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Author Topic:   Counter Rotate on right or left?

Whalerific posted 07-31-2003 01:00 PM ET (US)
Is it more common to mount a counter-rotating (left turning)engine starboard or port? A Mercury installation manual says port is more common, but Mercury technical assistance told me to put the counter-rotating on starboard. Is there a major difference in performance, ride or handling?
lhg posted 07-31-2003 02:09 PM ET (US)
I have always thought Port is for the CR engine, and Mercury's dual engine control is set up that way. With Mercury the CR engine requires a different set up in the shift cable arrangement at the control, which is why they offer two dula engine controls, one for CR and one for conventional rotation for the mid-range HP engines
I did, however, happen to see a very comprehensive Mercury rigging manual at a Whaler event, and there was some comment about the reverse situation. I think the issue involves setting up for maximum speed and prop thrust, gained by having the propellers rotate in toward each other, rather than away, as is conventional. Evidently, slightly more prop thrust is "captured" to propel the boat forward.
You might check to see how BW is setting up twins at the factory.
bsmotril posted 07-31-2003 03:19 PM ET (US)
I cannot think of a single dual outboard install I have ever seen where the CR motor was not on the port side.
BillS
captbone posted 07-31-2003 03:21 PM ET (US)
Racing boats have the wheels turn in and normal fishing boats have them turn out. Having the wheels spin out is better for 99% of installations.
Tom2697 posted 07-31-2003 03:43 PM ET (US)
captbone made a great observation...Turning in is faster but you lose low speed manuverability. Turning out provides better manuverability but you lose top end speed. With a boat that goes under 50 knots, set it up for manuverability.
This topic was just discussed a few months ago in a race boat magazine I read...I can't remember which mag though.
outragesteve posted 08-08-2003 06:44 PM ET (US)
FYI: With different props (3, 4, 5 blade, Mirage, Mirage II, etc) turning the props in tends to create more bow lift and turning pros out gives more stearn lift. Depending on what your ultimate goal is, you can make a choice. Manuvering is slightly improved with the "left on left" and "right on right" but that can be dramatic depending on the centerline spacing and engine mounting height. Anyone serious about prop selection would use only ss props. Keep the aluminum foil for emergency/spares.

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Author	Topic: Counter Rotate on right or left?
Whalerific	posted 07-31-2003 01:00 PM ET (US) Is it more common to mount a counter-rotating (left turning)engine starboard or port? A Mercury installation manual says port is more common, but Mercury technical assistance told me to put the counter-rotating on starboard. Is there a major difference in performance, ride or handling?
lhg	posted 07-31-2003 02:09 PM ET (US) I have always thought Port is for the CR engine, and Mercury's dual engine control is set up that way. With Mercury the CR engine requires a different set up in the shift cable arrangement at the control, which is why they offer two dula engine controls, one for CR and one for conventional rotation for the mid-range HP engines I did, however, happen to see a very comprehensive Mercury rigging manual at a Whaler event, and there was some comment about the reverse situation. I think the issue involves setting up for maximum speed and prop thrust, gained by having the propellers rotate in toward each other, rather than away, as is conventional. Evidently, slightly more prop thrust is "captured" to propel the boat forward. You might check to see how BW is setting up twins at the factory.
bsmotril	posted 07-31-2003 03:19 PM ET (US) I cannot think of a single dual outboard install I have ever seen where the CR motor was not on the port side. BillS
captbone	posted 07-31-2003 03:21 PM ET (US) Racing boats have the wheels turn in and normal fishing boats have them turn out. Having the wheels spin out is better for 99% of installations.
Tom2697	posted 07-31-2003 03:43 PM ET (US) captbone made a great observation...Turning in is faster but you lose low speed manuverability. Turning out provides better manuverability but you lose top end speed. With a boat that goes under 50 knots, set it up for manuverability. This topic was just discussed a few months ago in a race boat magazine I read...I can't remember which mag though.
outragesteve	posted 08-08-2003 06:44 PM ET (US) FYI: With different props (3, 4, 5 blade, Mirage, Mirage II, etc) turning the props in tends to create more bow lift and turning pros out gives more stearn lift. Depending on what your ultimate goal is, you can make a choice. Manuvering is slightly improved with the "left on left" and "right on right" but that can be dramatic depending on the centerline spacing and engine mounting height. Anyone serious about prop selection would use only ss props. Keep the aluminum foil for emergency/spares.