prop problems??

[hammer250v8]

here's the scoop...<br /> with my 4 blade 13.75 diameter 25 pich power tech i am turning 6100rpm's at full trim. after consulting power tech they recommended a new 4 blade to bring my rpm's up to 6700. they sent me a 14.25 diameter 23 pitch. with the new prop i can only turn 5100 rpm. what gives? just want an opinion before i send the prop back in exchange for somthing else. thanks...james

 

[tscott]

Re: prop problems??

Well, the way it typically works is for every 1" of pitch you add, subtract 200 rpms. For every 1" of pitch you subtract, add 200 rpms. So, 6100 rpms and they want you to have 6700 rpms so you would need to go down in pitch to about a 23. That is right but this is based on the same diameter prop.<br />They changed the diameter so I'm not entirely certain what difference that will make. Call the prop shop and tell them what happened. It may just be the diameter. That does make a difference.

 

[Jack Shellac]

Re: prop problems??

I wouldn't have thought that a 1/2" increase in diameter would have offset a 2" drop in pitch that much. It could be the cupping on the prop, but it's obviously not the right prop for your motor and boat. A discussion with the shop should get you headed in the right direction. Props are tricky and don't always perform how you think they will.