How do I find the recommended cruising speed?

Discussion in 'Sport Boats' started by Slimcobra, Feb 2, 2018.

  1. Slimcobra

    Slimcobra Member

    86
    Aug 14, 2017
    Port St. John, FL
    2000 Sea Ray 210 SunDeck
    Mercruiser 5.0 w/ Alpha 1 Gen 2
    I am plotting some courses with the Navionics app and I have my boat size filled in but I would like to add cruising speed as well. I have searched all the books I have and all over the net and have not been able to find the answer. Any suggestions? I have a 2000 210 Sundeck and to mee if the chop is low it feels good around 35 mph. Should I go with that?
     
  2. Lazy Daze

    Lazy Daze Well-Known Member TECHNICAL Contributor GOLD Sponsor

    Apr 21, 2009
    PA
    Various
    Various
    Roughly... most economical planing speed should be somewhere in the low to mid 3,000 RPM range. Compare that to the speed you get at that RPM. 35mph sounds high for an economy cruise on that boat. I'm guessing somewhere around 25mph.
     
    JVM225 likes this.
  3. juggernaut1

    juggernaut1 Active Member

    742
    Apr 19, 2015
    Perth, Western Australia
    2006 38 Sundancer
    8.1S / ZF 63V Drives
    I would go with what you typically cruise at as this will provide the most realistic eta and fuel burn on the Navionics app.
     
  4. Gofirstclass

    Gofirstclass Well-Known Member GOLD Sponsor

    Apr 20, 2010
    Tri Cities, WA
    1995 550 Sedan Bridge,
    2010 Boston Whaler 130 Super Sport,
    1981 Boston Whaler 130 Sport,
    CAT 3406C's, 580hp.
    Slim, I think Lazy nailed it. There are actually a few different speeds for any boat and the fuel economy will vary with each speed, sometimes dramatically.

    The lowest of those speeds is just about idle, but boats tend to wander side to side quite a bit and require constant steering effort to maintain a heading.

    Next up is "hull speed" and this will vary with the length of the hull at the waterline. There's a formula to figure it: 1.34 x square root of the length of the hull at the water line (LWL). That will be a very efficient speed.

    As you go above that speed the stern of the boat tends to sink down into the water because you're outrunning your bow wave. The bow rides high and the boat is plowing through the water. This is VERY a inefficient speed.

    As you increase speed your boat will transition from plowing through the water to riding on plane on top of the water. This speed, "planing speed" is also efficient and may be your boat's most efficient way to run. The bow drops and the stern of the boat is supported by the water running beneath the hull. This efficient speed may well be from about ~3200 rpm's up to ~4,000 rpm's.

    From there, the faster you run the less efficient your boat will be. WOT speed is REALLY sucking down the gas.
     
  5. Slimcobra

    Slimcobra Member

    86
    Aug 14, 2017
    Port St. John, FL
    2000 Sea Ray 210 SunDeck
    Mercruiser 5.0 w/ Alpha 1 Gen 2
    Thanks guys. I'll try to pay closer attention to rpm at different speeds while on plane and see what the lowest rpm I can run at and stay up on plane.
     
  6. Strecker25

    Strecker25 Well-Known Member SILVER Sponsor

    Nov 20, 2014
    Rochester, NY
    1998 290 Sundancer
    Twin 5.7EFI/Alphas, Kohler 4kw
    To help ballpark consumption I used this site.

    http://www.boat-fuel-economy.com/mercury-mercruiser-3.0-181-fuel-consumption-us-gallons

    I don't have fuel flow meters on our engines so instead I went for test runs at all different RPM's and recorded the GPS measured speed at each. I did idle, 1200,1500,2900(planing),3000,3200,3400,3600,and WOT

    Armed with the speed numbers I went to the page for our twin engines and was then able to calculate rough GPH/MPG at different speeds. Using a few different fill ups and tracking the mileage traveled I was able to verify that site is pretty accurate. Flow meters would be best, but they're expensive, so I thought this method worked pretty well.
     
    Slimcobra likes this.
  7. Maggieiscrazy

    Maggieiscrazy Member

    123
    Oct 14, 2016
    Northern Wisconsin
    240 Sundancer
    5.0. Bravo III
    IMG_0645.PNG
     
  8. Creekwood

    Creekwood Well-Known Member GOLD Sponsor

    Apr 26, 2009
    Oakville and Georgian Bay, Ontario
    '97 330 Sundancer
    2X 454 w/ vDrives
    When
    When I had my last boat I put a lowrance gps sounder on it. Then I added their fuel flow meter. It was plug and play at less than $100. Very handy.
     
  9. Leardriver

    Leardriver Member

    130
    May 24, 2016
    Denver, CO
    2004 270 Sundeck 8.1 Bravo III
    5.0, 5.7, 6.2 8.1 Bravo III over the years
    Here is a fuel flow chart for a 350 mag.
    As you can see, from about 3300 to 4200 RPM, you are using roughly the same amount of fuel per mile traveled, with the option of speeding up or down for conditions, bladder urgency, or dinner time. I was surprised that the efficiency was so high over 4000.
     

    Attached Files:

  10. Strecker25

    Strecker25 Well-Known Member SILVER Sponsor

    Nov 20, 2014
    Rochester, NY
    1998 290 Sundancer
    Twin 5.7EFI/Alphas, Kohler 4kw
    That's a great deal. We have raymarine gear. I believe the lowarance and garmin fuel flow units would work, but I'd have to build up a seatalkng to nmea network to get it all talking and at that point I would go for the fox-marine units at 250/each and get all the engine data I could ever want.
     
  11. Slimcobra

    Slimcobra Member

    86
    Aug 14, 2017
    Port St. John, FL
    2000 Sea Ray 210 SunDeck
    Mercruiser 5.0 w/ Alpha 1 Gen 2
    So now you guys have me scoring the internet for something I have for my car. I have a bluetooth adapter that plugs into my data port on my car that connects to my head unit running Android and I can see real time engine data on the screen. I see Fusion has something similar but does anyone know of an Android enabled app and adapter that for Mercruisers that works in a similar fashion?
     
  12. Strecker25

    Strecker25 Well-Known Member SILVER Sponsor

    Nov 20, 2014
    Rochester, NY
    1998 290 Sundancer
    Twin 5.7EFI/Alphas, Kohler 4kw
    https://fox-marine.com/
     
  13. Slimcobra

    Slimcobra Member

    86
    Aug 14, 2017
    Port St. John, FL
    2000 Sea Ray 210 SunDeck
    Mercruiser 5.0 w/ Alpha 1 Gen 2
  14. Strecker25

    Strecker25 Well-Known Member SILVER Sponsor

    Nov 20, 2014
    Rochester, NY
    1998 290 Sundancer
    Twin 5.7EFI/Alphas, Kohler 4kw
    Ah sorry I didn't read it close enough, I saw Android mentioned but didn't realize it was coming soon.
     
    Slimcobra likes this.
  15. JVM225

    JVM225 Well-Known Member

    Apr 8, 2008
    Farmingdale, NY
    2002 410 Sundancer, Monaco Edition.
    3126 Cats.
    Sounds about right to me.
     
  16. sbw1

    sbw1 Well-Known Member

    Oct 10, 2006
    West Michigan
    This is listed in my signature
    This is listed in my signature
    We don't pay much attention to a partucular cruising speed when plotting a course since that plotting usually takes place in a slip the day before going on the cruise. Once the course is in the computer, we will sometimes add different speed data to get various ETAs for further planning purposes. However, cruising speed on open large bodies of water is always heavily dependent on wave heights. You end up making the best speed that is comfortable, and the ETA is displayed based upon real conditions what ever those happen to be on the day of the trip.
     
  17. bobeast

    bobeast Dance the Tide SILVER Sponsor

    462
    Oct 22, 2017
    Isleton, CA
    2002 310DA
    350 MPI w/V-drives
    ^^ this ^^. In addition, the fox marine adapter hooks up to your NMEA 2000 network to display some of the data (although not as much) on your MFD. Definitely on my short-list.
     

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