The New York herald., 1879-02-08
Variations in the Dimensions Of
Iron Steamships.
The DANGER OF UNEQUAL EXPANSION.
Some Of the Disasters Attrib-
uted TO This Cause.
THE COMPOSITE PLAN

In second interview with MIR. Norman Wizard the
subject of the unequal expansion and contraction OF
iron In ships under differing degrees of temperature
was resumed in greater detail. and several illustra-
tions were adduced which tend to the force of
this startling theory. His confidence that it is the
real explanation Of the loss of many steamers
whose fate has until been wrapt in mystery
amounts to almost absolute certainty. Both sci
entiic knowledge and practical experience support
it, and the fact that ship builders. ship and
ship insurers have not before caused the matter to be
thoroughly sfted can only be accounted for by the
reason embodied in his own remarks:-
Immense vested interests" said he, ''are threat
ened with disturbance should it be conclusvely
demonstrated that the iron ships now ahoat are so
many death traps If ships made absolutely
safe except as against the natural chances of
shipwreck. the rates of insurance would of course
go down in proportion to the lessening of the risk.
Underwriters prefer certain degree of danger which
may serve as q constant stimulus of business to q
guarantee Of safety. You can't expect men who
have invested their capital in the building of iron
ships to favor their substitution by composite ones.
Nor can you expect that the companies which now
own large numbers of iron steamships will indorse
the invention OF anything superior to them"
VARIATION LENGTH.
'But to resume, Mr.. Ward the subject Of heat and
the appreciable variation of the dmensions?'
In steamship, say 400 feet long. its length. with
increased temperature of eight degrees would be
one inch greater. If the temperature eighty
degrees it would be increased from eight to ten
inches. OF the effect of unequal expansion con-
traction in iron there two three forcible exam
pies in the report of the Joint Committee Ord
nance to the Fortieth Congress- third session.
They remarked that hollow cast guns seemed
liable to species Of cracks peculiar to themselves
ffteen-inch gun burst open in it's entire length
from cooling too rapidly making detonation like the
firing of six xpounder. Another fifteen inch gun,
just after the removal of the barrel and while
water was passing through the bore at the rate of
eighteen gallons per minute. suddenly cracked
der owing to the too rapid falling of the temperature
Still another gun of the cabre burst from the
cause. Now. if such was the effect of unequal
expansion contraction in such great masses Of
iron large pieces of ordnance what must it be
In the thin shell Of an iron steamship?
The appearance of the outer skin Of iron vessel
Is often very deceptive have stood under one after
1t had been the dry dock account OF leaks age
and have been unable to discover where the imper-
fection lay. She foated of, and aftcrward
when the boilers had been heated again. tho leakage
would recommence. The unequal expansion evil
IDENTIFY the cause. She was again put upon the dock
and small crack was found along her side. When
she cool this closed as to be scarcely per-
ceptible.
FATE CAPTAIN.
''You probably remember the overturning of the
British turret war ship The Captain. Her bottom.
frame and inner and outer skins were composed of
iron. From line four Ave feet below the water
mark to line about the same distance above she
carried heavy belt of iron plating. eight or nine
inches in thickness. The coal bunkers situated
along her sides, below the lower edge of the iron
plating. This fixed to the sides, resting upon o
shoulder below, and fastened at intervals with
angle-rons. supporting also q thin inner skin
The butt joints OF the iron plating were not
fastened or riveted. but the ends were brought
quite together. Had the temperature been re-
duced it would merely have caused the
butt joints to open without putting any strain upon
the other parts of the structure. IT, on the other
hand, the temperature of the plates increased
a. to be much higher than that of the lower part of
the hull the immense force of the expansion would
% can very readily be seen, be than sufficient
TO break the bottom in two transversely. This
what actually took place. 1t noticed ut the time
OF the accident--when she went down with all on
board-that one of the coal bunkers below the belt
Of plating first filed with water and with such sud
dcnness that she Immediately careened over. slowly
at first, but then rapidly, until she was lost from
sight. This was on her very first voyage
The coal in one of her bunkcrs was probably pretty
nearly used up thus while it had previously acted
non-conductor, permitting the heat from the
boilers to affect the density of the iron plating. the
excessive expansion of which broke the bottom in
two. This and other terrible disasters have forced
the English Admiralty and English shipbudcrs to
recognize the advantages of having iron vessels
covered with outside skins of wood. 1t has been
found from actual trials that iron ships very
liable TO get foul at their bottoms. and
pedient heretofore resorted to in order to
prevent this has proved of any avail. Be-
sides the serious expense of frequently docking iron
ships for the purpose of cleaning their bottoms the
founess to which they are subject IN all seas and
climates causes great reduction of their speed. In
one case 1t was proved that ship capable, when in
good order of going fourteen knots an hour could
make when foul only twelve knots. and that exactly
twice as much coal was required per hour in her
furnaces to raise her speed to the original rate This
tact implies great item of wooden ship is
not apt to foul because her bottom is sheahed with
copper"
THERMo- Mo-ELEcTRrcAL INFLUENCE.
'Cannot copper be used for protecting iron hullsT'
mo. sir.
"why -
On account OF the galvanc action which il excited
aud which causes such rapid oxdizaton of the iron
part of the structure that 1t would he all destroyed
IN q very few weeks. On one occasion, having built
o wooden vessel for the government and desiring to
make her light possible. fastened her sheath
ing on with iron rivets, covered with copper. She
was launched and lay only six weeks in the water
when she began to leak much that IL was necessary
to place her ON dry dock and make q thorough ex-
animation. found that nearly all the holes from
the fastening through the bottom were open and
the ship just the point of falling to
pieces. The bolts in many instances reduced to
the size of knitting needles could find hardly one
which retained its whole original length. and none at
all which retained it's original diameter. All of the
fastenings had to be renewed with copper bolts"
HUILs.
What In the principle OF this strange ofcctY
ut Is very little understood 1t only occurs when
two metals are In contact the presence of salt
water. each having different thcrmoelectrical
qualities"
"But what bearing has this fact upon the security
of purely iron shipsr
"H 1t IL attempted to sheathc them with copper ms
II now being done quite often the iron bottom must
hrst be covered with plankng fastened 10 the sides
with iron bolts. Over this s placed another layer of
wood. which Ia secured to the frst with copper
screws or else with treenails. the former penetrating
only through part of the inner wooden skin. The
displacement OF the ship the area OF its
section is thus increased well it's weight At
the expense OF these disadvantages thereto ore, may
iron ships bc gafcly sheathcd with copper. II is,
however. necessary that there should be absolutely
NO contact of the two antagonistic metals.
III have gone into this digressun in order show
that shpowners are beginning act upon the u, s-
at.a Al.A