[616433]

Im looking for the best rpm for the least fuel consumption.I know the best way is with a flow meter, but its not in the budget.The Boat is a 24ft Pennyan flybridge (around 5000 lbs I think) mercrusier 260.I usually cruise about 3000 rpm WOT I think is about 3800 RPM.I know there are alot of variables, but if somebody else has any ideas on what they have found to be the best RPM with the same or close to my setup. I havn't found any websites that list any info yet. Thanks Mike M
MINI-LYNN II

 

[Calmwater]

That is a difficult question to answer. A boat engine is basically a car engine so the higher the RMPs the more fuel you use. The second piece of the problem is the higher the RMPs the faster you get where you are going. The last piece is the faster you go the greater the drag from the water. If you really want to know, my suggestion would be to pick a calm day, pick two point far enough apart so you can measure the amount of fuel you use, and then travel between those points at different RPMs. This will tell you what is the most fuel efficient RPM to travel at. For me I travel at an RMP level that allows the boat to get and stay on plane (around 25 – 30 mph) and I don’t go much faster then that. This strikes the best balance for me in terms of fuel usage and getting where I want to go in a reasonable period of time.

 

[Scratcher]

I think its going to depend on your carb, assuming of course its a carbed engine. If its a four-barrel carb you want to cruise at the rpm just below where the second butterfly valve opens and you start dumping fuel into all four barrels. On a typical inboard this is about 2900 rpm. If you listen closely as you increase throttle you can probably hear the point at which all four barrels kick in. Back down to just below this point and you should be very close to your most efficient cruising speed.

 

[Scratcher]

I should also add that at Boatus.com you can get a Navman fuel consumption meter for $149.00. Unlike most gadgets that little baby will probably pay for itself in less than a season.

 

[616433]

Scratcher thanks thats about what I do. The four barrell kicks in around 3200-3400 RPM so I run around 3000 RPM and that is about 20-25 MPH.This weekend I will check the RPM when it gets up on plane. Mike M