ACrooks69

Well I finally got some bugs worked out of my 383 yesterday and the new top speed went from 73 to 76 MPH. I feel the speed is now being limitied by the lifting characteristics of the prop/boat combination. The boat begins to chine walk / bounce at 73 and get a little more violent at 75-76. I assume this is because none of the boat is in the water. My RPMs are now running around 53-5400 and I would like to cut it down a bit so I was thinking of jumping to a 23 tempest from the 21 tempest I currently have. Are the lifting characteristics of props magnified by the RPM or will the increased pitch at the lower RPM have the same effect as the smaller prop at the higher RPM? I'm hoping the 23 Tempest will spin at a lower RPM and the prop won't lift the boat so high out of the water. It would be nice if I could find a 1 or 2 inch shorter Alpha drive but I bet those are far and few. Other info that may be helpful: 1991 SeaRay 185BR 20'2" 2400lbs dry, Alpha 1 Gen 2 with nosecone, 383 chevy~440HP.
I use to have a 21 Mirage on the boat before it went over 70, at that point that prop would lift the boat to high out of the water also. After a number of props tested, I have found the Tempest is the fastest, But I don't have access to every prop manufacturer. Can anybody here suggest a prop that won't lift the boat so high out of the water but still retain my speed? I do have a 21 cleaver and 23 cleaver (QSS). The 21 was slower and pulled close to 6000 RPM, the 23 would start to blow out so I don't know why that would be. I may try the 23 again since the boat is running better now. It may have been a prop venting issue. Would a Chopper prop have any benefit in my application.

ACrooks69

Anybody?

throttleup

A higher pitch prop will have more stern lift than a lower pitch prop. So a lower pitch prop spinning at a higher rpm will have less stern lift than the higher pitch prop at a lower rpm.

The chine walking is likely casued by the bow lift of the Tempest. The Mirage is also a bow lifting prop. Either changing the characteristics of the tempest or going to a prop with less bow lift, like a four blade should reduce or eliminate the chine walk.

Older boats without steps typically need the bow lift for speed. Newer boats with steps carry the bow naturally and can use stern lifting props and hgih drive heights to obtain higher speeds.

Matt

ACrooks69

Hmm. I didn't realize a four bladed prop would reduce bow lift. I would tend to think it would raise it. But I have never tried one so I guess I have no basis for thinking there. Would a Bravo 1 prop be a good candidate for trying? Any other suggestions of off brands out there? If I try a Bravo 1 should I stay with a 21" pitch and expect some RPM drop with the fourth blade, or should I step up to a 23? Also, larger diameter props tend to produce more lift correct? Do you think a prop with a smaller Diameter than the Tempest (I think is 14 1/4) would help? Anyway thanks for the info Throttle Up.