I have an old boat I am fixing up.  Its a 1963 16 foot fiberglass boat with at 40 hp evinrude motor.  The question is what size trolling motor can I get away with?  What thrust?  I want to stay 12 volt for the system. It will be bow mounted with foot controls.  I went to the minn kota website and they recomended 55 pound thrust.  Went to the motor guide website and recommended 40-76 pound of thrust.  Also, which brand would be the best one to buy.  The bassdozer website has an article and recommends motorguide. http://www.bassdozer.com/articles/c...otor.shtml

I think a 55# motor is about the largest 12v motor available, so your choice is limited right off. I can't see many differences between brands as I have seen kudos and complaints on just about anything that is available. If you are buying new be sure and get a unit that has digital control, also known as PWM or pulse width modulated. This technology really increases run time before recharge. Tom

I completely agree with Tom on getting a trolling motor with digital control. I have a 70# thrust Minnkota that will pull my 18'-6" glass boat around for about 10 hours at 1.5 to 2 mph while trolling. I'm running at 24v, so you won't get quite that much run time with a 12v system, but I was quite surprised at how long the batteries last with the digital control.

It's not black magic that digital control works. Instead of using a resistor to reduce the voltage to the motor, the digitals turn the power on and off rapidly, thus reducing the available power instead of wasting it as heat. Another plus is the near infinite speed control. Tom

Parts for older motors can be a problem. I have found that Sierra Marine is a good source for vintage parts. CarQuest auto parts has a tie in with Sierra. Also, NAPA has available a lot of parts for older marine applications. Tom

Sorry I'm a little late with this but I am a new member.  I used to own a Motorguide and Minn Kota service center.  The rule of thumb for thrust was 1 lb of thrust per 100 lb's of boat weight (that includes motor, batteries, gear, and people) is a minimum.  Also, shaft length is critical.  To get the minimum required shaft length, measure from the deck you are mounting it to down to the water and then add 12 inches.  This will give you a minimum shaft length.  I currently have a 55 lb 12 volt Motorguide with the wireless remote and it does fine on my 20 ft Bennington pontoon boat.
Good luck.
Norm