Boatnerd Discussion Forum

The following is from the 1955 edition of Design and Construction of Merchant Ships

On cargo and passenger ships, it is generally desirable to locate the propelling machinery about amidships. A rectangular compartment is the most suitable for arranging machinery and results in the least waste of space. Also it is desirable for passenger and crew comfort to have the accommodation amidships (close to the pitching axis and well forward of the propeller) which permits the machinery to be located under the largest part of the superstructure. This is not desirable space for carrying cargo since overhead cargo-handling gear cannot be installed economically. On most bulk carriers such as tankers, ore carriers and colliers, the machinery is located aft. This location is desirable for the tanker so to avoid the complication of cofferdams aft of the machinery and in way of the shaft tunnel as would be required with the machinery located space amidships. On ore carriers and colliers, cargo handling is improved by having one continuous uninterrupted cargo space as well as avoiding the obstruction offered by a shaft alley. On bulk carriers the relatively density of the cargo permits the allocation of a considerable volume for the machinery space without sacrificing the cargo-carrying capacity.
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My own thoughts:
Considering the need for higher oceangoing speed and the horsepower limitations of the inefficient steam propulsion plants available, ocean ships of that era needed finer lines than Lake boats so the width of the deck aft (before transom sterns were in vogue) was limited and a deckhouse located there would be longer. Other considerations are the space required for oceangoing vs Lake coal bunkers and bridge visibility.

The advent of steam propulsion began in wooden hulls both on fresh water and salt water and drove side paddle wheels for some years before the invention of the propeller. Setting the machinery and paddle wheels amidship proved to be the best placement in terms of pushing the hull and allowing cargo to be carried forward and aft of the power plant, distributing weight and stress over most of the hull. Even with steel hulls and the invention of the propeller, it was still considered good design on salt water to keep the machinery amidship for stability since "salties" ride up and down waves in the ocean. There were a few wood lake boats with propellers that had machinery amidship but they were soon surpassed by the classic lake freighter profile of wheelhouse forward, engine aft and long cargo hold in between, intended to go through the closer wave pattern the lakes make. The profile of wheelhouse and deckhouse aft isn't new to the lakes as a few boats, like the whaleback steamers, were built that way. This design became more widespread with salties before it was adopted on the lakes to reduce the cost of shipbuilding, less cost in placing everything aft.

I understand how Great Lakes vessel design evolved to the engine room at the rear and pilothouse at the stern before changing completely over to an all-aft cabin style in the early 70s. But does anyone know why ocean vessels during the late 19th and early 20th centuries evolved to have their engine rooms and accommodations in the middle of the ship before also taking on an all-aft design? It seems impractical to have such a long propeller shaft and it seems that it would have taken away some of the space available in the aft cargo holds. I believe that schooners and sailing ships were steered from the rear most likely to reduce the distance between the rudder and the wheel. I apologize for asking about a subject that could be considered outside of the Great Lakes.