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Most efficient RPM's for 8.1- 25'

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  • Most efficient RPM's for 8.1- 25'

    Was wondering if there is a cruising rpm point that would provide the most efficient fuel consumption, knowing that there are a number of variables that impact this. Have a 25' C/C with gas 8.1 Volvo. Thanks....

  • #2
    I can't give you any factual numbers on this. While researching the boat I did come across some fuel burn numbers for a Crusader 8.1 in a comparable boat (can't recall the boat anymore). Crusader is the same basic engine. I doubt Volvo fuel burn would be significantly different. FWIW, here are the numbers.

    RPM GHP
    3000 12
    3400 15
    3600 18
    4200 28
    4550 35 (Volvo max 4400rpm)

    I'm running C-5 stainless props on my boat in fresh water. There seems to be a sweet spot between 3400 and 3600 rpm where the boat is moving very nicely and the engine seems in a groove. I think at 3600rpm that I'm right at 30 knots (gps). Need to spend some time to build myself a chart showing rpm and boat speed then refer it back to these fuel burn numbers. Hope this helps.
    --Mike
    2004 Carolina Classic 25 - Little Dandy
    Volvo 8.1 DuoProp
    ocimaya.org

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    • #3
      Most efficient RPM's for 8.1- 25'

      Mike:

      Many thanks for your reply. By any chance do you have a sea strainer on your raw water intake? I have seen the postings related to the 25' not having one but wondered if you put one on the Little Dandy.

      Thanks,

      Greg

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      • #4
        No sea strainer on my boat. The thru hull has slots on the exterior that are supposed to keep junk out. No problems so far.

        http://www.groco.net/05-Cat/Sec-6.html
        If you scroll down about half the page, the one on my boat is similar to the STH model. Not sure what brand Mac uses, this might be the one actually installed.
        --Mike
        2004 Carolina Classic 25 - Little Dandy
        Volvo 8.1 DuoProp
        ocimaya.org

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