The Savannah morning news., 1903-07-04
EFFECT OF WAVES ON SHIPS.
What Causes the Rolling and Pitch
ing of VesAeIs.

In an article on problems in naval
architecture, Engineering of London
refers to the important question
whether hollow or straight lines confer
the greatest advantage in a ship. If
a hollow line warship pitches more
than straight-hne ship her guns can
not be fired with the same degree of
accuracy as would otherwise be the
case. This is more important whore
bow fire is being utilized to the fullest
extent in a chasing fight, when the
cruiser must make her best speed. The
question, therefore, to be determined
is as to whether these hollow lines
confer an advantage in speed to COM
pensate for the alleged tendency to-
ward Increased pitching. The conten-
tention is made that even in Channel
steamers, where length is also restrict
ed owing to the limited dimensions of
harbors, it has not been found neces-
sary to adopt hollow lines. factor
in the pitching of the ship is the rela-
ton of the length of the ship to the
length or period of the wave; and in
the design of British cruisers attention
is said to be given to the fact that the
waves in the English channel-the
probable venue of our naval actions
of the future-are much shorter than
in the Atlantic, and that consequently
short ship will be more suitable there,
while on the Atlantic a long ship will
give a better result
1t would certainly be interesting if
the staff of a James Watt experiment
al institution could make a sufficient
ly long SERIES of observations to deter
mine the average or prevailing length
or periodicity of waves in the channels
surrounding the United Kingdom, as
( well as on the great oceans, with a
view to assisting in the design of the
type of ship, both as regards length
and lines, which would give the great
est comfort in rough weather. 1t would
be possible, for instance, to ascertain
exactly the effect of pitching on Vari-
GUS sections at the entry, and to de-
termine the relative advantages of v
and sections-whether they conduce
to, or reduce, pitching motion. Hav-
ing determined this, it would be de-
sirable, in the case of Channel steam
ers, where high speed is wanted, to as
certain by tank experiments the effect
OF such variation of section on the
speed of the ship. A kindred question
has reference to the cutting away of
the forefoot and its effect on turning
| on speed, and on pitching
A point which might be considered
with profit to the sea voyager is the
| influence of a high beam wind on n
ship with open deckwork. Even with
ordinary Channel steamers it is becon-
ing the fashion to have one or two
promenade decks above the nodded di
| mansions of the ship. while in Allan
tic liners three such decks are now
adopted, and our experience suggests
that such openwork forms extensive
| pockets" for the wind with the result
that the amplitude of rolling IA in
creased more than would be the case
! If the wind could escape, as is the case
with ship having no such open work
above the nodded structure The tur-
| ret ship and the whaleback ship were
| introduced to overcome a somewhat
kindred problem resulting from the ac
ton of sea water in the wells" 1t has
been shown that with a sidelong wind
the pressure on railway trains increases
materially with the number of wagons
used, because of "pocketing" of the
| wind between the wagons. Thus. with
trains of the same capacity, but fitted
IN one case with f1fty-ton wagons, and
IN the other with ten-ton wagons,
thereby greatly adding to the number
the wind pressure was increased $50
per cent. 1t would be interesting. adds
Engineering, to know to what extent
the propulsive efficiency of a ship is
decreased and amplitude of rolling in
creased by such high deck structures.