Got a wee bit more time to deep dive this.....
Compare: How many of us actually get the advertised MPG from our cars?
1) It's a manufacturer's leaflet. They can't sell 2-stroke any more. It's in their interests to big up 4-st.
2) Quote (page1)
"Data used in the graph was obtained through in-house testing under uniformed conditions.
Results will vary depending upon operating conditions (boat design, size, weight (load), weather, etc.)"
Ok, so they bolted the engines to a clamp, ran them at theoretical optimuim to see how much they drink per hour. then multiply by a lot of hours to make the difference look bigger.
I'd like to see that done independantly on real boats- e.g that "uniformed conditions" test will likely not take into account stuff like Pol said above - you need to burn more fuel to lug the extra weight around amongst other things like appropriate prop pitch for your hull....
3) DT75 / DF70 and DT55 / DF 50
of course it's going to drink more!
4) The distances are in KM. Convert to nautical miles per L and the numbers aren't quite so spectacular. (0.91 Vs 1.07 for the 55/50 test) Also both were run at 4500rpm. Any Suz DT or DF owners like to tell us what their optimal cruising RPM is?
5) the idle numbers are what I said all along. That's where 4 stroke really
wins. (well, that and relative silence)
In summary - the numbers look good, but like all numbers that look a little too good to be true, I would treat with caution.
Yes, there will be incremental improvements - Computer flow analysis & the like is improving air - fuel mixing in cylinders all the time - but the same thing is going on with the DI 2- strokes. I'd like to see the same test done on, say a Last generation 'rude 2- stroke 60 and an Etec, or similar comparison on an Opti. Then run the same test with "DI 2- stroke vs 4- stroke". as well as the 2 vs 4 stroke. I.E. a three way comparison. Ideally then duplicated on real boats with data loggers as well to allow a proper comparison and to compare the lab to the waves.
What's that pig doing up there......?
Only then will we get a vaguely full picture..... which will then need fine tuned to each & every one of our differently set up RIbs!
Back to Chriis' original Q, Unless you are doing thoosands of hours a year at WOT, there's probably not a lot of difference in running costs.