1983 Yamaha 30EN Outboards Service Manual, Page 158Get this manual
Mounting two engines on boat
When two engines are to be mounted on boat, take the following steps: 1Distance between the two engines Two engines should be spaced 600 mm (23.62 in at least and symmetrically in reference to the center line of the boatOtherwise, the two engines may interfere with each other when they are steered simu Itaneously2Linking two engines Two engines should be linked by tie bar so that both can be steered equally and simu ItaneouslyThey should be positioned so that the two water streams produced by the two propellers meet each other at point about 25 to 30 (81.97 to 98.36 feet) behind the stern