counter rotating?

[greatsouthbaybob]

Is there a quick way I can check if a boat with twin i/os (alpha 1) is equipped with counter rotating props? I imagine by putting them in gear and turning with motor off? Thanks

 

[coleman kayak1]

Re: counter rotating?

If they have props- look at how the blades look. If they both go the same direction its not. If they go opposite direction it is counter rotating. Hope this helps.

For example- if your props are opposite (see picture) it is counter rotating

 

[greatsouthbaybob]

Re: counter rotating?

Thanks, out of curiosity, does anyone know what the result would be of putting a rh prop on a lh drive or vice versa?

 

[mcleaves]

Re: counter rotating?

The drive would run you backwards when throttling forward. You'd have to run the control for the drive backwards to use it. I've done it by accident, not by changing props, but on a VP drive installing the shifter linkage on the wrong side.

Boy was that a surpise first time I put it in gear!

M

 

[tommays]

Re: counter rotating?

The alpha drive will self destruct if you use the wrong rotation prop

They make a compleatly different version for left hand props



Tommays

 

[mcleaves]

Re: counter rotating?

The alpha drive will self destruct if you use the wrong rotation prop

I am most definitly not a merc guy, but why would this happen? Just really curious.. I wouldn't think the drive cares which way the boat is moving, or which way the prop is cutting the water.

M

 

[tommays]

Re: counter rotating?

The standard drive is set up to take a right hand prop

http://www.boatfix.com/merc/Servmanl/14/14b3.pdf

the counter rotation drive has a different bearing setup

http://www.boatfix.com/merc/Servmanl/14/14c3.pdf


Tommays

 

[bjcsc]

Re: counter rotating?

Think about the gears and how the teeth are cut. Just like an R&P in a diff. they are designed for certain loads/lash on the front face and totally different on the back. I can easily see how reversing the forces would lead to self-destruction.

 

[rodbolt]

Re: counter rotating?

actually its in which direction prop shaft thrust is taken on. the cut of the gears and the direction of input is the same, the right hand rotation picks the fwd most gear as "fwd" gear and the left hand rotation picks the aft gear as "fwd" gear.
most outboards do the same.
the cone clutch set up that volvo uses does not care as both ends of the prop shaft use tapered roller bearings that can accept radial and axial loads. all the cone cares about is that the input shaft turns to the left. to reverse the volvo cone units just requires the correct prop and select the upper or lower gear as fwd.
so much less complex and durable than anything merc ever built.
yamaha and BRP use about the same setup as the alph for the left and right hand units.. they used a complex setup of spanner nuts and bearings in the prop shaft bearing carrier then either flipped the shift cam or acuted the cable opposite of standard rottion.
but yes if you run the wrong prop on the wrong drive with a BRP,yamaha or alpha it will self destruct rather rapidly

 

[rodbolt]

Re: counter rotating?

oops sorry I forgot to answer your question.
to sight ID the drives if they have been tampered with is tough. if the shift linkage has not been mummoxed with then the left hand side will pull for fwd while the right hand side lower shift cable will push.

 

[mcleaves]

Re: counter rotating?

Thx for the edu-ma-cashun rodbolt.

M

 

[greatsouthbaybob]

Re: counter rotating?

Thank you for all of your responses. I was told the boat I bought had counter rotating drives, but the manual says both drives are rh. To complicate matters the boat was repowered this year and outdrives were rebuilt so I have no idea if they are indeed counter rotating or factory spec. The reason I asked about the mis rotating prop is one engine performed so badly I thought this may be the case. The boat has twin throttle controls quicksilver type, seperate throttle and shift levers...so rodbolt's answer was not quite clear to me. Will the props spin only in opposite directions in fwd with motor off if they do counter rotate? Thanks again

 

[rodbolt]

Re: counter rotating?

engine rotation is left hand for both. the difference is in the lower shift cable travel direction and the lower units. the left hand case is externally identical. the difference is in the propshaft bearing carrier and the thrust surfaces.
when you place the shifter at the helm,both, in fwd the cable that goes to the lower will move opposite one another, the L case pulls the lower cable for forward,which actually moves the clutch to the aft gear and the R case pushs the lower shift cable and moves the clutch to the fwd most gear in the lower.
both the aft and the forward most gear spin anytime the drive shaft spins, however they spin in opposite directions. the clutch is splined to the propshaft. if you move the clucth aft it turns to the left but the propshaft fwd thrust is now on the forwardmost gear. so now the shaft is spinning left and the fwdmost gear is spinning right while the thrust is causing the shaft to eat the gear surface. in the L case the thrust in fwd motion is taken by the aft gear by changing the setup of the propshaft and aft gear and bearing carrier.