Prop Help

[awe1979]

I have a 1996 cajun fish and ski. It has a 1995 Johnson V4 Cross flow 90 hp on it. I installed a jack plate and new tac per advice i got here. It has a 15 pitch alum. prop on it now. I test drove sunday and got 5500 rpms before having cavation. I had my fishing gear loaded in the boat and 2 people. Before the jack plate I could only get 5200 rpms. I jacked it up untill I just started to loose water pressure then back down 1/2 inch. Do I need to go with a 13 pitch prop. I want to buy a s/s prop. And yes the compression is good and yes the carbs open up all the way. Its a heavy boat. Its not a bass boat its a pretty deep V in the front and kind of flatens out in the back.

 

[steelespike]

Re: Prop Help

"Cavitation"I assume you mean ventilation.prop loses grip,What size boat?I would think you could stay with a 15 inch pitch.A stainless
should allow you to get to max rpm without ventilation.13 sounds extreme
to me.

 

[awe1979]

Re: Prop Help

17 Foot fish and ski. It starts to loose grip with with the water at more that 5500 rpms. Thats just less that 1/2 on the trim guage.

 

[steelespike]

Re: Prop Help

Like I suggested a stainless should improve the venting problem.It should also improve your speed.What is your speed at max rpm?

 

[awe1979]

Re: Prop Help

I dont have gps so I am not sure of the exact top speed. What kind of ss prop do you think?

 

[awe1979]

Re: Prop Help

Doesent a ss prop drop rpms?

 

[awe1979]

Re: Prop Help

Walleyehed any ideas on which style prop?

 

[steelespike]

Re: Prop Help

Doesent a ss prop drop rpms?

A stainless can reduce rpm but you are presently venting at 5,500 with ,it appears ,an ability to go beyond.With a stainless you should be able to push beyond that rpm/speed limitation making the same rpm and probably more speed.I only have specs for 89 90hp which are rated at 5,000 rpm. I would think 5,500 with a medium load and stainless prop would be a reasonable
expectation.

 

[awe1979]

Re: Prop Help

What brand or style of ss prop do you think would be best??

 

[steelespike]

Re: Prop Help

What brand or style of ss prop do you think would be best??

I can't help you with specifics but you don't need anything exotic just a stainless in the demensions you have now.

 

[walleyehed]

Re: Prop Help

In theory a stainless would drop rpm, but let's look at it this way....with a "good" quality SS prop, such as a Stiletto, possibly even a Turbo, we will be getting more over-all lift, #1. With that additional lift we have less area of the boat touching the water, so we have less drag. This alone, may be enough to pick up speed which lifts even more, and in most cases on this style of boat, it'll be enough to see an RPM increase.
This lower unit has just the holes for water pick-up, doesn't it?

 

[awe1979]

Re: Prop Help

Thanks walleyehed. I think it only has the screen on the lower unit that picks up water. In the nex few weeks I am going to order the ss prop. So the stiletto is the best choice correct? Thats kind of what I was thinking but I dont know much about props. I have a 13x15 pitch on now so I should get a 13x15 stiletto? When I first got the boat it had a 14x17 pitch which everyone was calling the long blade omc prop. Is a longer blade better?

 

[Dhadley]

Re: Prop Help

Blade design varies a lot but for this particular application I'd suggest looking for a Rake or even better yet a Turbo Lightning Jr. Both will have excellent bow lift which should help a Cajun and a little extra diameter which allows for the higher X dimension.

What rpm / speed were you turning with the 14 x 17?

 

[awe1979]

Re: Prop Help

4900 RPMS if I can think back that far. But I could trim it all the way out and never ventalate. Thats with out the jack plate. I could even go into the lift part of the trim a little and still not loose grip with the water. I dont have gps but the speedo always read 38. It might of hit 5100 once or twice on clam water. I still need to try and shoot for 5800 rpms right? I have got 5500 now and thats all she will do. DHADLEY what is your ideas on the prop pitch and size.