Prop size for 1997 Johnson 115 SPL

[egscharf]

Currently running a 13.25 x 19 on a 1997 johnson 115spl pushing a seaswirl striper 1850wa. Just did the timing, and engine is correctly dialed in to 26 degrees at WOT, however, Im only getting a max of 4200 rpms and about 25kts. Thinking of dropping to a 13.25 x 17. Recommended max rpm is 4500-5500. What do you all think?

 

[Bob_VT]

Re: Prop size for 1997 Johnson 115 SPL

Yes, you are correct.

Welcome to iboats!

The Seaswirl is a heavy boat and you should do better with a 17" pitch

Is this a new to you boat? I would get it weighed and make sure you have dry flotation. Water "stored" in the hull will rob performance due to the weight.

Based on your number's you could almost go down to a 15" pitch but I would check the hull weight first........

 

[egscharf]

Re: Prop size for 1997 Johnson 115 SPL

Thanks for the welcome Bob! I've owned the boat since april, but I run it at least 10 hours a week. Weight should be good, however, I usually carry about 130lbs. of water (via livewell), 100lbs of ice, and at least one passenger (200lbs), not to mention my toolbox and fishing equipment. The boat is rated at 2750 lbs. Hull is pretty solid, nothing to indicate a water storage issue. Could I really go wrong dropping to a 15? Sounds like the right course of action to me.

Yes, you are correct.

Welcome to iboats!

The Seaswirl is a heavy boat and you should do better with a 17" pitch

Is this a new to you boat? I would get it weighed and make sure you have dry flotation. Water "stored" in the hull will rob performance due to the weight.

Based on your number's you could almost go down to a 15" pitch but I would check the hull weight first........

 

[jestor68]

Re: Prop size for 1997 Johnson 115 SPL

5500 rpm(target) minus 4200 rpm(present) means you need to gain as much as 1300 rpm.

Putting a 17 will gain to about 4600 rpm. A 15 will gain to about 5000 rpm( good target; 115 hp at 5K rpm). A 13 would take you to about 5400 rpm( also a good target).

Right now, you're lugging that motor pretty badly. Not good.

 

[egscharf]

Re: Prop size for 1997 Johnson 115 SPL

Thanks for the reply.
I've been able to find a 14 x 13, and a 13.75 x 15. Which do you think I'd be better off with?
Like I said, I'm currently running a 13.25 x 19. I troll quite a bit, but also frequently run at WOT.

5500 rpm(target) minus 4200 rpm(present) means you need to gain as much as 1300 rpm.

Putting a 17 will gain to about 4600 rpm. A 15 will gain to about 5000 rpm( good target; 115 hp at 5K rpm). A 13 would take you to about 5400 rpm( also a good target).

Right now, you're lugging that motor pretty badly. Not good.

 

[jestor68]

Re: Prop size for 1997 Johnson 115 SPL

It appears that the 15 pitch would be the better choice for over all performance and fuel economy. As long as the motor can spin to about 5000 rpm, you'll be in good shape.

As an aside; the Mercury prop selector came up with a 15 pitch when I plugged in your info.

 

[egscharf]

Re: Prop size for 1997 Johnson 115 SPL

Awesome, I'll pick the 15 up and let you guys know how it runs. Thanks so much for the help!

It appears that the 15 pitch would be the better choice for over all performance and fuel economy. As long as the motor can spin to about 5000 rpm, you'll be in good shape.

As an aside; the Mercury prop selector came up with a 15 pitch when I plugged in your info.