There is one simple number that separates a good day of fishing from frustration. That magic number is called thrust.
A lot of folks believe they can buy any old trolling motor that are on sale at their favorite store. All they have to do is find one they like and can afford. They neglect the fact that water is heavy. Water resists. You’re not simply moving air, you’re moving your boat, its contents, the current, and the wind all together.
Why Thrust Matters for Trolling Motors
The chart above is a quick visual to pair your boat class with your desired voltage system. In a nutshell, it illustrates how a single twelve-volt battery barely move your kayak. It will be fried to death should you attempt to ram it into a three-thousand pound bass boat in headwind. So what’s the deal?
The basic formula isn’t too complicated to grasp if you take it out once. Here’s the rule of thumb: For every 100 pounds your boat weighs, plan on about twice that much thrust. That’s the bare minimum required when fishing in calm water protected from wind, with no current pushing your bow in different direction than before.
But guess what? You never really get those ideal situations do you? Current turns on its head. The wind gusts. Ice filled coolers is loaded onto the deck. There are tackle boxes filled with tackle from buddies who tagged along for the ride and want to use some of them. Your boat becomes overweight with all this additional gear, it completely alters the formula.
And that’s when suggested ratio comes into play. Increasing your requirement to 2.5 pounds per hundred gives you enough spare power to stay steady in a light chop or moderate breeze without red-lining the battery. Are you on a river run? Is there heavy cover? Is it tidal water? You’ll require even more. Just to stay in place will be three pounds per hundred. To show that ramp-up and explain it simply, chart displays how the max boat weight corresponds with the thrust rating. That way, you don’t make the all-too-common error of buying a motor too small because “it gets me there”.
Thrust power isn’t all about voltage. But voltage is equally important. If you own a canoe or a small jon boat weighing less than fifteen hundred pounds loaded, a simple twelve volt system are inexpensive and easy to install. However, if your boat exceeds this weight class, you run into a brick wall. Twelve volts are simply incapable of supplying the current required to power high-thrust rated trolling motors while not burning out your batteries in minutes.
This is why twenty-four volt systems using two batteries are common on mid-sized bass boats. The voltage allow them to deliver the amperage required to push motors up to an efficient level using seventy or even eighty pounds of thrust. When it comes to serious offshore fishing boat or large pontoons, there really is no choice other than three-battery thirty-six volt systems. The larger capacity pull more power from a deeper well while running higher thrust motors that can stress the batteries by pushing them harder.
But this isn’t just about getting the big motor started. It’s also about keeping up with boat all day long. Here again battery chemistry are a factor. Sealed AGM batteries provide a solid middle ground solution for recreational boaters looking for maintenance free performance at a lower price point. While Lithium will outlast and be lighter, they’re still a bit of an investment.
The other common areas of confusion include selecting proper shaft length. To determine the correct length, load your boat with normal equipment and then measure from the mount to the water line. Now add 20 inches for good measure. This ensures your propeller stay submerged deep enough to grab clean water instead of sucking in air from surface. Even if it has a high thrust rating on the label, a short motor will cavitate and suffer no matter what.
Choosing a trolling motor is not an exercise in chasing big numbers. It is simply being honest with yourself. Determine your true weight… Including passengers and gear, and compare that figure against the thrust recommendations. If you regularly deal with current or wind, size-up a bit. Yes, it adds a few dollars at purchase time, but it’ll eliminate hours of drift frustration down the road.
The next time you drop the anchor and hear boat quietly lock itself in position, you’ll understand why the math was important all along.