Thread: Prop advice?

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  1. #1
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    Prop advice?

    Anyone have a 189trx with a 150FS? What kind of speeds do you get. I run right around 50mph and think I might need a different prop. I have a Tempest Plus P21. I don’t know a whole lot about all the setup. I raised the motor on my jack plate to a point where I got a couple more mph, but if I go up any more my rpms go up but no increase in speed. Any dvi e is appreciated. Thanks

  2. Member lsufan334's Avatar
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    #2
    We need a little more information. pad to prop height. Are you reaching max rpm's at full trim? How heavy of a load when testing?

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    #3
    How many rpm's are you turning the 21 tempest at WOT/max speed now?

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    #4
    Hello, I will have to get the prop to pad height. (I’m at a campground for the week and have the boat at a dock. Not sure I want to give up fishing time to pull it out and measure until this weekend.) I initially did the testing pretty light. Half tank of gas, two people. I’m out this week fishing and have a little more gear and full tank of gas. I didn’t know weight could have this much affect. I’m clearly too high with the motor. With full gas tank I can’t trim up all the way without the prop slipping really bad. I’m hitting 5900 rpms but could probably exceed. I do only have the gauge in the dash and it sounds like it’s not the most accurate. Max speed is about 52 mph. Today I trimmed it to where I could really feel the prop slip, backed it off a little, and 5900 rpm-52 mph.

  5. Member lsufan334's Avatar
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    #5
    if your hitting the 5900 rpm your prop isnt slipping. Your hitting your rev limiter. It does feel like its slipping but thats just your engine trying to protect itself from over-revving. So you are basing your mph off of the factory gauge? If so I wouldn't trust those things for nothing. To get accurate mph you will need a true gps speed. You can acquire this from a gps fishfinder or possibly on a gps app on your phone. But 100% we need to know pad to prop height. If you are running too high then you will see a substantial drop in water pressure when you are trimmed up. Do you have a gauge to test water pressure? If so what is water pressure?

    Just for comparison. I am running the same boat with a 150 pro Xs. Pad to pro height of 3.75". 22p Tempest prop. Weight evenly distributed. By myself full tank of gas I am able to get 56-57 hitting 5750 rpm. I am wanting to go back to 21p tempest. My boat seemed to run better with the 21p Temest.

    If I was you i would set pad to prop height close to 3.75" leave the 21p on there and let her eat. LOL

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    #6
    I will give that a try. I am using gps speed and water pressure doesn’t seem to drop. Playing around today it’s very interesting that my hole shot seems really good, the bow doesn’t come up as high at low speed and if I don’t trim all the way it cruises very nice at 52 and 5800 rpm. I will try setting it at the 3.75” and report back. Thanks

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    #7
    Just measured prop to pad and I’m at 4” provided I measured correctly. I looked at the post that shows the pictures and is it correct to measure the center lowest point for the pad? At a full tank of gas if I trimmed up all the way I would hit 52 mph and exceed rpms. When I got down to half a tank it ran at 5800 rpms and 52 mph.

  8. Member lsufan334's Avatar
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    #8
    I would raise the motor to 3.75" and see what that does. I think I am acutally running a little higher than 3.75 I will check in the morning to confirm but yeah I would raise the motor a quarter inch and keep an eye on your wp. keep raising (as long as you are seeing results) just make sure to keep an eye on your water pressure.

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    #9
    What do you get for top speed? (I don’t have the Pro XS so might not be fair comparison). I remeasured today and was actually at 4.25”. I set it to 3.75 and need to get out on water to test. Do you notice a big difference in performance between a full tank and half a tank of gas?
    2017 Triton 189TRX
    Mercury 150FS
    Tempest Plus 21P

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    #10
    So I think I am finally able to give some valuable information.

    adjusted Prop to Pad to 3.75, I was at 4.25 and actually started almost 1 inch lower than that.
    Just under 1/2 tank of gas
    5 Seconds to plane
    53 mph
    5800 rpm maybe a little more. (I assume motor will tel me when I exceed limits)
    if I step on it slow I plane out at 3000 rpms

    amazing difference in everything at this height.

    Do I go up another .25 just to see?

    Any thoughts what happens with a full tank of gas?
    2017 Triton 189TRX
    Mercury 150FS
    Tempest Plus 21P

  11. Member lsufan334's Avatar
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    #11
    yeah as long as your water pressure is ok go for it. Im not sure of what wp is supposed to be for 4 stroke but i know the 2 stroke is 3-6psi idle and 11-14psi WOT

  12. Member lsufan334's Avatar
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    #12
    oh just saw your last sentence. you will lose some. The trx hulls do not handle weight well at all from what i have seen from mine.

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    #13
    I sent my prop in to Mark for some work. Will report back results when I get it back.
    2017 Triton 189TRX
    Mercury 150FS
    Tempest Plus 21P

  14. Member lsufan334's Avatar
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    #14
    oh your gonna deff be set up right. I have always wanted to blueprint and re-work mine. Just cant go that long without a prop. Have to fish too much. lol

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    #15
    Mark blueprinted my prop and now I understand how much the prop can change the performance. Top end is now 53-55 but that isn’t the real change. The boat pops on plane quicker and I can take off in much shallower water. Had it out for a week in Canada and believe there was a significant gas improvement. Probably both from coming on plane faster and I run 51-52 mph at 55-56K rpms instead of maxed. Thanks Mark and everyone for all the help. I may still play a little with the height. I’m at 3.75, may try 3.5 just to see.
    2017 Triton 189TRX
    Mercury 150FS
    Tempest Plus 21P