I would like to add an auxiliary outboard motor to my heavy 18-ft
fiberglass boat. I need it for (1) Backup "go home" power in case the
10-years old main motor dies (2) Trolling for fishes (3) Use it in
lakes that only allow no more than 9.9hp motor.

I would like to know how many horse power the auxiliary motor should
have. The boat is around 3000-lb (this includes everything like
people, fuel and cooler). It is 18-ft long and I figure that it has
16-ft at the water level. It is 12" draft. The hull is a semi-V. The
boat is a center console. I guess I am asking for a motor that can run
this boat right at the displacement speed (hull speed?).

Someone may say that bigger is better. But I cannot get more than
9.9hp motor because I need to use it in lakes that has
9.9hp-or-less-only limit. This sets the upper limit. I figure I
really don't need a large auxiliary motor because I will not run the
boat off shore (the boat is a "bay boat" and should not be used off
shore). And I will not run the boat when the weather is not good
because I am afraid of sea-sick.

I am hoping that I may be able to use something smaller than 9.9hp;
then I can save money on the motor and fuel. Moreover, I hope I can
use a small and light weight outboard motor that I can mount it in a
small row boat. If it is heavy, I probably will not be able to
dismount it at ease.

So, what I am asking a

- What is the displacement speed of my boat?
What horsepower of auxiliary outboard can run
my boat right at the displacement speed?

- What is the lowest limit (in term of horsepower) that
the auxiliary outboard should have without running the
risk of having the boat got stuck under normal wind and
current situation?

- What size do you recommend?

Thanks in advance for any info.

Jay Chan