Good question , depending on what units you have on the boat and what unit you buy as a hand held , it's a toss up if it could work . If both have a compatible SDcard , I would think the operating system would need to be from the same company . I have a Hummingbird Helix 7 , and a Garmin handheld GPS ---they are not compatible at all . Furthermore , there is a huge misconception generated by the fish finder companies . Accuracy of these GPS systems is far less than they are tying to make people believe. Commercial systems are only accurate up to plus/minus 3 meters ( 9 feet of variance best case ) . Commercial systems use a specific set of satellites and can not be as accurate as Government /military GPS coordinates. Government and military systems use a different set of satellites and are accurate to plus/minus 2 to 3 centimeters ( less than 1 inch ! ) . If SD Cards and maps are generated by Government systems , they are the most accurate , anything generated using commercial GPS satellites , not nearly as good.