Rotation

[Socks]

As I climb around this boat seeing what I have and attempting to learn as much as I can about the varies systems, I am curious. How do I determine the rotation of my Mercruiser sterndrives? More specially, how do i determine if one is counter rotating? Both props appear to be the same.

 

[Soulshine]

If you do in fact have one counter rotating drive it should be on the port side.

Your manuals (if you have them) should clarify as well.

Hook them up to muffs and run in gear for a minute and note clockwise or counter clockwise rotation.

The props should not be the same, but might appear so at a glance.

 

[Socks]

I'm striking out all the way around -- Can't fire up the engines at the moment -- I have a "downloaded" Owner's Manual but can't find anything in it about rotation. As I mentioned, the props appear to be the same. They are numbered the same (SS aftermarkets) with the exception of one ends in "A" and the other ends in "B".

 

[bobeast]

If you download the parts manual from Sea Ray for your model/year. It should list the props. Typically you will find 2 part numbers one for a "LH" or "L" (port) and one for a "RH" or "R" (starboard) prop.

My 310, for example is listed as:

1592724 PROP, 17"X 20"X 1.5" L3BMC NIBRAL H/S
1592732 PROP, 17"X 20"X 1.5" R3BMC NIBRAL H/S

Looking from the back, the port prop goes counter-clockwise, and the starboard prop rotates clockwise when the gears are in forward.

Since you have aftermarket props, I'm guessing the 'A' and 'B' designate which side. You'll have to look up the prop part number to know which is which, I suppose.

 

[JVM225]

I'm striking out all the way around -- Can't fire up the engines at the moment -- I have a "downloaded" Owner's Manual but can't find anything in it about rotation. As I mentioned, the props appear to be the same. They are numbered the same (SS aftermarkets) with the exception of one ends in "A" and the other ends in "B".

Your 83 270 didn’t come with counter rotating drives, but a previous owner may have done that modification. I did it in my 87 300.
If one prop has an A at the end of the number and the other a B, that might indicate something but the best way to tell if you can’t sstart them up is to visibly look at them. The blades on one prop will be tilted one way, and the blades on the other will be tilted the other way.
If they are tilted the same way in both props then you have standard rotation on both sides.

 

[Socks]

In my mind, the tilt of the blades should be different if it were counter rotating. I can set 1 prop on top the other and there's no different in the blades. -- But you raise a question. What is the Pros and Cons of counter rotating drives? If mine are standard rotation and I were to replace the Port --- should I go to Counter? --- Thanks for the info

 

[Soulshine]

You can also manually rotate the props with the drives in forward gear.

The will only spin in one direction and lock in the other. If this is the same on both sides you have two standard rotation drives.

 

[Socks]

Thanks, I'll give that a try tomorrow.

 

[Socks]

If turning the prop with the leveler in forward is an indication, then both are standard rotation (clockwise). If i were to replace the Port drive, would it be advisable to replace with a counter rotations?

Thanks

 

[JVM225]

If turning the prop with the leveler in forward is an indication, then both are standard rotation (clockwise). If i were to replace the Port drive, would it be advisable to replace with a counter rotations?

Thanks

Did you figure out yet whether you have Pre-Alphas, Gen 1’s, or Gen2’s?
You would have to get the right one for your drive.
I don’t think anyone ever made one for Pre-Alpha, OEM’s are hard to find for Gen 1’s because they didn’t make them until the later years, and the Gen 2 Counter Rotating lower unit should be fairly easy to come by. You can order them aftermarket and brand new from SEI for either the Gen 1’s or Gen 2’s.
I had considered doing that but was taking my time making the decision because of the mixed reviews I hear about SEI’s quality. That ranged from “they are fantastic” to I wouldn’t put them on my worst enemy’s boat. While I was debating it in my head I was lucky enough to come across a good used OEM lower unit so I never had to make the decision.
After doing it on my old boat I saw a benefit in handling around the docks. When backing in to slips I treated it pretty much like it had inboards. Kept them pointed straight, and just used the shifters to adjust position when backing up. IMHO it was a worthwhile upgrade. Made docking super simple.
I didn’t see any benefit to it other than that, but I guess an engineer could probably make some sort of argument for counter rotation when going straight. Even then though, I doubt it would be one that would make any noticeable difference to you.

 

[sbw1]

Counter rotation is used to offset the torque introduced by the spinning prop. Props turning in opposite directions make the boat go through the water more effectively by offsetting the torque factor. You may not notice torque when you take off if your boat has power steering but it is present and needs to be compensated for by adding a little steering input to keep the boat going in a straight line. Otherwise the tendency would be for the boat pull to the right. Steering needs to be slightly left of center to maintain the track when on plane. Dual counter rotating props offset the pull to the right and reduce drag. If you have ever flown a small single engine airplane, torque (p factor) is very apparent upon take off. You need pressure on the left rudder peddle to accelerate in a straight line down the runway. Otherwise you pull to the right and lose control at the high power setting needed to reach flying speed.

 

[Socks]

JVM, based on all the information everyone has provided, I have determined the drives are Alpha gen1. I have no concrete reason to think these drives are not working properly. They are pitted (electrolysis) and looks bad. My original intentions were to service them, new impellers, etc. However after looking everything over, I am leaning toward just replacing.

I've owned several inboard cruisers and I am familiar with the easy docking of counter rotating props. At this point, my choice would be counter rotating if I did replace the drives. But you are correct, finding counter rotating Alpha gen 1 isn't a easy task. Granted, I haven't shopped "new". So far I have been looking at used and/or rebuild Gen 1's.

SBW pointed out the torque factor of having counter rotating drives. I assumed, aside from the close quarters maneuvering, torque was a factor also.

Thanks for all the info. I'll keep posting as I move with the project.

 

[JVM225]

SEI makes and sells them new. Research them, and you’ll probably find as many opinions as I did on them.

 

[bobeast]

In my mind, the tilt of the blades should be different if it were counter rotating. I can set 1 prop on top the other and there's no different in the blades. -- But you raise a question. What is the Pros and Cons of counter rotating drives? If mine are standard rotation and I were to replace the Port --- should I go to Counter? --- Thanks for the info

The idea behind counter-rotating props is to eliminate prop walk or the tendency of your stern to be pushed towards the opposite direction of the prop rotation. (to port for a RH/clockwise prop, or to starboard for a counter-clockwise prop) In reverse, the prop-walk direction will be opposite and is usually more pronounced. This is why dual engines with counter-rotating props have a large advantage in slow speed maneuvering over a single engine or a twin with both props going in the same direction.

 

[SCORPIO]

I put an SEI counter rotating lower on my port drive and it really helps with docking.