prop selection

[dixieskiboat]

i have a dixie 190 ski boat around 18 feet with a yamaha 200 pro v on it. i have tried a 14 7/8 x 21 on it and top speed was around 60mph at 6200rpm(too many rpms i know). i then tried a 14 1/4 x 26 and top speed was 60mph at 5800 rpms per gps on both speed checks. seem to be having some cavitation problems with both props but more so with the 26 pitch prop(26 pitch prop is brand new wouldnt think it would be slipping). i cant seem to trim up hardly any from 2500 to 4500 rpms(running) without motor appearing to cavitate.by cavitation i mean motors revs and speed slows some dosent catch back until trimmed back all the way down. 21 pitch is mostly bad when turning. antiventilation plate appears to be bout 3 inches above bottom of boat. also if i put a fixed jack plate on the boat pushing the motor an extra 6 to 8 inches further back off the back of boat will this help overall speed. stumped. i have a buddy with same boat,motor, and 14 1/4 x 26 prop and it will run darn near the 70 mph mark and i have ran his boat at that speed. the only noticeable difference is his motor ventilation plate is even with bottom of boat. but i though the higher the motor out of water the faster? im stumped please help.

 

[hwsiii]

Re: prop selection

dixieskiboat, , You might try reading this for a better understanding of changing props for better performance, and for the major differences between aluminum props and stainless steel.

http://forums.iboats.com/showthread.php?t=369057

Try reading this and get back with me and let's see what we can do.



H

 

[dixieskiboat]

Re: prop selection

Thanks that was some good info so i guess rpm's dont mean squat if the prop isnt in the water like it should be. I believe i am gonna put a fixed position jack plate on the boat it will be easier to micro adjust the ventialation plate to the bottom of the boat. I see no reason for this boat not to run in the mid to upper 60's like my friends. I have just yet to squeeze it out of the boat . Any advice would be greatly appreciated.

 

[hwsiii]

Re: prop selection

Dixie, your problem is VENTILATION not cavitation, try lowering your prop by 1 bolt hole first and see if you can't trim the motor out more with less prop slip and more speed.



H