Results 1 to 8 of 8
  1. #1
    Join Date
    Sep 2009
    Location
    Puerto Rico
    Boat
    sea ray
    Details
    31 sundancer 2000
    Engine(s)
    mercruiser mpi 5.7 v-drives,westerbeke 4.5
    Posts
    58

    best cruising RPM's

    I'll like to know what's the best cruising RPM setting for my 2000, 310 da ,mercruisers EFI 5.7 300hp with V-Drives.

  2. #2
    Join Date
    Aug 2009
    Location
    Vermont
    Boat
    Sea Ray
    Details
    2002 Sundancer 300
    Engine(s)
    Twin 350 Mag, Westerbeke Genset
    Posts
    367

    Re: best cruising RPM's

    Some people say 3800, but I'd say it depends on the conditions and where you get best economy.

    We can get almost 2.8 mpg at around 3200 RPM on 1-1.5 ft seas but if it's really nice and calm we'll go faster because we still get around 2.5mpg almost to WOT and it's very comfortable. For us, the conditions of the water will dictate where you end up running. A fuel flow meter is really essential to determine where your boats best economy, for the conditions, will be had.

    Terri
    Best Regards,
    Terri

    2002 Sea Ray 300, 350 Mags, B/III, Westerbeke, Furuno Radar, Lowrance plotter/network
    Prior: 2000 Sea Ray 260, 7.4 MPI, B/III, 1996 Bayliner 225, 5.7 Apha, 1986 Galaxy 195, 3.0 Alpha

  3. #3
    Join Date
    Jul 2005
    Location
    Prosser, WA
    Boat
    Sea Ray!! Duh!!
    Details
    23 year old CLASSIC 300 DA!!
    Engine(s)
    16 cyl, 700 cu. in./Alpha I's
    Posts
    2,559

    Re: best cruising RPM's

    Generally it's slowest speed you can remain on a "crisp" plane. Typically around 3,300 rpms plus or minus depending on load, props and weather. Crisp, meaning not mushing through the water and tabs adjusted for a level ride but not fully deployed (unless this is required for some reason on your boat?). I usually set the rpms and then monkey with the trim on the Alpha's and trim tabs noting the speed changes on the GPS. If I've gained too many rpm's, then I'll back them down a bit and reset everything. Getting on plane with the engines tucked under and the tabs fully deployed I'll adjust the rpm's to around 3,200. From there I can gain two miles an hour(maybe more!) without touching the throttles and just trimming while watching the gps.
    1989 300 DA/Twin 350's
    1987 250 DA/454 Magnum :-( Sold
    Trailered in Spokane, WA
    Chevy Crew Cab DMax Dually

  4. #4
    Join Date
    Oct 2006
    Location
    Orange, CT
    Boat
    Sea Ray
    Details
    1999 270 Da
    Engine(s)
    7.4 MPI w/B3
    Posts
    935

    Re: best cruising RPM's

    Quote Originally Posted by Theresamarie11 View Post
    Some people say 3800, but I'd say it depends on the conditions and where you get best economy.

    We can get almost 2.8 mpg at around 3200 RPM on 1-1.5 ft seas but if it's really nice and calm we'll go faster because we still get around 2.5mpg almost to WOT and it's very comfortable. For us, the conditions of the water will dictate where you end up running. A fuel flow meter is really essential to determine where your boats best economy, for the conditions, will be had.

    Terri
    I am not trying to be adversarial but I find that hard to believe (2.8 mpg). I have a 1999 270 with the same power as you. I have a fuel computer connected to my gps and have checked it the old fashion way on a longer trip. I cruise at around 1.6-1.8 mpg at 27 mph. The only place I have ever seen your numbers in the harbor. Are you sure its not a typo?

    Mark
    1999 270 Sundancer - 7.4 MPI Bravo 3

  5. #5
    Join Date
    Aug 2009
    Location
    Vermont
    Boat
    Sea Ray
    Details
    2002 Sundancer 300
    Engine(s)
    Twin 350 Mag, Westerbeke Genset
    Posts
    367

    Re: best cruising RPM's

    Quote Originally Posted by boatrboy View Post
    I am not trying to be adversarial but I find that hard to believe (2.8 mpg). I have a 1999 270 with the same power as you. I have a fuel computer connected to my gps and have checked it the old fashion way on a longer trip. I cruise at around 1.6-1.8 mpg at 27 mph. The only place I have ever seen your numbers in the harbor. Are you sure its not a typo?

    Mark
    Mark, you're welcome to be adversarial (I'm an engineering manager...I'm used to it). I'm going by the Standard Horizon fuel flow gauge and how close my fill ups are to the gauge usage (so far they're within the limits of error of the gauge - 5%). But I have to admit, I've not done a truely scientific evaluation.
    I don't live on the Ocean, but on Lake Champlain, and others I've corresponded with seem to be in the same ball park. I've not corresponded with anyone who gets mileage as low as yours. For me, 2.5 is typical (calm or 1'/seas) where 2.8 is with the current (typ S>N on our lake). I can get down to the low 2's if I'm trimmed badly or weather is bad, but it's far from normal. 1.X is nothing I've seen yet, even at WOT.

    Maybe my gauge is under-reporting, but then I'd expect my fill ups to be inconsistent with my usage numbers and so far they don't seem to be.

    Or maybe you're 'harbor' weather is what I see as typical on Lake Champlain. The lake is only 10mi wide at it's widest point so we don't get big waves or big rollers (fetch is not that long).

    Also, I never cruise that slow (27mph) unless the weather is expecially bad.. When you're at 27mph, what is your RPM? What is your prop pitch? Do you have a bravo3?
    My prop pitch is 24" with a bravo 3. Boat is trailered and very clean. My bottom has no paint but does have a very smooth epoxy coat.. it's like glass.

    We have a few more weekends before winter, and I'll try to do a little more scientific study (the limitation being how consistently I fill my tank up each time). I'll report back.
    Best Regards,
    Terri

    2002 Sea Ray 300, 350 Mags, B/III, Westerbeke, Furuno Radar, Lowrance plotter/network
    Prior: 2000 Sea Ray 260, 7.4 MPI, B/III, 1996 Bayliner 225, 5.7 Apha, 1986 Galaxy 195, 3.0 Alpha

  6. #6
    Join Date
    Oct 2006
    Location
    Orange, CT
    Boat
    Sea Ray
    Details
    1999 270 Da
    Engine(s)
    7.4 MPI w/B3
    Posts
    935

    Re: best cruising RPM's

    Quote Originally Posted by Theresamarie11 View Post
    ...(I'm an engineering manager...I'm used to it). .....When you're at 27mph, what is your RPM? What is your prop pitch? Do you have a bravo3?
    My prop pitch is 24" with a bravo 3. Boat is trailered and very clean. My bottom has no paint but does have a very smooth epoxy coat.. it's like glass.....
    Funny - I am an engineering manager too :) Anyway - my prop is 22p w/a 2:0 ratio drive b3. I think my cruise rpm is about 3500 at the 27 mph. Now I do have bottom paint but I was just very surprised to hear your numbers. IIRC others here with the same boat has similar numbers to me. Besides, engineers never believe what they hear........... at first :)
    1999 270 Sundancer - 7.4 MPI Bravo 3

  7. #7
    Join Date
    Dec 2007
    Location
    Saanichton BC Canada
    Boat
    Bayliner
    Details
    2002 model 3788
    Engine(s)
    Twin Cummins 6BTA's
    Posts
    891

    Re: best cruising RPM's

    3500 rpm (or very close to it)... which is maximum torque / volumetric efficiency.


    "MOTLEY CREW"
    2002 Bayliner 3788

    Previous Sea Rays; '07 290 DA / '06 240 DA / '03 240 DA / '96 240 OV / '85 230 WE
    Future Sea Ray; '08 44 Sedan Bridge


  8. #8
    Join Date
    Aug 2009
    Location
    Vermont
    Boat
    Sea Ray
    Details
    2002 Sundancer 300
    Engine(s)
    Twin 350 Mag, Westerbeke Genset
    Posts
    367

    Re: best cruising RPM's

    Quote Originally Posted by boatrboy View Post
    Funny - I am an engineering manager too :) Anyway - my prop is 22p w/a 2:0 ratio drive b3. I think my cruise rpm is about 3500 at the 27 mph. Now I do have bottom paint but I was just very surprised to hear your numbers. IIRC others here with the same boat has similar numbers to me. Besides, engineers never believe what they hear........... at first :)
    Cool... what field? My field has nothing to do with boats (Semiconductor Development) but nevertheless, as you know, when you have a mind for engineering you can problem solve and design solutions across across many disciplines with a bit of practical knowledge to get you going. BTW.. I agree with you on never believing what you hear... I question everything too.

    To compare on RPMs, At 3100/3200 RPM I'm running between 29.X-31.X MPH. And it all depends on the water.

    After reading this I did did a couple of web searches and found some folks who were getting around 2.0/2.1 mpg (both single 454 and twin 4.3's...so almost the same mileage).

    To me this isn't much of an mystery (at first blush) given your boat is bigger (wider/longer) and quite a bit heavier than the 1' would indicate and has things like bottom paint, which I understand, can effect speed and efficiency. It's about 1300 pounds heavier dry. Which would indicate it probably has bigger tanks as well and all the things that goes with more area (more stuff added on to that dry weight).

    Anyways, I'll do more semi-scientific tests over the next couple of weeks to see if I have an issue with my numbers.
    Best Regards,
    Terri

    2002 Sea Ray 300, 350 Mags, B/III, Westerbeke, Furuno Radar, Lowrance plotter/network
    Prior: 2000 Sea Ray 260, 7.4 MPI, B/III, 1996 Bayliner 225, 5.7 Apha, 1986 Galaxy 195, 3.0 Alpha

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