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Try to reduce prop slip or let it rip ?

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  • Try to reduce prop slip or let it rip ?

    Per my last post I have tested two props on my tritoon and both have high slip numbers, around 40%. Powered by a Honda 150.
    Black max 3 blade 15.25x15 20mph@ 5000rpm
    Solas amda 4 blade 14.75x15 22@ 5500rpm
    Should I try a bigger diameter prop to reduce slip or just leave it as is ? Do you reduce pitch when trying to reduce slip ? It just seems 40 % slip is very inefficient and maybe getting it down would help the motor live longer not to mention gas mileage.
    Thanks!

  • #2
    Read thru your other post
    http://forums.iboats.com/forum/gener...poor-top-speed

    Your issue is its a toon, and it will take a lot more power to get the boat up. Tri's are great but they also require more HP to more due to more drag
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
    07 SeaDoo GTX
    Raw Water Pump Maintenance
    Merc Adults Only

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    • #3
      I understand that part, but I'd like to know if a bigger prop will reduce slip , not go faster. It seems to be wasting a lot of energy at 40% slip. Would a 16x13 prop be better than what I have ?

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      • #4
        more pitch,...bigger prop,..just dont over prop,..over torque the motor,... check what max rpm at WOT is supposed to be,...you could come down from that maybe 2-3k,...any more than that you could over torque the drive.
        1990 SeaRay 280 Sundancer w/twin 5.0 Mercruisers
        1988 SeaRay 230 Weekender w/ 5.7 Mercruiser
        1969 Starcraft Suncruiser 20V (project in works)
        1992 Winner 180 w/ 5.7 Mercruiser (like new w/cracked block)
        1989 SeaRay 290 Amber Jack w/ twin 5.7 Mercruisers (parts boat)
        1981 Thompson Sportsman 20' hardtop w/165hp Mercruiser (sold)
        1978 SeaRay 190 SRV w/ 160hp Mercruiser (sold)
        1975 Silverline 18' w/ 115hp Mercury O/B (sold)
        1960 Thompson 18' woody w/ 90hp Evinrude (dads boat, sold)

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        • #5
          On paper, I would think that all else being equal, as blade area increased, prop slip would decrease. Larger diameter props, and 4 blade props, would both offer more blade area than smaller diameter or 3 blade props.

          Still on paper, the downside to more blade area will be reduced performance at higher rpms and higher speeds due to prop friction/drag on the water. With this boat, I don't think higher speeds are going to affect what's going on.

          Bottom line, from a practical perspective, I'd be looking to compare props that allow the engine to turn up max rpm. I honestly don't know how you would predict 3 blade vs. 4 blade performance. I think it would be really interesting to have one of each, that would both allow max rpm, to compare them.

          Regarding a 13" pitch, our 2 tube Honda 90 boat is running a 13" Honda OEM 3 blade, turning it at 6K, and making 24-25mph when lightly loaded. Point being, if your engine is rated for 6k as ours is, you could still be picking up a couple mph, while likely having much more lively performance while getting there - while running a 13" pitch.

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          • #6
            Agree with others, need max rpm. The lower the pitch the less slip.

            Short example (long story): My 11K cruiser,
            Using 22 pitch 4 blade slip is 14 cruise and 12 at WOT, with max speed of 48 mph and will over tach
            Using 26 pitch 3 blade slip is 23 cruise and 21 at WOT, with max speed of 50 mph
            94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
            95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
            07 SeaDoo GTX
            Raw Water Pump Maintenance
            Merc Adults Only

            Comment


            • #7
              Power is a honda 150 and max rpm is 6000.

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              • #8
                So with a target rpm of 6k and this experience under your belt, it's not hard to endorse the 13" prop plan.

                Black max 3 blade 15.25x15 20mph@ 5000rpm
                Solas amda 4 blade 14.75x15 22@ 5500rpm

                The more difficult call will be 3 blade vs. 4!

                Comment


                • #9
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                  Update with a 16 x 13 3 blade black max prop.
                  23 mph @ 5500 rpm. This was in choppy water wwith a stiff wind. Mph did not drop heading into the wind and did not speed up going with it .it felt faster and it did not lose speed in a turn like the other props. I took my son tubing and it pulled him just fine.while perplexed with the outcome I am going to wait for a better day to test it again.

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