Originally Posted by GalaxyGirl
I have narrowed my trawler search to a 66' Cheoy Lee
or a 70' Widebody Hatteras, no one boat in particular as I am still in my planning stages and trying to decide whether to sell my house and take the leap this Spring or next year. But, I was wondering if anyone knows if it is possible to get a general idea of the fuel economy of a vessel by dividing the range by the fuel capacity?
If you know engine models, you can often find published performance curves... which would include fuel flow at given RPMs, etc.
For example, the curves for our engines indicate (just a few from the list): 2 GPH at 1000 RPMs, 3 GPH at 1200 RPMs, 10.4 GPH at 2000 RPMs, 13.4 GPH at 2200 RPMs, and so forth. Published data will often include power output and torque curves, too. If you have multiple engines, as I do, multiply
Mating that info with advertised cruise
speeds (especially if given associated RPMs) might get you closer to being able to compare boats.
In our case, I can relate fuel flow at given RPMs to known average speeds. For example, at normal cruise
speeds: 13.4 GPH at 2200 RPMs (x2) at 2200 RPMs (approx 20 kts) to derive MPG (20 kts ÷ 26.8 = ~.75 MPG). Or at just slightly above hull speed
: approx 8.5 kts average ÷ 6 GPH (total) at 1200 RPMs = ~1.42 MPG.
And so forth. And all theoretical numbers, of course, and also affected by sea states, tides/currents, wind
, bottom condition, etc.
Both of those boats will more likely be run close to hull speed, and the installed engines are very likely optimized for that... so both may get decent (enough, in the grand scheme of things) fuel economy.
I've not been able to derive anything useful from knowing advertised range (which is all over the map) and fuel capacity. Range was not fiigure that the manufacturer plublished at the time; range was published by various boating
magazines in their reviews
of the boat... but the ranges were simply calculated at various speeds.