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From Sail to Hybrids Part 2

January 3, 2014

The first major postwar development in ships’ propulsion was nuclear propulsion.

Nuclear-powered aircraft carriers and submarines became the backbone of naval strategy following WW II.

Nuclear-powered aircraft carriers could remain on station anywhere in the world for several months.

The same was true for nuclear-powered submarines.

Without nuclear power, ballistic missile submarines could not have formed the defensive shield, part of the triad, during the cold war.

Nuclear power allowed ballistic missile submarines to remain submerged for months on end, making it nearly impossible for any nation to know their location.

Without nuclear power, the electric, battery-driven, diesel submarine would have had to come close to the surface to use its snorkel to allow diesel generators to replenish the batteries. Snorkels could easily be seen by satellites, disclosing the submarine’s location.

Propeller design was perfected to virtually eliminate cavitation and allow submarines to cruise nearly undetected by even the best sonar.

Another postwar innovation was the use of aircraft derivative gas turbines to power smaller ships, including destroyers and frigates1.

The postwar period saw the adoption of new ship designs, such as roll-on-roll-off landing ships for the navy. Specialized underway replenishment ships, designed to carry liquid fuels, dry goods and frozen food became the norm for the service fleet.

In the commercial arena, container ships revolutionized the transport of goods and material around the world. They replaced break-bulk cargo ships where each piece of cargo was loaded separately, exposing the goods to damage and theft.

Bulk cargo, such as grain and bauxite, was loaded directly into cargo holds.

In December 1949, I watched a shipload of phosphates, delivered to the port of Keelung, Taiwan being unloaded by hand. Ramps were positioned from the dock to the main deck of the ship, and then more ramps were positioned from the deck into the holds. Coolies, with yokes across their shoulders, and with buckets hanging from the yokes, scampered up and down the ramps and into the holds, where the granular phosphate was scooped by hand into the buckets. When the buckets were full the coolie ran up the ramp to the main deck, then down the ramp to the dock where the phosphate was dumped into waiting trucks2. It took nearly two weeks to unload the phosphate in this manner.

This primitive use of labor, rather than power equipment, is a stark reminder of how energy from fossil fuels has changed people’s lives.

In the latter half of the century, cruise ships became popular.

Most container and cruise ships used diesel electric propulsion.

Steam was dying, but still found limited usage in the navy and commercial fleets.

Diesel electric and gas turbines became predominant

Another innovation in cruise and container ships and tankers was the use of thrusters.

These were located underwater in the bow and stern and pumped water so it was ejected to the side of the ship, pushing the ship sideways. This allowed large ships to maneuver in tight quarters, being able to rotate 360 degrees without tug boats or other assistance.

Another innovation, found mostly on cruise ships, was pods. The pod enclosed an electric motor with a slip ring so it could receive electricity from the diesel generators no matter which direction the pod turned. The motor was connected directly to a propeller. Each pod, of which there were usually two located at the stern of the ship, could rotate 360 degrees. They could, by rotating, push the ship sideways, or drive the ship forward.

One of the newest innovations is the hybrid propulsion system found on some navy auxiliary ships.

These ships normally cruise at relatively slow speeds, of around 12 knots. During operations they would need to travel at considerably faster speeds to keep up with combat ships.

This allowed auxiliary ships to be powered by two systems, one for cruising at slow speed the other for faster speeds during operations.

This arrangement is supposed to save fuel, which would not only save money, but also potentially reduce the need for frequent refueling.

USN Iwo Jima LHD-7. Stern opens for Landing Craft Air Cushion (hovercraft)

USN Iwo Jima LHD-7. Stern opens for Landing Craft Air Cushion (hovercraft)


While the LHD-7 was powered by steam turbines, with bull gears and water tube boilers, the USS Makin Island LHD-8, uses a hybrid propulsion system.

USS Makin Island uses diesel electric for slower speeds and GE LME 2500 aircraft derivative gas turbines for faster speeds. While this hybrid system is still experimental, it shows promise.

Propulsion systems have progressed from sail to steam, to diesel, to nuclear, to gas turbines, and now to hybrid systems – with a few variants along the way.



  1. Aircraft derivative gas turbines simplify logistics as jet fuel is also available for aircraft carriers.
  2. The word “coolie” appropriately describes workers of that time in Taiwan, and has no racial intonations.

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