How much thrust a loaded boat actually needs, what shaft length reaches the water, whether that is a 12, 24 or 36 volt motor — and how many hours the battery gives you at the draw you fish.
2,400 lb loaded · A breeze or a little current
58–82 lb of thrustBoth rules of thumb in circulation put a boat this weight in that range.
| Draw | Amps | Hours |
|---|
Thrust and wind allowances here are rules of thumb in wide circulation, not manufacturer specifications. The voltage bands, the amp draws and the 12 inches of submergence are Minn Kota’s own published figures, and your motor’s manual beats all of it.
Published figures checked 2026-09-20.
Quick answer: the two rules of thumb everybody quotes are 1 lb of thrust per 50 lb of loaded boat and 2 to 3 lb per 100 lb — and they are the same arithmetic at the low end. A 2,400 lb loaded boat wants 48–72 lb of thrust, plus roughly 10 lb more if you fish in a breeze. Minn Kota’s published bands are 55 lb or less on 12 volts (one battery), 68–80 lb on 24 volts (two) and 101–115 lb on 36 volts (three). For shaft length, measure from the bow deck or transom top straight down to the water and add at least 12 inches of submergence, then round up to a shaft you can actually buy.
Thrust: a range, because the rules are rules of thumb
Almost every calculator on this subject hands you one confident number. There isn’t one. Two rules are in wide circulation — one pound of thrust for every fifty pounds of boat, and two to three pounds for every hundred — and the first is simply the bottom of the second written differently. So the honest answer is a band, and this tool gives you the band.
Fully loaded is the part that gets skipped. Hull, engine, batteries, fuel, tackle, cooler and everybody aboard. A bass boat’s brochure weight and its weight on a Saturday morning are several hundred pounds apart, and the thrust you need is calculated on the second one.
Then add for conditions. The commonly quoted allowance is about ten pounds of thrust for a breeze or a little current, and more if you hold position against wind all day. More thrust costs you battery, never boat control — so when the arithmetic lands between two motors, the bigger one is rarely the mistake.
12, 24 or 36 volts
| System | Thrust | Batteries | Draw at full throttle |
|---|---|---|---|
| 12 volts | 55 lb or less | 1 | 1.2 amps per pound of thrust |
| 24 volts | 68–80 lb | 2 | 0.9 amps per pound |
| 36 volts | 101–115 lb | 3 | 0.55 amps per pound |
Notice the gaps. There is nothing published between 55 and 68 pounds, or between 80 and 101, and if your arithmetic lands in one of those the tool says so rather than quietly rounding you into a band. A motor exists either side of the gap; which one you want is a question about your boat and your budget, not about this page.
The amp figures are draws at full throttle, and they are the reason 24 and 36 volt systems exist: the same thrust at a higher voltage pulls fewer amps, so the batteries last longer for the same work.
Shaft length is where most people get it wrong
Too short is the mistake, and it does not announce itself on flat water. Minn Kota’s stated rule is to have at least twelve inches of the motor section submerged. So: measure from the mounting surface — the bow deck, or the top of the transom — straight down to the waterline, with the boat loaded the way you actually fish it, and add the submergence.
Then round up to a shaft length that is sold. A shaft that is slightly long can be set deeper in its bracket. A shaft that is slightly short ventilates in the first wave, and you will hear it before you see it.
If you fish standing up, or on water that chops, allow more than the twelve-inch minimum — the bow lifts, and the prop comes out. That larger allowance is a working figure rather than a published specification, and the tool labels it as one.
How long the battery lasts
Run time is amp-hours divided by amps, and the only honest input is the draw you actually pull. Full throttle is thrust times the amps-per-pound figure above, and almost nobody fishes at full throttle for an hour — so the tool shows the hours at a range of draws rather than pretending to know your throttle hand.
Two things move the answer more than the battery’s label:
- How much of it you can use. The conventional planning figure for a lead-acid or AGM deep cycle is about half its rated capacity, because taking it much lower shortens its life sharply. Lithium tolerates far deeper discharge, and 80% is a conservative figure.
- The Peukert effect. At high draw a lead-acid battery delivers less than its rated amp-hours. So the lead-acid hours are the optimistic version, and the harder you pull the more optimistic they get. Lithium is much less affected, and it holds its voltage as it empties, so the motor does not get weaker through the afternoon.