Brian
Not a naval expert by far, but during WW 2 Sweden was in a tricky situation. To survive we needed to both import and export stuff via ocean vessels. We traded with both Britain and Germany, they were together I believe the two largest trading partners we had. Each arrival and departure had to be negotiated with the two combatant nations. Germany had by that time taken both Denmark and Norway and for us we had to negotiate a safe passage through the so called Skagerak blockade if we wanted to move out into the North Sea and still further away. Then we needed to negotiate a safe passage through British waters as well. Vingaland was part of SOL (Swedish Orient Line) which was a shipping line not connected with Germany and presumably had an easier task negotiating via our Foreign Ministry a safe passage with Britain. These negotiations during the war years never included any promise of a safe conduct, just a permission to pass through certain blockades. Swedish vessels had to take their chances just like every other vessel in a given area.
Already at this early stage it was very much obvious that it was far safer to move a vessel in convoys and I am quite certain everyone concerned did their best to negotiate passage inside such convoys whenever possible.
Large numbers of Swedish vessels were sailing to German ports both in the Baltic and on the Atlantic Coast. Many were sunk as can be seen on Rolf Skiolds home page
http://www.mareud.com/
I think if you contact him you can get a far more detailed and comprehensive answer than I am able to give....
Cheers
Stig