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  1. #1
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    Terrible hole shot after hydraulic jack plate installed

    I've read NUMEROUS threads about this from many different angles and a bit stumped as to where to officially start. A little bit about the setup: 17.5' Norris Craft, 200hp Mariner, 10" hydraulic jack plate, 27 pitch SS prop with additional cupping, and a stabilizer plate from Bob's Machine Shop. With the motor trimmed all the way down, testing all inch positions of the jack plate (6" total travel), it can take me 15 seconds to get up on plane, if I can even get there. Sometimes I have to slowly increase my speed before dropping the hammer so I have some momentum.T boat just stands vertically, RPMs limiting at 4k, until it finally gets enough speed to plane out. Once it's up and trimmed out, no problem getting it smoothed to 70mph.

    I've read about aligning my prop with the pad, but found various different ways to measure and different values it needs to be set to. Another thing that comes to mind is since the motor is sitting back so far, I have that 10" cavity in the jack plate itself that can be holding back water and restricting me. I've considered putting at aluminum plate under it to prevent that water from following up and causing drag. Other than that mod, I'm not sure where else to start here.

    Before, I had a 6" manual plate with a wider stabilizer that was still not the best to get up, but at least it took less than 10 seconds. Since there is more weight off the back now, I'm thinking that the smaller stabilizer plate might be contributing to the degrade in performance as well.

    Any insight would be appreciated.

  2. #2
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    Want to say to much trim in. -10* is about as far in from level kinda have to find the sweet spot.

    If your getting a lot of water in the setbac it will drag pretty good.

    I like to start by setting motor visually level with water at rest. Then move trim in when testing. My personal boat likes 2.5* off in all the way. Any more in it torques the bow up just like if I forget and leave it trimmed out for speed.

  3. #3
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    So you're suggesting that with the extra setback I now have, too low of trim might actually be causing the same effect as being trimmed too high? Before I would have to trim down all the way for launch. I only messed with the jackplate height, not trim settings yesterday.

    Here's the new stabilizer plate vs the old, which was probably also helping keep the cavitation plate on the surface more where as now there is less surface area and my thinking was that the force of the water against the new plate was not enough to try and keep it above the water. The only reason I changed the plate was for aesthetics. Probably not a good reason to be changing.

    And I checked the jackplate and it already has a decent plate at the bottom of it to prevent sucking in a lot of water so I don't think that is the issue.

    Click image for larger version. 

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  4. #4
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    For starters, my main question is, with the jack plate in the lowest position and motor trimmer down (granted trim setting may not need to be fully down any longer for launch), where should my prop shaft be in relation to the bottom/pad of the hull? I think that alignment is a good place to start, but I am not sure of the measurement. I saw a 3.5" value in some of the threads that I can't find any longer, but I don't know if that meant prop shaft should be 3.5" lower or higher than the pad of the boat.

    But even still that doesn't make sense to me because the point of the action jack plate is to be able to raise the motor in shallow water with it still trimmed down to be able to get enough water to get on plane without digging into the ground.

  5. #5
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    It can happen. If the angles changed. Doesn’t have to though. (Friend has a -17 transom)

    3.5” below is a good spot to start jack plate setup.

    Idealy you can go all the way down on the hydraulic and get a real good bite. You will also be dragging more of the shaft. Then bring it up top. Or like you said operate in shallow like a flats boat.

    That a fair set up. Tough one to figure out.

  6. #6
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    So when referring to the 3.5" below value, what exactly is that referring to:
    • prop shaft is to be 3.5" below pad
    • top of prop is to be 3.5" below pad
    • cavitation plate is to be 3.5" below the bottom of the jack plate, which means prop is likely above the pad

  7. #7
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    Upset the center of effort of the hull. (ballance) You moved and added weight to the stern. The worst possible place on your hull and it doesn't like it. Bow hi is a weight dist. symptom..

    83 V-King, 96 Mariner, 200 hp ff block 2.5 w/a 28p choppa
    We gotta clean this liberal mess up, VOTE TRUMP TO MAGA!
    Rebuild thread:
    http://www.screamandfly.com/showthre...-it&highlight=
    http://www.screamandfly.com/showthre...cs.&highlight=
    Videos

  8. Likes rgsauger liked this post
  9. #8
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    I got the pad of the boat level and trimmed the motor so the cavitation plate is also level, parallel with the pad. With the jack plate at its lowest level, I measured with a straight edge from the pad to the lower unit, and finding the difference between that and the center of the prop nut. I measured in 2 different ways and both came out to be 3 5/8".

    I agree with @XstreamVking , this set back is really offsetting my center of gravity now. A few things I can try for now:
    • Move the engine further down on the jack plate. This will allow me to hole shot deeper (say 4.5" below pad) and give me a wider range of testing by adjusting the jack plate up/down to find the sweet spot
    • Add weight to the bow. I could throw a couple tube sand bags up front (70lbs each) that will help keep the nose down, though not an ideal solution IMO
    • Try a 4 blade prop. The current 27* cupped 3 blade may not be grabbing enough for the extra force that is now back there.


    Top speed is still great. Yesterday on some light chops with wind, I managed 69mph GPS at ~5400 if I recall. Certainly had more throttle I could give it, but at this point I started to get the chine walk to quickly backed off. Max I have probably had this (before changing to this new jack plate setup) was ~73mph before the shorts about got soiled.

  10. #9
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    That 200 needs to turn .more than 5400 imo, I think half of the prob is prop to much bite, I had a very very stern heavy bass bote but had no prob at all getting up , big plate ,little bote, and no hydrofoil of any kind,, with that said rpm could come up 500 rpm easy really, that would change everything, have anymore props to try ? Also use the wider foil mite help sum

    Also more setback means need more height, raise it. Is it hydrolic?

  11. #10
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    It's hydraulic and I have tried different heights. Lowered all the way down I am at the "average" 3.5" prop-to-pad distance, so I don't think I need to adjust it to drop any more, especially if the more set back means more height.

    The water wasn't slick so being able to test different heights was not consistent. I can say that measuring my new stabilizer plate vs the old, new is 10" wide where as the old was 21". I uploaded that image in post #3 above. The only reason for replacing the fins was to get something that looked cleaner, but now I think that extra width before was really helping me. Problem is I changed multiple things at once on this setup so it's back to tuning from scratch.

    I see the SE Sport 300 has a nice look to it and appears to be 17" wide. I wouldn't mind one being a bit wider either.

    What's the opinion on trim tabs vs going back to the wider stabilizer?

    While I don't have a different prop, it would be something I'd be interested in swapping out if I can find a few to test.

  12. #11
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    With all the info, think u need to pitch down. wot @ 5800 sounds better trim will have more effect for hole shot than jackingeup n down. also that pic of fin u show goes onstarboard side, im sure u know that. looks like a hoss prop, nice

  13. #12
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    Quote Originally Posted by Merc 2.5 View Post
    That 200 needs to turn .more than 5400 imo, I think half of the prob is prop to much bite, I had a very very stern heavy bass bote but had no prob at all getting up , big plate ,little bote, and no hydrofoil of any kind,, with that said rpm could come up 500 rpm easy really, that would change everything, have anymore props to try ? Also use the wider foil mite help sum

    Also more setback means need more height, raise it. Is it hydrolic?
    did u notice hes up on the last mounting bolt hole already.

  14. #13
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    Quote Originally Posted by KIRCHNER View Post
    did u notice hes up on the last mounting bolt hole already.
    Well just caught that, idk man I gotta say its more of a prop issue. I had 8in on a 15ft with 150 and 200 , either boat is very very water logged or u really need a prop change. I notice more people I add in my bote the less the over hub props like it, try and getbur hands on a 24 or a 26. U mite b pleasantly surprised with more top end and bottom

  15. #14
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    Quote Originally Posted by KIRCHNER View Post
    With all the info, think u need to pitch down. wot @ 5800 sounds better trim will have more effect for hole shot than jackingeup n down. also that pic of fin u show goes onstarboard side, im sure u know that. looks like a hoss prop, nice
    Yep, fin was just the one I grabbed to show the difference in width that could have been helping keep the bow down more. Prop is an original OMC 14.25 x 27*. I just had it cupped by D.A.H. https://www.dahpropellers.com/ I will call them up today, give them info on the new setup and see what they have to offer for suggestions. I know my dad (originally his boat) had tried a range of 25* - 29* to get the right hole shot and top RPM sweet spot with the fixed jack plate that I just removed. Hole shot was still not as good as it could have been in my opinion, but for the resources and money he had at the time, it worked well for him so I was not too inclined to change it until recently.

  16. #15
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    When you suggest a lower pitch, should I still stay with the 3 blade or would it be worth trying a 4?

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