I'm Confused**Jp vs Prop

[Jimmy Easterling]

Nitro Z6 with 115 Opti. Based on previous information from here: I raised the motor until the water pressure dropped below what it was prior to JP and then lowered it until the water pressure came back to normal. Place-Savannah River with a 3-4mph current and some turbulence. Three situations. Boat 1/2 tank of gas with full gear and me.First: No JP Laser II 20P 48-16990 (13 1/4 I think)- several months ago-against the current full throttle 45-46, with the current 47-48mph gps. Second: today with JP same 20P 5850-5900rpm, plenty of throttle left, 36 mph against the current and 47 with. I played with the trim, up and down and could not get any more. I did lower the motor some more and got 44 against the current but only 48 once from take off with the current, first turn it fell off and couldn't get it back. Prop plugs? Third: Put gas back in to make 1/2 tank and same gear. Today with Power Tech 3 blade 13.25 X 22P, 5850-5900rpm probably had at least 200rpm on throttle left- 44 against the current and 50 with the current pushing the limit with the rpm's. The 22p obviously did better and I still had some throttle left, try a 23 or a larger dia 22. Confusion: what happened to my original speed with 20p before JP and am I too high with the motor? I know the current in the river has some effect on the results because I was getting 46-47 easy with the 20p at Ky Lake last week.

 

[Jim B]

My first question would be what is the current motor height(propshaft to pad)?

 

[TOMMY RICH]

You also need to test it "out" of currnet to determine the right prop. With current the flow is always gonna be different.

 

[Jimmy Easterling]

Since I don't know any better, I leveled the horizonal fins on the lower unit with the trim then put a level from the lowest point at the rear of the boat, the center of the prop shaft is about 4 3/4 inches below that point. TEE, I am headed to Lake Murray in the morning with the 22p only and will have results from that tomorrow, taking sockets to make adjustments. Fishing first.

 

[Brian Ingersoll]

You're looking for a minimum of 15psi water pressure. I would guess you could probably come up an inch or so. See what you get in calm waters for the best height setting and then you can see if you need to change prop sizes. Also see if you have to use all your trim or not to get best top end.

 

[Jimmy Easterling]

Normal psi is 15-16 at 5850 rpm. If I raise the motor 1/4 inch, psi drops off to 12 psi.

 

[Jimmy Easterling]

I went to the lake today and was able to raise the motor about 1/2 inch on currentless water. 50.2 mph at 5900 rpm's and had at least 100 maybe 200 rpm left on the throttle.

 

[TOMMY RICH]

Crack er' all the way open...what's you MAX RPM?

Sounds about right as far as speed.

 

[Brian Ingersoll]

It sounds like you need more pitch, if you have rpm's to spare in the summer, you will have a lot left in the winter. I agree with Tee, sounds like you are getting a good top end.

 

[Jim B]

It soulds like you need more pitch for sure. From what i see on Merc's website the max rpm for the 115 is 5750. If you constantly overrev it Merc wont be too kind should you pop the motor and need a power head under warranty.

 

[Jimmy Easterling]

5900 is all I can run it, 2 seconds at above 5900 the guardian kicks in and drops it to an idle. TritonGlenn's buddy in Va is sending me a 23p and I will have to choose between the two. Question, should I need to adjust the jp again with the 23p? I have it max'ed out on height with the 22 for the water pressure to stay at 15psi.