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42 post 671N

Discussion in 'Post Yacht' started by bigjohn, Apr 5, 2016.

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  1. bigjohn, Apr 5, 2016
    #1
    bigjohn

    bigjohn New Member

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    There has been a lot of talk about cruising "trawler"speeds on a sport fish hull. Inevitably the evolves/devolves into crudding up turbos and fouling up high performance diesels operating at low RPM. That makes perfect sense. But what about the old 310hp 671N? I know there are many happy Post owners out there with this configuration. Is there any advantage to long range cruising at low RPMs in an 80's era 42 Post with 671N's? I would not expect trawler performance, but with 460(?)gallons of fuel, can you slow down, throw on the autopilot and significantly increase your range? Any thoughts are appreciated. Great Forum BTW. Thanks to all contributors, knowledge is power, keep it coming!
  2. baltimore bob, Apr 6, 2016
    #2
    baltimore bob

    baltimore bob Member

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    I've not run the numbers, but my 42 with 310's seems to be most economical at 18-19 knots. Unless you are in a flat calm, our boats don't make real good trawlers.
  3. bigjohn, Apr 6, 2016
    #3
    bigjohn

    bigjohn New Member

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    Thanks!
  4. Capt J, Apr 6, 2016
    #4
    Capt J

    Capt J Senior Member

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    I don't understand that comment. SF spend half their time at trawler speeds trolling and are designed for stability on the troll.

    Yes, you will get incredible fuel mileage on a SF at hull speed. The turbo's crudding up are a bit exaggerated. If you run them at cruise for 30 minutes every 6 hours seems to be no issues.

    I just ran a 72' MY with 12v92's 600 NM and ran it mostly at 1200 rpms.
  5. baltimore bob, Apr 7, 2016
    #5
    baltimore bob

    baltimore bob Member

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    If you are running 6-9 knots in a slop it is NOT a comfortable cruise! The engines don't mind at all.
  6. shawn, Apr 8, 2016
    #6
    shawn

    shawn New Member

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    It's hard to kill a 671N you can rum them all day at slow speeds. The turbo is a different story, they need to be run. If I am out all day trolling I will run both engines up no load and clear the turbos out several times a day.