Rpm

[ferdly1]

Bought the pontoon used. Can anyone tell me what the WOT RPM for a 2004 mercury 40hp engine would be. Also would like to know what pitch prop I need for the 18 ft fisher pontoon of the same year. The tach revs over 6k dont think that is right.

 

[achris]

Re: Rpm

For a 3cyl 4stroke 40hp, max rev should be 5500-6000rpm.

As for a propeller, the right one is the one that allows the engine to turn in the max rev range at WOT.... And that is done using a properly calibrated tacho (the dash tacho is not nearly accurate enough)... and trail and error. Merc have a prop calculator on their website, but that is a guide only. It will get you to a prop close to what you'll probably end up using, but needs to be verified suing the 'trial and error' method....

The table in the service book says around 8" or 9" of pitch, with a diameter of around 12-1/2"...

Chris.....

 

[carholme]

Re: Rpm

You should always provide your engine s/n as there are different models. If you have a two stroke, the WOT is 5000-5500.

If you provide a s/n, I may have the service manual which I can send you if you PM me with an email address.

Gerry

 

[MH Hawker]

Re: Rpm

Pontoon owners will often have a lower pitch prop on to compensate for the load, one on board it may over wind but add 2 to 6 people and its just right, and you can back off of the throttle with a light load. Personally I wont do that because I let others run mine at times.

 

[Silvertip]

Re: Rpm

The prop you need depends on whether the engine is "Big Foot" or standard. If it is a Big Foot, a 14 x 9P is the prop of choice (or at least the place to start). If the engine is NOT a Big Foot, you will need to experiment with much smaller diameter props because of the gear ratio difference in the lower unit. Standard Merc lower units on a pontoon are not the desired configuration. Yes -- it is done but a Big Foot is a much better choice.