Which Prop? - Crap Shoot - 1974 Mercury 650 on a 15' tri hull

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  • Which Prop? - Crap Shoot - 1974 Mercury 650 on a 15' tri hull

    WOW! LOVE THIS SITE!

    I have spent the last 9 months restoring a 1970 ArrowGlass "Tarpon" Tri Hull. New deck, floatation, transom, paint...etc. Also just rebuilt a 1974 Mercury 650 (65HP) 3 cyl to power the old girl. 120lbs on each cylinder.

    I am running a ProPulse composite prop that my friend Robert gave me. It is adjusted all the way out (17p) and I am able to get 29mph at WOT with myself and one other person - loaded with gas, battery, dry storage and cooler. The engine has no problem getting on plane (Light boat for a fiberglass) and will stay at 5000 RPM no matter where I set the prop (not sure if the tach is functioning exactly right). Being in Virginia, I am doing a lot of time on the James and Chickahominy rivers - both have their share of obstacles. This makes me very leary of having a plastic prop as a full-time prop, so I am looking for an aluminum prop.

    This is the second boat of this kind I've had. The only difference is the first one was a 1973 ArrowGlass Tarpon with a 50hp (1973) Merc and it would fly. I should never have sold it - so much fun - but I was younger and at the time wanted to go to a bigger boat (family thing). When replacing the floor, stringers, floatation and transom I was careful not to add more weight than original.

    My question is.... available props for this motor range up to 11"X17 pitch, and I would like a little more speed, but I'm not sure if that would be too much and bog down the ol' Merc and don't want to impede handling. I'm thinking somewhere around 3 blade aluminum 11" x 15" pitch. Am I in the right ballpark? Lower? Higher?

    I am going to try to post a picture of the boat so you guys can get a better idea of the size (bear with me, I'm a Harley buff). Any suggestions are GREATLY appreciated.. Thanks for your time and thoughts.

    Click image for larger version  Name:	Arrow-1.jpg Views:	1 Size:	118.2 KB ID:	48351

    Click image for larger version  Name:	Arrow-2.jpg Views:	1 Size:	101.2 KB ID:	48350

  • #2
    Ok, trying to find the gear ratio, I believe your's is 1.64 and RPM range 4800-5300
    foun that here. https://forums.iboats.com/forum/engi...nterchangeable
    40 & 402 2 cylinder.......................................... ..2:1
    40/45/50/500 4 cylinder......................................2:1
    50/60/650/700 3 cylinder....................................1:64:1
    650/75/80/800/850 4 cylinder..............................2:3:1
    900/90/1150/115/1400/140/1500.........................2:1
    1970-71 1150 & 1350.........................................1:78: 1

    Found RPM range here. http://download.brunswick-marine.com...roke/66-72.pdf

    be interested to check the engine height here. https://www.bandofboaters.com/forum/...gs-to-look-for

    As for pitch, with a decent aluminum prop, I'd say you'd expect somewhere around 10-14% slip. kinda varies on brand. Solas would be lower then that.

    I'd say try a 13 pitch to start with and hope for mid 30's


    Ken Reeves
    KR@Propgods.com
    941-735-5808

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    • #3
      AAAHHHhhh....!!! Thanks Ken ! I hope you're right. I'm going to look for one now. Thanks again.

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      • #4
        Awesome looking boat !
        I'm sure that one turns a lot of heads on the water.

        Ken Reeves
        KR@Propgods.com
        941-735-5808

        Comment


        • #5
          Ha Ha !! Thanks Ken. I've only had it out the one time so far. Had to know what needed adjusting. Weekday on Lake Anna - not many people there. Most people say "What th...why?" But I never was one to stick with the norm. Do you think a 14" pitch would be too much and do y'all sell props?

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          • #6
            I would go 13.
            I do sell props, I don't do returns on aluminum, so you can probably get it on Amazon quicker and cheaper.

            Ken Reeves
            KR@Propgods.com
            941-735-5808

            Comment


            • #7
              Thanks again Ken. I ordered the 13. I'll let you know what happens.

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              • #8
                sounds good, keep us posted

                Ken Reeves
                KR@Propgods.com
                941-735-5808

                Comment

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