Results 1 to 16 of 16
  1. #1
    Member
    Join Date
    Jun 2016
    Location
    New Jersey
    Posts
    1,165

    Prop Help - Aluminum Mod-V Hull

    I whacked my prop on some rocks while loading when the lake was low. I’m going to replace it but using this as a chance to re-evaluate if I have the right prop.

    Boat - Crestliner VT 18 (Aluminum Mod V hull)
    Motor - Mercury 115 Pro XS; 2.07 gear ratio
    Current Prop - Black Max 17P Aluminum
    Speed - 42-43 (gps)
    RPM - 6100-6200 (on board analog tach); if I trim any more the RPMs jump to about 6400 but the speed drops to 39-40 and the boat feels like it bogs down.
    Setup - Motor is in the middle hole.

    This is my first boat, so I don’t have much to compare it to in terms of hole shot and handling. They feel fine. I’m not looking to move the motor any, but if I could eek out a few extra MPH that’d be great.

    Note that when the boat was new we also tried a Spitfire X7 19P and the boat didn’t like that prop. We couldn’t get it turn it faster than 5100 RPMs (that was with the dealer trying various motor heights). That said; since then we’ve added some trim tabs because I was also having a porpoising issue which is now resolved. I’ve also since swapped a Maxxum for an Ultrex which is heavier.

    Let me know what you think!

    Thanks guys!

  2. Member
    Join Date
    Mar 2017
    Location
    Quebec/Canada
    Posts
    983
    #2
    If you stay with a Black Max prop, I would go up to a 19 P if the tach is any good.

  3. Member
    Join Date
    Apr 2015
    Location
    ponchatoula la
    Posts
    1,490
    #3
    Not a fan of aluminum props. Have u thought about a stainless

  4. Member
    Join Date
    Mar 2017
    Location
    Quebec/Canada
    Posts
    983
    #4
    I think the Spitfire X7 was a stainless prop, just that it's a 4 blade and not aluminium. That is like going up 4 pitches. That's why 5100 rpm. A three blade stainless of the same pitch (17 pitch) would probably be fine. Make sure your tach is showing the true RPM.

  5. Member
    Join Date
    Jun 2016
    Location
    New Jersey
    Posts
    1,165
    #5
    Thanks both, this is helpful.

    19P Aluminum or 17p stainless. Why do you have to go down a pitch for stainless; because it's heavier?

    Should I consider a 17P four blade?

  6. Moderator 21XDC's Avatar
    Join Date
    Sep 2004
    Location
    Westland Michigan
    Posts
    63,357
    #6
    Quote Originally Posted by Grahamb View Post
    Thanks both, this is helpful.

    19P Aluminum or 17p stainless. Why do you have to go down a pitch for stainless; because it's heavier?

    Should I consider a 17P four blade?
    Stainless has more grip/less slip. More efficient. Smaller hp motors don't see as much benefit with SS as larger HP motors and boats.

    Marks Props 317-398-9294, 1850 East 225 South, Shelbyville, Indiana 46176 propellerman59@gmail.com http://www.marksprops.com/index.html

  7. Member
    Join Date
    Jun 2016
    Location
    New Jersey
    Posts
    1,165
    #7
    Quote Originally Posted by 21XDC View Post
    Stainless has more grip/less slip. More efficient. Smaller hp motors don't see as much benefit with SS as larger HP motors and boats.
    What about a Black Max aluminum 19P vs a Spitfire Aluminum 17p?

    Thanks!!

  8. Moderator 21XDC's Avatar
    Join Date
    Sep 2004
    Location
    Westland Michigan
    Posts
    63,357
    #8
    I dont have any knowledge between the two other than a 3 blade and 4 blade.

    Marks Props 317-398-9294, 1850 East 225 South, Shelbyville, Indiana 46176 propellerman59@gmail.com http://www.marksprops.com/index.html

  9. Member
    Join Date
    Mar 2017
    Location
    Quebec/Canada
    Posts
    983
    #9
    It's difficult to compare two props that are different. You can use your baseline: If you go from a Black Max 17 to a 19P, you should go down 200 turns in RPM. You should be around 5900. You should get the same type of performance you got from the aluminium 17.

  10. Moderator 21XDC's Avatar
    Join Date
    Sep 2004
    Location
    Westland Michigan
    Posts
    63,357
    #10
    Quote Originally Posted by Real L View Post
    It's difficult to compare two props that are different. You can use your baseline: If you go from a Black Max 17 to a 19P, you should go down 200 turns in RPM. You should be around 5900. You should get the same type of performance you got from the aluminium 17.

    Actually it's about 200 rpms "Per pitch" So 2 inchs = 400 rpm change.

    Marks Props 317-398-9294, 1850 East 225 South, Shelbyville, Indiana 46176 propellerman59@gmail.com http://www.marksprops.com/index.html

  11. Member
    Join Date
    Mar 2017
    Location
    Quebec/Canada
    Posts
    983
    #11
    Thank you 21XDC - got that one wrong. It would be around 5900 so that is 400 less RPM.
    Last edited by Real L; 04-15-2021 at 06:11 AM.

  12. Member
    Join Date
    Jun 2012
    Location
    SW Wisconsin
    Posts
    4,731
    #12
    I would first see what hole your motor is mounted in. Most of us have it in the third hole. Lots of guys running a spitfire x7 in a 19 pitch or a 20 pitch laserll with some added cup.

  13. Member
    Join Date
    Jun 2016
    Location
    New Jersey
    Posts
    1,165
    #13
    Thanks all! Leaning towards keeping the Black Max and going up to a 19p.

    Quote Originally Posted by alanhore View Post
    I would first see what hole your motor is mounted in. Most of us have it in the third hole. Lots of guys running a spitfire x7 in a 19 pitch or a 20 pitch laserll with some added cup.
    Motor is in the third hole. It sounds like going up to four blade, and stainless, and up to 19P would be too much given where I’m starting.

  14. Member
    Join Date
    Mar 2017
    Location
    Quebec/Canada
    Posts
    983
    #14
    Deleted

  15. Member
    Join Date
    Jun 2016
    Location
    New Jersey
    Posts
    1,165
    #15
    Just circling back for anyone that needs similar help.

    I tested a 19P Black Max (3-blade), 17P Spitfire (4-blade), and 19P Spitfire (4-blade).


    I've decided to keep the 17P Spitfire. The 19P spitfire was maybe a hair faster (less than 1 mph) but it would also blow out occasionally while just going straight on calm waters. It was strange. Everything would be stable, I wouldn't turn or touch the throttle or trim and it would blow out. I may have been able to address that with adjusting motor height, but I wasn't interested in going that route. With the 17P I've gained a couple mph at the top end over my three-blade and can now hit 45; maybe even a little more.


    One other note that I realized in my research. Mercury also makes props under the name Quicksilver. They use the same molds as the Mercury props, but they tend to be a bit cheaper; note that they don't include a hub kit but even factoring that in they are still cheaper. I was able to reuse my old hub kit. I used the Mercury names above but I actually tested the Quicksilver Black Diamond (Same as the Merc Black Max) and the Quicksilver Nemesis (same as the Merc Spitfire).

  16. Member
    Join Date
    Mar 2017
    Location
    Quebec/Canada
    Posts
    983
    #16
    Thank for completing the information