First of all, I would caution you that making the BU-353 the only GPS source, and the laptop
the central distribution point, means that you're utterly dependent on the laptop being up and working to feed GPS data to the other devices, which is bad design. A better way is to have an independent source of GPS data that feeds other devices, INCLUDING the laptop... For example, get a US Globalsat MR350P
which has NMEA0183 serial out, and use it to feed everything, including your laptop via a serial-to-USB adaptor ($3 on ebay). Or use a MR350P for the 'boat' and continue to use the BU-353 for the laptop, which gives you independence and you have a back-up GPS.
To do it as you have asked, you'd need the serial-to-USB adaptor, and some software
to do the 'sharing'. Linux
has gpsd and other utilities for routing the data. I don't know an equivalent for Windows but a quick Google
brought up this
, which looks interesting.