What Size Trolling Motor Do I Need? Thrust, Shaft Length, and Voltage Guide
Published May 12, 2026 · Buying Guide · Factory-Authorized Insights
Buying a trolling motor is one of the more confusing purchases a boat owner makes. The wrong choice costs you in two ways: underpowered (boat won’t hold against wind, batteries die fast) or overpowered (paid too much, motor too heavy for your boat). Here’s how to spec the right one.
We install dozens of trolling motors every year. Call us BEFORE you buy — pre-purchase advice is free and we’ll save you from buying the wrong unit. But here’s the framework we use.
The Three Specs You’re Picking
- Thrust (measured in pounds) — how hard the motor pushes
- Shaft length (inches) — how deep the prop goes
- Voltage (12V / 24V / 36V) — battery system required
Get all three right and the motor works for years. Get one wrong and you’ll either upgrade in 18 months or limp through with reduced performance.
1. Thrust — How Much Do You Need?
The rule of thumb: 2 lbs of thrust per 100 lbs of fully-loaded boat weight, minimum.
For Florida conditions (wind, current, fishing all day), bump that to 3 lbs per 100 lbs for a reliable hold.
Thrust by boat type
| Boat type | Length | Loaded weight estimate | Thrust needed |
|---|---|---|---|
| Kayak / canoe | 10-14 ft | 300-500 lbs | 30-45 lbs |
| Jon boat | 14-16 ft | 600-1,200 lbs | 30-55 lbs |
| Bass boat (small) | 16-18 ft | 1,500-2,000 lbs | 55-70 lbs |
| Bass boat (mid) | 18-20 ft | 2,000-2,800 lbs | 70-80 lbs |
| Bass boat (large) | 20-22 ft | 2,800-3,800 lbs | 80-105 lbs |
| Bay boat / flats | 20-24 ft | 3,000-4,500 lbs | 80-112 lbs |
| Pontoon | 22-28 ft | 3,500-5,500 lbs | 80-112 lbs |
| Center console | 22-26 ft | 4,000-6,000 lbs | 105-112 lbs |
Florida-specific thinking
If you fish:
- Open Tampa Bay flats — wind is brutal, lean toward the higher end of the range
- Crystal River backcountry — protected, can go lower end
- Polk County chain bass lakes — moderate wind, mid-range works
- Saltwater offshore — current is the real enemy, max thrust
Don’t undersize. A 55 lb motor on a 20 ft bay boat will drain batteries trying to hold position in wind. An 80 lb motor on the same boat will hold easily at half power.
2. Shaft Length — Often Wrong
The most-undersized spec on DIY trolling motor purchases. Wrong shaft length = prop cavitation, lost thrust, motor working too hard.
The measurement
Measure from the top of the bow (where the trolling motor mount sits) down to the waterline at the bow.
Then add 16-22 inches depending on conditions:
- Calm freshwater: prop needs to be ~12” deep → shaft = waterline distance + 12”
- Average wind/chop: prop ~16-20” deep → shaft = waterline + 18-20”
- Heavy chop / offshore: prop ~24”+ deep → shaft = waterline + 22-24”
Common shaft lengths offered
| Shaft length | Best for |
|---|---|
| 36” | Small jon boats, kayaks |
| 42-45” | Bass boats with low bow |
| 52-54” | Most bass boats |
| 60-62” | Bass boats with high bow, bay boats |
| 72” | Tall-bow bay boats, large pontoons, offshore |
If you’re between sizes
Go longer. A too-long shaft has the prop deeper — fine, slight thrust loss. A too-short shaft has the prop cavitating in chop — catastrophic thrust loss when you need it most.
3. Voltage — 12V vs 24V vs 36V
This drives both motor selection AND battery setup.
12V (single battery)
- Thrust range: 30-55 lbs
- Best for: Kayaks, canoes, small jon boats, very calm conditions
- Battery setup: One Group 27 or 31 deep cycle
- Run time: 2-4 hours under typical use
24V (two batteries in series)
- Thrust range: 55-80 lbs
- Best for: Most bass boats, mid-size flats boats, weekend anglers
- Battery setup: Two Group 31 batteries wired in series
- Run time: 4-8 hours
- Sweet spot for most Florida bass anglers
36V (three batteries in series)
- Thrust range: 80-112 lbs
- Best for: Large bass boats, bay boats, tournament anglers, anyone wanting full-day run time
- Battery setup: Three Group 31 batteries wired in series
- Run time: 6-10 hours
- Sweet spot for tournament + bay boat anglers
Why higher voltage wins
For the same thrust, higher voltage:
- Draws less amperage → batteries last longer per trip
- Less voltage drop in wiring → consistent performance
- Cooler-running motor → longer motor life
Most pros run 36V even if 24V would technically suffice, because run time and consistency matter more than upfront cost.
The Real-World Recommendation
Most Florida bass anglers should buy:
- 18-20 ft bass boat: 80 lb thrust, 60” shaft, 36V
- 20-22 ft bass boat: 112 lb thrust, 62-72” shaft, 36V
- 22-24 ft bay boat (saltwater): 112 lb thrust, 72” shaft, 36V, Riptide (saltwater) series
Most Florida casual anglers (jon boat / small bass boat):
- 14-16 ft jon boat: 55 lb thrust, 42” shaft, 24V
- 16-18 ft bass boat: 70 lb thrust, 52” shaft, 24V
What Else You Need to Plan For
Buying the motor is half the cost. The full setup includes:
| Item | Cost |
|---|---|
| Trolling motor | $1,500 - $5,000 |
| Batteries (3x Group 31) | $1,000 - $2,700 (lithium more) |
| Onboard charger | $400 - $800 |
| Wiring + breakers | $100 - $300 |
| Installation (we do this) | $300 - $700 |
| Total project | $3,300 - $9,500+ |
This is why pre-purchase advice matters. The “trolling motor cost” online doesn’t include the supporting system.
Spot Lock or No?
If your boat is bass, bay, or flats — get the GPS anchor version. Spot Lock / Pinpoint / Force Anchor changes how you fish. It’s worth the extra $400-800.
If you fish strictly trolling for crappie or panfish — skip GPS, save the money.
We’ll Spec It For Free
Call us with:
- Your boat make, model, length
- Where you fish (lake names, saltwater locations)
- How long your typical trip is
- Your current fish finder brand (matters for motor selection)
We’ll tell you exactly what to buy. No sales pressure — we make money installing motors, not steering you toward specific brands.
📞 (813) 380-5145 — free pre-purchase consult.
Learn about our installation services →
About Nature Coast Trolling Motors
We're a Minn Kota Authorized Service Center and a MotorGuide Certified Service provider in Plant City, FL. We repair, install, and service every major trolling motor brand for anglers across Plant City and the surrounding Tampa Bay area.