A common mistake when building realistic vessels is a matter of balance. Either making the ship with the superstructure and smokestacks too close to the bow, or the stern. This is normally because most people begin work on the bow and work their way back, compressing the stern of the ship to stay within the envisioned length.

Realistically, a point to work off of is the smokestack(s). Midway between the smokestacks is normally around where the midpoint of the ship should be. This is because the smokestacks need to be as close to the boiler room as possible, and the boiler room is not a small part of any ship. The boiler room is normally slightly in front of single-smokestacks, or directly centered on the midpoint of multiple smokestacks. Ships needed to have their boiler rooms as far forward as possible to allow for the other machinery spaces needed to the stern. The turbines or pistons are always behind the boiler rooms because it simplifies and reduces the space needed for the prop shafts.

The Bismark is a good example of a single smokestack.

As you can see the boiler room is perfectly central with the smokestack above and very slightly behind.

An example of a ship with multiple smokestacks is the vanguard;

This also means that in most cases the smokestacks form the midpoint of the superstructure or substructure, not just because of where the funnels are, but because beneath the deck there's very little space for turret barbettes and magazines for larger guns.

There are some exceptions of course, notably ships like HMS Nelson and Rodney. In these cases the weight of the machinery and boilers (don't forget, the large boilers where full of water, and very heavy, not to mention the steel machinery), is offset by the combined weight of armour, magazines and turrets.

The nelsons where also different in that their boilers (which I've boxed in blue) where behind their engine rooms (in red), this was to move the smokestack further aft, where the exhausts wouldn't obscure the bridge, and was very complicated mechanically.


What does this mean in FTD?

In FTD the reasons for the placement of the smokestacks aren't there. Engines can be small and aren't heavier than other components and armour, so placing them anywhere isn't an issue. Adding to the ease of piping the exhausts to any location on the ship, and it's practical to have a smokestack absolutely anywhere. However, when trying to build a realistic looking ship, it's good to work out where your machinery will be. I like to build a ships main guns first, then the deck. Afterwards it's easy to decide where your engine rooms will be, and then the boilers fore of those, with the smokestacks directly, or slightly staggered above them.

Here's a good example of slightly poor placement, the ships smokestacks are firmly in the aft half of the ship, which would mean the boiler room will be very far back, leaving very little space for the turbines or reprocating engines and making the whole vessel very stern heavy.

You can see by this world-war inspired cruiser, the smokestacks are almost perfectly centered, with space for a boiler room beneath (blue), and the engine room behind (red). This leaves plenty of room fore of the boiler room for crew quarters, and the magazines beath each pair of turrets. Really however, the ship could use a single smokestack to save deck room.