If my experience with win8 is any indication, that could be your problem.
There are other possibilities:
It could be a corrupt save issue. If you repeatedly over-write the same save, it eventually gets corrupted and you see things like that. It's best to save in a new file each time. Most people use a master name, then just number each save. It's best to save while in port.
There are actually "rules" for saving a game in career mode while not in port. Try to save when:
On the surface
In clear weather
When there is nothing within sensor range
It could be a video card issue. sh4 is very graphic intense. Shared video ram will work, if you have enough ram to share. Best to have dedicated video ram. Until you can check, try turning down your settings.
Can you post your system specs. Maybe someone who knows more about computers will be able to help.
By the way, welcome to the boat. I think you'll like it here. You need to go on weather watch. Stay out on deck 24/7 and give hourly reports.