im reading about the very thing at this moment here
http://www.amazon.co.uk/Convoy-Merch...9929602&sr=1-1
a wonderful book i posted up not long ago.
apparently sinking times depend on many factors as has been outlined above. cargo; if its fuel or ammo it maybe a matter of seconds, if its wood it may float for days and make it back to port with damaged engines, heavily listing taking on water and burning to !!
weather is another strong factor.
if its in ballast it can bob along with a hole in its side with not
too much a problem.
so anything from minutes to days. some ships have been abandoned for days and crews have returned to try and save her.
one report says a crew member wanted to go back and get his winnings from a card game even though the ship was ladened with steel and russian bullion in its holds; he was prevented by his captain !!
there are many references and descriptions here in this wonderful book - especially the grim PQ17 convoy.
reading a book like this makes those 'virtual merchants' take on a whole look as i stalk and sink them.
if you want to know about life above the waves in all its conditions regarding the merchants, here it is...