I was taught to put in a wedge shaped piece of split firewood on the old 65 HP Merc, and later it's replacement 85 HP for long distance trailering. We never had an issue in decades of pulling the Big Boat around BC (a 16 foot Larson - not big at all).
After reading this thread I decided to check out the manuals from various Motors that I & my friends have.
The 200 HP Yamaha manual (Page 68 Section 4-3) says:
The Motor should be trailered and stored in the normal running position. If there is insufficient road clearance in this position, then trailer the motor in the tilt position using a motor support device such as a transom saver bar.
The 130 HP Honda manual (Page 84) says:
When trailering a boat with the outboard motor attached, leave the engine in the normal running position, if possible.
Use a motor bar to prevent the outboard motor from moving while trailering the boat. Refer to manufacturer's instructions for using a motor support bar.
The 100 HP Mercury Service manual (Pages 3& 4 of section 6c-2) says:
The remote control (or trim panel) is equipped with a switch that is used for trimming the outboard “up” and “down”, and for tilting the outboard for shallow water operation (at slow speed) or for “trailering”. The outboard can be trimmed “up” or “down” while engine is under power or when engine is not running.
While operating “up” circuit, the ram will continue to tilt outboard to full up position for trailering.
I could find no mention of any other support for the engine required. The dual mechanical support locks seem robust on this motor. This is an old motor.
The 35 HP Mercury manual (Page 210) says: Operating "Up" circuit will first move the two trim cylinders; see "Trimming Engine 'Up'," preceding. When trim cylinders are fully extended, the tilt ram will continue to tilt engine to the full "up" position for trailering.
I could find no mention of any other support for the engine required. This too is an old motor.
One of my friends have severely damaged the skeg on a couple of his outboards (two different boats) until I finally convinced him to tilt up the motors when trailering.
Thanks to the original poster (
@MRWood ) of this thread. It should make every reader of it at least think about what they do with their engines when trailering. It could save them a lot of grief.