Civilian ship repair yards have traditionally hired a lot of former U.S. Navy sailors who worked in “the trades” — machinist’s mates, enginemen, hull maintenance technicians and others — while on active duty. But the crop is thinning. The Navy is a lot smaller than it was 10 or 20 years ago. Fewer trades-type sailors have been needed since the Navy began outsourcing more of its maintenance work to civilian yards following implementation of its Fleet Response Plan.