Best fuel economy

Discussion in 'Announcements & FAQs' started by Forever Mates, Aug 5, 2014.

  1. IanBat

    IanBat New Member SILVER Sponsor

    Nov 19, 2011
    Sydney, Australia
    Pro Tournament 36' 1999
    Twin Cummins 5.9L 370hp B Series
    My best economy is with the keys out of the ignition.......anything after that hurts
     
  2. KC_Sundancer

    KC_Sundancer New Member

    Sep 8, 2009
    Munising, Michigan (Lake Superior) Pictured Rocks
    1985 270DA Sundancer,Simrad 4G Radar,Lowrance Gen2 GPS/Sonar/Structure Scan,F350 7.3l Diesel, tri-ax
    twin Mercruiser 185R's (v6's) w/SE106 drives, "High Five" stainless props, Mercury 280 RIB w/9.9 Mer
    There's the answer we needed. :grin:
     
  3. Sea Gull

    Sea Gull Active Member

    Oct 19, 2006
    CT
    2015 L650 Fly #509
    CAT C-18, 1,150 HP
    For what it's worth, I had to go back to my log books from the late 90s to see what the performance was like on my last gasser. It was a 370DA with fuel injected 7.4s. The best cruise was at 3300 giving 1.5nmpg. at 3450 the efficiency dropped to 1.25nmpg. That's a 17% difference (about 60 nm range on a tank of gas) which I consider to be pretty significant.
     
  4. Turtlesboat

    Turtlesboat Minister of Media TECHNICAL Contributor GOLD Sponsor

    Feb 4, 2007
    New York City
    1996 450DA, TNT, Caribe dink w/15hp OB.
    3126 427HP TD transmissions
    1.5nmpg is pretty damn good for a gas boat.
     
  5. rondds

    rondds Well-Known Member SILVER Sponsor

    Oct 3, 2006
    Jersey Shore
    2001 380DA
    Merc 8.1s (2008)...Hurth ZF 63 V-drives...WB 7.0 BCGD (2013), Garmin 8208 & 740 MFDs, GMR 24xHD dome
    Slight topic change here...

    Is it safe to say that you should run any engine at an RPM that is as low as possible to produce comfort and efficiency? On my 340 it just seemed that anything over 3300 RPM was a "strain." Does higher RPM produce more wear and tear and degradation over the life of the engine?

    Take an outboard motor. I'm making these numbers up... If you run it at 4400 RPM you can get, let's say, 2.5MPG b/c most of the boat is out of the water and you're flying along at 52 MPH. If you run it at 3600RPM and you drop to 1.7MPG, would it be true that the lower RPM, lower speed and lower economy numbers are healthier for that engine?
     
  6. firecadet613

    firecadet613 Active Member

    May 10, 2007
    Indiana
    '08 H240
    5.7
    3500rpm in my boat is the best economy, but the boat feels sluggish. 3800rpm is where I cruise for the best performance/economy mix, and the boat just feels like it is cruising right. 4100rpm is even better, but to avoid excessive wear I don't run it that fast. Last boat I'll buy with the smaller of the engines offered.

    It's not underpowered, but just can't cruise where it wants to without really spinning the engines.
     
  7. KC_Sundancer

    KC_Sundancer New Member

    Sep 8, 2009
    Munising, Michigan (Lake Superior) Pictured Rocks
    1985 270DA Sundancer,Simrad 4G Radar,Lowrance Gen2 GPS/Sonar/Structure Scan,F350 7.3l Diesel, tri-ax
    twin Mercruiser 185R's (v6's) w/SE106 drives, "High Five" stainless props, Mercury 280 RIB w/9.9 Mer
    Good question. The lower RPM and slower speed increases your engine hours to get to you destination. To expand the question: Are less hours at a higher rpm healthier than more hours a bit slower?

    Different set-up but I find it more efficient to be running a bit faster, on top of the water, 3800 rpm with v6's. You can feel the engines don't need to push as hard at a certain point, RPMS increase only about 200 but mph jumps almost 5. That sweet spot - water conditions permitting.

    It's all a big balancing act. I found you just need to get out there and keep track of how your running and try different scenarios to see what ends up working best.
     
  8. mistercomputerman

    mistercomputerman Active Member PLATINUM Sponsor

    Jan 6, 2008
    Virginia Beach, VA
    410 Sundancer - 2001
    Twin 8.1L Mercruisers - 2009
    I respectfully disagree.

    As of late you seem to have taken to verbal sparring with several of the members who dare to disagree with the thoughts you advocate. If you wish to do that, I am of the opinion that you should hang up your administrator/moderator hat and move back to the general membership and let someone more level-headed act as the administrator. I do not believe that you are not representing Jim's interests very well when you get into name-calling of the members here or act in a disparaging manner, close posts after you put in the "last word", or delete posts entirely because of personal reasons (what happened to the ECM thread), just to name a few.

    On the other hand, as a regular member not endowed with super-powers, feel free to engage in all the name calling the new administrator will allow.
     
  9. Mikemapva

    Mikemapva Member

    477
    Aug 6, 2007
    Potomac River, VA
    2001 Chaparral Signature 300
    Twin 5.0 Volvo DPs with 7KW Kohler
    As another data point, my 250DA with the 7.4L and Bravo 1 was most efficient around 3200 RPM's according to my Navman fuel flow meters. My new boat, does not have any type of fuel measuring devices, but it seems that if my sweet spot is 3000-3200 RPM's with my 30' Chaparral running twin 5.0 Volvo's with duoprops. I haven't run a full tank through to confirm numbers though.
     
  10. dpmulvey

    dpmulvey New Member SILVER Sponsor

    Dec 19, 2007
    Homeport: Charles City, VA
    1999/2007 330 Sundancer Hardtop.
    6.2 Merc Horixons
    1.5:1 Velvet Drives
    [slight hijack]

    If the 340 is running the 9x22 tabs, try getting them enlarged to 18x22. I did it and it made all the difference in the world in ride and fuel consumption. I average 1nmpg @ 3450 RPM @ 22kts.


    Now back to our regularly scheduled program.

    [/slight hijack]
     
  11. Sea Gull

    Sea Gull Active Member

    Oct 19, 2006
    CT
    2015 L650 Fly #509
    CAT C-18, 1,150 HP
    That does seem high. Maybe that was only the fuel burn of one engine, meaning 0.75 nymph was the actual burn with both engines. My memory is failing me.
     
  12. Turtlesboat

    Turtlesboat Minister of Media TECHNICAL Contributor GOLD Sponsor

    Feb 4, 2007
    New York City
    1996 450DA, TNT, Caribe dink w/15hp OB.
    3126 427HP TD transmissions
    I'm still impressed you have logs that far back. I can't find what I wrote down yesterday.
     
  13. searay40dad

    searay40dad New Member

    Oct 23, 2006
    Western KY/Panama City FL
    2001 480 Sedan Bridge w/ Novurania RIB
    660 hp CAT 3196's
    That was what I was thinking when I read your numbers (the .75 part not your memory is failing). My 3 former 7.4L gassers ranged from .6 to around .8...one was smaller and two larger than your 370. The two 400's never met a fuel dock they didn't like.
     
  14. rondds

    rondds Well-Known Member SILVER Sponsor

    Oct 3, 2006
    Jersey Shore
    2001 380DA
    Merc 8.1s (2008)...Hurth ZF 63 V-drives...WB 7.0 BCGD (2013), Garmin 8208 & 740 MFDs, GMR 24xHD dome
    1.5 is good for a diesel boat!

    I get 1.4mpg...at about 1400 rpm! Still only gives me a usable range of 360 st miles.
     
  15. searay40dad

    searay40dad New Member

    Oct 23, 2006
    Western KY/Panama City FL
    2001 480 Sedan Bridge w/ Novurania RIB
    660 hp CAT 3196's
    yep, it is. for comparison if anyone's interested...

    fuel.jpg
     
  16. Hifirush

    Hifirush Member

    542
    Mar 21, 2014
    North Padre Island
    1998 330 DA, 7.4 MPI with V-Drives, raw water cooled, Westerbeke
    twin 7.4 MPI’s with V-Drives
    David,

    I’d love to talk with you about that! I’m seriously thinking of doing the same thing, I saw that another member who has 340 did it and I have had that on my research and maybe do it list!

    Matt
     
  17. Chris Nowell

    Chris Nowell Active Member SILVER Sponsor

    Nov 28, 2011
    Lake Okanagan, Kelowna B.C.
    '05 622 Hardtop w Alaska Bulkhead, 270 Mercury Marine sport inflatable, pulled by a 6.0L Silverado
    4.3 MPI Merc w Alpha I drive, 5 hp 4 stroke Merc aux.
    welcome to the forum, Forever Mates:grin:
     
    Last edited: Aug 6, 2014
  18. dpmulvey

    dpmulvey New Member SILVER Sponsor

    Dec 19, 2007
    Homeport: Charles City, VA
    1999/2007 330 Sundancer Hardtop.
    6.2 Merc Horixons
    1.5:1 Velvet Drives
    you won't regret it. I brought Saint Max from Wilmington, NC to RIC and with full original tabs at 3800 RPM I could barely get the bow over. Now granted, the boat was mis propped plus a number of other things Marine Max did not disclose, however, with the new tabs and properly fitted and tuned PropScan props, my numbers went from a bow high 3800 RPM 38 GPH 20 knot dog to a bow proper 3450 RPM 22GPH 22knot cruiser.

    YMMV.

    Let me know if I can assist in any way.
     
  19. New350ec

    New350ec New Member

    14
    Jun 29, 2014
    Lake St. Clair
    1991 Sea Ray 350 EC
    (2) 330hp Mercruiser
    Just respectfully checking the math here. 3500rpm, 36gph, 21mph. So,in 10 hours of running you burned 360 gallons and covered 210 miles. The same trip, running at 3250 rpm you're burning 31gph at 19mph. To cover the same 210 miles, you need to run 11.5 hours @ 31gph,burning a total of 356.5 gallons. So, over 11.5 hours of running you only saved 3.5 gallons total! That's what is deceiving about fuel economy on the water. Burning more fuel per hour can be MORE beneficial if the added speed cuts down on the total running time.

    Edit - 11.05 hours of running time (at 19mph) = 342.5 gallons, not 356.5! At 342.5 you saved $78.75 over 10 hours, which s a decent savings for sure.
     
    Last edited: Aug 7, 2014
  20. Hifirush

    Hifirush Member

    542
    Mar 21, 2014
    North Padre Island
    1998 330 DA, 7.4 MPI with V-Drives, raw water cooled, Westerbeke
    twin 7.4 MPI’s with V-Drives
    Hi David, PM sent!

    Matt
     

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