B3 prop alignment

boatman37boatman37 Member Posts: 797 ✭✭✭
So read somewhere before about aligning the B3 props to eliminate vibration. Then remembered reading something about only the 3x3 props need properly aligned? I have the 4x3. Even if I try to align them they change after a few revolutions anyway?

Also, I added grease to the rear cone washer (first washer that goes on). None on anything else other than the shaft and splines. Pretty easy to pull them back off if I need to change something.
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Answers

  • LaReaLaRea Member Posts: 7,505 ✭✭✭✭✭
    Right.  If you have a 4-blade plus a 3-blade, you don't have to align them.  If both props have 3 blades, you should align them.  
  • boatman37boatman37 Member Posts: 797 ✭✭✭
    Awesome. Thanks! Yep, one 4 blade and one 3 blade
  • raybo3raybo3 Administrator Posts: 5,455 admin
    LaRea said:
    Right.  If you have a 4-blade plus a 3-blade, you don't have to align them.  If both props have 3 blades, you should align them.  
    Not true. I contacted merc a few year ago and they flat out told me that there is no such thing as aligning your props. I will see if I can find the e-mail and post it. 
    2002 342 Fiesta Vee PC Point Of Pines YC Revere MA. popyc.org     raybo3@live.com
  • aero3113aero3113 Member Posts: 8,777 ✭✭✭✭✭
    Check out this thread. I know 4x4 prop set up it doesn’t matter.

    https://rinkerboats.vanillacommunities.com/discussion/861/prop-timing-torques-specs

    2008 330EC
  • raybo3raybo3 Administrator Posts: 5,455 admin
    Found it:
    MERCRUISER CUSTOMER ASSISTANCE <mercruiser.customer.assistance@mercmarine.com>
    Fri 4/21/2017 10:23 AM
    • You
    Ray,
    There is no special timing of the props. Service manuals for engines and drives are available from local dealers or by calling our Publications Department at 920-929-5040, option #4. Have your serial number ready when ordering.
    Thanks,
    James
    MerCruiser Consumer Support

    2017-00054090
    -----Original Message-----
    From: raybo3@live.com [mailto:raybo3@live.com]
    Sent: Friday, April 21, 2017 8:39 AM
    To: MERCRUISER CUSTOMER ASSISTANCE <mercruiser.customer.assistance@mercmarine.com>
    Subject: 

    Contact Request:
    Name : Ray 
    Address :
    City/State : 
    Zip : 

    Home Phone : 
    Work Phone : 

    Email Address : raybo3@live.com

    Serial Number : 
    Model Number : 
    Dealer Name :
    Boat Manufacturer :
    Boat Model :

    Contact By : Email

    Comments:
    I have a twin Bravo 3 drives. My question is do the props have to be "timed/aligned"? If yes is there an online manual for this. Thank you for your help.

    Mercury Marine
    mercruiser_customer_assistance@mercmarine.com
    https://urldefense.proofpoint.com/v2/url?u=http-3A__www.mercurymarine.com&d=DwICAg&c=tjPg1sbLxZ1bjgTYa5hhdw&r=FEQWMy8t0qVEVOymqTeqBMVeLlfR66Wd26pDhpbyAhJy52Gjwpo5ZejkaibZ_Oj7&m=QgsNEbY6VvzuK92b0MB4xtuZmHSs-23Fe4yO09LJ4w0&s=Klr2U2CSt7hoq_R2C1JyFY8t_6PVhoHuQ2JHfIG6eUQ&e=
    2002 342 Fiesta Vee PC Point Of Pines YC Revere MA. popyc.org     raybo3@live.com
  • boatman37boatman37 Member Posts: 797 ✭✭✭
    Cool. I spun them and they are never in the same place each revolution so didn't figure it mattered
  • LaReaLaRea Member Posts: 7,505 ✭✭✭✭✭
    Well, this is what @Alswagg said a few years ago on this topic:

    Alswagg said:
    Prop alignment is critical for proper thrust wash.  This is basic hydrodynamics taught in Merc drive class  
  • boatman37boatman37 Member Posts: 797 ✭✭✭
    edited April 2020
    So where do we find how to properly align? My manual doesn't mention anything about it. I have the whole satchel full of all the booklets that came with it. I have one 3 blade prop and one 3 blade
  • reneechris14reneechris14 Member Posts: 3,134 ✭✭✭✭✭
    Make sure the 2 blades don't cross under the cavitation plate at the time.
    2005 Rinker FV342  Pawcatuck river,Ct
  • LaReaLaRea Member Posts: 7,505 ✭✭✭✭✭
    This is the manual page that has been posted here before.  @raybo3 that Merc tech must have assumed you have 4/3 props.

    Trashman said:
      

  • raybo3raybo3 Administrator Posts: 5,455 admin
    @LaRea maybe but I did give him my serial numbers. 
    2002 342 Fiesta Vee PC Point Of Pines YC Revere MA. popyc.org     raybo3@live.com
  • Cableguy GregCableguy Greg Member Posts: 5,011 ✭✭✭✭✭
    LaRea said:
    This is the manual page that has been posted here before.  @raybo3 that Merc tech must have assumed you have 4/3 props.

    Trashman said:
      

    This is how I align my props every spring. 
    2008 280 Express Cruiser, 6.2MPI, B3, Pittsburgh, PA "Blue Ayes"
    Go Steelers!!!
  • LaReaLaRea Member Posts: 7,505 ✭✭✭✭✭
    I'd love to know the real explanation for this.  Those I've read seem to be idle chatter that is uncluttered by facts.  It's for vibration, it's for cavitation, you need it on a Merc but not on a VP, you need it on aluminum props but not stainless, yada yada yada.  
  • raybo3raybo3 Administrator Posts: 5,455 admin
    edited April 2020
    OK take a look at this. See if you see the same thing I see.......
    https://www.youtube.com/watch?v=Zo1l1RncrvI
    2002 342 Fiesta Vee PC Point Of Pines YC Revere MA. popyc.org     raybo3@live.com
  • boatman37boatman37 Member Posts: 797 ✭✭✭
    Seems like with a 4/3 no matter what you do they will cross together at every point around the circumference at some point with enough revolutions?
  • IanIan Member Posts: 2,774 ✭✭✭✭
    LaRea said:
    This is the manual page that has been posted here before.  @raybo3 that Merc tech must have assumed you have 4/3 props.

    Trashman said:
      

    This is how I align my props every spring. 
    Why - do you take them off? They shouldn’t go out of alignment....

    Regards,

    Ian

    The Third “B”

    Secretary, Ravena Coeymans Yacht Club

    https://www.rcyachtclub.com/

  • LaReaLaRea Member Posts: 7,505 ✭✭✭✭✭
    I take mine off to scrape and paint the drives and clean the props.  It's a ritual of spring.  But I have 4/3 props so no alignment.  
  • reneechris14reneechris14 Member Posts: 3,134 ✭✭✭✭✭
    I take my drives and props of every year. Shine them up and check things out
    2005 Rinker FV342  Pawcatuck river,Ct
  • LaReaLaRea Member Posts: 7,505 ✭✭✭✭✭
    @raybo3, that video is not what Merc recommends.  You don't align the props relative to each other or to the logo positions.  You align them relative to the cavitation plate. 

    Install the forward prop.
    Rotate it until one blade points up.  
    Install the rear prop with one blade pointing down.  It doesn't matter where the logos are.
  • raybo3raybo3 Administrator Posts: 5,455 admin
    @LaRea that video is the complete opposite of what the timing "should" be. In the video both blades are under the cavitation plate. 
    2002 342 Fiesta Vee PC Point Of Pines YC Revere MA. popyc.org     raybo3@live.com
  • Cableguy GregCableguy Greg Member Posts: 5,011 ✭✭✭✭✭
    edited April 2020
    icoultha said:
    LaRea said:
    This is the manual page that has been posted here before.  @raybo3 that Merc tech must have assumed you have 4/3 props.

    Trashman said:
      

    This is how I align my props every spring. 
    Why - do you take them off? They shouldn’t go out of alignment....
    My boat is in a storage facility. They are rather expensive to grow legs. Call it cheap insurance. I have always removed my props when the boat is being stored, whether it is in a boat yard or a storage lot. With them off, I am able to clean up and regrease the splines.
    2008 280 Express Cruiser, 6.2MPI, B3, Pittsburgh, PA "Blue Ayes"
    Go Steelers!!!
  • LaReaLaRea Member Posts: 7,505 ✭✭✭✭✭
    @raybo3 the video from On Board with Eddie is kinda funny.  When he starts, the props are aligned backwards (rear prop is upside-down).  After removing them, he carefully reinstalls them the same position (and it's still wrong).  

    Wrong way:

  • raybo3raybo3 Administrator Posts: 5,455 admin
    @LaRea when I posted the link that's what I meant when I said see if you see what I see....lol
    2002 342 Fiesta Vee PC Point Of Pines YC Revere MA. popyc.org     raybo3@live.com
  • boatman37boatman37 Member Posts: 797 ✭✭✭
    I remove my props every year to clean and grease the shafts and clean the props

  • rasburyrasbury Member Posts: 8,218 ✭✭✭✭✭
    I don't get it, they counter rotate..they are never in the same position to each other, how could you possibly align them? Not saying anyone is wrong, I'm just not grasping it!
  • WillhoundWillhound Member Posts: 4,183 ✭✭✭✭✭
    They counter rotate, but at a fixed ratio. So the points that they pass each other don't vary.
    "Knot Quite Shore" - 2000 FV270
  • raybo3raybo3 Administrator Posts: 5,455 admin
    Why wouldn't they "key" the props if align is so important? Very easy to do with the spline................ Just say'n
    2002 342 Fiesta Vee PC Point Of Pines YC Revere MA. popyc.org     raybo3@live.com
  • Cableguy GregCableguy Greg Member Posts: 5,011 ✭✭✭✭✭
    rasbury said:
    I don't get it, they counter rotate..they are never in the same position to each other, how could you possibly align them? Not saying anyone is wrong, I'm just not grasping it!
    You don't want the blades creating the wash/thrust under the cavitation plate at the same time. That would happen if you put both props on with both props blades lining up at the 12 o'clock position. 
    2008 280 Express Cruiser, 6.2MPI, B3, Pittsburgh, PA "Blue Ayes"
    Go Steelers!!!
  • LaReaLaRea Member Posts: 7,505 ✭✭✭✭✭
    Yes, that's it exactly.  The top position (12 o'clock) is different from the rest of the circle for two reasons.  (1) The water flow there is turbulent from flowing around drive body.  (2) That's the place where you're most likely to get cavitation badness (or ventilation) because the hydrostatic pressure is lowest there.  

    Apparently, if you have the front and rear blades passing through that space at the same time, it creates vibration, or cavitation, or both.  
  • LaReaLaRea Member Posts: 7,505 ✭✭✭✭✭
    edited April 2020
    I was stewing about this last night because I couldn't figure out an easy way to explain it.  So I geeked out and created these animations.  

    Each one shows counter-rotating props viewed from behind.  Any time there are two blades passing each other at the 12 o'clock position, the animation pauses and the blades turn red.  

    First we have two 3-blade props (3x3) that are aligned incorrectly.  You can see that every time a blade of the rear prop passes the top, a blade of the front prop is also there.  It happens three times during every revolution.  



    Now a 3x3 correctly aligned as specified by Merc.  You never get both blades passing the top at the same time.  



    Next is a 4x3 setup (4 blades on the front prop, 3 on the rear).  They never line up at the top, although it does get close a couple times.  



    Actually, it is possible to mis-align a 4x3.  You can have two blades line up at the top.  However, it only happens once per revolution, and only if you line them up perfectly wrong like this.



    (updated the graphics, added cavitation plate and skeg)
    Post edited by LaRea on
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