Originally Posted by sgunes
As some have pointed out, most of the manufacturer's range estimates are not with a fully stocked boat, generators running and possibly facing adverse currents and wind
So, your 30-40% deduction will get me the actual safe range.
To do 800nm safely (with some 20% reserve) I would have to find something that is advertised as 1200-1400nm.
I disagree on the characterization of manufacturer's range estimates. Most are very careful and make it clear exactly what they're based on. The various reviews also are accurate in that regard as they test with excellent equipment
and state the conditions. But in the past two years I've used many different boats and found fuel usage to be right on target. Now one note, most are done with 10% reserve but again that's clearly stated and easy to convert to what you feel is adequate reserve. Also, very few are done at the absolute best fuel usages.
Now when you're full of everything and heavily loaded, obviously it will worsen. So I guess what I'm saying is it's not the estimates, it's our use of them that is critical. I just looked at a test on a Carver 34 and it states "2 persons, full fuel, no water
, 50 lbs of gear". I read a test of a Grand Banks
54 that read, "full fuel; 200 gal. water
, 10 persons, 500 lb. gear
So, be cautious, not because their estimates are misleading but because they may not represent your situation or your level of reserve desired. One factor often overlooked is sea conditions. On a trawler
going against the current
and winds can be important.
The reserve is a very complex issue. I've heard many numbers tossed out. Some say 30%. But much long range cruising would have to stop at 30%. 30% of 200 gallons is one thing, but when it comes to 10,000 gallons of fuel it's excessive. One thing we do is look at range at an economical mode but not our absolute best. Then we know we can always slow if necessary. Also make sure along the way you've conserved so when you reach half way you have more than half a tank left.
Here's an example. The boat we are on as I'm typing this. Tested range is on 54 degrees, light seas, two way average, full fuel, full water, 3 persons, 600 lbs. and based on 90%. Given that range at 20 knots is 550 miles, at 12 knots is 1382 miles, at 10 knots is 1734 nm. So what do I know. Well, we're not in light seas, we have 2-3' wind waves and 8 ft swells at 13 seconds. We have 8 people, not 3. We have far more than 600 lbs. At least four or five times that. Now we've actually tested usage some today. In spite of conditions it's very little different than the tests. I attribute it to newer engines with slightly better economy. If I had to go 1700 nm how would I feel? Well, the 10% would scare me and the 1734 at 10 knots too close. But I also know that the lowest speed tested of 10 knots was both engines at 1000 rpm
. So we slowed to 750 rpm
to test. Our range at 750 rpm is 2500 nm. Would we normally run that? No. But could we to increase range, yes. Could we go to one engine
, yes. Still I'd set my comfort level at 1500-1600 nm.
My point is too that you need to know your own boat. Take flow equipment
on a sea trial if you're doing a trial and survey
. Every boat is slightly different. Study your boat at all speeds. Don't estimate just in "we took this trip mostly at this speed and used this much." That's decent for an estimate but that's not something to base long cruises on and doesn't equip you to know all the options. The equipment isn't expensive and it's accurate.