Jack Plate

Discussion in 'Boat Yard Basics' started by gflinders, Nov 21, 2009.

  1. gflinders

    gflinders Well-Known Member

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    Hey all, been a member for a while, been one of those who have been lurking around getting as much info as possible and must say that I have learned quite a bit.  A little bit about me is I just graduated from Physician's Assistant school and my schedule just freed up quite a bit.  For my graduation present I put a solicitation on Craigslist for a Gheenoe and scored a Gheenoe Highsider for $300.  I already had a trailer for it since I sold a "Tippy" aluminum boat to someone who already had a trailer for it.  I then bought a 1988 Evinrude 9.9 hp motor from a guy who donated it to my scout troop I help out with.  The guy is now in his 80's and bought it brand new and states he "only used it 8-9 times in my canals behind his house then parked it in my garage for 20 years."  The motor is incredible and the grease is on it is still white.  I will put pics up of it in the coming days.  So far I have had the carbs rebuilt, replaced the water pump and the thermostat and it runs amazing!  Any way, I just bought a fixed jack plate but don't think it will work very well because it sits 6" above the transom so the cavitation plate sits about 4" above the bottom of the boat.  Now I am stuck wondering if I can rework it so it works.  If not I will make a jack plate.  I have visited this forum posting several times.  http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1235777190  also this one http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1192143821/15  If I can't rework what I have, I will either make the one from Dillon Racing or I have pm-ed anytide for a plan for his jack plate.  My questions are as follows.  #1: Does anyone have a Highsider that has a jack plate and what is the best running length above the transom where it runs good and there is now worry about damaging the motor by running it too high.  #2: I went to a local aluminum fabrication place and they were going to charge me like $150 just for the pieces to make the Dillan racing jack plate and that was with me putting it together and drilling the holes.  Is this a good price, honestly seemed a little pricey to me but I will pay it if others say that it sounds fair.  If not, does anyone know where the best place to get the 1/4" 90 degree aluminum is?  Any help would be GREATLY appreciated.  I would just like to add that I think it is wonderful how helpful everyone is here and I love the website. 
    Thanks,
    Greg

    [​IMG]

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  2. Brett

    Brett > PRO STAFF <

    Could you post a closeup-larger side view image of the riser plate?
    With a little minor modification we can probably get that one to fit.
     

  3. gflinders

    gflinders Well-Known Member

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    Thanks again for the response, I too think it will work with a little tweeking.  Basically, it sits 5 1/2 inches up off the transom and so I think I can cut the sides a little bit.  Just wondering how much I need to cut them.  Anyway, here are 5 different pictures.  I picked it up off of Fort Myers Craigslist today for $15 so if it don't work then at least I am not out much.

    [​IMG] top of plate that is 9 inches wide
    [​IMG] Back of plate that is 12 inches long
    [​IMG] Side that is 5 1/2 inches tall
    [​IMG] Another side shot
    [​IMG] Front that is 9 inches tall.
     
  4. Brett

    Brett > PRO STAFF <

    We can get it awful close with a few measurements.
    Place a carpenters level against the keel and level the hull
    With the hull level and the outboard clamped directly to the transom,
    adjust the engine tilt until the cavitation plate is level also.
    Then with the level flush with the underside of the transom
    check the vertical distance from the top of the level to the underside of the cavitation plate.
    Then check the horizontal distance from the bottom/back of the transom to the water inlet.
     
  5. gflinders

    gflinders Well-Known Member

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    Ok, took a bit to get it level, but the bottom of the cavitation plate is 5/8 inch below the furthest part of the bottom transom. The water inlet is 9 1/4 inches where the groove begans and 10 3/4 inches where the groove ends back from the transom. This was without the riser plate.
     
  6. Brett

    Brett > PRO STAFF <

    Now for the fun part... ;)
    With the riser plate in place and the hull still level
    and the motor on the riser plate with the cav plate level
    How far above the bottom of the transom is the cav plate?
     
  7. gflinders

    gflinders Well-Known Member

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    5 3/8 to the bottom of the cavitation plate, 5 1/2 to the top, and your right, that was fun with the riser plate not being bolted on, lol. Once again, I really appreciate this
     
  8. Brett

    Brett > PRO STAFF <

    Now we need the distance from the bottom of the cav plate to the top of the water inlet
    and the distance from the bottom of the cav plate to the closest point that a propeller blade can get
     
  9. evanslmtd

    evanslmtd Well-Known Member

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    g
    I've got a Highsider that I built a Jack plate (from Dillon Racing plans) for. I'm running an 88' Johnson 15 HP motor (with a stock Alum. prop) on it. At this time, I'm running the Cav. plate about an 1" above the bottom of the boat. At this height I still have a good hole shot and don't blow out on sharp turns. I'm sure that I could go up another inch or two without having problems, and might do so at a later date. But for now, I'm pretty happy with the way the boat runs.
    To answer your second question, yes, you can damage a motor by running it to high to cool properly.
     
  10. gflinders

    gflinders Well-Known Member

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    Bottom of cavitation to water inlet is 7/8 inch and bottom of cavitation to top of propeller blade is 1/2 inch
     
  11. gflinders

    gflinders Well-Known Member

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    Hey Barry, I appreciate it, that does help because it sounds like we are running pretty much the same outfit. If you don't mind me asking, (and if you do I don't mind) did you make it yourself or did you have it made and how much did it cost however you did it?
    Thanks again,
    Greg
     
  12. Brett

    Brett > PRO STAFF <

    We want to keep the top of the inlet and prop safe below water level on plane,
    So we keep the smaller of the 2 prop/inlet measurements, 1/2 inch
    then add the 5/8 inch that the motor hangs too low
    then add 7/8 of an inch for the 9 inch setback from the transom to the inlet...
    Total correction is 2 inches in order to play it safe and maintain water pressure.

    I see that all my calculations agree with an existing setup... ;D
    Still, it was a fun way to kill an evening.
     
  13. gflinders

    gflinders Well-Known Member

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    Thanks so much, now just to verify, are saying that the riser plate can sit two inches above the transom or that the cavitation plate can sit two inches above the bottom of the transom?
     
  14. Brett

    Brett > PRO STAFF <

    The top of the riser plate can be 2 inches above the top of the transom.
    The cav plate ends up at 1-1/2 inches above the bottom of the transom.
    So 5-3/8 subtract 2 means you'll need to cut 3-3/8 inches from the bottom sides of the riser plate.
    You could probably set it higher with a cupped stainless prop if you wanted to spend the money.

                                                  :cool:

    Is it worth all the effort for the 2 inches?
    Me, I'd hang it straight on the transom and go fishing.

                                  [smiley=happy.gif]

    I'm thinking that riser plate is for hanging a 20 inch shaft outboard on a 15 inch transom.
     
  15. gflinders

    gflinders Well-Known Member

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    Touche, I agree that 2 inches isn't going to do much for me other than maybe make me think that I can run 8 inches shallower and ripping my transom off, lol.
    Well I appreciate you doing this for me, like I said to begin with, it is great that you can go somewhere and get an answer.
    Greg
     
  16. Frank_Sebastian

    Frank_Sebastian Well-Known Member

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    In regard to aluminum cost, I buy structural ¼"X 3" X4" in 25' lengths for $106.00 or about $4.25 per foot.

    Regards,
    Frank_s
     
  17. gflinders

    gflinders Well-Known Member

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    That sounds like a good price because it would only take about 6 feet to make the jack plate. Where could I get it from at that price? Thanks again for the help.
     
  18. Frank_Sebastian

    Frank_Sebastian Well-Known Member

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    I get mine from Sebastian Aluminum. Make sure to ask for structural rather than architectural.
    If they won't cut it for you at that price (most shops at least double the price of cut goods) I will sell you 6' at my cost. I am supposed to get 25' delivered next week.

    Best regards,
    Frank_S
     
  19. anytide

    anytide Administrator Staff Member

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  20. evanslmtd

    evanslmtd Well-Known Member

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    Greg
    Sorry it took so long to answer your post. but I've been out of town.
    I made the JP using the free plans on the Dillon Racing Site. It was a pretty simple build. A buddy of mine was able to get the Alum. Angle for me out of the scrap box where he works so I didn't have to pay for it. I laminated two pieces of 3/4" Marine plywood together to make the 1-1/2" thick motor board. I'm thinking that the JP cost me around $25.00 to build including the SS nuts, bolts, & washers and paint. However, that's not including the cost of the Alum. angle.