A battleship never takes longer than 4 turns to build. If your city has 40+ free production, you simply build it. If it has less, then you build 1 turn, then buy up to 120 (city-walls) and let it finish the remaining 40 shields. And if this takes you longer than 3 turns, you should rather build caravans for Hoover Dam than battleships.
With 4-turns, you pay 16 gold (with v5) for the baracks-time which is equivalent to 8 shields or 5% of the total costs. This is less than the chance to lose your non-veteran battleship against even a puny sail or unfortified settler - and you need two fights on avg. to get promoted.
ignatius
