An internal antenna unit can't be mounted flush or like on the bow with screen facing up. The screen has to be kept facing forward, the top of the unit facing straight up. That's not good if you have to scrunch down to see it. An external unit head unit can be oriented in any position, above you facing down in a cabin, below you facing up. You can't have a canopy over an internal unit. All GPS positions are referenced to the position of the head unit. I prefer the external antenna unit. I have two antenna pucks, each mounted over their own transducers. That allows precision positioning, matching GPS location to what is displayed on the sonar screen. If an internal unit is on the console and transducer is on the transom, error is always built in, whatever the distance is betweeen antenna and transducer.
When setting a waypoint I let the unit collect at least 10 positions which are averaged and compared to WAAS data, allowing extra satellite signals to get through.
The internal unit makes more sense if transferring it to the tow vehicle for a trip. You wouldn't have to mount an antenna outside the truck.
Jim
