thanks for all info's guys now i am more clear.besides i dont know that the merchants will be armed at late 41' or at 42' .i will be more careful during that times.currently i am using %38(or so) realism.
p.s; For the first time i got a report from Bdu that a large convoy is nearby wheeeee!

i've changed my pilot course and now getting close to convoy.i dont know whats expecting for me.wish me luck !