Johnson 110hp prop pitch? SS vs. Alum?

[Cucaracho]

I have a tracker magna 17 with a Johnson 110hp model 1989 runs great, but it has a 13x17 aluminum michigan prop and the throttle can go way past the recomended rpm of 5,800 and the speed at the 5,800 point is about 35mph. What do you suggest to make the WOT at 5,800, a 19" pitch prop? Aluminum or SS? , I want to improve the top speed. What top speed should I expect? I installed a fin on the motor, is this any good for the motor or does it create more drag than good?

 

[walleyehed]

Re: Johnson 110hp prop pitch? SS vs. Alum?

First, we need to know how high the rpm will go with the prop you have now....it's not going to hurt a thing..
With stock reeds it'll maybe go to 6400-still not a problem.
With the crossflow, 5800 is the target with a normal load at WOT...6000 wouldn't be a bad thing but you may gain some speed with the right disign in a higher pitch at 5700-5800.

p.s. My boat in my avitar pic was dead-on 6300 it's seen near 1000 more than that. you won't hurt your engine finding what it will turn...it's the best way to determine which way we need to go for the correct prop.

 

[Cucaracho]

Re: Johnson 110hp prop pitch? SS vs. Alum?

I will check how high the RPMs will go this weekend. The last time I checked they got up to 6,400

 

[Dhadley]

Re: Johnson 110hp prop pitch? SS vs. Alum?

Make sure your tach is set on "6".

 

[Tacklewasher]

Re: Johnson 110hp prop pitch? SS vs. Alum?

Make sure your tach is set on "6".

I'm guessing the tach is set wrong as some of the numbers don't quite make sense.

At 5800 rpm, a 17p prop, a 2:1 lower end and 10% slip, you should see 42mph.

34mph is 27% slip.

Unless I have something wrong (like maybe the gear ratio)

 

[walleyehed]

Re: Johnson 110hp prop pitch? SS vs. Alum?

Don't lay too much cash on that speed....unless it's GPS we really don't have a clue.
The slip ratio with aluminum on that rig is likely closer to 14-15% without some set-up work...I get 10-11% with a Turbo1 and a jackplate to maximize my performance.....don't know that I've ever had better than 15% with any aluminum.

 

[Tacklewasher]

Re: Johnson 110hp prop pitch? SS vs. Alum?

Really? I'm getting about 8% with my 17p aluminum. 5100 rpm and 38 mph (tach and gps). Motor all the way up and trimmed all the way out with no venting.

Doing even better with my 15p stainless Stilletto. Same speed (or a tenth less) and 5500 rpm.

And I still have a jackplate I could install. Not sure what it would do for me but might get me a few more rpms and a little more speed (still trying to break 40).

 

[walleyehed]

Re: Johnson 110hp prop pitch? SS vs. Alum?

8% is common to high-performance bassboats with high-tech props and total-performance set-ups.
We could have Dhadley add his 2 cents, but I don't feel there is the possibility to achieve 8% with aluminum.
#2., If you can trim your engine to max travel with no ventilation, your engine is quite a bit too low and your efficiency is even lower.
That's kinda rule #1 besides hitting the top of the RPM band.......if you can trim all the way, you're too low.

What engine are you running?

 

[Tacklewasher]

Re: Johnson 110hp prop pitch? SS vs. Alum?

1981 Evin 115. Moved all the way to the top hole. It will vent a bit with the alum, gotta trim in to turn. Need to really play with the stainless on but need a calm day when I'm not rebuilding my kitchen to do it.

It's on an 18' Starcraft which is pretty light. 2 people with some lunch and stuff but not a normal load (no fishing gear and my downriggers by themselves are heavy).

Back to the op, I'm guessing he needs to test with a gps to see if that is his speed numbers. His slip still seems out of line to me.

 

[walleyehed]

Re: Johnson 110hp prop pitch? SS vs. Alum?

1981 Evin 115. Moved all the way to the top hole. It will vent a bit with the alum, gotta trim in to turn. Need to really play with the stainless on but need a calm day when I'm not rebuilding my kitchen to do it.

It's on an 18' Starcraft which is pretty light. 2 people with some lunch and stuff but not a normal load (no fishing gear and my downriggers by themselves are heavy).

You have the same boat I have....in my avatar.
I had a 115 Rude on it with 4" setback and in the 4th hole, I was getting about 42 with a 17P Nauticpro SS. But....I'm running on most lakes at 3200-3700ft elevation. You should have no problem getting to the 40 mark. If so, there's always the Turbo Jr.....
The 115 sold and I put an extra 85hp version of the 115 with 6cyls on a bob's 4-n-1 plate....42 is now my mid cruise speed.

 

[Cucaracho]

Re: Johnson 110hp prop pitch? SS vs. Alum?

With the GPS the top speed at WOT is 38mph and the RPM's at 6,400.......I had 3 adults on the boat when I tested it yesterday. What do you suggest? Maybe 19" prop SS.......what brand?..........

 

[Cucaracho]

Re: Johnson 110hp prop pitch? SS vs. Alum?

A 19" pitch prop should take me to 5,800 rpm's............but what speed should I expect? will this prop make my boat more fuel eficient?

 

[Cucaracho]

Re: Johnson 110hp prop pitch? SS vs. Alum?

Any opinions? I really apreciate it, thanks.

 

[Tacklewasher]

Re: Johnson 110hp prop pitch? SS vs. Alum?

from a 17p to 19p you should lose 400 rpm.

Assuming the same slip % (I still calc about 26% slip), you'll be right at 40 mph.

Same approx slip % and a 21p would get you 5800 rpm at 42.5mph.

But I'm still thinking you should be able to improve your slip %.

 

[Tacklewasher]

Re: Johnson 110hp prop pitch? SS vs. Alum?

1981 Evin 115. Moved all the way to the top hole. It will vent a bit with the alum, gotta trim in to turn. Need to really play with the stainless on but need a calm day when I'm not rebuilding my kitchen to do it.

Had a fairly calm day on the water and played a bit with the stainless and found it vented more than I like in turns. Probably going to go down one hole.

I do have a manual jack plate I could put on, but I'll wait until I rebuild my transom.

So, how do you make a 115hp with an extra 85hp work on a boat rated for 150hp

 

[walleyehed]

Re: Johnson 110hp prop pitch? SS vs. Alum?

"So, how do you make a 115hp with an extra 85hp work on a boat rated for 150hp "

150 decals, of course.......

 

[walleyehed]

Re: Johnson 110hp prop pitch? SS vs. Alum?

I think we need to look into some other things here...
Is the 19P and 21P both cupped?
Do you have anything mounted on the transom with-in 12-14" of center on either side?
Is your skeg bent at all?
Can you list a P/N of that 17P MW?

 

[Cucaracho]

Re: Johnson 110hp prop pitch? SS vs. Alum?

How can I improve slip %?
I am really lost here...........your advice is very helpful, thanks.

 

[Turbo1]

Re: Johnson 110hp prop pitch? SS vs. Alum?

I'm with the other folks here....I think you have a tach issue or a prop with no cup-maybe worn off.
The numbers just don't add up. Your slip is about what can be expected on a pontoon.

 

[Cucaracho]

Re: Johnson 110hp prop pitch? SS vs. Alum?

How can I check it the tach is set up on "6" and working right? Because the prop seems to be in good condition..............so the problem should be the tach......