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Re-Prop / Setback Plate / Both??

Discussion in 'Boats, Blinds, & Gadgets Forum' started by agtex42, Aug 8, 2018.

  1. agtex42

    agtex42 New Member

    Messages:
    15
    Joined:
    Sep 14, 2016
    I've been playing around with motor height/trim and believe I've done just about everything I can to maximize the efficiency of the setup without adding/replacing components.

    My aluminum prop has seen better days, it's not horrible but there are nicks and scrapes all over the leading edge on all three blades. I currently don't have a spare and am considering re-propping to try to eek a bit more performance out of the setup and have a backup on hand.

    Here are the specs on the boat (yes it's underpowered but the whole rig was dirt-cheap and it fits the needs for the time being!):

    Tracker Grizzly 1648 w/ '15 Yamaha F25 (No PTT) - Tested rigged for normal use (approx total weight 1150 lbs) with weight distributed evenly.

    GPS Speed 25.8 MPH, RPM 6180, Factory Yamaha Aluminum Prop 9 7/8 x 10.5 (13% slip)

    The motor is mounted on the transom and is approximately 1/2" above the keel when level, but my running trim setting puts it closer to dead even with the bottom of the hull. The AV plate runs just under the surface at WOT but the wake is not as clean as I think it could be.

    I'm considering going with a PowerTech SRA3, undecided on pitch at the moment. 10x10 would probably be a safe bet but I might be able to get away with a 10x11 given that I'm currently on the high side of the RPM range for the motor. I'm trying to decide whether or not it'd be worth considering a setback plate as well to get the prop back in cleaner water (and gain a bit more running height). The boat has a bench seat so I'd likely keep the setback between 3-4", I don't really want to sink the money into a PTT unit because I don't plan on keeping the boat for more than a few years.

    I'm ready to pull the trigger on a prop, waiting on some return calls from the local guys/PowerTech; in the meantime I'd be interested to hear yall's thoughts on the matter as well!
     
  2. chuck99z28

    chuck99z28 New Member

    Messages:
    23
    Joined:
    Aug 10, 2016
    How does the boat sit in the water the way it is? Does it squat low in the back or fairly level?
    I put a 4" setback on a 1648 and found that shifting the motor weight back 4" significantly lowered the the stern. I had little to gain and the lower rear caused me to take it back off. I didn't do the math to determine how much rear weight that equaled. Just saying that it is something to consider if you're already heavy in the back.
     
  3. 1995 US1

    1995 US1 Moderator Sponsor Moderator

    Messages:
    11,089
    Joined:
    May 25, 2003
    Location:
    Benton, Arkansas
    Stick with a 10 pitch. Aluminum props flex under load and effectively reduce pitch. So, your 10.5 inch pitch prop may drop to an 8 pitch on takeoff then rebound back to 10.5 when not under max torque. The stainless will not flex under load. Sounds like your motor is low. Get a decent prop. then start moving the motor up 1/4" at a time until it blows out when turning hard. Then drop it 1/4" and go. That should put your cav plate above the water when running. Keep the motor turning 6000 plus at wot, that is where that motor makes the most torque.
     

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