Interfacing with NMEA 0183
NMEA 0183 is electrically similar to RS-422 and RS-485 (but without the 485's addressing) which uses differential signaling (btw Seatalk-1 is single ended). These standards are old and well proven, RS-422 is point to point while RS-485 is more like a bus, with each node has an address preventing several nodes to transmit at the same time.
Converters to bridge between RS422/485 differential voltage signaling to USB are readily available. In this way the yacth server can read and write onto the NMEA network. Remember that the NMEAS 183 is not a bus, but rather a point to point network, unlike the new NMEA 2000.
An example of such a USB to RS422 converter can obtained from a variety of sources, one example is : USB 2.0 to RS485/RS422 (this one is isolated, USB from RS422)) or for a more industrial type (with holes for fitting it) USB to rs422 / 485 / serial 232 / TTL.
An example is shown below, this one is isolating and is the one I have used, available at Aliexpress.