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  1. #1
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    Crestliner VT 18 Prop Help

    Hey guys. I need a little prop help.


    I have a new Crestliner VT 18 with a Mercury four stroke ProXS 115hp.


    The motor is in the second hole from the top.


    I ordered the boat with the a Spitfire X7, but it was on backorder so the dealer put a BlackMax 17p on it. With the BlackMax, I'm hitting 5500 rpm with no trim and hitting 39mph. I can trim it one or two blips to get to 5900rpm and 42 mph. Beyond that it starts to porpoise significantly. I have trimmed it up to 6300rpm and hit 49mph, but it was not pleasant; it was like riding a bucking bronco.


    The dealer sent me the Spitfire X7 19p. With it I'm getting 4600rpm with no trim and 36.5mph. I can trim it up to 5000rpm and 42mph where it begins to porpoise. Beyond that there is significant porpoising.


    I know most people are pairing the 115 ProXS with the 19p X7, but it doesn't seem like I'm getting nearly enough rpm or performance. Mercury has a performance sheet showing 6150rpm and 50.5 mph with the Crestliner TC18, which I think is the same hull. They also report mounting hole 2.


    I don't carry a lot of weight in the boat but I did try shifting around what I do have and it didn't make a difference.


    Any suggestions? I'll reach out to the dealer too, but I wanted to try to educate myself a bit before I do so.


    Thanks all.

  2. Member
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    #2
    I talked to Mercury and they confirmed the Spitfire X7 should be the right prop for this engine/boat, and also confirmed that I'm not getting enough RPMs. They thought this could be a motor height issue. Maybe raising it a hole could get additional RPMs and also help the porpoising issue.

    Thoughts?

  3. Member tjsellsfords's Avatar
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    #3
    Also waiting to hear what anyone has to say I'm only getting 5,300 with the standard aluminum prop in the second hole.
    2017 Crestliner VT 18 DX
    Mercury 115 ProXS
    Motorguide X3 70lb 24V
    TP Express Mach 4 13 x 19
    "Follow Me," Jesus told them, "and I will make you fish for people!" Mark 1:17


  4. Member
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    #4
    I should be able to give you some numbers for comparison really soon. I'm still breaking it in, but after the next hour I can start driving it more normal and playing with things. So far I'm not seeing any of the things you're having issues with. I'm out of town now, but when I get back home I'll check motor mounting and verify prop on mine.

  5. Member
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    #5
    Thanks Matt. Eager to hear how yours is performing.

    I talked to Crestliner this week. The rep said I might need trim tabs added. When she sent me a pic of what they look like, I pointed out that the boat already came with those from the factory. I sent her a picture back (actually a picture of TJ's boat) and she confirmed they were the same thing. She said they sometimes need a second set further to the outside and/or motor needs to move.

    Taking it to the dealer isn't exactly easy/convenient for me, but I'll probably get it there later this summer.

  6. Member
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    #6
    I have a 21 pitch Turning Point Express SS prop. Turns 6150 Rpms with me alone, full tank & gear & 51+ mph on Mercury smart gage. About 5400 & 48+ mph with 3 people... It took me some time at the helm to get it dialed in, but it is great now. About 20 hrs on Pro XS 4s... 2016 boat.
    Rip them Lips!!!
    2016 Crestliner VT 18 115 Pro XS

  7. Member
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    #7
    Quote Originally Posted by JwSnipes View Post
    I have a 21 pitch Turning Point Express SS prop. Turns 6150 Rpms with me alone, full tank & gear & 51+ mph on Mercury smart gage. About 5400 & 48+ mph with 3 people... It took me some time at the helm to get it dialed in, but it is great now. About 20 hrs on Pro XS 4s... 2016 boat.

    When you say "dialed in," do you mean that you learned how to operate it, or do you mean trial and error with props and motor height? What hole is the motor in? Any additional info you can give would be appreciated.

  8. Member
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    #8
    Ass time at the helm. Yep, learning how to trim it just right. After my motor had about 15-18 hrs on it, it seemed to open up a bit. I can only raise my motor one more hole.
    I am on the 4th hole down from top. Bottom 1 hole open below. My pic won't upload for us...
    Rip them Lips!!!
    2016 Crestliner VT 18 115 Pro XS

  9. Madfish
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    #9
    I know my set up is a little different because i am running the CT engine, but i went up to the 3rd hole ----running a 23 tempest plus --could do a 25----turning 6,000 rmp @ 53.6 mph on my VT 18----

  10. Member
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    #10
    Mine is mounted in the 2nd hole from the top. I can spin my Spitfire X7 19P prop out the roof. Not sure how accurate my analog tach is, but I can get to 6300 and still have throttle and trim left. I'll have to agree with JwSnipes, nothing replaces getting familiar with the rig. I trimmed up too high a couple of times today and blew out. I finally found the "sweet spot" after several runs. Keep after it, once you get a better feel for the rig it gets easier each time.

  11. Member
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    #11
    Interesting.

    Mine starts to porpoise with just the slightest trim. Is there a chance there's smooth water trimming past the porpoise zone?

    What kind of speed are you gettin Matt?

  12. Member
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    #12
    Didn't think to check speed on my GPS, but the speedo was reading mid-upper 40s. I haven't experienced any porposing at all, but I generally run as much trim as I can and maintain good ride and prop grip. Have you tried trimming up more? Mine really shines when I get it out of the water some.

  13. Member
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    #13
    When I've trimmed up more it keeps porpoising, but the speed keeps going up, it's not like the prop slips. I managed to hit 49 once by continuing to trim, but it was terrifying and must've looked ridiculous. If I keep trimming up it also gets a side to side wiggle.

  14. Member
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    #14
    I had the same problem with my Lowe stinger. They sent me 2 thin wedges to install under the hull. Problem completely solved.

  15. Member tjsellsfords's Avatar
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    #15
    Thanks!
    Quote Originally Posted by Beagle33 View Post
    I had the same problem with my Lowe stinger. They sent me 2 thin wedges to install under the hull. Problem completely solved.
    2017 Crestliner VT 18 DX
    Mercury 115 ProXS
    Motorguide X3 70lb 24V
    TP Express Mach 4 13 x 19
    "Follow Me," Jesus told them, "and I will make you fish for people!" Mark 1:17


  16. Member
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    #16
    I've decided to drop the boat with the dealer this weekend so they can take a look at it. He's thinking that a set of transom wedges may be needed.

    More to come...

  17. Member
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    #17
    Had the same problem with my 2013 Lowe 18HP, which came with 1/8" welded bead on the 2nd and 3rd Steps at the transom. I got a pair of wedges from Lowe, but traded it before I had them installed. You're not going to be able to trim without some wedges or welding. Dealer will be able to fix it.
    2015 Ranger RT188 DC; BassCat Storage Box; Mercury Optimax 115ProXS;
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  18. Member
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    #18
    Just got off the phone with the dealer. He's been playing around with the boat and this is where he landed...so far.

    He tested raising it up one hole and up two holes. Being up one hole performed better; I gather this means the third hole. He also added the transom wedges.

    He tried it with both the Black Max 17p and the Spitfire X7 19p. He too couldn't get the X7 to spin fast enough - 5800 RPM with the Black Max and only 5100 with the Spitfire X7. He had the motor hooked up to his computer and also hooked it to his dyno and said it's performing well; this combo just doesn't like the X7.

    He had another guy in the boat and was getting 46mph gps with the Black Max, with no porpoising. I was only able to get about 42mph solo before porpoising. He said that he could continue to trim and get it to porpoise, but at 46 and 5800 rpm it was solid. He's going to talk to Crestliner and Mercury to see if they might recommend another prop.

  19. Member tjsellsfords's Avatar
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    #19
    I just don't understand why the X7 is only turning 5,100 for you. I was thinking about ordering one at some point but I'm not sure now. If the transom wedges got you to 46 with no porpoising I will probably get them to install them on mine too. I'm going to PM Matt and see exactly how his is set up.

    I just remembered his is command thrust. I went to Mercury's site and the command thrust gear case is 2.38:1 and our engines are 2.07 to one, so that explains some of the difference between 5,100 and 6,300 but not all of it. The difference between 2.38 and 2.07 is a little over 15%. That doesn't quite get you to 6,000? hmm? And he's in the 2nd hole.
    Last edited by tjsellsfords; 07-17-2017 at 09:26 PM.
    2017 Crestliner VT 18 DX
    Mercury 115 ProXS
    Motorguide X3 70lb 24V
    TP Express Mach 4 13 x 19
    "Follow Me," Jesus told them, "and I will make you fish for people!" Mark 1:17


  20. Member
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    #20
    My boat came with the wedges. The motor is in the 2nd hole from the top. I've got a 19P Spitfire (not the X7 as stated above) and the standard (2.07 ratio) lower unit. I can spin mine to 6200+ RPMs and maintain good bite going in a straight line. It will lose grip in turns when trimmed that high and one more blip on the trim blows it out. Seems strange you can't get that X7 up in RPMs more. I could see losing some going to the different prop material, but that's a lot. I too am re-thinking my plan to upgrade to the X7, maybe I'll just hold what I've got for awhile and see where I end up. Right now with two adults and gear I can get 45ish MPH at 6200+ RPMs. Solid ride, no porposing at all. I don't really see any speed increase from around 5800 RPMs and up, so the prop is slowly loosing bite at that point.

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