As another note, if ships had their heavier machinery installed while on the ways, the lough would have to have been dredged to accomodate the deeper draft. For example, when Nimitz-class carriers are "launched", they are nearly full-weight, in comparison with the Olympic-class hulls and their contemporaries. As a result, the departure of the hull to the fitting-out wharf requires timing with the tides to allow for maximum clearance from the riverbed (of course Mr. Standart can confirm or correct this.)
So, it would be a bit more prudent to fit heavy machinery in the ship after she's launched, to lighten the load on the ways, and to avoid the unpleasant incident of running aground in the lough.
Adam