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  1. #1
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    Question Prop/ Jack Plate fine tuning on 70hp Evinrude

    Hey guys, have not posted in a while. Been chasing my tail over a year on setup now. I believe I am finally close. And I need a little help fine tuning. 17' Mod V aluminum side console with a 70hp Evinrude 6" setback jack plate.

    I had been chasing issues with bow lift, porpoising, and some others. Added trim tabs and have been playing with them and think I am close. They got rid of the porpoising. I am running a 19pitch SST prop now, turning 6200rpm loaded down at 38-39mph GPS. My numbers gave me 18% prop slip. I do notice I have a little slip sometimes on take off, and in the mid range, but then it hooks in and goes.

    The prop is a little corroded, and I am going to send it in to get polished and cleaned up. Should I have them add cup, chop the tips? Or make any adjustments that will help out, or leave it alone and just get it polished. Manual tilt, and manual jack plate if that matters.

  2. #2
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    Two words:

    bigger motor.

  3. #3
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    Quote Originally Posted by SS Minnow View Post
    Two words:

    bigger motor.
    The boat weighs well under 1000lbs. Originally had a 35 Mercury. Hopefully the day never comes, but if it does I will probably go with a newer 75 with Power TnT.

  4. #4
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    Scream & Fly,

    70hp with 1000 lb =

    Yawn & Nap

  5. #5
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    "Well under 1k lbs"? Needs b bout 4 or 500 for what u r wanting with a 70. Seems my buddy had a walk thru pleasure boat ,water logged and everything else u could imagine and he was round 35mph I guess. I know his boat weighed over 1k
    With the same rude 70

  6. #6
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    PhillnJack ! I think it could run faster, know of a 70 on a StarCraft aluminum about that size that does a few more mph.

  7. #7
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    If the props not made for piercing the surface/ or surfacing it will gain a lot of slip. If the gear ratio is over 2:1 you might also have slip issues with 3 blade if it pierced.

    Get a good wax on the hull as well to slick it up.

    Theirs plenty of small engine guys and galls not all of drive cookie cutter 2.5s
    '06 Tracker All-Fish/Tournament V-18 90 Optimax, 46.8 gps Goal one complete reach 45 mph.

  8. #8
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    Trim could be worth 10mph with a tight prop. I have seen it first hand on my dad's 18 starcraft.

  9. Likes phillnjack liked this post
  10. #9
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    sounds more like hub is spinning. 6200 19 pitch omc sst prop.. why on earth are you running trim tabs ? these are like brakes.
    Trim tabs are not to stop porpoising or help on holeshot, they are to help level the boat side to side. put tabs at highest setting.
    trim the motor to be more level when running if you dont have power trim. .
    With sst 19 prop you need the cav plate no higher than 3 inches above the bottom of the boat, you take it higher you lose speed and will slip on pull away.
    clean the prop with a wire brush on a drill, and then sharpen the leading edge... my boat all up weight with me 1200 pound plus.. I get 43mph at 6,000 rpm.
    sst props are normally very good for low slip prop. take prop off, mark the centre and the outside and then go for another ride, then take prop nut off and see if
    the marks have moved. if so the hub is spinning. as in pics below, can mark it at the back or front ..
    front is easier as you just need to remove nut and washer to see if anything has moved.

    just how I would do it all before sending prop anywhere...
    sst props are not a bow raising prop, they raise the stern due to low rake blades.
    13X19 OMC SST PROP IN PIC AFTER CLEAN UP
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  11. #10
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    Sorry for adding this late, but I missed this thread in the early parts. 38~39 mph is darn good for a 70 horse on an aluminum boat. You don't mention the year model, is this a pre-1984 or later model? The later ones will have a 10~15% advantage since ratings went to the prop that year. Speed on the water comes from thrust applied straight ahead and the boat "flying" as best it can on top of the water. Trim and lift are great if used correctly. Phil is 100% on with those tabs....just adding more surface drag. Remember this, water is 814 times more dense that air!

    Both of mine were crankshaft rated. The first, a 1980 Johnson ran my little 15 foot fiberglass 33~34 mph (old style speedometer with pitot tube) and my new restored 1975 model (in the video link) is running 33 mph on the GPS at 5,600 rpm. This video shows my 850 lb boat and 500 lbs of passengers/gear with a 17P SST mounted. I show this because we ran an 18" Raker with the same, exact weights to 4,900 rpm and a slower 32 mph. I love the SST because the hole-shot was a full 4 seconds quicker to 30 mph. It took us 10 seconds to reach the 30 mph mark with the taller wheel.

    https://www.youtube.com/watch?v=zTUPzc-rqRg

    Your 6,200 rpm with the 19 SST, you should easily turn a 20" Raker to 5,400~5,600. The Raker is a bow lifting prop and will not slip nearly as much as the SST, even at elevated height. I'd want to see photos of your transom and running surface before recommending a long-rake performance prop like the Raker though. These do best when there is a Pad-V surface to support the weight. With the Raker you could easily over-trim and shove the bow further down in the water - messing up the 4 degrees of angle of attack and just adding more wetted surface.

    Fishing? SST.
    Skiing and pulling tubes? SST
    I like the SST props for durability, cost, and general performance. They are great compromise propellers that do most things very well. In my case, it's quicker out of the hole and it's faster at top. No, the SST won't carry the bow and it will blow out if I'm trimmed up. The Raker will "bite" and hold the water, but in all of my applications with 70's, 90's, and my GT150 - Rakers came with a hole-shot penalty.

    Gordon
    Last edited by Gordon02; 06-03-2019 at 11:01 PM.

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