Crawford avalanche. (Grayling, Mich.) 1879-19??, 1892-08-25
CRAWLING MICHIGAN. THURSDAY AUGUST 25. 1892
MAY az BROKEN EASILY.
Ships Propellers Sometimes Disabled ey
Trfning Causes--Corrosion I'm WateR

Trtning Causes-Corrosion In WaveN
The propeller of a steamer Is an
Insignificant object compared with
the huge body IL propels against the
forces OF wave and wind,
but the Brooklyn Eagle says they
come to grief frequently in a variety
of waves A few days ago the red ID
steamer Venezuela, in a calm sea,
without "a breath Of wind almost,
suddenly lost one blade of her screw,
just as suddenly and with as little
cause or notice as oyerripe fruit drops
from its parent bough Around the
dry docks are numbers Of gigantic
propellers, and In one stage or other
OF dilapidatiOn. Some are cast In the
solid, that is TO say, the hub through
which the shaft passes and the fans
which extend from 1t are one solid
casting. Others are built, or cast,
rather, in sections; the hub Is one
and each fan or blade Is another,
which fit into bases made for them
in the hub, where they are screwed
on by huge bolts that are set in the
hub casting. Where one fan or blade
is broken It is easily replaced, as the
makers retain the models OF all
wheels or propellers, as they are In
differently called, which they cast.
Then the entire wheel is not rend red
useless, as in the case when solidly
cast propeller, like the Venezuela's,
comes to grief. 1t is extraordinary
to see the proportion of vessels that
arrive having received some damage
to their kpropellers. Occasionally
damage is done by the shaft racing,
as it is technically called. That is
caused by the steamship plunging
head on into the trough Of a big sea
and so elevating the stern and the
propeller that 1t is completely out Of
water, and being suddenly rid Of the
resistance the engine runs away, SO to
speak, just as an ordinary engine will
do when driving belt slips off or
breaks Occasionally propellers are
broken by striking floating logs orice
and rarely by striking whale or
large fish, when it is much the worse
for the fish.
But there is one curious fact always
noticeable about propellers; that is
that the extremities of the blades
are eaten away as though by some
corrosive acid. They are pierced with
holes of greater or lesser depth, which
weakens the points of the fans SO that
they snap off These corrosions are
said to be caused by the action Of the
water, but it seems strange that the
wearing should take the form OF
honeycombing the mental instead of
wearing 1T away smoothly as the mere
friction Of striking the water might
be supposed to do. Recently screws
or propellers are made of different
combinations Of brass and other
metals, especially for steam yachts,
and are very costly. A short time
ago Pierpont Morgan's yacht struck a
rock in the sound. The force OF the
blow smashed one blade clean off, al
though fastened on by eight or ten
two-inch bolts secured by massive
nuts, and the second blade was curled
up by the blow just like a sheet OF
lead. This wheel was only a three
bladed one, and yet ii cost the COM
paratively enormous sum OF 81, 800.
1t was made OF composition metal
resembling brass in color, called May
anese bronze. In large ocean steam
ships. If the propellers are not Of one
solid casting, it is usual to cover the
nuts and bolt points which fasten the
fans to the hub with a cement. This
is so tenacious and becomes so hard
when once set that it rarely breaks
until its removal becomes necessary,
when it gives the workmen a hard
tussle TO remove il.