Can't build tripple turrets for/aft with TPS 2 over 18kts

[kyle]

I don't have a save but could re-produce this easily starting a new game in 1920 and auto-building (game designing) a BB.

The AI will build a BB with 4 tripple turrets then in the design check won't allow it due to hull form for ships faster than 18kts.  This goes on well beyond where the US was building tripple turrets on battleships such as Arizona.  Something is fishy and it's not a submarine .  
I have to build twin for and aft, tripple superfiring.  What tech advancement is preventing 4x3?

[wlbjork]

The answer is that the TPS system on board the Pennsylvania-class battleships is considered the equivalent of level 1.

A three-inch torpedo bulkhead was placed 9 feet 6 inches (2.9 m) inboard from the ship's side and the ship was provided with a complete double bottom. Testing in mid-1914 revealed that this system could withstand 300 pounds (140 kg) of TNT.