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Counter rotation or dummies

Old 09-23-2019, 08:41 PM
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Default Counter rotation or dummies

Please explain, why are some twin OB’s counter rotating and some not?

Advantages/disadvantages?

Thx.
Old 09-23-2019, 09:15 PM
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It is for a twin engine application. One will be standard rotation and the other will be counter rotation. However some use a counter rotating engine as a single and works fine.
Old 09-23-2019, 10:11 PM
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Yeah. If you had two props rotating in the same direction, the prop-walk would be twice as bad as for a single prop. With two props spinning in opposite direction, the prop-walk is effectively cancelled out.
Old 09-23-2019, 10:25 PM
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And even with hydraulic steering, with same-wheel twins the steering will be easier in one direction vs the other. With mechanical steering you likely wouldn't want to take your hand off the steering wheel.

Slow speed maneuvering in both F & R is easier ( same P & S) with opposing props. ( In N it doesn't make as much difference . )
Old 09-24-2019, 12:17 AM
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In the northern hemisphere, standard rotation works better. In the Southern Hemisphere, counter clockwise rotation is preferable. It has to do with the Coriolis effect. Not to be confused with the Corleone effect, which is when you piss off The Godfather. Opposing rotation cancel out the gyroscopic forces, which act perpendicular to the direction of movement and axis of rotation. If you look at water draining, a toilet flushing or a hurricane, you can observe this effect in the consistent direction of rotation they spin.
There is a pretty even balance in the number of vessels that spin their props in either direction, so this cancels out any global forces and the effect it may have. Too many of one, or the other, and Poseidon gets pissed and you see the effects in the weather. You wonder why we are having more frequent storms, floods and hurricanes? Too many objects spinning in a counter rotation to what is normal.
Don't be that guy. Spin your props to the right if you live north of the equator, and left if you live south. The world depends on you.

Co·ri·o·lis ef·fect
/ˌkôrēˈōləs iˌfekt/
noun
PHYSICS
  1. an effect whereby a mass moving in a rotating system experiences a force (the Coriolis force ) acting perpendicular to the direction of motion and to the axis of rotation. On the earth, the effect tends to deflect moving objects to the right in the northern hemisphere and to the left in the southern and is important in the formation of cyclonic weather systems.

Last edited by SeaCat22; 09-24-2019 at 12:24 AM.
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Old 09-24-2019, 12:48 AM
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with all due respect-- Our Regal and SkipperLiner are both twin engine boats and my old 24' Reinell had twin 318 Chrylsers, and none of these boats have counter rotating props... and none of them has ever exhibited the prop-walk or 'left turn steer' mentioned. All of these boats are/were fully driveable for miles with no hands on the wheel...

Think about this for a second-- sterndrive engines rotate clockwise on the bow-side of the boat, and their props rotate clockwise from the stern-side of the boat. The purpose of this is to- you guessed it- to counteract torque! So what's going to happen if you set up for a counter-clockwise prop on the starboard engine? The port engine and its opposite-rotating prop will be creating neutral torque, but the starboard engine and its same-direction-rotating prop are now creating gobs of torque- considering that for every action there's an equal and opposite reaction, what's absorbing all that "opposite reaction"? The boat! The whole time the boat's underway the starboard engine & drive is trying to rotate the port side of the boat upward, while the port engine & drive are cancelling out each other's torque. How is this supposed to help anything? The opposite turning props might push the drives apart-or together- which may help the boat go straighter, okay, but what of the unbalanced torque against the boat? Seems to me the only way to fully balance out torque is with counter rotating engines AND props. Then you'll have it all. Short of that, best torque balance seems to be identical CW engines and their CW rotating props...
Old 09-24-2019, 01:04 AM
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Originally Posted by Frantically Relaxing View Post
with all due respect-- Our Regal and SkipperLiner are both twin engine boats and my old 24' Reinell had twin 318 Chrylsers, and none of these boats have counter rotating props... and none of them has ever exhibited the prop-walk or 'left turn steer' mentioned. All of these boats are/were fully driveable for miles with no hands on the wheel...

Think about this for a second-- sterndrive engines rotate clockwise on the bow-side of the boat, and their props rotate clockwise from the stern-side of the boat. The purpose of this is to- you guessed it- to counteract torque! So what's going to happen if you set up for a counter-clockwise prop on the starboard engine? The port engine and its opposite-rotating prop will be creating neutral torque, but the starboard engine and its same-direction-rotating prop are now creating gobs of torque- considering that for every action there's an equal and opposite reaction, what's absorbing all that "opposite reaction"? The boat! The whole time the boat's underway the starboard engine & drive is trying to rotate the port side of the boat upward, while the port engine & drive are cancelling out each other's torque. How is this supposed to help anything? The opposite turning props might push the drives apart-or together- which may help the boat go straighter, okay, but what of the unbalanced torque against the boat? Seems to me the only way to fully balance out torque is with counter rotating engines AND props. Then you'll have it all. Short of that, best torque balance seems to be identical CW engines and their CW rotating props...
Wtf. Lol
Old 09-24-2019, 06:47 AM
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For many of the earlier years the popular sized Mercruiser I drives did not have counter rotation gearcases and the owners lived with twin engines with right hand props. Power steering installed on the motors as standard equipment took care of the prop-torque effect.

Some larger MCM models had a form of counter rotation but they were not as common except on large and/or fast boats..
Old 09-24-2019, 08:56 AM
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Depending on how the counter rotation is oriented can also impact the hulls performance (bow lift vs stern lift).
Old 09-24-2019, 10:47 AM
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I think the OP is asking why some twin engine outboard set ups spin the props outward in forward which is the traditional way vs some have the props spinning inward in forward. Both set ups are counter rotating, just in different directions.

I've driven both and like the maneuverability around the dock of the traditional set up where the props turn outwards. The push/pull effect is in the same direction as the prop walk. Some think that inward turning props give more lift and are a little more efficient but on one boat we swapped the lower units to change from inward to outward rotation and I didn't notice any difference in performance.
Old 09-24-2019, 12:28 PM
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Originally Posted by Scrambler1 View Post
I think the OP is asking why some twin engine outboard set ups spin the props outward in forward which is the traditional way vs some have the props spinning inward in forward. Both set ups are counter rotating, just in different directions.

I've driven both and like the maneuverability around the dock of the traditional set up where the props turn outwards. The push/pull effect is in the same direction as the prop walk. Some think that inward turning props give more lift and are a little more efficient but on one boat we swapped the lower units to change from inward to outward rotation and I didn't notice any difference in performance.
Define Outward vs Inward. I think I know what you mean but I don’t want to assume. Just draw lines from the list on the left to the list on the right.
.
Starboard CW
Outward
Port CW
Inward
Starboard CCW

Port CCW
Old 09-24-2019, 12:40 PM
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My contender 23 t came with standard and counter rotating 200 hpdi's. Lost lower unit of counter rotating motor. Mechanic had another standard rotation lower. Put it on and honestly could not tell a bit of difference. When I repowered with new 4 stroke 200's I went with both standard rotation. Handles like ot always had. Allows me to carry one spare prop and saved 1500.00.
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Old 09-24-2019, 01:14 PM
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Use in twin outboard set up
Old 09-24-2019, 02:16 PM
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Originally Posted by SeaCat22 View Post
In the northern hemisphere, standard rotation works better. In the Southern Hemisphere, counter clockwise rotation is preferable. It has to do with the Coriolis effect. Not to be confused with the Corleone effect, which is when you piss off The Godfather. Opposing rotation cancel out the gyroscopic forces, which act perpendicular to the direction of movement and axis of rotation. If you look at water draining, a toilet flushing or a hurricane, you can observe this effect in the consistent direction of rotation they spin.
There is a pretty even balance in the number of vessels that spin their props in either direction, so this cancels out any global forces and the effect it may have. Too many of one, or the other, and Poseidon gets pissed and you see the effects in the weather. You wonder why we are having more frequent storms, floods and hurricanes? Too many objects spinning in a counter rotation to what is normal.
Don't be that guy. Spin your props to the right if you live north of the equator, and left if you live south. The world depends on you.

Co·ri·o·lis ef·fect
/ˌkôrēˈōləs iˌfekt/
noun
PHYSICS
  1. an effect whereby a mass moving in a rotating system experiences a force (the Coriolis force ) acting perpendicular to the direction of motion and to the axis of rotation. On the earth, the effect tends to deflect moving objects to the right in the northern hemisphere and to the left in the southern and is important in the formation of cyclonic weather systems.
This leads to the obvious question of the possible oceanographic/ meteorologic effects of triple setups. These are clearly getting more and more common at least in the northern hemisphere and i wonder if the inherent imbalance in rotation might produce a net disturbance in the corleonus whatchamacllit. Especially if there are more triples in the northern than the southern hemispheres. Ill bet there are. Someone should alert that passionate little swedish girl as this could very well have implications re sea level and climate change.
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Old 09-24-2019, 02:39 PM
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Originally Posted by dfriverside View Post
My contender 23 t came with standard and counter rotating 200 hpdi's. Lost lower unit of counter rotating motor. Mechanic had another standard rotation lower. Put it on and honestly could not tell a bit of difference. When I repowered with new 4 stroke 200's I went with both standard rotation. Handles like ot always had. Allows me to carry one spare prop and saved 1500.00.
‘zactley

i am the OP...this is what i was getting at. Our harbor patrol boat runs dual zukes...it’s a custom aluminum hull-heavy-but they are not CR and it handles fine.

Maybe it’s somewhat hull dependent? Some boats do torque steer a bit.
i don’t know, i am a bit puzzled by it.
My new boat is CR, we’ll see how that handles.
Old 09-24-2019, 06:01 PM
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Originally Posted by triggerman View Post

This leads to the obvious question of the possible oceanographic/ meteorologic effects of triple setups. These are clearly getting more and more common at least in the northern hemisphere and i wonder if the inherent imbalance in rotation might produce a net disturbance in the corleonus whatchamacllit. Especially if there are more triples in the northern than the southern hemispheres. Ill bet there are. Someone should alert that passionate little swedish girl as this could very well have implications re sea level and climate change.
Good to see someone gets it.
This may be a factor in rising ocean levels in the northern hemisphere and conversely falling in the southern. You never hear about South American countries worrying about rising ocean levels and coastal encroachment. They need more boats on the other side of the equator...with left swing props, to pull some of the water south.
It's a mater of global equilibrium.
Old 09-24-2019, 07:32 PM
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Originally Posted by SeaCat22 View Post


Good to see someone gets it.
This may be a factor in rising ocean levels in the northern hemisphere and conversely falling in the southern. You never hear about South American countries worrying about rising ocean levels and coastal encroachment. They need more boats on the other side of the equator...with left swing props, to pull some of the water south.
It's a mater of global equilibrium.

This is all moot, haven’t you heard? The earth is flat and Antarctica is just the edge of what we know, and it holds the water in. Oh and the direct route from South America to Australia is right over the USA.
Old 09-24-2019, 08:42 PM
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Originally Posted by proaudioguy View Post
Define Outward vs Inward. I think I know what you mean but I don’t want to assume. Just draw lines from the list on the left to the list on the right.
.
Starboard CW
Outward
Port CW
Inward
Starboard CCW

Port CCW
Does not appear to be what he was talking about but what I called outward would be
Starboard prop clockwise in forward
Port prop counter clockwise in forward
Old 09-30-2019, 10:22 AM
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Originally Posted by Scrambler1 View Post


Does not appear to be what he was talking about but what I called outward would be
Starboard prop clockwise in forward
Port prop counter clockwise in forward
Yea thats what I wanted to think too but it wasn’t clear.
Old 09-30-2019, 11:23 AM
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by the way - if you are running two engines - one standard rotation & one counter rotation & you mix up the propellers..........the boat goes in reverse. Or when you try & go in reverse you are really going forward - For example you try & back off the trailer & you run over the truck.


ask me how I know....
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