I'm new to this subreddit and I'm not sure if this fits considering the Iowa - class is still around. However, if someone can tell me, I would be greatly appreciative.
For the reason of me asking for anyone who may ask, I'm designing a computer case that uses 3 200 mm fans and I'm trying to get the scaling right.
From page 3 of this paper, describing the reactivation of the Iowas 16in turrets, the turret barbettes (the holes they fit in) have a maximum diameter of 35ft 1in. It also gives dimensions for the turrets themselves, and for the foundation on which they sit.
On a related note, the turret design of the Iowa class was a wonderful example of how you can have miscommunication between two groups that really should be talking to each other.
It had been decided to use longer 16"/50 guns over the 16"/45 guns used in the preceding South Dakota class to give at least some firepower improvement to match the healthy growth in displacement. This would require a larger turret diameter from the South Dakotas too. However, the Bureau of Ordnance, responsible for the guns, either implied or outright stated it had a design that didn't need any increase. So the Bureau of Construction and Repair, responsible for the ship design, assumed it could stick with the same diameter. However the Bureau of Ordnance decided that it actually did need a larger diameter for a satisfactory turret design. But it failed to pass that piece of information along. So you ended up with a design for a ship and a design for its turrets that couldn't actually fit together.
This discrepancy was discovered only at the very end of the design process. Since increasing the diameter would have meant an unacceptable increase in ship displacement, the only solution was a brand new lightweight gun design.