Impellers difference 2011-14 and 2015 up

[Philip]

Anyone know why the impellers are two different pitches on 2011-14 242s and the same for 2015 and up?

 

[Ronnie]

As I understand it, Yamaha used to outfit their twin engine boats with offset pitched impellers to account for the efficiency differences in the port and starboard pumps. That is, one side (I don’t know which) is more efficient at taking in water than the other because of the way the hull is angled compared to the rotation of the impellers since both impellers spin in the same direction. By offsetting the impeller pitches the engines should be at the same rpm throughout the throttles range and therefore the boat should track in a straight line instead of drifting to one side or the other. By analogy offsetting the impeller pitches is like getting a front end alignment on a car. In 2015 Yamaha stopped the offset impeller practice with no explanation as to why, I think it was a cost cutting measure but unless the boat’s ECM somehow adjusts the rpm of one of the engines to account for the last of offset impellers one engine should always be spinning at a different rpm than the other throughout the throttles ranges.

Note: if you purchase aftermarket impellers you buy the same impeller for both sides but have one pitched slightly differently than the other, I think the pitch difference is only 1.5 degrees.

 

[Philip]

Hmmm I know the hull was redesigned in 15. Maybe that was reason. I have a 16 242 Lse and rpms are exactly same. I have a set of impellers I had refinished for my 11 but sold and thought I could use until I seen difference.