The Washington times., 1901-09-07
SHEATHlNG OF WARSHIPS.

on Naval Progress recently issued by
the Navy Department. to the sheathing OF
ships, Section of the volume being
given up entirely to this subject. Tho
trend of opinion abroad is given as fol
lows:
The practice of sheathing war vessels
with wood and copper which had in re-
cent years become so common was in
tended primarily to enable the vessels TO
have continued cleanness of bottom, and
thus maintain a minimum resistance to
propulsion, even though they had TO keep
the sea for long periods and We're for
years on foreign stations. where there
was no suitable drydocking accommoda-
tions and in waters where they were ex-
posed to very rapid fouling.
Another advantage claimed for sheath
ing war vessels is that the wood planking
outside a steel skin adds to its capability
of taking hard rubs, and thus we find
about six years ago Sir William White
stating: For many of the services which
have to be performed by the smaller
classes of H. NJ. ships, it is most desira-
BILE to have stout wood bottom protect
ed by copper. Bare thin iron or steel
plating is unsuitable. under such condi-
tions, both to withstand the shocks of
the OI
rapid corrosion in tropical waters con-
tanning large quantities OF vegetable
matter; and, he pointed out, that while
formerly such small vessels were of COM
posite construction, now sheathed vessels
were employed
THE practice of sheathing the bottoms
of vessels is however. not without serious
drawbacks, foremost among which is the
bt,t hi ha
sheathing was in every way satisfactory
would be of minor Importance, and would
be possibly almost neutralized by the les
sened expenditure of fuel in maintaining
high speed, and by the saving effected
by less frequent docking and cleaning. In
bygone years the adoption of iron bolts in
fastening the sheathing resulted in their
rapid deterioration, owing 20 galvanic ac-
ton, but now it is usual to adopt bolts
of naval brass; and as long as these me-
tai bolts can be kept perfectly water
tight. and the salt water prevented from
getting into contact with the steel plating
and framing. all is well This desirable
condition is, however, not always main
tafned, and. owing to the failure to alb
soiutely exclude sea water, in some cases
the steel plating has been badly attacked.
while In other instances the fitting of the
sea valves and other connections have
been seriously damaged. During August
1900. H NJ. cruiser Ariadne was found to
be leaking at her moorings at Portsmouth,
and 1t was assumed that Kingston valve
mad been left open, but after the vessel
was dry docked it was ascertained that
the corrosion of the bolts both inside and
outside the hun had been so extensive
that the mounting of one of the under
water fittings had fallen OFF, allowing a
great thrush OF water. The corrosion of
the outer bolts of II. NJ. cruiser Spartiate,
a sister vessel, had previously been de-
tt~cst- fts.rl
found that the inner bolts had also been
corroded Similar experiences have oc-
CURED in foreign war vessels which have
wood and copper sheathing, and 1t Is said
that the Russian admiralty is dispensing
with wood and copper sheathing in vessels
now being built, although in the new coast
defence ironclad General Admiral Aprak-
sin, now under construction, the bottom
will be wood sheathed but covered with
steel instead of copper sheets
There Is another objection to the use
of copper sheathing which appears to be
well grounded, viz, its Injurious effect on
vessels which are not so sheathed. owing
to a gaivanic current being set up and
severe corrosion ensuing III the unsheath-
ed vessel. Such an experience, IL is stated,
recently occurred to steel vessel OF the
Italian navy moored to the same buoy
with copper -sheathed vessel and a SINH
lar occurrence is reported from kronstadt
Undoubtedly the great reason for using
copper sheathfng is because of its anti
fouling qualities but even in TINS respect
its efficacy is being questioned, and ap-
parently rot without reason. According
to the 'Kronstadt Vestnik.' the Russian
first-class cruiser Pamyat Azova. which
had copper-sheathed bottom, always
showed on dry docking at Vladivostock a
very foul bottom, whereas other ships not
copper sheathed, but coated with an anti
fouling composition, showed much less
marine growth, although both classes of
vessels were stationed in the same wa
ters. 1t also appears that Few years
.tasaf ha
Just related. il was decided to coat a
few square yards on the bottom of the
cruiser Pamyat Azova with Holzapfefs
anti-fouling composition, and when In
the following year the vessel was again
dry docked the composition was perfectly
clean. This trial has been repeated on
larger scale, and should it again prove
successful. as is probable, the question
arises, Why continue at such an enor-
nous expense to apply wood and copper
sheathing? 1t must be remembered that
in recent years there have been great
advances made in the manufacture OF
compositions, the skill of the
most eminent chemists having been re-
Questioned to secure improved mixtures.
and it is only reasonable to anticipate
that a composition can be manufactured
with at least as effective anti-foulinS
qualities as copper sheathing.
1T Is stated that the Germans will dis
continue sheathnG their large ships. They
claim that recent improvements in anti
fouling paints etc, Will render 1t unnec-
essary to dock a ship oftener than once
a year, and in that time their experience
shows that the outboard delivery valleys
and other openings in the underwater
body become so foul that even a sheath
I'd ship must be docked yearly, and there
fore no advantage is gained by sheath
ing.
'The average speed of a ship that has
been shcathed will be less than that of
IN unsheathed ship with displacement
hat is much less than that of the sheath
I'd ship, corresponding to the increased
due to the sheathing. The
ship Will have a higher max
mum speed when clean, and after
years cruising in the worst tropical |
waters she will be as fast If not faster |
han the sheathed ship of the same horse
power. but having a displacement great |
n by the extra displacement due to her |
;heathing. The expense of sheathing and
he difficulties and expense of repairing
sheathed ships are so great as to decide |
n favor of unsheathed ships.
''The Italian Minister of Marine states |
hat the Italian battleShips and armored |
.ruisers are not TO be sheathed. He is of !
he opinion that the expense is too great |
o make it advisable. 1t might save fire. |
luent docking. but il is found to be nee |
'ssary to dock ships not only to clean |
heir hulls but also to examine the un |
ler-water fittings. and the sheathing |
loes not obviate the necessity of docking |
The anti-corrosive and anti |
ouling paints used by the Italian navy, |
hough not perfect, are very good and /!
leep the hulls of their ships fairly well |
small cruisers destined for long cruises |
n foreign waters might be sheathed to |
ldvantage, but the cost for larger ships |
nd the increased displacement caused by |
render it inadvisable for them