Help with jackplate!

Discussion in 'LOCAL ILLINOIS TALK' started by spikespack, Dec 14, 2007.

  1. spikespack

    spikespack New Member

    Messages:
    14
    State:
    illinois
    Hello, Brothers! I have a Tracker Tundra 18' with a Merc 150 Optimax. It has a 25 pitch prop and turns 5000 RPM @ 50 mph. Seems pretty slow. Will a jackplate help and how? I need to bring the RPM's up to 5750 and I don't want to get rid of my $575 prop! Thanks for any help!
     
  2. Big Dav

    Big Dav New Member

    Messages:
    1,016
    State:
    Southwest
    First welcome to the BOC.
    I don't know for sure how much it will raise the RPM's but I think it would raise them some. Since the motor/prop would be moved back, up or down, and into "cleaner" water it should make the prop a little more efficient and increase you top speed. Or at least that is what i get from all the reading I have been doing on jack plates. I would say you will still be looking at changes in the prop to increase that many RPM's, but i am no expert in any way.:big_smile:
    There are guys on here that have forgotten more than I will ever know. I am sure someone will be along to correct me if I am mistaken and get you going in the right direction.
     

  3. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Firsts as a rule of thumb I've used my own formula over the years and its worked fine for me . Put the boat on a level drive way and use a 4' carpenter level on the rear of the center pad near the transom, level exactly the boat center pad with the trailer tongue jack. Next remove the prop and use a torpedo level on the prop shaft , use the trim to get the shaft perfectly level. Take a RIDGE straight edge and lay along the rear 2 to 3 feet of the pad perfectly flat and let the straight edge protrude beyond the pad to the gear case. Calculate using the exact center of the drive shaft to establish how much you are truly above or below that pad bottom in correlation with the pad verses the center of the prop shaft. This is called in the racing world inches or tenths of inches on V bottoms high or low from "split shaft" this is where that dimension or plane strikes or runs from the exact flat bottom to the exact center of the shaft. If the center of the shaft is 1" above that plane your rig is 1" above split shaft and so on. In the THEORY I've used ( and this is a primitive starting point ) for Evey one inch your jack plate is in length you can raise the gear case up 1/8 the of an inch from exact split shaft and still remain in "clean" "hard" water.. If your engine is bolted directly to the transom I suggest no higher than exact split shaft high ..Example if a jack plate is 8 inches long ( dimension from the boat transom to where the motor bolts on to the other side of the jack plate ) you can in theory go up 8 - 8ths of a inch or 1 "..All boats are different and have their own sweet spots , alot has to do with the particular hull and or overall rig your working with. Raising a High Performance Engine ( or any engine as for as that goes ) with a low water pick up on the lower unit ( which is a must , if this is not a low water pick up added to the lower unit the engine being jacked will quickly run out of engine cooling water pressure and engine will be damaged BEFORE the optimal speed and handling can be achieved ) jacking to optimal and is the only way to get your rig to its ultimate potential and to handle to an optimal set up . Dialing in these boats,motors, gear cases, and props combos are a trial and error game and must be done in small increments and the results of each change needs to be recorded for future movements and to see what helped and what hurt...
     
  4. Mark J

    Mark J New Member

    Messages:
    9,407
    State:
    Four Oaks, NC
    Prop shop.
    Never spend 600 dollars on a prop without using one.
    Props can be altered from their factory configuration from alot to a little depending on the material.
     
  5. Bryan8552

    Bryan8552 New Member

    Messages:
    422
    State:
    nc
    And be sure to have it loaded, as close as possible, to the way you're going to be running it day in and day out. You'd be surprised what difference it makes to add five bags of ice, a livewell full of water and an extra person to the boat.