Fuel consumption figures 12V71 at 670 hp

I'd guess at economy cruise which will be about 8-9kts and light seas you'll be around 25-30gph with the generator running. Your fuel consumption will go up exponentially from there to around 70-75 gph at 16-17 kts. That's a rough estimate given a semi-displacement hull form and a 40 kw generator with A/C and refrigerators running.

My numbers come from delivering and running a lot of different boats over 20+ years. A 91 Broward with 12/71s may have done 12 on 18gph a side + Generator, sounds more likely to me. For an example, right now I run a 110' Kingship (displacement hull) with electronic 3406s rated at 550hp. I just ran from Brisbane to Cairns at 10.5 kts using 35gph at 60% load. When I put the throttles down to 100% load I go to 12.6 kts (hull speed) and burn 71gph, also add generator fuel. If I slow it down to 8 kts I burn 18gph.

7-8 kts may see 18 on both, might make 9 on 22 in glass smooth water. Don't forget about that genny running 24/7 either....

It doesn't matter what motoryacht they're installed in, if they're both propped to hit 2300 rpms at WOT, then fuel burn should be very similar. I ran a 75' Hatteras MY 6200 NM's with 12v71 TI's. At 800 rpm's I'm burning about 8gph with both engines and doing around 8.5 knots. At 1000 rpm's they're burning around 12 gph's for both engines and I was doing 10 knots properly balanced. Once you go past 1,000 rpm's they start drinking the fuel, at 1200 rpm's you're at 25gph's for the pair. I would run them 6 hours at 1,000rpm's then bring them up to 1950-2000 rpms for 30 mins to clean them out as DD's recommendations. At 1950-2000 rpm's I'm burning 80-90gph depending on load, speed etc.....(If it was balanced right with weight/fuel and cruised at 17 knots it was closer to 80gph, if it was at 15.5 knots and not quite on plane closer to 90gph)

Browards have a relatively flat stern, and the ones I've ran have a good hull speed. So I would guess at 1,000 rpm's you should be doing 10 knots in a 100' +/- Broward, one I ran with an extension did 12 knots at 1,000 rpms. The fuel burn you've been hearing sounds right.

here are some figures for the fuel burn of a 70ft bertram MY on yachtworld with those same engines, 12 knots @ 1500 RPMs= 30 gph; 16 knots @ 1800 RPMs = 50 gph. and 1200 RPMs=10 knots and only 13gph. I could back these figures up as I crewed on the same type of vessel from Trinidad to Martinique and back which is about 550 miles. We cruised at 1200-1300 rpm doing 10 kts and we burned a little over 700 gallons and this includes running the generator for 4 days.

hope this helps

max

I am planning to purchases a 90 McQueen Motor Yacht with 12v71's. Do you think the fuel consumption would be similar to the Boward?

Thanks for the info. I will put it to the test next month. We are going from Seattle to Panama for the winter.

Hi,

You might want to check that number, the industry accepted value is a lot closer to 3.78541 lts to a US Gal.