Re: New Boat Owner needs advise trailering
You are confronted with two different issues: (1) guarding against damage to the outboard motor, and (2) guarding against damage to the boat's transom where the outboard motor is attached.
As to (1) ... if you have enough road clearance beneath the motor to travel with it tilted down in a vertical position, you don't need anything to protect it. If, however, the motor must be tilted up to provide sufficient road clearance, you need something to hold it in that position. The tilt lock mechanism that comes with the motor is NOT to be used for this purpose (per Yamaha), and using the hydraulic tilt/trim (if you have it) is not recommended either. The "motor toter" (or other similar device) holds the motor in a tilted up position and eliminates the stresses that would otherwise be placed on the hydraulic tilt/trim system.
As to (2) ... whether you travel with the motor all the way down, or tilted up, its weight is 100% supported by the transom of your boat, and your boat is built strong enough to take it when being operated in the water or sitting still on the trailer. However, it may be that your boat's transom is not strong enough to tolerate the increased torque (twisting forces) which are applied from the weight of your motor as your rig bounces down the highway ... and that is where a "transom saver" comes in ... to transfer some of those "up and down bouncing" forces off your boat's transom and onto the trailer frame, thereby reducing the chance that you will damage your boat.
While trailering an outboard motor in a tilted up position, a "transom saver" does double duty, protecting both the motor and the boat, but its use depends upon the availability of a suitable trailer cross member beneath the motor to which the transom saver may be attached.