6-71N fuel burn & speed info

[eze2bme]

For anyone’s info and use, here are some performance numbers from today’s run on my 1979 43DC with 310 HP Johnson & Towers 6-71N’s (DD) with N-80 injectors (3300 hrs). The racks were set and calibrated 120 hours ago; fresh oil change; fresh fuel filters; and the bottom was clean. 24x24 props. In fresh water at average water depth of 80 feet with 8-10 mph head wind and 1-2 foot swells.

1200 rpm - 7.3 knots
1400 rpm - 8.2 knots
1600 rpm - 9.3 knots
1800 rpm - 10.1 knots
2000 rpm - 11.2 knots
2200 rmp - 12.8 knots
2450 rmp (WOT) - 16.4 knots

Fuel burn per engine according to FloScans:

1200 rpm - 1.5 gal/hr
1400 rpm - 2.5 gal/hr
1600 rpm - 5 gal/hr
1800 rpm - 7 gal/hr
2000 rpm - 9 gal/hr
2200 rpm - 11.5 gal/hr
2450 rpm - 15 gal/hr

 

[spartonboat1]

Thanks for that great info.

I made a similar earlier post, but realized this weekend that I had posted mph figures, but represented as knots; so my post was incorrect. Yours is a great update!

So I watched my numbers on the GPS this last weekend and made sure they were in knots. My figures in freshwater match yours in a similar vessel, '72 43'MY with 310hp J&T.

I hope my fuel consumption is a good. The old rule of thumb I had read was .7 mpg, but most of yours are better than 1.0 mpg, which is very good indeed. Using your figures at 2200 rpm, I calculated 1.1 nmpg or 1.3 smpg, using 1.15 conversion factor for knots to statute mph.

With 375 gallon tankage (unfortunately, I know that to be accurate), I try not to get below 25% reserve, which would be roughly:
> 95 gals rsv or
> 280 gals runtime fuel (94 and 281 computed).


Using your values as inputs, that would allow 312 naut miles or 358 stat miles of running distance on the 281 gals runtime, and 106 naut miles or 122 stat miles of reserve. Since the State of Michigan has a network of safe harbor marinas every 26 miles or so (except Lake Michigan south of Mackinaw City- other stretches?), then 95 gals should be reasonable on the Great Lakes, esp. MI.

Hope my spreadsheet entries were correct.

Thanks again!

 

[Freestyle]

Thanks for the update. The knots - mph difference had me kind of disappointed in my boat's performance. (1976 DC w/ 283 hp J&T 6/71N).

I have tried to replicate that info by keeping a log. But the dipstick method of fuel measurement has a few inaccuracies your flo-scans must have solved.

I assume my lower horsepower rated engines would get a little better mileage. Does cruising in salt water increase efficieny because of the added buoancy or are there other factors? (Other than current).

With the high price of fuel this summer I have slowed to the 8.2 range. I am thinking about backing it down even further given the 2.4 knot mpg you get at 1200 RPM's.

Thanks again for the info.

Bruce
at anchor Key West, FL