Who's good with props..?

Discussion in 'General Discussion' started by mnm99, Nov 17, 2019.

  1. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
    Yea I know, It's never good enough...lol. Winter is here and I want to play again.

    A few years ago I had my props re-pitched because I was above my WOT range of 4200-4600. I was at 4730 so I ended up going from a 18x21 with a .125 cup to a 18x22 with a .075 cup. After that I was at 4620 for some reason and gained like 3mph. So last year I had them go over the props again and add a .250 cup. My speed right now is 28 to 28.5 mph at 3450rpm and a WOT of 38.5 at 4560-80 rpm. I called ACME props and talked to him for a while. He suggested there 18x23 with a .043 cup. He told me it would gain around 1 mph on the top end at 4450rpm and .75 mph at cruise. Well if you do the math, there is no way i'm spending $3500 for that. So I'm thinking...safe RPM range is 4200-4600. What's stopping me to add another 1 degree of pitch and take out .125 cup or so. I would drop like 150 rpm bringing me to around 4400 rpm. I should gain better mph at cruise. I know optimal rpm is 4600, but if the range is 4200 to 4600 I should be good? right? I'm not sure how my gas mileage will do also after? Right now I'm burning 32GPH right at 28-28.5 mph. Here are some scenarios.

    Current =WOT 4580 rpm with 22 pitch prop .15.26 slip at 38.5 mph

    Proposed =WOT 4400 rpm with 23 pitch prop .16.73 slip at 38 mph
    Proposed =WOT 4400 rpm with 23 pitch prop .15.63 slip at 38.5 mph
    Proposed =WOT 4400 rpm with 23 pitch prop .14.54 slip at 39 mph
    Proposed =WOT 4400 rpm with 23 pitch prop .13.44 slip at 39.5 mph
    Proposed =WOT 4400 rpm with 23 pitch prop .12.35 slip at 38.5 mph


    Current =CRUISE 3450 rpm with 22 pitch prop .18.19 slip at 28 mph

    Proposed =CRUISE 3450 rpm with 23 pitch prop .21.74 slip at 28 mph
    Proposed =CRUISE 3450 rpm with 23 pitch prop .20.35 slip at 28.5 mph
    Proposed =CRUISE 3450 rpm with 23 pitch prop .18.95 slip at 29 mph
    Proposed =CRUISE 3450 rpm with 23 pitch prop .17.55 slip at 29.5 mph
    Proposed =CRUISE 3450 rpm with 23 pitch prop .16.15 slip at 30 mph
     
  2. Express 390

    Express 390 Active Member GOLD Sponsor

    304
    Sep 14, 2018
    South Shore of Long Island NY
    1986 SeaRay 390 EC
    1993 SeaRay 290 DA single 7.4 /Bravo 2
    Twin 454 Crusaders inboards 4 blades
    Just my opinion I wouldn't be too concerned with WOT 4200 -4600 your just going to tear your motor's up.
    What does it take to keep you on plane at a cruise speed you can live with. I just hear of so many people having motor problems with todays newer styles I think running hard destroys them. Again my opinion!
     
    Last edited: Nov 18, 2019
  3. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
    When selecting props you NEED to know WOT. That doesnt mean that's what I'm using it for. Your absolutely wrong though. Sorry. Wot determines where your cruise will end up. If you dont keep it in that range that's what kills motors. Too low and your lugging too high and its over revving. I never run at wot unless I'm testing out my prop.
     
    JVM225 likes this.
  4. Express 390

    Express 390 Active Member GOLD Sponsor

    304
    Sep 14, 2018
    South Shore of Long Island NY
    1986 SeaRay 390 EC
    1993 SeaRay 290 DA single 7.4 /Bravo 2
    Twin 454 Crusaders inboards 4 blades
    My intention was not to insult you the specs are under ideal conditions witch we don't have. Wind and current all play a part here all i'm saying , Is don't get crazy about your top number. As I Said Just my opinion !
     
    JVM225 likes this.
  5. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
    Sorry! I didn't mean to come off that way. I apologize.. The top number is what you really have to go by though. Anything you do to a prop is determined in the end by the top rpm range (ie 4200-4600). below 4200 and your lugging as i mentioned above your over revving. I know perfect is keeping it at 4600, but wondering if 4400 would really hurt engine and gas mileage.
     
  6. Express 390

    Express 390 Active Member GOLD Sponsor

    304
    Sep 14, 2018
    South Shore of Long Island NY
    1986 SeaRay 390 EC
    1993 SeaRay 290 DA single 7.4 /Bravo 2
    Twin 454 Crusaders inboards 4 blades
    You don’t have to apologize just having a Boat discussion what does SeaRay spec the prop size at?
     
  7. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
    Searay specs it out with 21 and slight pitch and 21.5 slight pitch. I confirmed that we can go higher than spec. All my numbers are with 8-10 people and full of fuel. If I tested with 2 people and 1/2 tanks I'd probably be higher rpm.
     
  8. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
    Just stopped at my prop shop and gave him my spec sheet. Curious to see what he says. I'll post back
     
  9. Express 390

    Express 390 Active Member GOLD Sponsor

    304
    Sep 14, 2018
    South Shore of Long Island NY
    1986 SeaRay 390 EC
    1993 SeaRay 290 DA single 7.4 /Bravo 2
    Twin 454 Crusaders inboards 4 blades
    Good luck
     
  10. sbw1

    sbw1 Well-Known Member

    Oct 10, 2006
    West Michigan
    This is listed in my signature
    This is listed in my signature
    IMG_4230.JPG If it was me, I would have accepted the 4680 and called it a day.
     
  11. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
    Yea I know. I have issues...lol
     
    Tacoma290 and sbw1 like this.
  12. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
    Prop shop got back to me. He want's to leave the cup and all 1 degree of pitch. Said I would drop 150 rpm. This will get me at 4400 rpm WOT within the range of 4200-4600. My cruise at 3450 should get me to 29 - 29.5 mph. I'll be happy with that! Every time they worked on my props, they were right on with the RPM.
     
  13. saopm

    saopm Member SILVER Sponsor

    766
    Oct 6, 2010
    North Fork - Long Island, NY
    2007 340 Sundancer
    Mercury 8.1s Inboards
    Which prop puller did you use?
     
  14. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
    saopm likes this.
  15. KevinC

    KevinC Well-Known Member

    Feb 25, 2011
    Long Island, NY
    2004 340 Sundancer
    Twin 8.1 V-drives
  16. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
  17. mnm99

    mnm99 Well-Known Member

    Oct 2, 2015
    Long Island
    2004 340 SeaRay Sundancer
    Twin 8.1 Merc
    Okay, I'm going to wait till the end of next season. I can't justify spending the money right now with 2 vacations coming up..lol I guess I'll have to go 1 more season before I try it out.
     

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