best cruising revs merc 5.7 ol638945

[glyn]

Hi guys i'm a virgin in need of help and advice, i've just bought a bayliner 2855 yr 2000 with a merc 5.7 serial no ol638945 none efi. i've just taken her from falmouth to the river dart (dartmouth) in south devon uk (should have been a great trip but 200 meters vis in dense fog for most of the way stopped any enjoyment) i seem to have used a huge amount of fuel for a 70 mile trip, like half a tank (50 uk gallons) i cruised at 3000revs. what is the most efficient cruising revoloutions for this engine ???.

 

[achris]

Re: best cruising revs merc 5.7 ol638945

A 28 foot boat is a LOT of boat for a 5.7 litre engine... Most boats that size have twin 5.7s or a 7.4 as a minimum. As such I would expect your fuel consumption to be high, you're real asking a lot of that small engine. Given the figures you supplied, I'd say that's about right. And 3000 is a good speed for economy, if the boat's on the plane... Best speed for economy is usually just as the boat levels out once it's up.

I have a fuel flow meter and have found that to be invaluable for fuel economy.

Chris.......

 

[QC]

Re: best cruising revs merc 5.7 ol638945

I am guessing she was still squating pretty good at that RPM. What speed is 3000? Do you have trim tabs? Might be better at 3500, and in some rare cases fuel efficiency is better at 4000 RPM. As Chris noted the only way to really know is a flow meter. The other way is to study lots of test data. Just recognize that they are always better in the tests as there is no gear on board

 

[achris]

Re: best cruising revs merc 5.7 ol638945

...they are always better in the tests as there is no gear on board

And one really skinny guy driving... :

 

[QC]

Re: best cruising revs merc 5.7 ol638945

I don't know any 28 foot cruisers that get 3 MPG . . . I think he meant he used 50 gal (Imperial = 1.2 US Gal). Half of a 100 Gallon tank