New prop cavitating during hole shot

[tony_cliffy]

I am still tring different props to try and find the "right one" to stick with. This is for my 2004 Johnson 115HP 4-stroke that has a "5000-6000" WOT range. Johnson techs said get it to 6000 RPM for WOT. Boat is a 20' semi-V Crestliner utility boat. Basically a large aluminum center console.<br /><br />orig. prop - 14x19, redline+, speed unknown<br />Old prop - 14x23, 5500 WOT, 43 MPH<br />new prop - 13.25x21, 6300+, 39 MPH at 6000 (but went to 6300+ which was not desired)<br /><br />This new prop is a Turning Point aluminum prop for my engine. I am surprised it added so many RPMs to my engine and I actually had to hold back when I saw I was getting to 6300 RPM's. It also was much slower across the board. My main problem is it was cavitating at lower RPM's when I tried to accelerate. The 14x23 allowed me to give it a mild hole shot to help get it up on plane. This new prop requires me to accelerate slowly until the boat is moving along pretty good, then give it more and more throttle to get the bow down and the RPM's all the way up. I originally had a 14x19 that did not do this, it just spun too many RPM's, so I am wondering if this new prop design just isn't good for my situation. One would think the 14x19 would have also cavitated like the new one assuming I am just putting too many HP's through it. Should I look for a different brand or is something wrong with my setup or handling skills?

 

[LubeDude]

Re: New prop cavitating during hole shot

Is there a chance that this new prop has no cup? I think your best prop would be a 21P Stainless. What type of boat are we talking about?<br />---------------------<br />

 

[tony_cliffy]

Re: New prop cavitating during hole shot

LubeDude,<br /><br />(You have given some great advice about this same boat on other threads) but it is an aluminum Crestliner "utility" boat 20'. It has a little bit of V but is mostly a big jonboat.<br /><br />Yes - it has some cup. I'm not sure how to indicate how much though.<br /><br />I'm wondering if it has to do with prop diameter. I notice my Johnson prop is a 14 (14x23) but all the aftermarket aluminum prop makers build a 13.25. They say the performance is the same but perhaps it isn't quite the same. I can't find an aftermarket 14" diameter prop like Johnson/Suzuki make for this engine. The aftermarket maker recommends I go to their 13.25x23 to get more pitch.

 

[tony_cliffy]

Re: New prop cavitating during hole shot

Dhadley,<br /><br />I edited my original post to more clearly state that the 13.25x21 prop actually ran beyond my recommended WOT of 6000 and to 6300+. Previously it might have suggested I only hit 6000 at WOT. Sorry.

 

[Jdeagro]

Re: New prop cavitating during hole shot

Your "old prop" looked like it was the best from the viewpoint of WOT Speed and RPMs. (14 x 23)<br /><br />I am guesing that the acceleration to plane was a challange with that much pitch. That is why the origional pro was lower pitched. (14 X 19)<br /><br />What is it you want to accomplish? Top Speed? Easier to Plane? Better Fuel economy?<br /><br />No matter what you do with a prop it will be a comprimise.

 

[tony_cliffy]

Re: New prop cavitating during hole shot

Less concerned with holeshot and mileage. Mostly want 6000 @ WOT and best speed across RPM band. Want to cruise around 4500 if I get enough speed out of it, otherwise need to turn it higher.<br /><br />Actually it got up on plane at the 14x23 best of all three I have tried so far. The 13.25x21 cavitates when trying to get up on plane so I have to get on plane slowly. I think the 21 pitchis probably best but now thinking the difference between the 14 and 13.25 in the diameter is having an effect on my testing. If I stick with the 13.25 then I ned to go back up to a 23 pitch. This will help lower my RPM's but am wondering the net effect on speed between a 14x21 and a 13.25x21???

 

[imported_JD__]

Re: New prop cavitating during hole shot

tonycliffy,<br />Your cavitation problem is (lack of) prop diameter, pure & simple. I tried 13.5 diameter props on my Johnson 140 4-stroke, same problem. Your 115 is geared 2.59:1 compared to the 2:1 +/- on most two strokes. It needs the large diameter, stay away from props designed for 2-strokes or you'll have head-aches like I've had. Stiletto/Turbo is making props specifically for 4-strokes. I ended up with a 14X24 Stiletto on my engine, best thing I have tried all way 'round.<br />JD

 

[tony_cliffy]

Re: New prop cavitating during hole shot

JD,<br /><br />I have been thinking exactly about that diameter dilemma except I don't have anywhere near your experience to think it all the way through. My problem is I want to stick with aluminum because I fish the lower James and feel the risk of dinging/denting my prop is very high due to the locations I fish and the shallow water I navigate. Everybody seems to make the 13.25 or 13.5 diameter aluminum props and not 14 like the factory. I was trying to get an aftermarket prop to save money (easily 1/2 the cost of a Johnson/Suzuki prop). I am starting to think a 14x21 SS Stilleto is probably my best bet (I was told they don't make a Turbo for my engine).<br /><br />Do you know of anybody making a good 14 diameter series of aluminum props that would work???

 

[imported_JD__]

Re: New prop cavitating during hole shot

tonycliffy,<br />It has been a headache. I got the engine in March and have been trying props ever since, finally getting it dialed in. If you're going aluminum, your best bet would probably be an OEM Suzuki/Johnson 14". The second best performing prop for me (on my rig) is a Merc Trophy 13-3/4" X 23 4-blade. The Johnson 140 is splined the same as the Merc 115-125, think the Johnson 90/115 is the same. Merc's Flo-Torq adapter kit #835283Q1 will allow you run their props. Maybe you could try out a used Merc propsomewhere? From my research the Trophy 4-blade is the only prop close to 14" diameter with a small hub. Otherwise, if you get the right diameter hub, the blades are small. Get the right size blades then you're looking at the big hub. Send me your email address if you like. I have some other info to pass on that may be helpful.<br />JD<br />jabshire@cablenet-va.com

 

[chris in va]

Re: New prop cavitating during hole shot

That top speed seems a tad low also. You should easily run 48 or so with that setup IMO. Too bad you can't run SS, it would really boost your performance.