This method of creating a pseudo-LAN seems to work well for multiplayer games. A multiplayer session can be easily set up on one person's PC and played using Tunngle and TeamSpeak.
Download the Tunngle utility (currently a beta) from
www.tunngle.net then and install it. Create an account at the same website and finally confirm your registration on receipt of their email.
Start the Tunngle.net program and enter username and password; set up an automatic logon if you wish. When connection to Tunngle is made, go to Simulation/Silent Hunter III and double click.
That's it. Leave Tunngle there in the background and start Silent Hunter III proper. In SH3 go to Multiplayer/LAN Game/Create Game (or Join game)/......
I'm not sure its necessary, but if you host, add port forwarding to your router setting 17997 to 18003 for both TCP and UDP. Also make sure that Windows Firewall Exception settings include SH3.