 

A friend of mine has a 28 Profile cat that I need help with the boat ran 106 @ 5900 with a 34 bravo so we bought a 36 bravo the boat run 100 @ 5000 it has a 1.5 Imco Sc on a 3" rise stand off box why such an extreme change in rpm with just 2" of pitch if I changed the drive ratio would the boat run faster if I stepped back on the pitch say 32 bravo or is there another prop that might work better?
Thanks for your help!
EWB

I'm no expert, just an armchair gearhead.

but at that speed and rpm range, could it be the cam is "peaky" to pull 5900 rpm. there may be too much drag at 100mph to not allow the engine to pull past 5000 rpm. look at the power curve.
maybe labbing the 36 or cupping the 34 or smaller dia on the 36 are options.
check the prop slip to see where they are at

ask the experts directly ( houston prop, throttle up, etc)

When I checked the prop slip on Bams web site it is almost 20% with the 34 maybe one of the experts will chime in.
Thanks Rambunctious
EWB

were is this Bams web site?

thanks

is he having trouble getting the boat on plane? your drive might be to high? going with the gear change and a 30 are 32 prop might be a good choice, also what kind of H.P is his engine making?

rpm difference
 

were all the props stock and out of the box,This is a large variance between the two sets,just wondering if they are or has a set been altered?Darin

Called Herring said he would make a 32 six blade and should put my slip around 4 to 7% if It will turn it may be that will put it over 110.
Thanks Guys.
EWB

Do you know what the peak horsepower is on the motor and at what RPM? My motor makes peak power at 6,400 RPM and I have a 1.3 gear ratio. I could only turn the motor to about 6,000 with a lab 34 four blade but when I put on the lab 32 four blade, it increased the RPM to 6,300 and I picked up several mph. Knowing what RPM the motor makes peak power is very important to answering this question.

Good luck, R/R