Best fuel economy

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

  1. Forever Mates

    Forever Mates Member

    47
    Aug 3, 2014
    Owen Sound Ont. Canada
    1996-Sea Ray 270 Sundancer 7.4l Single Garmin echoMap 50s
    Single 7.4l Mercruiser Bravo 111 Drive
    Hi My 1996 Sundancer with 7.4 lt single seams to run well at 3000rpm at approx 25mph. Is this about the best for this size of boat.
     
  2. 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
    LOTS of variables. Question 1. Is you engine capable of hitting the the high side of the manufacturers WOT range with a couple of pax, 1/2 fuel and full water? 70-80% of manufacturers recommended WOT is supposed to be optimum. If so, that seems like a great speed for that boat with that setup and optimally, you should be (SWAG here) in the 26-28 MPH range.

    Question 2. Is that GPS speed or dash board speedo speed. GPS is the only reliable gauge.

    Question 3 and most important.... are you going to be more comfortable going faster. If not, then 3000 RPM and 22 knots is good for you. Personally, 22 knots is the sweet spot for my boat, however, I feel 22 knots in Saint Max is a bit fast for these old eyes. If I am single handing, I slow down to 19 - 20 knots and am a lot more at ease. With an experienced set of eyes aboard, I'll kick it up to 26 knots.

    YOU have to know your zones.

    hth
     
    Last edited: Aug 5, 2014
  3. Forever Mates

    Forever Mates Member

    47
    Aug 3, 2014
    Owen Sound Ont. Canada
    1996-Sea Ray 270 Sundancer 7.4l Single Garmin echoMap 50s
    Single 7.4l Mercruiser Bravo 111 Drive
    Thanks for your reply Its also a dual S.S. prop set up I am comfortable at the 20 - 25 mph range for comfort and safety ,I was just curious to know if this was a good speed for reasonable gas mileage, I worked it out that at this speed and rpm I would have a range of about 9.0 hrs of fuel. It has a 100 gallon tank. Where we are located most ports are around 2-3 hrs away for fuel. The boat cruises great at 10-15 mph too but to make it there a little quicker the 3000. rpm seems to work good. This mph reading was GPS. Thanks
     
  4. ImpulseIII

    ImpulseIII Active Member

    Oct 3, 2006
    Jersey Shore/Venice FL
    2001 410 Sundancer
    Caterpillar 3126TA
    Can you back that statement up with any specifics? 3500RPM as a sweet spot seems a bit arbitrary to me considering all the variables that would come into play..
     
  5. fwebster

    fwebster Well-Known Member TECHNICAL Contributor PLATINUM Sponsor

    Oct 6, 2006
    Middle Tennessee ; Panama City Beach, FL
    1996 450DA
    3116 Caterpillars
    No so fast.............

    In 1996 Sea Ray offered two 7.4L engines in the 270.....a carbureted 300hp version and one with MPI rated at 330hp. I don't know which the OP has, but the 300hp 454 fed with a carburetor is in the "suck fuel like no tomorrow mode" at any rpm's above 3200. The carburetor secondaries are vacuum opened and that occurs somewhere between 3100 and 3300 rpm, depending upon load, engine vacuum, altitude, and a host of other variables. Run the 300 hp version at 3500 rpm and you may need a fuel dock to get home because fuel burn goes up almost by a factor of 2X with the secondaries open.

    I have no idea what the most efficient cruise/rpm setting is for the MPI version. Maybe someone who owns one can help us here....................
     
  6. Forever Mates

    Forever Mates Member

    47
    Aug 3, 2014
    Owen Sound Ont. Canada
    1996-Sea Ray 270 Sundancer 7.4l Single Garmin echoMap 50s
    Single 7.4l Mercruiser Bravo 111 Drive
    Hi Frank thanks for the reply I,m quite happy cruising at 20 mph with the four barrels closed so i think that works for me I,ll just tell people to hold supper i will be a bit late lol Thanks again . As a new member to this club i,m glad i found it. Look forward to more questions and answers. I have the 7.4 carb model.
     
  7. MonacoMike

    MonacoMike Well-Known Member SILVER Sponsor

    Sep 15, 2009
    Indiana lakes and Lake Michigan
    97 270DA 5k Kohler A/C,
    85 Monaco 197
    7.4 300hp BII,
    260hp Alpha 1
    I have the 7.4 carbureted model with BII and 3200 RPM is the most efficient RPM on plane per my Garmin with fuel flow meter, somewhere between 3300-3400 the quads open and the meter goes off the charts.

    MM
     
  8. fwebster

    fwebster Well-Known Member TECHNICAL Contributor PLATINUM Sponsor

    Oct 6, 2006
    Middle Tennessee ; Panama City Beach, FL
    1996 450DA
    3116 Caterpillars
    So, does that mean your answer for the OP was:

    a. generally right
    b. generally wrong
    c. pretty much misleading
    d. any of the above
     
  9. ImpulseIII

    ImpulseIII Active Member

    Oct 3, 2006
    Jersey Shore/Venice FL
    2001 410 Sundancer
    Caterpillar 3126TA
    This is clearly a case of Ready-----Shoot-------Aim
     
  10. 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
    If I ran my previous boat (1989 twin 7.4 MIE Carb'd) at 3500 RPM, I'd burn 36gph and make 21mph. 8 open barrels is an arterial bleed of money. No way is that the speed I would be able to run the boat. My sweet spot was around 3250, 19mph, 31gph (as per GPS and FloScans). Give me a tail wind and I'm up to around 20mph at that RPM. 10-15kt headwind, down to less than 18mph. 1/4 tanks of fuel, up to darn near 21mph. Depending on conditions, I'd make 0.59 - 0.70 mpg. Thus my former nickname ("Pokey").

    This boat is a different animal. 2k lbs heavier, no flybridge, 8.1s... and at 3400RPM I'm making 23mph at less than 29gph. Much less dependent on wind. Weight is always a factor. Thrilled to be averaging 0.80mpg at cruise. On the trip back from AC, which involved a 36 mile run on the mighty Atlantic climbing up and down 4' rollers, I still averaged 0.80mpg (these numbers pulled off the engine computer, displayed on the Garmin).

    I would say that each and every gasoline engine is going to have it's own most efficient RPM, when it's installed on a boat. GPH is not the only measure. Sure, on a dyno, you may have a tolerable fuel burn at 3500RPM, but running an a$$-heavy 10 ton gasser at that RPM will make your MPG drop like a rock. Run that clip in a pocket cruiser and it may turn out to be optimal.
     
  11. rcmafgny

    rcmafgny Active Member

    Oct 10, 2009
    Long Island, NY
    2008 33 Sundancer; Kohler Gen set; Simrad electronics
    Twin 8.1 Horizons w/ V Drives
    I resemble the 3500 rpm as optimal in my pocket cruiser!

     
  12. 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
    [​IMG]
     
  13. mistercomputerman

    mistercomputerman Active Member PLATINUM Sponsor

    Jan 6, 2008
    Virginia Beach, VA
    410 Sundancer - 2001
    Twin 8.1L Mercruisers - 2009
    I have a question. If you are going to actively engage in verbal sparring with the populace of CSR, should you hang up your Administrator hat?


    How to Be an Administrator in an Online Forum

    Maintain a neutral, positive voice in the forum at all times. A major part in the role of a forum administrator is to professionally moderate and manage heated discussions and conflicts. Tailor your responses to forum posts and discussions in a manner that adheres to forum rules without becoming too emotional. For example, if a forum member posts an angry comment about another member, politely remind the angry forum member that personal attacks and comments on other members are not permitted in the forum
     
  14. MonacoMike

    MonacoMike Well-Known Member SILVER Sponsor

    Sep 15, 2009
    Indiana lakes and Lake Michigan
    97 270DA 5k Kohler A/C,
    85 Monaco 197
    7.4 300hp BII,
    260hp Alpha 1
    I should add that my boat is has most options and is loaded to the gills. I really need to swap props and I likely would run at a higher RPM without opening the quads.

    MM
     
  15. northshore

    northshore Well-Known Member SILVER Sponsor

    Jan 17, 2011
    Cleveland, OH
    1989 340 Sundancer
    Raymarine E90W Radar/Chartplotter
    Twin 454 Mercruiser 340's
    I gotta ask - you're not a Linux guy are you?
    Reason I ask is once upon a time, my coding style was poo-poo'd by a college prof who told me that's not how Torvalds would do it when doing a Linux driver. He hung up because he did not like me laughing at him.

    I gotta admit ya got some big stones for telling Scott how to behave in his house.
    I would have clipped your account immediately.
    Keep in mind this is an opinion - just like the one that you expressed.
     
  16. Steve S

    Steve S Active Member SILVER Sponsor GOLD Sponsor

    627
    Jun 5, 2007
    Northern IL.
    2000 400 Sedan Bridge with twin CAT 3116's

    2000 340 Sundancer - SOLD!
    210 Monaco 1987 - SOLD!
    Twin Caterpillar 3116's 350 HP straight drives
    OK. Time to throw my hat in the ring... After cruising for some 85 nautical miles yesterday here is what I found. At 3200 rpm my 340 Sundancer would barely hold plane and felt sluggish and like it was mushing. Fuel fuel and 4 people, no water in the tank. It would barely plane with full tabs. At 3400 rpm it would maintain cruise. At 3500 it cruised nicely after I burned off some fuel but at 3600 rpm it sounded like I hit a sweet spot, and it didn't need that much on the tabs. Round trip I burned slightly over 1/2 tank. I filled up prior to departure and now the needle is barely off the the 1/2 tank mark. (I know a scientific estimate.) Let's call it 110 gallons. That is .77 NMPG. So right in the ballpark I expected. Even if I burned 120 gallons... that is .71 NMPG. When I departed the wind was S-SW at 6 or less. Waves less than 1' with a smooth ride. Halfway home the wind turned out of the NE and got stronger. Waves 1-2' with little patches of "whitecaps" Choppy ride the last few miles into the wind..
     
  17. fwebster

    fwebster Well-Known Member TECHNICAL Contributor PLATINUM Sponsor

    Oct 6, 2006
    Middle Tennessee ; Panama City Beach, FL
    1996 450DA
    3116 Caterpillars
    The "big freaking deal" is the accuracy of the information we put out on CSR to insure that readers are not misled. Your answer was clearly wrong for the boat in question simply because it is carbureted. Had you taken the time to examine the variables instead of trying to argue the correctness of a gross generalization, then you would see your answer was misleading to the OP. I believe it is incumbent upon those of us whom Mr. Maier has labeled "technical contributor" to be sure the information we post is on point and accurate. In this case, it was neither.
     
  18. IanBat

    IanBat New Member SILVER Sponsor

    Nov 19, 2011
    Sydney, Australia
    Pro Tournament 36' 1999
    Twin Cummins 5.9L 370hp B Series
    You two guys sure its not winter there?

    Maybe you should move here, it is at least the last month of winter.......even if we are complaing of 20C - 22C being cold.....and 18C freezing
     
  19. quality time

    quality time Well-Known Member

    Oct 30, 2007
    Upper Chesapeake Bay
    2003 480DB and Kencraft 190 CC
    QSM11's
    Why not just say this from the get go?



    Sent from my iPad using Tapatalk HD
     
  20. fwebster

    fwebster Well-Known Member TECHNICAL Contributor PLATINUM Sponsor

    Oct 6, 2006
    Middle Tennessee ; Panama City Beach, FL
    1996 450DA
    3116 Caterpillars
    Scott,

    You cannot have your cake and eat it too. Here is your first comment:

    Generally speaking, 3500 RPM is the most efficient mpg in gasoline engines. THen you went on to defend that generalization by citing "numerous boat test articles"

    Now are you saying you were addressing only carbureted 7.4 powered 270DA's? That is a horse of a completely different color.



    My problem with this whole issue is the accuracy of information that we, who are supposed to be "technical contributors", post on CSR. Your first statement was a blanket generalization posted and argued as fact. I am quite comfortable with my position on accurate information and have absolutely no intention of backing off when I see gross generalizations posted as iron glad proven fact when I know better. If you keep diluting the quality of the content on CSR with inaccurate generalizations, then just get used to answering questions.
     

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