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  1. #1
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    PROP 86 MEAN 15 86 90 MERC

    Took the boat out Sunday, windy, raining with a one foot chop or swell. Had two people 225lbs. & 135lbs., 3/4 tank of full, two live wells full, three batteries & loaded down with tackle & gear (including three 15lb anchors)
    Boat: 1986 Mean 15 (15'6")
    Motor: 1986 Mercury 90hp straight to transom
    Prop: Aluminum three blade Mercury, Pitch unknown (original I would assume)
    RPM's: unknown (Tach not working)
    Speed: 41.3mph (Garmin GPS)
    Hole Shot: Don't know the difference of a bad one or a good one, lol
    On Plane: Starts in 3 seconds & fully in 5 seconds
    Trim: tucked all the way in to start & back up less than a quarter (porposes after that) but ran better in rough water trimmed up.
    Question is with that information can anyone recommend a prop for better performance or am I dreaming? Where can I find the pitch information on the prop?
    Thanx in Advance
    Ruu

  2. Member MMosher's Avatar
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    #2
    Ditch the aluminum prop for a SS

  3. Member
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    #3
    Already figured a S.S., but any idea of pitch & make?
    Thanx Ruu

  4. Member
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    #4
    Current prop is a 17 pitch

  5. Member
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    #5
    I have a 88 with a merc 90. Had a aluminum prop when I bought it and changed it out to a 3 blade ss 21 pitch. The boat runs great with one person and light tackle get 2 people and boat struggles to get on plane. The boat truly needs more horsepower. I never experimented with props due to the cost.

  6. Member
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    #6
    I figured out what my current prop is 13.250" Dia. 17 Pitch Mercury Black Max
    Changing to a 21 Pitch prop of any material would seem by the numbers anyway cut way down on the HP of the motor by as much as 1,500 RPM's. That would explain the problem you experience with the added weight & plane issue. My tachometer doesn't work & i'm coming to the conclusion that knowing the RPM's of my motor when running flat out with the current 17 Pitch aluminum prop is must parameter to know to see what direction to go. If i'm getting the full or a little above factory spec's RPM's now @ 17P then getting a S.S. prop with 16P or17P should be ok & gain performance from no distortion. Not sure if I gain any real efficient performance with a 19P S.S. over a 17P S.S. I think i need to have my tachometer problem either repaired or replaced to do this right. Guess my rebuild isn't over with after all! lol
    Any information on where to get OEM instrument replacement parts or repair, I'm all ears again! Also if I am making this more difficult than it should be from over thinking, Please I'm really all ears lol
    Ruu

  7. Pat Goff
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    #7
    Yes, the tach is critical, that motor is rated for 5,250 max rpms. It's kind of a grunt motor, and it doesn't like to spin a ton of R's.
    Your challenge is going to be setting up for a load, you're going to have a big swing between loaded and light, so my advice is:
    Get the tach working.
    Loak it like you're fishing, run it WFO, and let's see what it's doing exactly.
    I'm guessing the right wheel is a 19P Lazer II, but let's see what the boat tells us.
    Pat Goff

    Two degrees from center
    of nowhere.
    Smithwick TX.

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  8. Member
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    #8
    Thanx Pat, Advice taken, found a connection that isn't connected tucked behind the throttle control unit. When I have some time will look for the other male connector & trace the wires, might just be why gages are not working!

  9. Member
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    #9
    Found the reason the for the speedometer not working! plugged hole in lower unit & broken water line that runs thru the lower unit into the hull. Anybody know where it goes once into the hull & what it connects too??

  10. Pat Goff
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    #10
    Connects to back of gauge. Boat speedometer is never to be trusted.
    Pat Goff

    Two degrees from center
    of nowhere.
    Smithwick TX.

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  11. Member
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    #11
    Well noted, will trust the GPS. So that line runs straight to the back of the gauge without any type of diaphragm along the way? I will still splice the broken line together just so that it works. Or does a splice screw up the actual reading & splicing the line back together a waste of time? Do I need to actually remove the lower unit & replace with a new line from the motor to the gauge thay is just one solid piece? If thats the case it can wait until I have to remove the lower unit for another reason since I dont really need it, now anyway.

  12. Member
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    #12
    I wouldn't worry about that speedo gauge. I would get an accurate reading tach and you can gps speed various ways. If you don;t have a graph with gps speed you can use an app on a smartphone. Your 41 mph gps may be about max for that setup with that load. With the proper rpm reading you will have a starting point. I kinda think stepping up 2 pitches from a 17 to a 19 may be too much.
    GETFISHED !!!

  13. Member
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    #13
    Yup I agree, Working on what's wrong with the original one now. My GPS MPH reading was off of my Garmin 73svEchomap (new unit) so that should be pretty accurate. Just been trying to buy a house out here in Los Angeles for last 3months (never seen so many cracked pools) and has been really occupying all my time.
    Thanx again to all for the information.
    Ruu

  14. Member
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    #14
    Well got the original tachometer working & took the boat out today!
    I got 40mph today but had a heavier guy than when I got 41mph out of the boat a couple weeks ago. The tach read 4,900 RPM's @ 40MPH & 4,700 @ 39MPH difference in the two runs was that I trimmed the motor up A bit more!
    So hope now this information is more helpful in figuring what make, pitch, model, & material prop!
    Thanx to all in advance!
    ohh yea forgot nailed 10 rainbows today!


    Ruu

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