I have a 70lb thrust MK Edge on the boat now. What kind of change should I expect moving to an 80lb MK Fortrex?

The issue I have is that this boat is a 21' Skeeter SL210 and when there are 3 people on the boat and the wind blows 20mph or more (Common for west Texas), I can not move the boat forward. I'm hoping that I can move up to the 80lb and be ok instead of having to buy another battery, on bank charger, and everything else needed to go to a 36v 101lb thrust.

You will notice the difference.

10 pounds difference (sorry that was too easy)

More seriously, I went from a 65 pound MG to a 75 MK on my old Pantera II BassCat and it did make some difference but it was still just enough on windy days. Last two boats I've had 36V MG 109's with no problems at all!

I don't think an 80 is going to improve you in the conditions you are describing. I have a 19ft bass boat with an 80 and it has trouble in wind like that with just me in it.

That is what I am afraid of. I want to learn how to fish offshore and it's a pain in this boat.

I got a 210 also. I spent the money and upgraded to a 101 36 volt and it was the best thing I could have done.

That's a big boat for 80lbs

Yep. It had a 65lb on it when we bought it. It broke and I got a great deal on a 70lb edge when I didn't have any money saved up and it has been on there long enough.

I guess I will have to bite the bullet and switch over to a 36v system.

Upgrade to 36v and be happy. 10 pounds might not even be noticeable, depending on the unit

I have a 19'8" Phoenix (granted yours is a foot longer) with an 82lb Motorguide with trojan batteries. It will hold me up extremely well on windy stuff, just doesn't run through real thick grass like a 109 will. IMO, if you're going to upgrade, I would go ahead and cram another battery in and go with as big as you can afford.

It's definitely undersized, that's a lot of boat for 70lb, let alone 3 guys, gear and wind. If resources allow upgrade to 36, you will immediately notice your love life improves, you'll jump higher and run faster.

You definitely want to go to 36v. If you go with 80 lb thrust, you will wish you went bigger.

Check out trollbridge, I believe Yandina is the mfg., it is a relay system that will charge 3 or 4 batteries using a 2 bank charger. It also charges them from the boat alternator and even from the tow vehicle if you add a power cable with a trolling motor plug to your trailer harness.
I have been using this setup for years charging 2 trolling batteries and one starting battery off of a 2 bank onboard charger and the outboard alternator.

True dat! There is no such thing as too much thrust from a troll motor. Plus with a 36 volt system, your batteries last so much longer than with a 24 volt. Bite the bullet and do it. If you "upgrade" to an 80#, you will be disappointed very soon after.

I have a Triton 186. If I could figure a good way to get another battery back there, I would go 36v. Especially fishing off shore in windy conditions. That being said I upgraded to a 82#, 24v motor guide last year from a 70 something pound thrust and it has made a huge difference. So you will notice a difference.