Be aware that there are NMEA0183 and NMEA2000 protocols, and the two most likely are not compatible, and additionally Garmin may have their own proprietary communication protocol. Your Garmin will most likely have the ability to connect to one of the NMEA protocols, but may not have the ability to connect to the other without conversion electronics. Depending on what you need, Actisense make conversion devices, but don't normally sell direct to the public. Instead you have to buy through one of their associated retailers. Additionally if you need, or chose to go down the route of using an Actisense device, you have to chose carefully which of the devices you require for that conversion. Even then you may have to download some extra information to update the firmware within that device to configure it for your specific requirement. Actisense are helpful if somewhat confusing at times, such that you may find it a bit of a minefield to get exactly what you need, so good luck in that respect as these things are not always as straightforward as you may like.