I usually have a large number of yards. Each major class gets its own yard. The reason simply is, I like to build a squadron in one go. With few yards, I would have to build, for example, the three BBs, then retool for the BC and build them, then again retool for the CV and after those have finished, retool again for the JBC. When those finaly gets finished, the BBs are very likely at least obsolecent, if not obsolete, so I´d have to retool to the new BB again, for refit. Basicly, the squadron would never realy be ready for action, because part of it is either not build yet, or in refit.