Info says that 'trainers and unique crewmembers' can't be reassigned to
another ship. I took this to mean that specials can't be transferred
(apparently once they could be, but people ended up selling their surplus
trainers etc) and tried to move few better trained sailors to my secondary's
ship. However it turns out that anyone promoted over Rank4 is 'unique'.
This seems overly restrictive, surely transferring non-specialists can't be
too unbalancing, especially if restricted to ships owned by same character. As
of now, whole feature appears completely pointless.