mvweebles
Guru
- Joined
- Mar 21, 2019
- Messages
- 7,644
- Location
- United States
- Vessel Name
- Weebles
- Vessel Make
- 1970 Willard 36 Trawler
I haven't looked at VUP in 20+ years so don't remember what was there. Jim Leishman (PAE /Nordhavn) updated the book around 2000 or so so the numbers may be fairly recent. If it's based on HP per ton or something, I have never been able to correlate.What’s your opinion on how to view the miles per gallon reported in the addendum in the back of “Voyaging under Power”? Appendix C. It’s owner supplied and date of passage isn’t mentioned so one cannot know if current navigation instruments and flow gauges were used. Still would think if you averaged numbers for a particular engine/boat they wouldn’t be too far off. Do you agree?
Owner reported consumption numbers are notoriously inaccurate. The exception are the long distance folks like the N47 post a few up from here in this thread. They do it the old fashioned way. Fill up before leaving. Run 200+ hours straight. Fill up again. Do the math.
I've also been on some very recent boats with electronic controls. Theoretically, they should give a very accurate accounting of fuel used. They seem to be off by a good 10% or more.
There was a recent thread of a couple on a fairly large (65?) Hatteras going from Gibraltar to US. Fuel was going to be really tight for them - they had some longer distance runs and had confidence in their numbers. Given the critical nature of being wrong, I believe their estimates. But most owners are wildly optimistic with their fuel burn estimates.
Honestly, when I was delivering, I used a general rule of 1 gal per mile at hull speed, and would adjust up/down based on size, twin vs single, planing vs SD vs FD. No magic. Just a wild guess based on experience. For the most part, over 50-100 hours of running, my guess was usually pretty good. If I'd listed to owners estimates, I'd still be floating 50 nms off Cape Mendocino
Peter