by Maj. Michael Snyder, US Army
Updated 22 February 2000
Just some comments on high speed engineering plants in aircraft carriers
in specific and other warships in general. While much of a steam
powered ship's emergency power generating capability is independent of
her engineering plant (diesels or gas turbines), normal and combat electrical
requirements are met by turbogenerators using steam from the ship's plant.
Unless a ship has a steam generating capability equal to the requirements
of her turbines at full power and her electrical system at full load, something
has to give. You can reduce load or speed. Therefor, in combat,
electrical loads could conceivably reduce steam available for speed.
Most known flank speed data for warships is based on builder's and/or acceptance
trials. These trials probably don't represent the requirements placed
on the steam plant in combat situations. A modern warship's sustained
combat flank speed may be 2-3 knots less than the published trials figures.
The difference between the "Fletchers" rated flank speed between 1942 and
1945 was not just due to displacement "creep," but also to the loss of
available turbine steam to the increased electrical load of electronics
and power operated armament (but not to the extent of modern warships).
This is more complicated for modern CVs as their catapults are steam operated.
Steam is bled from the engineering plant to power the catapult piston for
launch. Aviation operations will place an additional requirement
for steam on the engineering plant, in addition to speed and electrical
If I remember correctly, mismanagement of steam input to catapults actually
drained the steam from the engineering plant of the British test carrier,
steadily reducing her speed to a creep. One would suspect that a
US CVN's engineering plant was designed to produce sufficient steam under
adverse conditions (sustained steaming, foul bottom, tropical waters, etc)
to maintain battle speeds, meet electrical power requirements for all those
radars, ECM/ECCM, etc., as well as feed the 4 catapults during combat air
operations. This would leave an excess of steam during less stressful
operations, which would be reduced by not operating the plant at max capacity
(shutting down 2 of 8 reactors, taking boilers off-line, etc). One
of Norman Friedman's points about the adoption of nuclear power in Russian
surface ships involves the electrical load needed to sustain modern naval
electronics. The Kirovs use the nuclear plant for cruising and generating
capacity and boost speed with the conventional steam plant. The need
for excess and readily available steam may even have been a factor in the
French decision to go nuclear with the De Gaulles.
Back to the
Naval Technical Board