Evening star. [volume] (Washington, D.C.) 1854-1972, 1930-02-23
CAWTATION TESTS
CONDUCTED HERE
Naval Designers Watch Pro-
peIIer Action on Models
at Navy Yard.
Have YOU heard of cavitation?

The word is one which Is used almost
exclusively by designers of naval vessels
and their power plants, and while it
may not mean much to the layman, it
means a great deal to the naval de-
signer. who seeks the maximum in speed
from his power plant and the propellers
which push vessel through the water.
Just now cavitation is receiving a lot
of attention from the highly trained
technical men who design the craft
which uphold the power of Uncle Sam
on the high seas. If one of the new
10000-ton cruisers which the Govern
ment plans to build is a knot or two
slower than cruisers of a similar class
owned by an enemy power, it may
mean the destruction of the United
States ship. This disparity in speed is
likely to be caused by cavitation.
Briefly, cavitation is the condition OBJ
tanning when a propeller is driven
faster than can be accommodated by
the water in its vicinity. Propellers of
a vessel can be driven so fast that they
create a vacuum behind the blades.
which is not filled with water fast
enough to furnish the thrust which
comparatively imcompressible water
would furnish If it remained at the
blade of the propeller.
So cavitation is a real phenomenon
and the solving of the problems con-
nected with its manifestations have
very real value in war and peace times
If cavitation can be reduced or its eff
fects neutralized. marine engineers will
have partially solved the problem of
securing the utmost in marine speed
with the minimum power consumption
And reduction of cavitation some day
may mean winning or losing a naval
battle for the United States.
Scientists Conduct Tests.
In long, low building at the Wash
ington Navy Yard keen-eyed scientists
today are watching closely the results
of tests on models of destroyers and
cruisers made exactly like the larger
vessels will be, but on smaller scale,
and are discovering some facts that
may be of considerable benefit in max
ing Uncle Sans sea fighters the fastest
things af1oat. Delicate intricate and
highly sensitive instruments record the
facts on the small scale models as they
are drawn and propelled through the
water in q great basin 470 feet long.
made to reproduce as nearly as posi-
bic the actual conditions of a ship in
her own element. All over the United
States shipbuilders and constructors
watch the work at the model basin of
the Washington Navy Yard with the
interest they must show to keep abreast
OF the latest developments in marine
design. CaVltat1on is only one of the
many problems which still await solu-
ton, for even though marine construc-
ton has progressed considerably since
the first caveman set forth on the I'M
known sea in a dugout canoe, many
problems still remain to be solved.
Plan More Model Basins.
The experimental model basin is the
only one of its kind in this section of
the country. but it may have a COM
petitor in the private shipbuilding field
shortly. for ship construction con-
Germ at Newport News, Va. is consid-
ering building model basin. The
Navy Department now has plans for
three more model basins to handle ex-
periments on the three chief phases of
the work which will lead to advances
IN the scence of marine engineering and
construction. These three phases are:
Ship model experimental work, air.
plane and motor boat model work and
experimental work in connection with
shallow-draft craft, such as tugboats
and river craft.
The main use for the existence of
model basins has been the wish to OBJ
tain the fastest vessels for the mini
mum expenditure of power To deter
mine how marine design may be i'm
proved to obtain this end, the basin at
the washington Novy Yard was built
in 1898. and has continued to expand
and grow in importance until today it
is recognized as the main laboratory
for improvement in marine engineering
science.
The building housing the basin is of
brick with a steel trussed roof and a
monitor skylight nearly its entire length
Dimensions OF the water surface are
approximately 470 feet by AZ feet. the
depth is IA feet and more than l, 000, 900
gallons Of water are required to fill it.
The water is supplied by the city mains
iS r1nf tod ~,
of the lessened density Of city water
as compared with sea water. a COM
pensating factor of 2l2 per cent of diff
ference must be allowed in the compu-
tations of the craftsmen and marine
architects. In this basin models of
every ship OF Importance built by. the
United States Navy since 1898 have
been tested for speed, conformation and
other factors which govern that quality
known as "seaworthiness.
Propelled by Electric Motors.
On moving carriage propelled along
rails by great electric motors models Of
ships are drawn through the water at
speeds running up to 15 knots an hour,
while their own small propellers cleave
the water at their miniature sterns
This carriage is a huge affair. of more
than 40 tons in weight and moving at
such speed in such limited space. its
stopped from maximum speed within
a limited area, and for this purpose
many safety devices have been incorpo-
rated to prevent the great mass of steel
from leaving its rails and crashing
through the end of the building.
Why would it not be possible to
equip light cruisers with steps or flanges
which would give them something of
the speed Of hydroplanes and fast,
light speed boats equipped with such
devices?" one of the marine craftsmen
was asked.
Because" he said, these craft do
not get up enough speed to use the ma
rine steps and their construction would
be more apt to be a drag than help"
In this matter of Cavitation," he
vas asked, why would 1t not be pos
sible by a vane treatment of the bot
tom Of the ship to cause a depression
of the ships propellers at high speed
and this reduce the vacuum by getting
the propellers far below the surface?"