How much does your boat weigh? I sometimes (not often, though, as I love to row) put a 30# thrust Minnkota Endura on the back of my glass Don Hill mini-drifter for an added assist when attempting to reach the head of tidewater (or a little above) on a couple of streams. Sometimes I get a late start and have to fight the current after the tide changes.
Its not quite enough to power me up over most tailouts or slots, though. LOL I remember one time when I had the motor's shaft clamp tightened down, holding the motor straight and going full bore, with me rowing like a madman trying to make it up a slot, and it looked like I was starting to inch my way up the slot, still rowing like a machine, when one of my oars popped out of it's lock...Ha! Denied! Lucky for me there was just a nice open pool below.
I wouldn't go more than 40# thrust, as the motor gets bigger and heavier and draws more juice. I have a 50# thrust Minnkota Riptide saltwater motor that is too heavy to put on that boat, and requires a heavier battery, and really sucks the juice at top speed. Your boat might handle more weight and thrust, though.
The boat weighs 128 lbs, however im 6'7" 300 lbs, all my gear and my chunky pug dog probably puts the load closer to 350. Im planning on using it mainly on larger stillwaters to help out when it gets real windy. Ive never used a trolling motor before. How many mph can you go with a 40lb thrust? On average whats the battery life on them?
Can't answer how fast you'll go with a 40#er. I go maybe 4 to 5 mph tops with my 30# thrust on the mini-drifter, and only a little faster with the same motor on my 13' squanoe.
The 40 # thrust should move you faster. A group 24 battery would probably be about the right size.
You don't want to run them flat out top speed for long, or the battery gets quickly drained...two hours (+/-) flat out will drain it completely. Doing slow trolling, with wind drifting and anchoring up to cast, one charge should last all day with enough charge left to assist back to the ramp. Slap the battery on the charger asap when you get home.
The 30 # or even a 28# would be all you needed for trolling.
I've been thinking of getting a 40#thrust Riptide saltwater motor.