Click for Abeking Click for Westport Click for MotorCheck Click for Nordhavn Click for Burger

Fuel consumption figures 12V71 at 670 hp

Discussion in 'Technical Discussion' started by Tom H, Apr 17, 2010.

You need to be registered and signed in to view this content.
  1. Tom H

    Tom H New Member

    Joined:
    Apr 17, 2010
    Messages:
    18
    Location:
    Magnetic Island, Queensland Australia
    Hi there. Is anybody able to please help me with fuel consumption figures and hull speed at different rev's for these engines. I have a late 70's model 92 foot Broward, 18'6" beam with stabilisers weighing around 90 ton loaded. I haven't yet set foot on the vessel, but for the sake of some pre voyage route and fuel planning could do with some help. I'm looking for the most economical range. I have some information available from the previous owners but tend to think they are a little light on.
  2. Henning

    Henning Senior Member

    Joined:
    Sep 22, 2009
    Messages:
    940
    Location:
    Ft Lauderdale FL
    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.
  3. Tom H

    Tom H New Member

    Joined:
    Apr 17, 2010
    Messages:
    18
    Location:
    Magnetic Island, Queensland Australia
    Hi, thanks for the reply. on what hull are you basing this on, is this personal experience or estimate. I have figures on a 77 Hatteras doing 8 knots claiming 11.4 gph and a 91 Broward owner claiming 10-12 knots at 18 gph. These sound light but a lot more encouraging than yours.
  4. Henning

    Henning Senior Member

    Joined:
    Sep 22, 2009
    Messages:
    940
    Location:
    Ft Lauderdale FL

    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.
  5. Tom H

    Tom H New Member

    Joined:
    Apr 17, 2010
    Messages:
    18
    Location:
    Magnetic Island, Queensland Australia
    He was claiming both which seems low. I'll sit back and see who else can provide numbers, preferabley a Broward owner would help. It's just trying to prepare for that Galapagos thru Marquesas Islands leg, all will be revaled in the Carabean but will help with buying bladder bags in the USA.
  6. Henning

    Henning Senior Member

    Joined:
    Sep 22, 2009
    Messages:
    940
    Location:
    Ft Lauderdale FL
    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....
  7. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    14,432
    Location:
    Fort Lauderdale
    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.
  8. Trinimax

    Trinimax Senior Member

    Joined:
    Jan 18, 2010
    Messages:
    237
    Location:
    Trinidad and Tobago Yacht club
    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
  9. Tom H

    Tom H New Member

    Joined:
    Apr 17, 2010
    Messages:
    18
    Location:
    Magnetic Island, Queensland Australia
    Max flow per engine

    Thanks for the input. What is the Max flow per engine so I can order the correct gauge for a flow scan? More fuel figures especially on Browards or different hulls appreciated
  10. Captain Dee

    Captain Dee New Member

    Joined:
    Aug 2, 2013
    Messages:
    4
    Location:
    Kerrville Texas
    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?
  11. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    12,647
    Location:
    Satsuma, FL
    Consumption per rpm? yes, per hull speed? hard to say. We have 12v71ti in our 58' Bertram MY. Most of the numbers above are close per rpm. Per hull design those numbers varied greatly.
    Good luck.
  12. Tom H

    Tom H New Member

    Joined:
    Apr 17, 2010
    Messages:
    18
    Location:
    Magnetic Island, Queensland Australia
    My consumption figures

    Wow this threads been around for a while. I bought the 93 foot Broward and motored it across the Pacific to Australia in 2010. With a fresh bottom job doing between 6.5 to 7.5 knots most of the 9600 NM we averaged 4.2 litres (3.88 litres to a US gallon) per nautical mile inc the generator. Ran around 900 RPM 24/7 with a 15 minute 1500 RPM burst twice daily. Had to close the doors to avoid the smoke alarms going off for the first few minutes till she cleared. Runs beautiful, no soot, no smoke. Magnificent engines
    With 18 months on the anti foul and a little grubby-
    850 RPM 32 LPH
    900 RPM 36 LPH
    1050 RPM 50LPH
    1200 RPM 70 LPH
    1500 RPM 120 LPH
    If anything the flow scan is reading a little high which I don't mind as it compensates for the generator.
    For those interested in one engine running, always using the down sea motor, we found around a 10% drop in speed which the 2 -3 knot current on the equator during the 3400 NM stretch negated and even sped things up. Aprox a 10% increase in fuel consumption on the one motor at the same time.
  13. Captain Dee

    Captain Dee New Member

    Joined:
    Aug 2, 2013
    Messages:
    4
    Location:
    Kerrville Texas
    Thanks for the info. I will put it to the test next month. We are going from Seattle to Panama for the winter.
  14. K1W1

    K1W1 Senior Member

    Joined:
    Sep 30, 2005
    Messages:
    7,388
    Location:
    My Office
    Hi,

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