I have a boat very similar to Glen-l's Eagle 22 ft. semi-displacement
lobster boat. The main motor is a 110hp 2 stroke which gives me all
the power I need. I also have a Yamaha 30hp 2 stroke kicker which I
use for low speed cruising at about 8-10 knots. The kicker is mounted
on a Garelick heavy duty (up to 40hp) auxiliary motor bracket.

The Yamaha is old and tired and gets very disappointing gas mileage.
I would like to switch over to a 4 stroke kicker, which means probably
having to change the mounting bracket. I would like the smallest
motor possible that will give me about 8 knots cruise at 3/4 power.
I'm looking for good fuel mileage and long range. I don't care about
speed and hole shots, and planing isn't an issue.

Here is a horsepower to speed chart Glen-l supplies for the eagle:

6 knots 10 SHP
7 knots 12 SHP
8 knots 16 SHP
9 knots 21 SHP
11 knots 27 SHP
13 knots 32 SHP
15 knots 43 SHP
18 knots 56 SHP
20 knots 70 SHP
22 knots 88 SHP
25 knots 105 SHP
27 knots 125 SHP

The question I have is would these same values apply to the Bigfoot or
"high thrust" motors? Would there be an advantage to going to a high
thrust motor for long range, low speed cruising? I'm just not
understanding these high-thrust, big prop motors, so please bear with
me.

Thanks,
Syl