Unraveling the interplay of two counter-rotating helical vortices - YouTube
Counter-rotating propellers - Wikipedia
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Suzuki Dual Prop System - YouTube
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Contra-Rotating Propeller - an overview | ScienceDirect Topics
P&D Marine, Inc. - Volvo Penta - Forward Facing Superiority
Contra-rotating propellers - Wikipedia
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HYDRAULIC THRUSTER BTH386 Ø 386 mm - Twin counter - Rotating propellers - boat length from 22 - 40 m | Damarine
Yamaha Twin Rotating Propellers (TRP) - YouTube
So if you have 2 counter rotating propellers. If you want to make a hard turn should you full astern the engine on the side of where you want to turn but
Boat Propellers for Sale, Stainless Steel Boat Props - iboats.com
Standard verses counter rotating props | Pensacola Fishing Forum