Need help for prop on a pontoon boat!

[rosbertos]

I have a 1998 Sylvan Mighty Mite, 18 foot pontoon with a total weight of boat, motor, fuel, and passengers of 1,600 lbs. It has a 1998 Johnson 25hp (J25ELEC) with a max RMP of 5500 RPM. I think the prop that is currently on it is a 3 blade 11x9. WOT rpm is only 4000....I have been messing with the tach to see if there is a problem, but it seems to be fine. GPS speed of 10.4 mph max. Does this sound like my prop is good but the tach is bad or what?

 

[steelespike]

Re: Need help for prop on a pontoon boat!

I think your speed is reasonably close; My 18 with a 50 does 18 or 19 double the hp is good for about 8-10 mph.and I haven't
fine tuned the setup.your 1500 rpm short and the smallest prop I show is an 8.
While small motors make up more rpm per inch I think we can be pretty sure one inch isn't going to make up 1500 rpm.So either your tach is off or your motor is sick/very poorly setup.You may be able to borrow a shop tach to check against yours.

 

[rosbertos]

Re: Need help for prop on a pontoon boat!

It must be the tach...the motor runs smooth and goes from idle to WOT and back without so much as a sputter. The current tach is a Teleflex Amega...any suggestions on a new one that isn't too spendy? (10 pole, 5 pulse..the Teleflex is $65...I'd like to keep it around that)

 

[steelespike]

Re: Need help for prop on a pontoon boat!

Sorry the only tach I have any info on is the Tinytach it is an induction tach somewhat unorthedox. about $40 and easy to install.Assuming your motor is a 2 cylinder it would work on any 2 cylinder 2 stroke regardless of number of poles.