How Much Thrust Do You Need in saltwater trolling motor?
When considering how much thrust is required with a trolling motor used in saltwater conditions, it’s important to take a step back to look at the various factors that go into this decision.
Let’s break it down to different kinds of motors and consider those first.
Transom Mount Motors
The transom mount only suits certain kinds of boat. It has brackets that clip on and can be adjusted to different angles once fitted to the side of the boat.
The higher up the transom motor will be fitted, the longer the shaft needs to be to get the prop in the water deep enough to get purchase in the water. Over 16-inches requires a shaft length of 42-inches. Over 10-inches requires a shaft length of 36-inches and below 10-inches can run with a shaft length of 30-inches.
Bow Mounted Motors
With a bow mounted motor, you face a situation where the trolling motor might be the auxiliary engine too. A spring mounting system allows the motor to be movable to avoid damage should a boat to boat or boat to shore impact occur.
Fresh water vs Saltwater
With a saltwater trolling motor, its protected from the corrosion typical of operating any kind of boat at sea. With fresh water on a lake, that’s not a concern.
Different Shaft Lengths
The typical shaft length is 42-inches. However, it does depend on the type of boat and the mounting system which puts the trolling motor at a different height above the water and thereby requiring perhaps a longer shaft.
What you want is a prop that sticks below the water’s surface at least 6-inches or more to get purchase through the water. Calculate the distance from the mounting to the water’s surface and then add 20-inches beyond that.
When buying a trolling motor from https://marinebatteryguides.com/best-trolling-motor-battery/, one of its specifications is the pounds of thrust it delivers at top speed. You can use the measurement of 75-pounds of thrust comparing well to 746-watts of electrical output or a single horsepower (roughly). For instance, a 12-volt motor uses 720-watts of power while drawing down 60-amps. Remember with more voltage, there’s more available thrust.
Trolling motors come in 12-volt, 12 to 24-volt, 24-volt and 36-volt options. When opting for the greater amount of voltage, you’re edging up to the 50-100 pounds of thrust. The appropriate amount of thrust depends on the boat and what it requires to move successfully through the water at a reasonable pace. Most boats fit between the 12-volt and 55-pounds of thrust level and the 24-volt and 80-pounds of thrust level; only the larger boats require more.
Buying too much motor compared to the boat size can create a size and weight issue. Usually, a good rule of thumb is 5-pounds of thrust per 200-pounds of weight for the boat.
Match the voltage and pounds of thrust sensibly. Trying to use a low voltage coupled with a high pounds of thrust leads to greater amperage use on the battery. Balance usage appropriately for the right mix.