Gas powered Trolling Motors
A common questions people have when trying to select a motor is “How long will this motor run out on the water?” To answer this question, it's necessary to know two things: a battery's amperage hour rating and a motor's amperage draw.
Amperage Hour Rating: Marine batteries are rated on a metric called “amperage hours”, which is an indication of how long a battery can supply a consistent amperage. The larger the rating, the more power the battery can hold, and the longer it will be able to power a motor at a given speed. For example, a 100 amperage hour battery is one that would be able to supply 25 amps of power for 4 hours (25 amps * 4 hours = 100 amp hours) before running out of energy. Alternatively, the same battery could also supply 10 amps of power for 10 hours (10 amps * 10 hours = 100 amp hours) before running dry You can think of the amperage hour rating as being similar to a gas tank in a car – the larger it is, the more energy/fuel it can store, and the longer it can power a motor.
Motor Amperage Draw: The second factor we need to compute estimated run time is motor amperage draw. A motor's amperage draw rating refers to how much amperage (or current) a motor draws at a given speed. A motor's exact amperage draw rating isn't always easy to find, but should be available from the manufacturer or, if it's a motor we stock, from a TrollingMotors.net representative.
In order to approximate how long a certain motor will run on the water, you simply take the battery's amp hour rating and divide it by the amperage draw. For example, for a motor that pulls 20 amps at medium speed using a 100 amp hour battery, the run time would be:
100 amp hour rated battery / 20 amp draw = 5 hour run time
Most manufacturers will only list a motor's maximum amperage draw at top speed, so you may need to estimate other amperage draws at various speeds using the max speed amperage draw as a baseline.
For a general idea of approximate amperage draws by motor size, please see the chart below. Please note that these are approximations only and results will vary based on exact motor figures, batteries used and water conditions.
It's important to note that water and weather conditions can significantly affect battery performance. A motor drawing 20 amps to move a boat at medium speed in calm conditions may need 30 amps to move the same boat in strong wind or waves. If you plan on using your motor frequently in windy or stormy conditions, you'll want to factor this into your calculations.
There are a few things you can do to get the most run time possible from your battery & motor combination.See also:
What power trolling motor do I need? | Yahoo Answers
No one complains of buying too much thrust in a trolling motor. They all come with speed controls so that going against the wind or current more thrust is available.
Hull design makes a huge difference. Vee and semi vee hulls will require less thrust at low speed than a planing hull. Plane hulls work when there is less wetted surface.
Bottom line is to get as much thrust as you are willing to pay. The 12 volt systems are more popular because 24 volt is a nuisance of dealing with more batteries and a lot more out of pocket expense and maintenance time.
For trolling at 3 to 4 mph I wou…