Prop Analysis

[jarway]

Purchased 1982 150HP Johnson (Model J150TLC) which came off of a deck (pontoon-type)boat and installed on a 19-foot V Hull Al Center Console (1986 Sea Nymph CC-191) (V-hull approx 1800 lbs.) which I restored. Motor started fine and ran OK with muffs in driveway. Idled at 2500 rpm and could increase throttle to > 5000. Took it for a test run at the local lake and it would not plane out or go more than 10 mph. Suspect cavitation problem but not exactly sure. Much turbulence behind stern but no thrust. Tried trimming up or down with no apparent difference in speed. Have a tach but unsure if it is working properly but it says it is running between 3500 and 4500 rpm. (WOT rating is 4500 to 5500 rpm). Prop size 14.25", 21 pitch, 3 blades, Aluminum. Propellor tip clearance to hull is 26.5 inches, approx. 20 inches from centerline of prop below water surface. Motor mounted in middle hole positon of 3 mounting holes. Cavitation plate is even with the keel. <br /><br />Any advice about whether this could be a prop problem (too much pitch?) and if so what would the recommended prop size and pitch be for this configuration of boat and motor. Thanks in advance.

 

[the rebel]

Re: Prop Analysis

Try another prop, sounds as if yours is slipping. That should be a nice rig you have. BWJ

 

[jarway]

Re: Prop Analysis

Thanks BWJ. Any recommendations though on where to start? Size/pitch. I know there are speed props and power props but not sure how they rate out in size and pitch. I guess I'll contact the local boat shop and see if I can try out some props. Don't want to start buying props just to experiment. Any other ideas?

 

[mfinucan@sympatico.ca]

Re: Prop Analysis

Try dropping to a 14.5 x 19P or maybe down to a 17P. Should probably drop right to the 17P with the rpm's you are getting. Even a 21P should give you a lot more speed and RPM. I have a similar weighted boat with a 14.5 x 19P aluminum prop and get 49 MPH at 5100rpm and I could easily drop to a 17P to get the RPM higher. Sounds like the prop does not have enough water to chew on?! Just my thoughts. Good luck.

 

[jarway]

Re: Prop Analysis

Thanks JV,<br />I got a couple of props from a friend of mine to try. 15 X 17P and 14.75 X 19P. Am thinking like BJW that the current prop may be slipping in the rubber gasket. Am anxious to try out with new props but headed to the Bassmaster Classic this weekend as spectator so boat test will have to wait until next week. <br /><br />Will weigh back in with a report about the results of the next test. Hopefully it is that easy of a fix. If it is, can the prop be rebuilt and that gasket replaced? Is it worth trying with that prop? <br /><br />Will be back in touch.

 

[the rebel]

Re: Prop Analysis

The 17 would definately put you out of the water quicker and pull much harder, just watch your revs. Out of the 17 and 19 you should be able to deduce which one your boat set-up likes best. 5500 will be a good target rpm if you still get out of the hole good. If your 21 is still in good shape it will be worth re hubbing at the right price, even if you only use it as a back-up. A prop shop can tell you in a hurry if it needs a new hub. You can go 2 inches either way with the pitch of the blades. So what I am getting at is, if your boat feels right with the 19 you are experimenting with you can go back to 19 with the 21 that you have. I would be more concerned with what your prop guy charges for re-hubbing and pitching the blades, because I have seen some good prices on new props right here on this site. BWJ.

 

[jarway]

Re: Prop Analysis

BWJ,<br />Just returned from the lake where I spent 8 hours touring and fishing after the boat came up to plane with the 15 X 17P prop. My GPS wasn't working but got 34 MPH on the wheel sensor on the Lowrance with the 17 and 35 MPH with the 19. 17 performed much better by getting up to plane much quicker but I'm a little concerned that the tach peaked out >6K and the 19 brought it down to 5500 where it should be (4500 to 5500). Not sure tach is reading right though since the motor didn't seem like it was reving that high.<br /><br />Anyone have any recommendations about size/pitch before I go out and invest in a prop. I'd appreciate hearing back. Boy was that a relief!!!