Re: kicker motor choices
Here’s the deal on short verses long shaft.
A long shaft "may" drag in the water if not raised up high enough, typically a little adjusting of the bracket height solves the problem.
When using a short shaft on an I/O the problem can be in getting the prop deep enough to get a good bite, plus have the power head high enough to not be dunked in rougher water.
The adjustable bracket will move the motor back a bit from the transom which can make it more likely to be dunked, so a long shaft is desired.
I have used both short and long shaft for decades and you can get both to work, but long and extra long shaft motors are normally a better choice.
For trolling the deeper you can get the prop and the higher you can get the power head out of the water the better it is.
If you plan to use it for trolling, and not just as a backup, don't buy a single cylinder small motor, they tend to be louder and vibrate a good deal more than two a cylinder model. This doesn't seem bad at first, but after a short time it can become rather annoying.
Every boat and type of fishing will be a little different, so you will get different opinions on what the perfect setup is, none are perfect for all applications, so it needs to be fine tuned for your exact boat and method of fishing.
I don't like trolling with the main motor, I trolled for 9 hours yesterday and didn't use 3 (maybe less than 2) gallons of fuel with my 8hp Merc. Why put mega hours on a much more costly and less efficient big motor when you can run a kicker for pennies and replace it in 15 minutes with another one if it dies.