Prop question

Discussion in 'Props' started by Mr Efficiency, May 18, 2017.

  1. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    I have acquired a couple of Mercury 115hp 2-stroke 4-cylinder motors this week, both were mounted on the same boat previously, the props on each are identical size and handedness, but they are stamped 'port' one, 'starboard' the other. What is the diference here ? I reiterate, they are both right-hand rotation.
     
  2. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell . . . . .

    Lol, one's for the port and one's for the starboard silly!
    Perhaps the bottom ends are different.
    Maybe the previous owner was delirious and felt the need to label.
    Maybe (s)he was experimenting on some strange tangent that needed ID'ing the props.
    Maybe...
    We could go on all day speculating.
    Why do you think they're labelled, Mr Efficiency?
    ;)
     
  3. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    It is a bit of a puzzle, I have seen plenty of twin outboard set-ups, but never port and starboard except in CR set-ups. A previous owner was certainly fastidious, as they present as very well looked after, there being minimal sign of rust around the yoke and mounts, tilt tube etc, though used in salt water, and being around two decades old. Maybe they have been re-cupped or repitched and are slighly different, and their L-R placement is to iron out a handling quirk of the boat they were on. But I don't have a clue.
     
  4. jorgepease
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    jorgepease Senior Member

    That's my bet since I have had the exact thing done on an old boat I used to have.
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Yeah, I'd also error on the side of caution, unless you can have a conversation with the previous owner. It's possible one prop has had some tweaking, so needed to be marked.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I'll take a closer look for any visible differences, could not see any on casual inspection. Engine RPM may tell a story once running on the boat.
     
  7. BlueBell
    Joined: May 2017
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    BlueBell . . . . .

    Everything will likely be fine so long as you play along I suspect.
    Maybe they labelled them just to mess with the next owner's brain.
    Can you find out who serviced them?
    VIN or a serial number trace of service or parts purchases...?
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    The trail has gone a bit cold, the previous owner never used the motors, he bought and stored them for two years with the intention of switching one to a 20" shaft to fit a ski boat, but I'd say found out that is not an economic thing to be doing. He told me he bought them off a chap that had them fitted to a "wooden" monohull boat, which suits me as they would not have been much chop were they fitted to a cat, ( the most common use for XL motors of that size, in that era, where spray and mist tends to shorten the life of outboards markedly. They are going on to a cat, and any slight difference in the props probably won't be an issue with hydraulic steering, and the general way the boats handle, but I was just puzzled by the need to have them different.
     
  9. fredrosse
    Joined: Jan 2005
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    fredrosse USACE Steam

    In the machine world where I have worked for several decades, it is considered good practice to record the location of various identical parts when dis-assembling, so that when they are re-assembled they go back to the same location. This often does not matter, yet the practice is a safeguard against the possibility of an anomaly in a part that may cause an issue.

    For example, when we pull pistons for a new set of rings, each piston goes back to its original cylinder, even though they may be theoretically all the same, better to not take a chance when it is so easy to follow this practice. It is hard to imagine this being required for two identical props, but if the person doing the work on the machine did not know if it mattered, (s)he would be considered as following good practice to just mark everything.
     
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  10. Mr Efficiency
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    Mr Efficiency Senior Member

    I never considered that possibility, but one owner certainly seems to have been methodical.
     
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