Delaware gazette and state journal. (Wilmington, Del.) 1883-1902, 1892-02-11
SHIPS OF Woop or uErA1.
An interesting Talk on the Topic OF
Throe Materials, Wood, Iron and Steel,
Used for shipbuilding.

on the subject of the materials used for
building ships appeared in last Sundays
Now York Times:
Tho three materials used in the con-
struction of ships in general are wood,
iron and steel. Wood has been in use
from time immemorial. Iron is only
about so years old, and steel is easily
within the memory of every man Of
moderate years. The Importance of The
three materials are inversely as stated,
steel being the most valuable, then iron,
and last wood. Noticeably is this so in
the construction of swift steamships, for
wood is unsuited TO the great engine
power nowadays put into ships; it can
not properly stand the strain.
II Is because of iron and steel that YES
sells OF such great size as are now being
built are possible. No better example
can be given than the Great Eastern. Of
$4,000 tons register and $50 feet long,
built of iron.
Iron ships are superior to wooden
ones in the following particulars: Light
ness combined with strength, durability
when properly treated, ease and cheap
ness OF construction and repair, and
safety when properly constructed and
sub-divlded. In wooden ships 1t has been
found that about one-half of the total
weight Of the ship is required for the
hull, whereas in iron ships only from
30 to 40 per cent of the weight is thus
taken up. For instance, in wooden
armored war ship, the weight of the
hull being 80 pdr cent of the displace-
ment leaves 30 per cent for the weights
70 be carried In an iron armored war
ship the weight lof the hull is only 40
per cent, leaving go per cent for weights
70 be carried.
The tensile strength of iron is from
10000 pounds to 10000 pounds per
square inch, and this strength can be
secured throughout all the metal used,
80 that the material worked into the ship
Is uniform and homogeneous. These are
: qualities wanting in wood; the greatest
care cannot eliminate such weak spots
rs are due toi the presence of knots,
crossgrain, hidden defects, &c. Gener-
ally, good sound timber may be said to
have a strength to resist pulling apart
(tensile strengih) of about ID, 900 pounds.
Another point to note is that iron is
elastic and wood is not, so that greater
margin of safety must he allowed the
latter than the former, hence greater
weight. This quality of lightness is
we'll illustrated by the chief constructor
Of the English navy, Mr.. w. H. White,
in his "Man,ial of Naval Architecture"
to which the writer of this article is in
debted for many facts Mr.. White says
British oak may fairly be taken as
the standard timber, and its weight per
cubic foot is about one-ninth that of
iron, while its ultimate tensile strength
might be about one-fifth that of iron.
Here, then, the timber apparently gains
st.. an in No r1It 90 at,
compared with its weight"
But there is no certainty that the
piece of tinber selected will reach the
average strength, and to guard against
defects not discoverable on the surface
of the wood and to compensate for the
want of elasticity, larger factor of
safety would have to be employed
E about 10 for timber as against four or
five for iron.
Gas a simple illustration, take tie
bar oak one square foot in sectional
area; it would probably have an ulti-
mate terlsile strength of $40 tons,
(nearly 5000 pounds per square inch
but would only be trusted with NOV
a.qge,,,a5 of So or go tons. An iron bar
re ,viio, weight would have a sectional
uhat i. anu one-ninth square foot and a
~ ainetrength of 800 tons, but owing
casticity and the confidence felt
Il hadn' Uniformity of strength, IL would
he Whole ed with load of 70 or 80 tons,
lstant. Estate the comparison somewhat
he Office lily, an iron bar capable of safely
beet of fieing the same load as the oak bar
ne grounonly have tensile strength of,
he roof, 10 tons, which would be eauiva-
1rnace. o a sectional area of 10 square
eIe.ned Fl. The oak bar would weigh "a
MI lren Is per foot of length; the equiva-
eli W to,ar of iron would weigh about As
sot Goods per foot of length"
urh to olen in ship-building it comes to
My Cling pieces together, as, for ih-
l5m ance, in making ships keel or her
'Itible beams, the weakness caused by
1.-THE fing the pieces of wood together be-
ced lines an element of strength in rivet-
7fEe dothe iron. No matter how it may be
Nm anessary to treat the pieces of metal,
he nefether by riveting or yelling or by
b alargle irons, the iron stands far above
efore wood in resistance of tensile strains.
eally IS only when resisting strains of com
he fiession that there is tendency of iron
uildiiates to buckle, and this is guarded
ames ainst by making the plates thicker
an is required for other strains or by
.s1,,yinforcing them.
raze, Metal permits of q variety of shapes
ows ntirely beyond the possibilities of
an wood, and in this way a ship can be
~ 70 strengthened and fashioned so as to re-
ton, sist strains without resorting to clumsy
sv Membranes, such as the old knees,
I dead wood, and extra frames so neces-
tr;t Bary to wooden ships safety and that
!, :, occupied so much valuable space.
g Durability is quality of iron that is
m not yet thoroughly determined. In gem
arc eral, wooden ship may be said to last
''' about is years. Some last longer, but
there will be much patching and renew
ing to be done. The rules Of Lloyds
~ allow about IA years as the average
b durability of the best-nuilt timber YES.
b sells.
Iron is not subject to the internal
sources of decay to which wood is liable.
Worms and marine animals cannot in
jure it, nor will it rot from imperfect
ventilation. Neither can the parts worl,
loose from the motion and straining Of
the ship, allowing water to get in and
cause decay. The danger to iron lies in
the rusting or corroson, especially in
the underwater parts, outside from the
sea water and inside from the bilge
water. The only prevention is careful
watching, cleaning and painting, and
even with all this supervision galvanic
action is likely to do some damage
Therefore, the life Of an iron ship il
limited, and in the present state Of
knowledge of the subject may be Sci
down as approximately 30 years, for
though ship will last longer, extensive
repairs will have to be made that will
cost considerable money