Wars anal Wayzring
191
channel combines features of both tank and tunnel, by circulating
water past a stationary model as in the tunnel, While retaining the
free water surface of the tank. In the NPL circulating channel some
one and a half million gallons of water are kept moving in a highly
ordered ow. Although ofcially commissioned only in 1967, the
channel has already proved a valuable asset in various ship designs
including that of Cunard’s Queen Elizabeth ][
.
Many investigations in the laboratory centre on improving the
speed of ships by reducing resistance met by hulls moving through
water. The two principal causes of this hydrodynamic drag are the
frictional resistance resulting from the viscosity of the water, which
‘sticks’ to the submerged parts of the hull, and the wavemaking
(Froude) resistance produced as the bow pushes away the water and
creates a surface wave. Both types of resistance are closely related
and, until the advent of the circulating channel, very difcult to
distinguish in some advanced hull designs. Alec Silverleaf, the
Deputy Director of NFL, gives an interesting example of this,
found with the bulbous and ram bows built on many modern cargo
ships. The theory behind these projecting bow structures is that the
protrusion acts as a ‘false’ bow to create a wave system which at least
in part cancels out that of the ‘real’ bow. However, the NPL
scientists found that the novel bow—forms often have a much more
signicant effect on the viscous drag than on the wave resistance
because a well—shaped and suitably placed ‘snout’ can radically alter
and improve the ow of the water around the hull. The practical
elfect of this nding is that later designs can take advantage of the
benecial eects of large ram and bulbous bows without incurring
some of their penalties, particularly the indi"erent performance in
any but the calmest of seas, by modifying the design.
Thanks to Froude, the ndings in the laboratory are generally
conrmed in the full—scale ship, but neverheless actual performance
at sea forms an important source of feedback for studies on models.
One of the principal activities of the British Ship Research Associa—
tion (BSRA), since it was formed in 1945, has been to make full—
scale tests and trials on ships. And in 1958 agreement was reached
between BSRA, the National Institute of Oceanography and NPL
to co—operate in a joint programme of research into the sea—going
qualities of ships. Naturally enough, trials at sea involve far more
unknowns than one would expect in the carefully controlled con—
ditions of the laboratory. Take for example the question of collecting
191
channel combines features of both tank and tunnel, by circulating
water past a stationary model as in the tunnel, While retaining the
free water surface of the tank. In the NPL circulating channel some
one and a half million gallons of water are kept moving in a highly
ordered ow. Although ofcially commissioned only in 1967, the
channel has already proved a valuable asset in various ship designs
including that of Cunard’s Queen Elizabeth ][
.
Many investigations in the laboratory centre on improving the
speed of ships by reducing resistance met by hulls moving through
water. The two principal causes of this hydrodynamic drag are the
frictional resistance resulting from the viscosity of the water, which
‘sticks’ to the submerged parts of the hull, and the wavemaking
(Froude) resistance produced as the bow pushes away the water and
creates a surface wave. Both types of resistance are closely related
and, until the advent of the circulating channel, very difcult to
distinguish in some advanced hull designs. Alec Silverleaf, the
Deputy Director of NFL, gives an interesting example of this,
found with the bulbous and ram bows built on many modern cargo
ships. The theory behind these projecting bow structures is that the
protrusion acts as a ‘false’ bow to create a wave system which at least
in part cancels out that of the ‘real’ bow. However, the NPL
scientists found that the novel bow—forms often have a much more
signicant effect on the viscous drag than on the wave resistance
because a well—shaped and suitably placed ‘snout’ can radically alter
and improve the ow of the water around the hull. The practical
elfect of this nding is that later designs can take advantage of the
benecial eects of large ram and bulbous bows without incurring
some of their penalties, particularly the indi"erent performance in
any but the calmest of seas, by modifying the design.
Thanks to Froude, the ndings in the laboratory are generally
conrmed in the full—scale ship, but neverheless actual performance
at sea forms an important source of feedback for studies on models.
One of the principal activities of the British Ship Research Associa—
tion (BSRA), since it was formed in 1945, has been to make full—
scale tests and trials on ships. And in 1958 agreement was reached
between BSRA, the National Institute of Oceanography and NPL
to co—operate in a joint programme of research into the sea—going
qualities of ships. Naturally enough, trials at sea involve far more
unknowns than one would expect in the carefully controlled con—
ditions of the laboratory. Take for example the question of collecting