Hi Niggle,
Welcome to the Forum.
If you want to play missions involving ferries you first need to buy the latest version called "Ship Simulator Extremes" (€ 40). Along with it you also have to buy the "Ferry Pack" (€ 15). You can also buy the fishing trawler "Sigita" for € 5 and your SSE will be complete in all respects.
It would be strongly advisable to buy all these products from www.shipsim.com . I would suggest the DVD for Ship Simulator Extremes instead of the download unless of course you do not want to wait for the delivery of the DVD. As for the Ferry Pack and the fishing trawler, you have no choice as they are only available as downloads. You can also get all of these products through Steam, but unfortunately there have been complaints about this version.
I hope your present computer's configuration is suitable to run Ship Simulator Extremes. Please do not be under the impression that since SS 2008 ran well it will be able to support SSE. Check out the System Requirements (attached below) before you purchase SSE.
Please also register the License key(s) of your copies of SS 2008 in your Profile in this Forum. You will then get access to all boards of SS 2008. Do the same when you get your copy of SSE too.
Regards
vin_sun