Originally Posted by Chris
I think people tend to get hung up on RPM especially if your tacho is not too accurate...
Why sacrifice top speed just so you get your ideal RPM reading on the tacho?
Most engines are designed to work within a band of about 1000 RPM at top speed anyway for instance my Etec is rated at 4500 to 5500 RPM.
I find the best results are running the 18" prop which gives me a top RPM of around 5400 on the tacho. On my previous engine (Johnson 90) I found that the best results were obtained running the engine at around 5200 RPM (on the tacho) I suspect the tacho on this engine was at least 100 RPM out though so I may have only been pulling 5100 RPM.
Its more about power band than RPM.
Maybe i phrased thast badly , What I meant was that my boat was clearly overpropped when i got it . It felt sluggish at slower speeds and the motor was labouring trying to keep it on a slow plane. and only reaching 4500rpm at wot at 40mph . One pitch lower and its really lively and reving to about 5k , i just expected to get an increase or at least the same top speed not less as the motor must surely now be in its power band .
However cruising is better and lots more economical and thats what really counts for a pleasure boat.
I would like to try an alloy prop the same pitch as the stainless one I bought just to set my mind at ease , but where do you stop prop testing , finding a loan prop is near impossible and as these threads prove its a trail and error art that no one can give reilable advice on.
I have no reason to doubt the rev counter is far out