39 
FOI^EST AND STREAM. 
i^o^. 13, mi. 
Notes on the Tacht Defender a>ndL the Use of 
Aluminum in Marine Construction, 
BY EICHMOlirD PEAKSON' HOBSOK, ASSISTANT NAVAL 
CONSTKUGTOR, UNITED STATES NAVY. 
Eeprinted by permissioa from the Proceedings of the ITnited * 
States Naval Institute. 
Copyrighted by the U. S. iSowaZ Institute. 
(Continued from page 374.) 
The features that determine cost ia a structure, are: first, 
tlie cost of production, or first coat; second, the cost of main- 
tenance, or care: third, the length of life. 
D,— COIVIPABISON FOR TTEST COST. 
The cost of production, or first cost, ia made up of cost of 
material as supplied by the dealer or manufacturer, cost of 
labor expended in construction, deterioration of plant en- 
tailed, and interest on capital invested. The cost of labor is 
here taken to include draughting, superintendence, supply 
of power, etc, 
I. Cost of Material. 
a. Rolled Material. — The cost of ordinary mild steel used 
in hull construction may be taken at 2 cents per pound for 
both plates and shapes. 
The cost of aluminum has not reached a steady level, con- 
tinuing naturally to fall veith the increase and improvement 
In methods of production. Roughly speaking, this increase 
in production has doubled each year for several years past, 
and though, for other causes, the fall in price has not been 
so rapid, it has been pronounced, and must be expected to 
continue for some time to come. 
It is difficult, therefore, to assign to aluminum a definite 
value, and any value assigned must be considered as only 
momentary. For the purpose of comparison, however, the 
cost of rolled aluminum at the present time may be taken at 
40 cents per pound for plates and 60 cents per pound for 
shapes, giving, compared with steel, the ratios per unit 
weight of 30 and 30, respectively. 
(1) Plates. — As seen above, the ratio of weights for steel 
and aluminum in tension is .5 for equal ultimate strength, 
and .35 for equal elastic strengths. For plates, therefore, 
the ratios of cost in the two cases are 10 and 7, respectively. 
The ratio of weights of plates for equal bending moments 
is .44 when working to the ultimate limit and. 36 when work- 
ing to the elastic limit. The ratios of costs, therefore, are 
8.8 and 7.3, respectively. 
The ratio of weight for equal stiffness is .648; the ratio of 
costs, therefore, is 9.6. 
(3) Shapes of proportional dimensions. 
The ratio of weights for equal bending moments when 
working to the ultimate limit is .55 for I beams and .58 for 
angles. The ratios of costs, therefore, are 16 and 17, respect- 
ively. 
The similar ratios when working to the elastic limit are 
for weight .37 for I beams and .4 for angles, and for cost 11 
for I beams and 12 for angles. 
The ratio of weights forequal stiffness is .4for I beams and 
,63 for angles. The ratios of costs, therefore, are 12 and 18, 
respectively. 
b. Cast Material.— It will appear below, if not already 
evident, that aluminum is unfitted lor heavy ship castings, 
such as stems, steruposts, shaft struts, etc., by nature of its 
small resistance to unusual violent shocks. The compari- 
son, therefore, need extend only to small castings for fittings. 
The cost of cast-steel for hull fittings may be taken gener- 
ally at 10 cents per pound. The cost of cast-aluminum for 
the same fittings may be taken at 60 cents per pound. The 
ratio of costs, therefore, per unit weight, is 6. 
In the range of cast hull fittings, the castings and parts of 
ca.stings serve the function of covering like plates, of stiff- 
ness like shapes, and attachments like simple bars. 
Some castings and some parts of castings are designed 
with special regard to ultimate resistance, and others are de- 
signed with special regard to elastic resistance. The resist- 
ance in some cases is simple, in others compound. Taking a 
general mean for equality of resistance, the ratio of weight 
is .48. The ratio of costs therefore, is 3.9. 
Many cast hull fittings are made sometimes of cast steel, 
sometimes of cast brass; many are made exclusively of cast 
brass. It is therefore interesting to note that the compari- 
son of aluminum with brass in these cases would give a ratio 
of weight of about .3, and of cost about .9. Recalling, too, 
that the two metals are more or less alike in relative softne.ss 
and ease of working, it may be said roughly that the alumi- 
num fittings, giving the same strength as brass fittings, have 
the same cost, with only one-third the weight. 
It should be borne in mind, however, that this comparison, 
as also the comparisons with steel, assumes a degi-ee of per- 
fection in casting aluminum scarcely warranted at the pre- 
sent moment. It is given, however, in view of the rapid 
progress being constantly made in the new art of casting 
aluminum. 
S. Cost of Labor. 
a. For Rolled Material. (!) Hullworkproper.—Foraieel, 
the cost of labor ia large hull work, plates and shapes may 
be taken at 4 cents per pound. For aluminum, on account 
of its newness and limited application, definite figures or 
results, and estimates of the coat of labor in construction are 
lacking, and, despite of efforts, have not been attainable. 
The comparisons, therefore, must be limited to a general ap- 
preciation only. 
The term labor, in estimates of hull construction, includes 
all operations of transportation and handling in yard and 
in shops, all operations of preparation of the material, 
laying off, punching, shearing, planing, bending, flanging, 
trueing; all operations of adjusting and securing in place, 
bolting, drilling, riveting. 
In operations of transportation, handling and adjusting, 
the great lightness of aluminum work, less than half the 
weight of corresponding stetl work, permits of marked econ- 
omy in the number of men and length of time required. 
In operations of tool work, planing, shearing, chipping, 
drilling, etc., the greater softness of aluminum insures a 
similar marked economy. The same feature of softness gives 
a marked economy iu riveting, all work being riveted cold, 
doing away with the portable forges, and reducing the num- 
ber of riveting gangs. 
On the other hand, the greater elastic elongation, and the 
immensely smaller ultimate elongation of aluminum, cause 
the operation of shaping, rolling, bending, flanging plates, 
bending and trueing shapes, to be more difficult and more 
delicate, requiring longer time and greater skill. This draw- 
back, evidently, is much more pronounced for shapes than 
for plates, the operation of trueing under the beam set in- 
volving, indeed, danger of destroying the integrity of the 
shapes. 
The relative importance or amount of labor in these vari- 
ous operations depends evidently on the nature of the piece 
of work. Taking hull work throughout, and considering 
all the operations involved, the advantage sets emphatically 
to the side of alumin um in the case of plates, but is probably 
against aluminum in the case of shapes. 
For the sake of continuing the numerical comparison, the 
advantage of aluminum over steel for plates is estimated at 
35 per cent,, while the advantage of steel over aluminum for 
shapes will be taken at the same figure. These figures, how- 
ever, must be regarded as results of inductive judgment only. 
Thus for aluminum, the cost of labor in large hull work is 
taken for plates at three-fourths, and for shapes at five- 
fourths the cost of steel for the same work. 
Taking the weight ratios roughly at one-half, the cost of 
labor becomes for plate work 6 cents per pound, and for 
shapes 10 cents per pound. 
(2) Hull fittings.— For rolled steel, the cost of labor in hull 
fittings may be taken broadly at 20 cents per pound. 
The observations on the comparison for hull work hold in 
general for hull fittings. The operations of transportation 
and handling, however, become of less consfqueuce, reducing 
the advantage of aluminum. On the other nand, the opera 
tions of shaping and trueing become, likewise, of less conse- 
quence, while the operations of small tool work, chipping, 
drilling, etc , become more pronounced in favor of aluminum. 
For the present purpose, therefore, the price ratio may be 
taken at three quarters for shapes as well as plates; with the 
same weight ratio, the cost of labor for aluminum hull fit- 
tings becomes 30 cents per pound. 
7j. For Vast Material. — Confining the comparison, for the 
same reason as given above, to small castings for hull fit- 
tings, the cost of labor for steel castings may be taken 
broadly at 12 cents per pound. The co.'*t of labor for alumi- 
num castings for the same fittings may be taken at 16 cents 
per pound, giving a cost ratio of about two-thirds, using the 
same weight ratio of one-half. 
S. Other Costs. 
All other costs, including deterioration of plant, interest 
on capital invested, shop expense, supply of power, drafting, 
superintendence, etc., may be grouped together. For steel 
work the cost of the whole group may be taken at 25 per 
cent, of the cost of labor, in which the allowance for deteri- 
oration of plant is taken at about 10 per cent, per year, and 
the interest on capital invested at about 10 per cent, per 
year. 
For aluminum, it is evident that the lightness and soft- 
ness will materially reduce the cost of deterioration of plant 
and shop expense, requiring less power, with less strain on 
machines, and less usure and dressing of tools. The group 
cost may be taken at four-fifths the cost for steel work. 
These rates give the following results: 
For Boiled Material. 
Cost of Group 
Labor. Cost. 
For steel hull work, plate.s and shapes ,, 4c. per lb. leper lb. 
For aluminum hull work, plates 6c. per lb. 1.6c. per lb. 
For aluminum hull work, shapes ,,,,10c. per lb. 2c. per lb. 
For sleel hull flttioB's, plates and shapes 20c. per lb. .5c. per lb. 
For aluminum hull flitings, plates and shapes. 30c. per lb. 8c. per lb. 
JFov Ca.st Material. 
For steel hull fitilnfra 12c. per lb. 3c. per lb. 
For aluminum hull flttings... .........Itc, per lb. 4. tic. perlb. 
4. Summation for First Cost. 
The results thus found for the elements making up first 
cost are assembled in the following table: 
FIRST COST, CENTS PER LB. 
For Hull Work 
Places 
Shape.s . . . . , 
For HuLii Fit 
tings: 
Plate work.. 
Shapes 
Cast fltnngs 
Steel. 
Alomxnum. 
10 
1.6 
2 
8 
8 
4.8 
47.6 
72 
78 
98 
80.8 
1^ 
tea 
"5 a 
.43 
.48 
.43 
.48 
.46 
IS 
3.83 
4.98 
1.24 
1.74 
1.48 
The striking feature of this table is the reduced ratio of 
total costs, due to the fact that cost of material in which 
steel has so heavy an advantage is but one item, while cost 
of labor and other costs are items of much greater conse- 
quence, in which the advantage is slightly on the side of 
aluminum. 
The results are specially pointed out in connection with 
the applications below, but attention may be called at once 
to the uniformly small weight ratio, a saving of over one- 
half in weight, and the comparatively small cost ratio for 
hull fittings and small castings, and to the marked difference 
of cost ratio between plates and shanes for hull work, the 
comparison for first cost thus pointing to the adaptability of 
aluminum in the following relative order: flr.st, to plate 
work in hull fittings, with increase over cost of steel work 
of only 24 per cent.; next, to small castings in hull fittings, 
with increase of 48 per cent.; next, to shapes in hull fittings, 
with increase of 74 per cent. ; next, to plates in hull work, 
with 3 8 times the cost of steel; next, to shapes in hull work 
with 5 times the cost of steel. 
E.— COMPAKISON FOR COST OF MATNTENANCE AND CAEE 
AND LENGTH OF LIFE. 
Obstructions have Stood in the way of every advance inhu- 
man industry. Scarcely an advantagehas been won without 
antagonism and offsetting disadvantage. When, therefore, 
not many years since, the industrial world, wrestling with 
steel and iron, saw aluminum appear above the horizon as a 
commercial article, promising the great de.sideratum of 
strength without the penalty of weight and excessive hard- 
ness, it felt a thrill, and the more impetuous, foreseeing cor- 
rectly the inevitable reduction of cost, thought that man 
had come into a new province without the strife of conquest, 
proclaiming in effect an al-.dictation by terrestrial nature of 
her inexorable law of struggle. 
The marine engineer and architect felt the elation above 
all others, for wtight in construction material is the Goliath 
of their enemies. Only prudence and conservatism inter- 
posed to prevent precipitnte application of the new metal. 
The conservative asked if aluminum was in truth a fully 
constituted David. The first reconnaissance showed an ob- 
stacle in the road, of huge proportions, not to be removed 
by the hand of a boy or the aim of a sling. Salt water and 
salt air were found to attack and disintegrate the metal. 
Three notable cases of aluminum construction followed 
each other in rapid succession, the Vendenesse, built in 
France in 1893 and 1893; the Foudre, built in England in 
1893 and 1894, and the Defender, built in the United 
States in 1894 and 1895. All three of these craft more than 
realized the expectations of performance, but all of them 
have demonstrated the weak point of aluminum. All have 
been exposed in varying conditions to the corroding action 
of salt air and saltwater, and have contributed to the knowl- 
edge of this unfortunate phenomenon. 
The Vendenesse, sloop rigged sailing yacht, built at St. 
Denis, has her shell plating, decks and bulkheads of 
aluminum, 6 per cent, copper alloy, while her frames, keel 
and stringers ai-e of steel, the weight of hull by this disposi- 
tion being but 18 per cent, of the displacement. 
Shortly after launching, in December, 1893, she was 
dropped'down to Havre, and lay in the salt-water basin for 
about four months without attention. Her waterline show- 
ing signs of corrosion, she was docked and her bottom was 
found bare, with the paint off' about 200 square meters of 
surface, part of the paint at least having been scraped off by 
obstacles while coming down the Seine. Examination 
showed corrosion wherever the metal was exposed, pitting 
being particularly pronounced around the edges of bare 
spots. 
An investigation as to the causes of such pronounced 
results in so short a time showed, however, that part of the 
corrosion was undoubtedly due to galvanic action that set 
in from the proximity of a schooner with copper bottom, 
and, moreover, the ba.sin received sewer discharges and had 
imperfect renewal of water. 
The subsequent history of the yacht showed conclusively, 
however, that the metal would be attacked whenever ex- 
posed. It showed also practically continuous slow galvanic 
action, even between plates, both of which were of alu- 
minum. The joints swelled and strained the rivets. One 
plate only would be corroded, showing lack of homogeneity 
and the existence oE a voltaic circuit. 
The deck plating was irregularly attacked; plates here and 
there had to be removed. The linoleum covering gave partial 
protection, but not immunity. 
The excellent nautical qualities and the mechanical be- 
havior of the metal made the yacht a decided success, but it 
was found that a specially prepared paint had to be used, 
and that special care and almost constant attention were 
still necessary for even imperfect preservation. 
The Foudre, second class torpedo boat, 60ft. long, 9ft. Sin. 
beam, 4ft. draft, built by Yarrow for the French Grovern- 
ment, and intended for the torpedo cruiser Foudre, is built 
practically throughout hull and hull fittings of aluminiim, 
worked cold, realizing a saving of about 2}4 tons, equal to 
about half the weight of hull, and about 2o per cent, the 
weight of total boat. 
The stem and sternpost are of galv.anized steel; the rivets, 
where exposed to bilge water, were of ii'on, elsewhere they 
were of aluminum; the inner tube of smoke-stack and deck 
plating around smoke-stack exposed to heat, and a small 
part of the deck where special strength are required, are of 
steel. The propeller is of aluminum bronze. 
The bottom and inside throughout were painted with red 
lead, and the deck was covered with rubber canvas glued on. 
After successful trials in the fall of 1895, on which the speed 
realized was IJC knots in excess of contract speed, the boat 
was taken to Cherbourg and left at moorings all winter, ap- 
parently without being vi-sited. 
When examined the following spring, corrosion was found 
to be practically general. The outside of hull was pitted 
wherever exposed, and the inside was corroded practically 
throughout. Conning tower and hull fittings, exposed only 
to the salt air, were likewise uniformly corroded wherever 
uncovered, though the rubber canvas was effective in pre- 
serving the deck. 
The result showed that red lead favored and produced cor- 
rosion. Moreover, when once begun, corrosion continues 
unless the metal is thoroughly scraped and cleaned before 
painting again. To clean the parts thoroughly would have 
required taking the boat to pieces, so general was the corro- 
sion. The interesting little craft, so unfortunately treated, 
was practically given over to inevitable disintegration. The 
five sister boats, first ordered of aluminum, were changed to 
steel, and the torpedo cruiser was converted to an ordinary 
first-class cruiser, though it does not necessarily follow that 
this conversion was due alone to the failure of the alumi- 
num boat. 
Referring to the method of construction of Defender, given 
above, it will be recalled that the top side plating, deck 
beams, deck strapping, and upper fittings are of aluminum, 
4 per cent, nickel alloy, the bottom plating is of bronze, and 
the stem, frames, floor plates and stiffening angles, bilge 
stringers, inverted angle bulbs under deck beams, the two 
deck beams inclosing mast, tie plates around mast, stepping 
socket, bed plate fittings and supports and chain plates are 
of steel, while the rivets are of bronze, making thus an inti- 
mate association of the three metals. 
After completion afloat at Bristol in July, 1895, Defender 
was taken to New Rochelle, E.Kamined tnere, the alumi- 
num top-sides were found to be in bad condition, with paint 
off in patches, particularly along waterline, showing signs 
of corrosion along the seam of juncture of bronze and alumi- 
num. 
She was docked, washed, sand-papered and painted, and 
was similarly treated three times more before leaving for the 
races in September, on each of which occasions there were 
evidences of corrosion wherever the aluminum and bronze 
were in contact, and, to a less degree, wherever aluminum 
was water-washed. 
Returning to New Rochelle after the races she was next 
examined iu January, 1896, and was found to be corroded 
practically all over, corrosion being found underneath the 
paint, even where it appeared solid. The inside, too, was 
slightly corroded all over, with severe corrosion in closets. 
She was scraped throughout, '"ashed with benzine and 
given four coats of paint on the outside and two coats on the 
inside. It maybe recalled, in referring to painting, that the 
bronze surface of bottom is left bare. 
The next examination, five months later, in June, showed 
corrosion at the waterline, along the seam of juncture of 
aluminum and bronze and around rivet heads, a few rivet 
heads having fallen off, also corrosion around the chain 
plates, apparently due to leakage from deck. Corroded 
parts were scraped and touched up and deck leaks stopped. 
The above examinations were made by the care-taker of 
the vacht, from whose log record the information is taken. 
Two months later, in August, as previously referred to, an 
inspection was made by the writer and the results, as above 
given, were fully confirmed. 
It was found, in addition, that the cast fittings on deck, 
such as deck light frames, exposed on the whole to spray and 
salt air only, were iu the last stages of consumption, and in 
many cases the spongy, honeycombed metal could be broken 
and crumbled with the hand. On the outside along the 
seam of junctuieof aluminum and bronze, a close inspection 
showed a series of small mounds for practically the whole 
length. Upon puncture these mounds were found to be 
raised by the gray powder of corroded aluminum. On the 
iuside this gray powder of corrosion covered the ledge 
formed by the top tif the iuside plating, the system being, as 
seen above, the rais"d and sunken system, and by jarring 
the sides more powder would sift down, showing a general 
process of corrosion. 
Additional rivet heads were found fallen off and an ex- 
amination of the fracture showed the force of rupture to be 
mechanical, thei-e being nothing more than usual verdigris 
on the surface. The only way to account for this breaking 
off of rivet heads i.s the supposition of strains set up by the 
swelling due to the corrobiou of the plates connected, com- 
bined with the slight elongation capable of being sustained 
by bronze. This swelling, as seen above, was found on the 
Vendenesse, and, moreover, appears inevitable when it ia re- 
called that the process of corrosion forms a less compact 
substance, more bulky, than the metal. 
Down from around a number of rivet heads and from the 
edges of the chain plates extended the yellow-brown streams 
of lion corrosion. The steel frames and other steel work are 
being corroded by the bronze rivets and plates. The ves- 
sel presents undoubtedly a series, a network, of voltaic cir- 
cuits, and it would be intereatiog to have a galvanometric 
survey. 
Thus in Defender, too, we see a full realization of all the 
mechanical advantages sought in aluminum, and full satis- 
faction ol behavior under stress of service; but we see, too, 
upon her the doom of a short life. In her system are working 
the fatal germs of the phthisis of corrosion. 
Besides the three notable cases of the Vendenesse, Foudre 
and Defender, there have been others iu which aluminum has 
been used to a greater or less extent, furnishing additional 
experience on preservation and length of life. 
The Forban, first-class torpedo boat, built for the French 
Government in 1893 and 1894, by Normand, at Havre, had her 
low-pressure pistons and piston valves, and her conning 
tower, galley, framing for turntables, torpedo tubea and 
other fittings of aluminum, realizing a saving in weight o£ 
