How to Position an Auxiliary Motor on the Transom of a 18-ft Power Boat?
 

I am planning to get an auxiliary outboard motor (likely to be a Yamaha
High Thrust T9.9), and mount it on the transom of a 18-ft center
console. I have a couple questions related to exactly where to
position it:

1. I have a 115hp main outboard motor already mounted at the center of
the transom. Should I mount the small auxiliary motor in the left of
the main motor or in the right? Does this really matter? I prefer to
mount it left of the main motor if I can do that.

2. What is the minimum distance between the main outboard and the
auxiliary outboard? I guess the auxiliary outboard is supposed to be
mounted as much at the center of the transom as possible in order to
push the boat properly, right? But the main outboard already takes the
center place. Therefore, the auxiliary outboard must be off to the
side. I am trying to figure out how close I should place the auxiliary
outboard to the main outboard. Does this really matter anyway? I have
a feeling that the rod that links the main outboard and the auxiliary
outboard together may dictate how close I can put them together.

3. I would like to know how deep I should position the auxiliary
outboard into the water. I have found two rules in the downloaded
owner manual of Yamaha outboard. The first rule says that we should
keep the cavitation plate at least 1 inch below the bottom of a boat if
the outboard is being used as a main motor of the boat. The second
rule says that we should keep the cavitation plate several inches below
the water surface if the outboard is being used as an auxiliary motor
in a sail boat (something to do with the sailboat tends to roll
around). How do these fit into my case? Because my boat has a semi-V
bottom, its sides are higher than the center. If I follow the first
rule, I assume I should position the cavitation plate of the auxiliary
outboard one inch below the bottom of the boat that is slightly higher
than the lowest bottom of the boat because the auxiliary outboard is
not centered in the transom. Is this right? If I follow the second
rule, I will position the cavitation plate in a different place than if
I had followed the first rule. Which one is correct?

4. I will mount the auxiliary motor on a motor bracket that can lift
the motor up or down vertically. But that motor bracket seems to be
designed for being mounted on a flat transom. But the transom in my
boat is slightly curved. How should I mount the motor bracket onto my
transom? Do I need to use some shims? How do people normally handle
this situation?

Thanks in advance for any info.

Jay Chan