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Thread: Is it possible to run higher RPM's than actual?

  1. #1
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    Default Is it possible to run higher RPM's than actual?

    There is a question here...I was running back from Eshamy Bay last weekend about 30 minutes before slack tide, when I was running from the Eshamy entrance to Main Bay my RPM were reading 4000+ at times up to almost 5,000 and I was having a hard time staying on step and keeping the boat speed above 20kts. As the tach was reading these high RPM's the motor sounded like it does when it's running at 3,000 to 3,600 RPM's....Is it possible to have the RPM's on the tach read hight than the actual RPM's? Does anyone have an explanation? Once I got past Main Bay and around the corner heading to Colross the tach read a normal RPM for the speed I was going and the motor (RPM's) sounded normal and I could cruise at 22-24kts no problem. Can a current running under the boat in opposit direction do this?

  2. #2
    Member fullbush's Avatar
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    You were probably cavitating w/ a following current, once you get around the corner the current is usually going south, or you had some debris like weeds or something causing cavitation

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    Member Frostbitten's Avatar
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    Sounds like two issues there.

    1) Tach reading - sounds like your tach gauge isn't functioning properly. I've had a similar issue with my tach reading as high as 7K with absolutely no change in the sound of the motor, no change in speed or percieved power. I haven't located the gremlin yet, but I suspect it's in the gauge itself as I can tap on the gauge and the needle drops back to where it should be.

    2) I can't say I've noticed current causing me to lose speed...water moving past the hull is water moving past the hull. Were there any significant swells or wind when you were having difficulty staying on step? What were the seas at the time? I can see any of these being a factor, but not necessarily the current.

  4. #4
    Member fullbush's Avatar
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    Quote Originally Posted by Frostbitten View Post
    Sounds like two issues there.

    1) Tach reading - sounds like your tach gauge isn't functioning properly.
    Most marine tachs have a 3-position switch on the back for 4,6,or 8 cylinders might check and see if yours is in-between one of these settings

  5. #5
    Member Dupont Spinner's Avatar
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    Faulty gauge most likely......mine will run up over the 6000 rpm's. Pretty common in a marine gauge....not sure why. Check your grounds and electrical connections. I was planning on putting in an Autometer gauge over the winter. I am basically running on my Garmin using the SOG reading and STW to set my boat at running attitude.

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