Coastal defence ships in ocean escort service

How effectively could smaller navies' coastal defence ships switch to ocean trade escort duties after going into exile?

Their coastal hull forms would usually make open-ocean escort work difficult.

Ships built for local coastal defence are usually poorly suited to open-ocean work. Hull shape is a substantial part of the problem when trying to give them an ocean escort role. German barges proposed for Operation Sea Lion provide a comparison: a vessel's original operating environment limits what can reasonably be expected of it elsewhere.