Evening star., 1901-07-20
HEIGHT OF OCEAN WAVES.

Largest Ever Observed Were Forty
Feet From Trough to Crest.
From the Scientific American
There has been a good deal written lately
about the height of ocean waves. An arti-
Gle In our contemporary knowledge has
been largely quoted In which the writer
gives some very interesting figures regard
ing observations made in the South In
dian ocean. between the Cape of Good
Hope and the Isles of st. Paul and New
Amsterdam. this being a region where
westerly winds prevail almost without a
change the year around. 1t was in this To-
cality that the highest waves on record,
according to the writer. were observed the
measurement of thirty waves at various
times during the day showing an average
height of 23.63 feet. the largest of observed
waves being 37.53 feet in height Lieu
tenant Paris. who made the observation
had to climb to the twenty-second rung
of the shrouds before he obtained the level
of the crest.
In these days of colossal steamers with
towering superstructures, it Is not neces-
sary to do any climbing of the shrouds to
observe the height of the waves Going
ftom deck to deck, the passenger, with
little experience. can find position in
which sitting or standing the crest of the
highest waves will just coincide with the
line drawn from his eye to the horizon.
u
officers of the ship what is the height of
the deck on which he is standing; adding
to this the distance from the deck to his
eye. he can obtain a fairly approximate
estimate of the height of the waves. In
making an estimate of this kind however
care should be taken to make the obser-
Vat1ons when the vessel is in the trough
between two big seas. and on a fairly even
keel. the observer standing amidships and
as near as possible to the center line of
the vessel The upper deck of the big
gest OF the Atlantic steamships is from 30
to 81 feet above the normal waterline, and
1t is very rarely. even in the heaviest At
lantic storms, that the crest of a wave will
reach the height of the observers eye
When it does, it is probable that the ship
herself is moving over one of the cross
seas which frequently intersect the regular
line of Atlantic rollers.
Perhaps the most accurate gauging of the
height OF ocean waves ever carried out
that which was recently discussed in
a paper before the Institution of Civil En-
gireers Of Great Britain by William Shield
who gave the results of observations made
during storm at Peterhead, North Britain
when the wind varied in velocity from so
to 90 miles hour. The method of obser-
walton was as follows: Sights were taken
along the breakwater with a view to as
certaining the height of the waves they
ran into the bay between the breakwater
and the opposite shore. The water along
the line of the sights was from go to 63
feet in depth. The sights. which were 61a
feet in height. were placed at intervals of
40 feet along the coping of the breakwater,
the level of which is % feet above low
water. AS the tide gauge registered feet
at the time the observations were taken,
the line of sight must have been 1917 feet
above saltwater level. According tc Mr..
Shield. wave after wave passed by carry
ing an unbroken crest at least feet above
the line of sight, and, therefore, 22h feet
above the saltwater level. The wave
period varied from 13 to II seconds, and
the length Of the waves between 800 and
700 feet. Assuming that the troughs of the
waves were as far below the saltwater
level as their crests were above 1t. the
height Of the waves would appear to have
been IS feet; but it is recorded that the flat
ness of the trough curve as compared with
the curve Of the crest seemed to indicate
that the height Of the crest above and the
depth Of the trough below the saltwater
level were not identical. 1t was considered
by the author of the paper that the crests
OF the waves were to some extent raised
by the friction of the sea-bed. Hence, 1t
was estimated that. on the ground that the
volume Of water above the saltwater level
must correspond with that OF the trough
below 1t. the height Of the waves from
trough to crest closely approximated to 40
feet. These figures, it will be observed. are
greater than those recorded as having been
observed in the South Indian ocean and
elsewhere. due allowance being made for
the tendency of the waves to become steep
er and loftier as the friction of the sea-
bed tells uDOn them,