Recommended all around prop for '98 Yamaha 115

[BOAH]

I bought a '98 yamaha 115 that I'm putting on a 1972 21' Starcraft. The prop that came on the motor is a 14" 20 3-bladed stainless steel prop. It's a solid hub (not vented) and I can't find the manufacturers name on it. The mechanics that I've shown it to both said that this is a high-speed prop and definitely not what I need on that motor.

I like to fish and sometimes drag the kids around on the tubes. I like to cruise around 35 or so. Not interested in doing 55.

What kind of prop would you suggest I look for?

Thanks for your help.

 

[steelespike]

Re: Recommended all around prop for '98 Yamaha 115

There is probably no doubt the 20 is too much prop but::
I would start with the original prop you have, it will serve as a base line.Do a lightly loaded test get us the wot rpm and gps speed.
We need the figures at wot to evaluate your setup. Once we have you setup with the right prop you can run at what ever speed you like.
If you don't want to mess with the ss prop start with a 17" al. prop like the Solas Amita. It may be undersized but you can run it by making sure you don't go over the rated rpm until you can replace it.
Of course there is a chance a 17" is too much prop in that case you would need to replace in a more timely fashion as it will make the motor work too hard.

 

[BOAH]

Re: Recommended all around prop for '98 Yamaha 115

Thanks, steelespike. I'm taking it to the lake tomorrow for a run. I'll report back.

Thanks

 

[BOAH]

Re: Recommended all around prop for '98 Yamaha 115

Wow, glad I ran it. Here's my experience. The operating range according to the manual is 4500 - 5500. I could only get it up to 4900. I installed a new throttle and shift cable so maybe I don't have the throttle cable adjusted correctly?

Anyway at 4900 with 3 people in the boat it ran at 38 mph. 38 is OK but here's where I ran into problems. When pulling the kids behind the boat, I ran into problems with cavitation going only about 12 mph. This is definitely not good. With the kids back in the boat, it seemed to run fine.

I'll adjust the throttle and shift cables before the next trip.

Is that enough for recommendations on a prop that would work better for me?

Thanks.

 

[steelespike]

Re: Recommended all around prop for '98 Yamaha 115

You need about 600 rpm a 17" prop should put you there though going from ss to al makes things a little unpredictable.
Are you saying you get ventilation(cavitation)at 12 mph?Do you trim down for slow speeds?
Perhaps the motor is mounted a little high.The prop may be causing problems being so far over sized.
The 17 may solve this as well. The Solas Amita and Rubex have a good reputation. Rubex is the same prop with a removable hub.

 

[BOAH]

Re: Recommended all around prop for '98 Yamaha 115

So I picked up an aluminum reconditioned Yamaha prop. 17 pitch and I think it's 13 1/4. Anyway, I took the boat out today and it ran great with that prop and had no problems with cavitation.

Now that I know what a difference the prop can make, I can think about a SS prop.

Thanks for your help!

 

[BOAH]

Re: Recommended all around prop for '98 Yamaha 115

I ran this prop for a solid week of fishing and diving. I want to make sure it's being as efficient as possible so I'm looking a little closer at my numbers.

21' Starcraft
115 Yamaha 2 stroke
2:1 gear ratio
17 pitch aluminum prop
4900 RPMs
32 mph

According to the calculator I looked at, the slip with these numbers is 19. What could I do to get more efficient and better gas mileage?

 

[BOAH]

Re: Recommended all around prop for '98 Yamaha 115

bump...

 

[Sea Rider]

Re: Recommended all around prop for '98 Yamaha 115

Are you still achieving 4900 with 17 prop with 3 onboard ? How about with you alone with lightly loaded boat ?

Happy Boating

 

[steelespike]

Re: Recommended all around prop for '98 Yamaha 115

We need to go back to the lightly loaded test for wot rpm and gps speed.
At 4900 your slip would tend to be higher.

 

[BOAH]

Re: Recommended all around prop for '98 Yamaha 115

OK. I'll test as soon as I can and report back.

Thanks

 

[BOAH]

Re: Recommended all around prop for '98 Yamaha 115

Ran it again yesterday. Had 2 people in it. At 5400, it ran at 38 mph.

This is the best info that I have at this time.

 

[MARV1]

Re: Recommended all around prop for '98 Yamaha 115

I'd try a SS 13.25x19 and you'll get the same rpms and more speed... These have a rev limit of 6300rpm, same as a 130hp. Good luck with it...