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Author Topic:   Counter twins

jwestwood posted 08-19-2013 03:07 PM ET (US)
I currently have twin 90s on a '74 outrage 21 which are common rotating. How difficult is to change rotation and what might be the cost. Steering would be much easier. Thanks for your help.
L H G posted 08-19-2013 04:32 PM ET (US)
You have a couple of choices, but it's not likely a counter rotating 90 is one of them. Outside of racing, I don't know of any brand that has mid-range counter rotating engines at the 90 HP level.
You can do one or a combination of:
--set your trim tabs to help counter the steering pull
--trim you engines up to point where you have equal pull in both directions. This varies based on boat speed, but also gives you the most efficient running position.
--raise engines on the transom. This reduces propeller torque feedback to the wheel
--replace your steering cable. It could be old and worn out, giving you increased friction.
--convert to Sea Star I hydraulic steering. When I put classic twin 115 Mercury engines on my 21 Ooutrage, that's what I did. I have virtually no pull at any trim position. Because of the narrow transom configuration of the Ribside 21, I had to use the transom mount cylinder.
The cylinder "steers" the dual engine tie rod.
http://smg.photobucket.com/user/lgoltz/media/Outrage%2021/Scan_Pic0008. jpg.html?sort=6&o=18#/user/lgoltz/media/Outrage%2021/Scan_Pic0008.jpg. html?sort=6&o=18&_suid=1376943879274035234438695619963
jimh posted 08-20-2013 09:39 AM ET (US)
In hydraulic steering systems, there is no "pull" on the wheel. I believe that check valves in the hydraulic system absorb the forces created by the engine on the steering actuator, and those forces are not transmitted to the wheel. It is only when you wish to turn the wheel that you feel the force created by the propeller torque.
Jeff posted 08-20-2013 06:47 PM ET (US)
I ran a 22 Gaurdian (Outrage) with twin Mercury 150's for years. Both were standard rotation due to the hull needing to run 20" twins. I saw little... actually no ill effects for running that set up on a hull of that size. I would not be overly concerned with running your 21 Outrage in the same manner. I would recommend the Sea-Star system Larry noted. It will make your life at the helm a lot easier all around.
Plotman posted 08-20-2013 11:04 PM ET (US)
Agreed with what Jeff said. I have CR twins on my 22 outrage (25" engines on jack plates) and I have been on another boat with twin 20" engines of the same brand. I didn't notice a difference.
jamesmylesmcp posted 08-21-2013 06:49 AM ET (US)
I converted a 20 inch 150 Optimax to counter rotating by changing the driveshaft in a 25 inch counter rotating lower unit. The results are noticable as it eliminated a list the was present at speed, it also seems to hold better in turns.The engines are on a Revenge 25 Walk-Around.
jwestwood posted 08-21-2013 12:24 PM ET (US)
Great stuff!! Thanks much to all of you!! Be well.
Tom W Clark posted 08-21-2013 12:36 PM ET (US)
I ran my Revenge 25 Walk-Through for a couple years with a pair of 150 HP Mercurys that were both standard rotation. I then converted one to counter rotation and it eliminated the steering torque caused by two propellers turning the same way and reduced the list to port just as James describes.
While it is true that there is no "pull" at the wheel with hydraulic steering, that does not mean there is no pull on the steering system. The combined steering torque can be very substantial, especially at WOT and at high trim angles, so high that it took both my arms to make a course correction during WOT test runs before converting to counter rotation.
By using counter rotating motors all that pull is canceled through the tie bar and the net force on the steering system is nil.
Having said all that, there are no counter rotating gearcase for 90 HP motors that I know of. What "twin 90s" do you have?
Tom W Clark posted 08-21-2013 12:39 PM ET (US)
Another huge advantage of counter rotating motors is that docking becomes easier because one motor will tend to pull the stern in one direction in reverse and the other will pull the opposite way.
jimh posted 08-21-2013 12:55 PM ET (US)
Manufacturers of hydraulic steering systems generally specify the maximum horsepower that a cylinder can be used to steer. If you look at the details, you will see that in the case of twin engine installations, a particular steering cylinder will be rated for much more horsepower in a twin engine installation if the engines are counter rotating compared to an installation of twin engines with non-counter rotating engines.
jwestwood posted 08-21-2013 03:07 PM ET (US)
To Mr. Clark: The 90's are 1988 Yamahas. FYI I still have the saddle tanks(15 gals) if any interest out there.
Tom W Clark posted 08-21-2013 04:14 PM ET (US)
Yeah, no such thing as a counter rotating gearcase for your motors.
L H G posted 08-21-2013 04:31 PM ET (US)
Twin engines on the old 21's need to be installed all the way up. Mercurys have the added advantage of five sets of bolt holes, and I have mine mounted in the 5th set. Even at this height I can run Mercury's conventional Black Max aluminum props with no ventilation at all. On the Yamahas, with only 4 sets of holes, they should defintiely be all the way up to reduce steering torque as much as possible.
jwestwood posted 08-22-2013 10:50 AM ET (US)
LHG: Not looking at motors right now but do recall that the mounts are about 2, perhaps 3 inches above transom top. Sounds like the best bet is to better manage the trim at various RPMs. Thanks again.

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Author	Topic: Counter twins
jwestwood	posted 08-19-2013 03:07 PM ET (US) I currently have twin 90s on a '74 outrage 21 which are common rotating. How difficult is to change rotation and what might be the cost. Steering would be much easier. Thanks for your help.
L H G	posted 08-19-2013 04:32 PM ET (US) You have a couple of choices, but it's not likely a counter rotating 90 is one of them. Outside of racing, I don't know of any brand that has mid-range counter rotating engines at the 90 HP level. You can do one or a combination of: --set your trim tabs to help counter the steering pull --trim you engines up to point where you have equal pull in both directions. This varies based on boat speed, but also gives you the most efficient running position. --raise engines on the transom. This reduces propeller torque feedback to the wheel --replace your steering cable. It could be old and worn out, giving you increased friction. --convert to Sea Star I hydraulic steering. When I put classic twin 115 Mercury engines on my 21 Ooutrage, that's what I did. I have virtually no pull at any trim position. Because of the narrow transom configuration of the Ribside 21, I had to use the transom mount cylinder. The cylinder "steers" the dual engine tie rod. http://smg.photobucket.com/user/lgoltz/media/Outrage%2021/Scan_Pic0008. jpg.html?sort=6&o=18#/user/lgoltz/media/Outrage%2021/Scan_Pic0008.jpg. html?sort=6&o=18&_suid=1376943879274035234438695619963
jimh	posted 08-20-2013 09:39 AM ET (US) In hydraulic steering systems, there is no "pull" on the wheel. I believe that check valves in the hydraulic system absorb the forces created by the engine on the steering actuator, and those forces are not transmitted to the wheel. It is only when you wish to turn the wheel that you feel the force created by the propeller torque.
Jeff	posted 08-20-2013 06:47 PM ET (US) I ran a 22 Gaurdian (Outrage) with twin Mercury 150's for years. Both were standard rotation due to the hull needing to run 20" twins. I saw little... actually no ill effects for running that set up on a hull of that size. I would not be overly concerned with running your 21 Outrage in the same manner. I would recommend the Sea-Star system Larry noted. It will make your life at the helm a lot easier all around.
Plotman	posted 08-20-2013 11:04 PM ET (US) Agreed with what Jeff said. I have CR twins on my 22 outrage (25" engines on jack plates) and I have been on another boat with twin 20" engines of the same brand. I didn't notice a difference.
jamesmylesmcp	posted 08-21-2013 06:49 AM ET (US) I converted a 20 inch 150 Optimax to counter rotating by changing the driveshaft in a 25 inch counter rotating lower unit. The results are noticable as it eliminated a list the was present at speed, it also seems to hold better in turns.The engines are on a Revenge 25 Walk-Around.
jwestwood	posted 08-21-2013 12:24 PM ET (US) Great stuff!! Thanks much to all of you!! Be well.
Tom W Clark	posted 08-21-2013 12:36 PM ET (US) I ran my Revenge 25 Walk-Through for a couple years with a pair of 150 HP Mercurys that were both standard rotation. I then converted one to counter rotation and it eliminated the steering torque caused by two propellers turning the same way and reduced the list to port just as James describes. While it is true that there is no "pull" at the wheel with hydraulic steering, that does not mean there is no pull on the steering system. The combined steering torque can be very substantial, especially at WOT and at high trim angles, so high that it took both my arms to make a course correction during WOT test runs before converting to counter rotation. By using counter rotating motors all that pull is canceled through the tie bar and the net force on the steering system is nil. Having said all that, there are no counter rotating gearcase for 90 HP motors that I know of. What "twin 90s" do you have?
Tom W Clark	posted 08-21-2013 12:39 PM ET (US) Another huge advantage of counter rotating motors is that docking becomes easier because one motor will tend to pull the stern in one direction in reverse and the other will pull the opposite way.
jimh	posted 08-21-2013 12:55 PM ET (US) Manufacturers of hydraulic steering systems generally specify the maximum horsepower that a cylinder can be used to steer. If you look at the details, you will see that in the case of twin engine installations, a particular steering cylinder will be rated for much more horsepower in a twin engine installation if the engines are counter rotating compared to an installation of twin engines with non-counter rotating engines.
jwestwood	posted 08-21-2013 03:07 PM ET (US) To Mr. Clark: The 90's are 1988 Yamahas. FYI I still have the saddle tanks(15 gals) if any interest out there.
Tom W Clark	posted 08-21-2013 04:14 PM ET (US) Yeah, no such thing as a counter rotating gearcase for your motors.
L H G	posted 08-21-2013 04:31 PM ET (US) Twin engines on the old 21's need to be installed all the way up. Mercurys have the added advantage of five sets of bolt holes, and I have mine mounted in the 5th set. Even at this height I can run Mercury's conventional Black Max aluminum props with no ventilation at all. On the Yamahas, with only 4 sets of holes, they should defintiely be all the way up to reduce steering torque as much as possible.
jwestwood	posted 08-22-2013 10:50 AM ET (US) LHG: Not looking at motors right now but do recall that the mounts are about 2, perhaps 3 inches above transom top. Sounds like the best bet is to better manage the trim at various RPMs. Thanks again.