Grades of gasoline are rated by their resistance to detonation.

That's it.

If your boat pings and knocks when running regular, try running
premium. If it runs fine on regular, use it.

I pull a 2800lb boat/trailer combo with an '89 toyota pickup truck.
The truck has a 22RE 4cyl and and A43 4speed automatic transmission.
The trailer has surge brakes. I put in an three row radiator and a
transmission cooler. When I pull the boat, I make sure to run
premium. It pings and rattles like mad, on regular. No nasty noise
when I run premium. She runs fine on 87 octane when not pulling a big
load. Travel on flat roads is not a problem. Climbing hills takes
time.

Here is the link to wiki for octane ratings -

http://en.wikipedia.org/wiki/Octane_rating

Run premium if you NEED to. Save your money if you don't. Buying a
higher octane rating than you need is a waste of money.

Google is your friend. More than you will ever need to know is on the
'net.