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Old 04 June 2013, 14:12   #1
Country: UK - Wales
Town: Swansea
Boat name: Space Hopper
Make: RibTec
Length: 5m +
Engine: Evinrude E-Tec 75
Join Date: May 2012
Posts: 76
Does this RPM sound correct vs speed?

I am trying out a new prop as well as fitting a new rev counter as the previous one didn't work when i purchased the boat.

Its a 75hp merc two stroke on a 5.5metre Ribtec, with 4 people she is doing 41mph roughly according to the GPS, however the rev counter is saying that I am only doing 2100rpm.

The prop i am using is a stainless steel Vengeance 18P, and in fairness it goes like a rocket. However i have noticed i am using probably about 20% more fuel than when i had my previous prop on which unfortunately had no markings for pitch on it, but it only had a top speed of about 32mph. It was revving noticeable higher though compared to the one i have on now.

Is my rev counter correct and its way over geared, or would i not achieve that sort of speed with those sort of revs, want to find out if my rev counter is misleading me

The manual says my engine should be running WOT between 4750 and 5250 rpm.

Any help would be great!

mctaggart is offline   Reply With Quote
Old 04 June 2013, 15:01   #2
Country: UK - Wales
Town: Here
Boat name: doggypaddle
Make: Avon 5.4 Searider
Length: 5m +
Engine: yamaha 80
Join Date: Jul 2007
Posts: 1,107
your rev counter must be miles out maybe its set for the wrong number of alternator poles/cylinders.
i would guess its reading approx Half and maybe you're over propped?
40MPH at around 4200RPM sounds believable.
I am usually not as green as i am cabbage looking.
doggypaddle is offline   Reply With Quote

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