fuel mileage

[wolfe1974]

Hello,

I was wondering if there is a rough formula for fuel mileage for I/O or non outboard motors. I have seen the 10% of horsepower at WOT for outboards but what about "regular engines".

 

[QC]

Re: fuel mileage

The 10% rule is good with older outboards. I/Os are getting down to 7% but WOT fuel use doesn't mean a whole lot.

Cruise MPG with modern stuff (OB and I/O) is:

16 - 18 footers sometimes see 5, but consider 4 for range calcs

19 -21 ft see 4 but use 3

22 - 25 ft. will get 3 but maybe use 2.5

Older stuff and most IBs are worse. Modern jets are getting closer.

The largest assembly, and pretty good variety, of data is at BoatTest.com. Remember that these boats are all new, usually setup perfectly, and very lightly loaded. Top speed and MPG numbers are never reached once delivered. They get loaded up and conditions are more variable, and are often 5 - 10% slower than shown.

 

[Texasmark]

Re: fuel mileage

"Bein" in the user part of the industry for the last 50+ years, technology has been a marvel. Used to be that you needed a 4 cycle I/O to get any reasonable mpg, but with today's 2 cycles as refined as they are, and surely the 4 cycle OB's, mpg worries are really a thing of the past. It depends more on "the rest of the story" as to what you get.

Mark

 

[wolfe1974]

Re: fuel mileage

I guess maybe a better way to state my question is if I am comparing 135hp outboard and 135hp I/O of the same vintage would they get comparable mileage if the boats were the same size

 

[QC]

Re: fuel mileage

Depends on the vintage and the technology. 4 stroke to 4 stroke since mid 90s. Pretty close 2 cycle carbed vs. 4 cycle I/O from early 80s is a mess. Ratings were different and technology is different.

 

[H20Rat]

Re: fuel mileage

I guess maybe a better way to state my question is if I am comparing 135hp outboard and 135hp I/O of the same vintage would they get comparable mileage if the boats were the same size

it is never that straight forward. Even with identical hulls, the difference in weight might make the lighter outboard more efficient. But if the hull carries the extra weight well, the I/O might be better.... fun stuff!