Time for a new prop and properly sized......

[CAPTKEV85]

1985 sea ray seville 25 foot cuddy cabin with 260 merc 5.7 4bbl rochester. On the boat right now is a 14.5x17 3 blade michigan prop reman from previous owner. Well I ran a ground hard and tore up the prop. Now I want to buy a new prop with more speed because I feel the boat can do more. At 3000 rpms shes on plane but at 18mph. WOT is like 4650 which is to high to a 350 small block I think book says 4400rpms. top end is 27 mph. I also recently fixed my trim tabs so boat is out of the water more but did not notice and speed increase. Any ideas on new dia and pitch... The boat seems to rev high when im planing like im cavitating or something. Also I'm looking at a new prop that is in the market. Here is the site. http://www.turningpointpropellers.com/ Thanks everone.

 

[craze1cars]

Re: Time for a new prop and properly sized......

I think one of your figures is way off...possibly indicating a problem other than the prop. I'm not sure which of your data is inaccurate.

Do you know your outdrive ratio? It's important for accurate calculations.

If you think you're ventillating (sucking air into the prop), then raising the motor yet higher out of the water using trim tabs will make it even worse. So if you're indeed ventillating, you have inaccuarate top RPM data and your prop is not responding like a 17 normally would because of extreme slip....

Are you ableo to trim down by raising tabs and lowering your power trim until the ventillation stops?

 

[CAPTKEV85]

Re: Time for a new prop and properly sized......

Ok well you were right on numbers. I brought out my actron rpm reader and the original tach is way off. I just bought a faria and it matches the tester. So now the WOT on the motor is 4200 with motor trimmed down with out ventillating. Max speed is around 26 mph. Also retested planning off with drive down and no cavatation at all. So With the new test it seems the rpms are different and going with the trim down and playing with the trim tabs there is no more ventallating. Now I still want to get more mph's but is this possible? Will a 4 blade perform better?

 

[Tail_Gunner]

Re: Time for a new prop and properly sized......

Ok well you were right on numbers. I brought out my actron rpm reader and the original tach is way off. I just bought a faria and it matches the tester. So now the WOT on the motor is 4200 with motor trimmed down with out ventillating. Max speed is around 26 mph. Also retested planning off with drive down and no cavatation at all. So With the new test it seems the rpms are different and going with the trim down and playing with the trim tabs there is no more ventallating. Now I still want to get more mph's but is this possible? Will a 4 blade perform better?

Yes larger boats do well with big eared pusher props....Solas amita fills the nitch along with a michigan wheel reviewed in Walleyhed's prop review above...Sounds like a 15 pitch 4 blade would do you well.