T.A. Gardner wrote:Then there's the space needed for the various hoists as well as passing powder, and moving (likely) one-and-a-half ton shells onto the shell hoists.
My view is that such details need be thought through before making a claim for an alternative history. All-too-often, the ideas presented were superficially thought through and no thought given to the details of how something would actually work.
Here's an earnest suggestion for making things more productive here: Instead of assuming that I haven't thought of something and assuming you're one step ahead, maybe ask, "Hey TMP, do you have space for all those shell/powder hoists? Won't they get tangled?"
Well thanks for the question, I have in fact thought about it.
First, some broad observations:
-Despite the spaghetti-looking layout of the Iowa turret from the side, an over-head view shows how little of the floor space is actually occupied by the powder/bag hoist channels, were they vertical. I've marked them in red below:
...it should be obvious that very little of the turret floor space is taken up by hoist chutes. A little arithmetic confirms this: The turret pan floor area is ~1,000ft2. Three 4ftx2ft powder carriages, and 3 ~1.5ftx1.5ft shell hoists add up to ~31ft2 or ~3% of floor space.
-I'd estimate a ~67ft diameter for a 20-gun 18in turret. That's 4x the area of an Iowa turret's pan floor (remember no armored barbette so turret D <= working space).
-Multiplying 31ft2 by 20/3 and (18/16)^2 we have ~260ft2 of for the powder carriage shell chutes on a vertical plane. That's ~6% of the turret's floor area. About twice as much as in Iowa but still not much.
-Unlike the Iowa's turret layout which is constricted in its lower dimensions by torpedo bulges, the Mega's can use the full width all the way down if necessary - therefore all powder/ammo tracks are vertical, unlike Iowa's and every BB I've seen. These vertical chutes make the schema much simpler.
Here's a rough sketch of a possible layout:
...this doesn't correspond to the 67 foot diameter I mentioned above but I didn't feel like doing a new drawing or doing the post over.
Nonetheless the basic principle should be easy to see: The rows of horizontal lines represent the top of the powder hoist, where bags load into the cradle. Forward of these rows are shell hoist columns (dual in this diagram due to laziness - i.e. one next to another) through which shells pass up to the shell handling deck for loading into the shell cradle.
This layout could represent the schema of the powder-to-gun loading deck and a lower, vertically-corresponding powder-hoist-loading deck.
Or you you view the orange circle as representing a separate, vertically-corresponding deck for powder-hoist loading.
Or the back row could represent a deck to which no hoists lead - the powder comes in from magazines on the same level as this deck (we're ~30ft below the armored deck at this point). That means only one row of hoists - the other cradles are loaded directly by cart from the magazines. Then the cradle is raised to ramming position (recall that the gun pit is separated from the powder cradle unlike in all designs I know - another benefit of practically unlimited space).