new to boating & confused

[saigonbilly]

I bought a used 2000 model aluminum xpress 17 ft. Bass boat with yamaha 60 hp 2 cycle engine . Previous owner said Motor not used much, boat and motor very clean.
the boat , motor ,trolling motor, 3 batterys, 10 gal fuel, and myself weight about 1, 600 lb.
the motor has a s/s 14x17 prop , why will the rig at full throttle, planed off untill cavitation stops only turn 2600 RPM ? GPS SPEED IS 35 MPH. please reply

 

[Maclin]

The tachometer is not reading correctly When I plug the numbers into a prop calculator and assuming around a 2.3 gear ratio, an engine would have to be spinning at around 5600 rpm to go 35mph with a 17p prop. Using 2600 rpm with those same constants only yields 16mph.

 

[saigonbilly]

Thanks for the reply , got any input on how to check the rpm gage ?

 

[Silvertip]

Look at the back of the tachometer and you will see a calibration dial. Gently (repeat "gently") turn that dial back and forth a few times and then set it on the 6P position. See if that puts the rpm in the proper range.

 

[saigonbilly]

I will look tomorrow and see if I see what your talking about...thanks for your input !

 

[saigonbilly]

I found tHe plastic screw at bottom of tach. And gently turned back & forth a few times and reset on 6 , before Iit was set on 5.
had to go with the other half to black friday ritchual today but tomorrow will see what happens .... again tthanks for your input !

 

[saigonbilly]

Still reading 2600 RPM @ 37 mph on gps .

 

[steelespike]

Time for a new tach.I can confirm your rpm is "about" 5600. at 35 mph.
You could get a permanent tach or an induction tach that could be used to test all kinds of motors.
Tiny Tach is one of the brands,

 

[b.gagnon]

It has to be a bad tach......... You are getting good performance for a 60hp!