2001 yamaha f115 yamaha 4 stroke issue

sinz8

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Joined
May 3, 2013
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Hi I have a 2001 lund fisherman 1700 with a Yamaha f115 and it is not going as fast as it should. some people tell me its a problem with the prop. I have a 17 pitch prop and would like to know if this is the right prop. it should go 40 or so mph and its only going 28-30 mph its suppose to be about 5600 rpms and its at about 4200-4300 rpms
 

jestor68

Commander
Joined
Jun 12, 2012
Messages
2,308
Re: 2001 yamaha f115 yamaha 4 stroke issue

According to the slip calculator, your 2.15 gear ratio turning a 17 pitch at 4300 rpm equals a theoretical speed of 32 mph and 29 mph with an 8% slip.

So it seems that your prop is doing pretty much what is expected of it. The question is why isn't a 115 HP on a 17 ft boat turning a 17 pitch prop not doing more?

Since your 115's recommended full throttle rpm range is 5000-6000 rpm; with the HP rated at 5500 rpm, you might have issues other than a propeller size. Could the fact that the motor is 11 years old have something to do with it? Do you have any idea how many hours are on the motor? Is the motor mounted at the proper height(AV plate one inch above the keel)? How long have you owned the boat/motor? (What is your history with the motor?)

To give you an idea of what it should be doing; the prop selector indicates your boat(calculated weight of 2342 lb) should be able to turn a 17 pitch prop at about 5500 rpm @ 38 mph. This presupposes a new healthy motor developing rated power.

The performance tests on the Yamaha web site indicate (with like size boats) speeds in the 40+ range at rpm's of 5700-6000 turning 18/19 pitch props.

So it appears that your motor is not performing up to par for whatever reason.

A full service dealer should be able to dyno it to see what's up.
 

sinz8

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Joined
May 3, 2013
Messages
3
Re: 2001 yamaha f115 yamaha 4 stroke issue

Thank you, I am indeed bringing it to a marine tech. We had bought the bought used from a dealer so no history. I was being told from other people on fourms on another sight that it could be Spark, Prop, and fuel got any idea if it could be that. Thanks again.
 
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