I bought a used Bass Tracker 17' last fall, which came with a Mercury 50 hp and a Motorguide 46 12V. I fish on the Potomac River and its feeder tributaries, but would like to also hit some local lakes, but none will allow the 50 hp (in some cases no outboards are permitted). If I upgrade the Motorguide 46 to a bigger Minn Kota, maybe with 24V, will I see a significant improvement in boat speed (e.g., maybe 3 mph to 5-6?).

Yes

Just going to 24v won't double your speed. You can get 24v at about 67 # of thrust and that won't be enough. I seriously doubt if the biggest one can get you 6 mph. However, you will get better performance, more staying power, and more speed when you go larger. If your budget allows, go for the most thrust you can get and add some length to the shaft of the new one.

If your tmotor battery has age on it then get 2 new ones. Get at least 27 series and as many reserve amps as possible (200 is ideal).

Thanks for the info. Right now I have a 42" shaft I think. Will getting a longer shaft be a problem if I am in shallow water?

24 volts is only going to be a little more efficient, will do nothing for speed.

Going to a higher thrust will add some speed, how much will only be known once you try it.

Two blade props give the most speed but don't do well in weeds and moss.

Three blade props give less speed but do better in weeds

Four blade props are the slowest but work the best in weeds.

If you want speed, get a larger thrust, at least 60 lb (or more) and a long bladed, two blade prop.

According to my gps, my MK 87# moves my 20' boat at 6 mph (max on a good day), but that does not mean it will move a lighter boat any faster.

If you don't need a longer shaft, don't get it. When you start moving it up for shallow water, the head can get in the way.

24 volts is only going to be a little more efficient, will do nothing for speed.

Going to a higher thrust will add some speed, how much will only be known once you try it.

Two blade props give the most speed but don't do well in weeds and moss.

Three blade props give less speed but do better in weeds

Four blade props are the slowest but work the best in weeds.

If you want speed, get a larger thrust, at least 60 lb (or more) and a long bladed, two blade prop.

That sounds like what Motor Guide has for their prop choices. The Safari 2 blade has longer blades, is slower (less pitch)than any of the other types, but better in weeds which is just opposide of the smaller 2 blade prop. The Safari is .6 mph slower on a 36V motor than the 3 blade Machette.

The short blade 4 blade prop is old school and not even listed as a replacement prop in recent history.

Overall the new Minn Kota Weedless Wedge 2 is the most weedless without giving up speed. Some have adapted it to a Motor Guide for its weed performance, expecially on the Potomac River.

In trolling motor performance, adding voltage adds motor rpm and usually the prop is the same between the 24V and 36V models with some 12V models using the same prop.

Thanks again for the help.

I have a 15' aluminum bass style boat. I had a 55# 12v Minnkota and the boat went 2.1 MPH on GPS. I just upgraded to a 70# 24v MK and it goes 3.4 MPH. Seems faster than that though.

....Bill

I forgot what my top speed is, I'll check next time out. I have a Motor Guide Tour 36V motor on my Tracker PT 170 TX.

The 24V or 36V set will obviously give more battery life while running the trolling motor wide open for extended periods. A 24V set sounds about right for your tin boat and situation.

My 18' Ranger goes 5 MPH with MK 80 and a three bladed prop.