The Difference
Most modern fish finders include a built-in GPS receiver and chartplotter, combining sonar and navigation in a single unit. External (standalone) chartplotters are dedicated navigation screens without sonar capability. A decade ago, anglers often ran separate units for sonar and navigation. Today, combo units have largely replaced that approach for small-to-mid-size boats.
| Factor | Built-In GPS (Combo Unit) | External Chartplotter |
|---|---|---|
| Cost | Lower (one device does both) | Higher (separate purchase) |
| Screen Usage | Shared between sonar and mapping | Dedicated navigation screen |
| GPS Accuracy | Equivalent (same chipsets) | Equivalent |
| Chart Options | Full charting (Navionics, C-MAP, LakeVü) | Full charting |
| Complexity | Simpler setup | Additional wiring and mounting |
| Best For | Most anglers, single-screen setups | Multi-screen boats, dedicated nav needs |
When Built-In Is Enough
For the vast majority of freshwater anglers and inshore fishermen, a combo fish finder with built-in GPS provides everything needed. Modern combo units offer the same GPS accuracy, chart compatibility, and waypoint management as standalone chartplotters. The only trade-off is sharing screen real estate between sonar and mapping views.
If you run a single screen on your boat, a combo unit is the clear choice. Buying a separate sonar and separate chartplotter doubles your investment, wiring, and mounting requirements without providing meaningfully better performance.
When External Makes Sense
Standalone chartplotters make sense on larger boats that run multiple screens, where dedicating one display exclusively to navigation provides a safety benefit in busy waterways or offshore. They also make sense when the chartplotter needs to share radar overlay, AIS (Automatic Identification System) data, or autopilot steering — functions that benefit from a dedicated, uncluttered screen.
Some offshore anglers also prefer a dedicated chartplotter for its large-format display optimized for chart viewing, with sonar handled by a separate screen. This dual-screen approach ensures navigation information is always visible without needing to switch away from sonar views.
The Verdict
Built-in GPS combo units are the right choice for 90% of anglers. They deliver excellent sonar and navigation in one device, reduce cost and complexity, and offer the same GPS accuracy as standalone units. Consider a dedicated chartplotter only if you run a multi-screen setup where one screen must always show navigation.
Frequently Asked Questions
Do I need a separate GPS chartplotter and fish finder?
Not for most boats. Modern combo fish finders include GPS chartplotters with full mapping capabilities. A separate chartplotter only makes sense on multi-screen boats where dedicated navigation display provides a safety benefit.