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FOREST AND STREAM. 
[Oct. 30, 1397. 
Notes on the Yacht Defender and the Use of 
Aluminum in Marine Construction. 
BY BICHMOND PEARSON IIOBSOK, ASSISTANT'KAVAL 
CONSTEUCTOE, UNITED STATES NAVT. 
Efepriuted by permission from the Proceedinga of the United 
States Naval Institute. 
Copyrighted by ihe JJ. 8. Naval Institute. 
Nocraftin the annals of yachting centers about herself si\ch 
features of general interest as the yacht Defender. Perhaps 
the greatest series of races in these annals is the one that 
represents in its sphere the great fact of modern times— the 
greatest fact, it inay prove to he, of all time — the rise of the 
New World, a rise to greatness that has reached, and in 
some respects has passed the point of successful rivalry with 
the Old World. 
Among the yachts connected with the series of races for 
the America's Cup. Defender is in many respects unique, 
standing head and shoulders above all" the distinguished 
number. 
The last races came at a time of high tide in yachting 
interest both abroad and in the United States, when rivalry 
was keenest and the evolution of the racing craft seemed to 
have reached its maximum. The determination to win baclc 
the lost trophy was made j ears in advance, and one can 
FI(J. 
trace the course of deliberate, scientific, tireless effort to this 
end, till at last it seemed, with great reason, that invincibil- 
ity had been reached in Valkyrie III. 
It was Immediately recognized in America that the defense 
of the Cup could not be left to any yacht yet built; moreover, 
the time after challenge would be too short to permit exper- 
ment, A'"alkyrie III was the successor to a dynasty that 
reached its climax of perfection before the challenge was 
sent; while the American champion might be expected to 
follow the line of its predecessors, and might be expected to 
be the climax of a sequence of representatives, yet there was 
but one chance of producing the climax. 
The sense of danger aroused the American yachtsmen to 
the necessity of cooperation. Effort combined and centered 
upon producing a single craft. The order was placed with 
Herreshoff Bros., of Bristol, U. I,, and cost and all other con- 
siderations were subordinated to the one object — speed. The 
yacht built must win. 
It was natural, under these conditions, to expect boldness, 
for the builders, though sure in execution, have been char- 
acterized by boldness in design. 
The shape this boldness took for realizing a maximum of 
power was along the line of weight distribution, for lowness 
of center of gravity, rather than along the line of maximum 
metacentric radii, "or power of form. The advantage of ex- 
cessive lowering of the center of gravity, instead of the rais- 
ing of metacenter, becomes apparent, without further ex- 
planation, from reference to the fact that power of weight, 
determining the position of the center of gravity, does not 
incur, as does power of form, determining the position of the 
metacenter, the increase of head resistance and frictional 
resistance that sets in when the vessel heels or is in a sea- 
way. , 
The method adopted for lowering the center of gravity 
consisted not only in placing a maximum weight of lead on 
the deep fin-keel, as found also in the challenger and otter 
yachts, but algo in reducing to a minimum the upper 
weights, the saved weight appearing in the form of add'- 
tional lead on the keel, being equivalent in eiiect to a trans- 
ference of weight downward through a great resistance. 
The reduction or economy of weight, particularly of high 
weights, which thus constituted the characteristic feature 
of the yacht, places her construction alongside of marine 
construction in general, and of naval construction in partic- 
ular, where weight of hull and fittings affects intimately the 
limit of the military qualities themselves. 
This coincidence of purpose alone would make the yacht 
an interesting study for the naval architect, but the form 
the purpose took enhances the interest, makes it general and 
intense, for it adopted a new material— aluminum— which, 
from its extreme lightness, has been offering great hopes to 
the naval architect, but which, from its corrosion in salt-air 
and salt-water, has checked, if it has not effectually shat- 
tered these hope,9. Moreover, the conditions were peculiarly 
such as to constitute a severe test of the virtues and failings 
of the new metal. 
In view of this similarity of purpose with naval construc- 
tion, particularly the bearing on torpedo-boat construction, 
and of the value of experiment with aluminum, the Navy 
Department directed an inspection of the yacht and a re- 
port on her "method of construction." This report is given 
in Part I. practically as it was made after inspection at 
Bristol just before the yacht left the builder's hands. 
In August, 1896, more than a year afterward, a second in- 
spection was made at New Rochelle, through the courtesy 
of C. Oliver Iselin, Esq., to determine the conditions of pre- 
servation and the conduct of the new material in the face of 
the deteriorating conditions of service. Since it is on the 
question of corrosion that the use of aluminum for marine 
purposes hinges, an effort was made to throw, if possible, 
some additional light upon the subject, particularly at the 
present time, when, notwithstanding the advantage it offers, 
aluminum has been unfavorably passed upon, both abroad 
and in this country, upon grounds that appear to be incom- 
plete Samples of corrosion taken from Defender, also a 
sample of a corroded aluminum plate, together with a 
sample of the salt water in which, in a closed vessel, the 
corrosion took place, the latter furnished by Prof. A. H. 
Sabin, were sent to the chemist at the Navy Yard, New 
York, with directions for a qualitative and a quantitative 
analysis, with a view to determining the phenomena of cor- 
rosion in the particular case, the attacking agents, the sol- 
uble and insoluble oroducts. 
The value of an intimate knowledge of the phenomena is 
evidont, serving as it would as a basis for research and ex- 
periment to find preventative preparations. 
A sequence of heavy pressure in the chemical laboratory 
has prevented as yet the analyses, and effort to hasten 
them since tile writer's detachment from the New York 
Navy Yard has been of no avail. Only an incomplete, 
preliminary analysis of the corrosion from Defender has 
been reported, an analysis so incomplete as to be of no mate- 
rial value. 
It has therefore been decided to give in Part II. the result 
of the study of the subject of the adaptability of aluminum 
for marine construction, without the original data hoped for 
on the question of corrosion. 
PAKT I.— THE METHOD OF COKSTETJCTIOK OV THE tACHT 
DEFENUEE. 
1. — Preliminary Description. 
The boat was examined while afloat at anchor. Her gen- 
eral form is indicated in Pigs. 1 and 3. Her approximate 
hull dimensions are as follows: Length over all, 122ft. 3in ; 
length on l.w.l., 90ft ; maximum beam, 23ft.; beam at l.w.l., 
22ft. ; draft, extreme, 19ft. 
The idea that gives the distinguishing feature to this ad- 
vance type, as will be seen below, is the realization of ex- 
treme sail-carrying power from a great metacentric height, 
initial and under inclination, realized from the disposition 
of weights. Though realizing a high position of the meta- 
center from an elevated position of the center of buoyancy 
and long metacentric radius, the extreme is reached in the 
low position of the center of gravity. 
The great metacentric height and consequent sail-carrying 
power is derived more from the element of weight than from 
the elements of form. 
The method adopted in realizing the low position of the 
center of gravity is that of reduction in weight of hull and 
fittings and the addition of weight to the keel, weight being 
taken from the upper portions and added to the lowest point. 
The method of realizing a reduction of high weights is the 
use of light materials, of light scantlings, with a light method 
of construction and fastenings. 
The reduction of frictional resistance and of liability to 
deterioration are sought in the use of bronze, manganese 
bronze, for water-washed portions. 
The features of the distinguishing methods thus identify 
the construction, in the objects sought, with the construc- 
tion of vessels of war, particularly torpedo vessels and tor- 
pedo boats. 
2. The Method of Construction. 
Referring to the sketch of the midship section. Pig. 8, the 
construction is as follows: 
1. The Skhleton.— A steel angle, 4in. x4in., closed to the 
angles of the waterlines, from )^in. to Hin. thick, forms the 
stem and binds the ends of the shell plating, with double 
riveting, rivets of bronze for the bronze platinp, diameter 
^^in., and of aluminum for the aluminum plating, diameter 
Mill- 
A bronze casting, 4in. deep by 20in. wide, of the form indi- 
cated in sketch, forms the keel. On its under side is attached 
the lead, shaped to the form indicated, secured by bronze 
tap bolts Sin. long by l}4ia. diameter. The bronze shell 
plating extends to cover the lead, reducing the frictional re- 
sistance, and giving additional support, securing to the lead 
by bronze taps Sin. long by H.m. diameter. 
The frames are steel angle bulbs made in two parts be- 
tween the keel and topsides, strapped and riveted as indi- 
cated, spaced 20in. throughout, an angle being sitbstituted 
for the bulb at the forward extremity, frame No, 1. They 
.stop at the keel, which is spanned by floor plates of X^n. 
bronze plating, 12in. high, secured to the frame on each side 
by five rivets of %in. diameter. Alternate frames have in 
addition deepened floor plates, of 7 32in. steel, extending, as 
shown, to the angles uniting the frames at about one third 
their height from the keel. These angles are steel, 2in. x 2in. 
amidship, and IMin. x la.jin. forward and aft. The frame 
angle bulbs are i'j^in. x 2iu. amidship The following is their 
scantlings throughout, beginning forward: Frame No. 1 is 
an angle, as stated above; from frame No. 2 to frame No. 9 
the angle bulbs are 23'^fn. x IJ.^'in.; No. 10 is ?Aimx1%\n ; 
from No. 11 to No. 24 they are Sin. ; l;^.iin.; from No. 25 to 
No. 44 they are 33v>'iu. <2\u.; from No. 45 to No. 58 they are 
Sin. < l>.iin ; from No. 5S to stern they are 2' i'in. ■ l>0n. The 
dimensions for the bulb of the frame angle bulbs, S}4m. >^ Sin. , 
are ;<«iu. - 9 IGiu. 
About 4>ijft. above the steel angles that bind the two sides 
of the frames are wooden beams, 3}4'in. .< IV^in., secured lo 
the frames, adding stiffness and forming support for the 
platform or lower deck 
The beams of the upper or main deck are aluminum angle 
bulbs, Sin. x2in., spaced 40in., fitted to only alternate frames, 
the frames without beams ending without fittings under the 
deck stringers. The beam arms are secured to the frames 
Strake No. I, covering the lead and overlappiiig the keel 
and lower part of frames, as indieated iu sketch. Pig. 8, is an 
outer strake of manganese bronze, 5-16in. thick amidship, 
secured to the lead by bronze taps ?£in. diameter and .5in. 
long. The lap with strake No. 2 is secured by two rows of 
rivets of bronze °4m. diameter. 
Strake No. 3 is an inner strake of 5 16in. manganese bronze. 
The lap with strake No. 3 is double riveted, Hm. bronze 
rivets. 
Strake No. 3 is au outer strake of >^in. manganese bronze. 
The lap with strake No. 4 is single riveted, }4iQ. bronze 
rivets. 
Strake No. 4 is an inner strake of 7-S2in. manganese bronze. 
The lap with strake No. 5 is single riveted, }^in. bronze 
rivets. 
Strake No. 5 is an outer strake of 7-32in. manganese bronze. 
The lap with strake No. 6 is single riveted, Min. bronze 
rivets. 
Strake No. 6 is an inner strake of }^in. manganese bronze. 
The lap with strake No. 7 is single riveted, ^in. bronze 
rivets. The L.W.L. falls on this strake near its upper edge, 
between the water line and the aluminum plate above. 
Strake No. 7 is an outer strake of «sin aluminum. The 
lap with strake No. 8 is -single riveted, ^in. aluminum rivets. 
Strake No. 8 is an inner strake of Kin, aluminum. This 
strake is the highest. The upper edge secures to the back of 
the angle bulb, forming the top line. The lower ends of the 
strips securing beam arms, fall on the lower part of this 
strake. 
The decks are of wood, 2>^^in. thick for the main deck, and 
>sin. thick for the lower deck. Liners are fitted over the 
beams of the main deck between the strapping plates. The 
deck planks are secured to each other by horizontal nails, in 
addition to being secured to the beams. Around the mast a 
steel tie plate, 5ft. .3in. ■ 3ft. 4in. ■<%iB., secures the ends of 
the strapping plates and the four beams in the vicinity. 
Thus, the coverings cousisfc of manganese bronze for the 
water-washed portions of shell plating, and aluminum for 
the top sides, with wood for the decks, and steel for special 
plates. 
3. Fittings. —The socket for stepping mast is made of 
steel angle bulb, 5in. < SKin., bent to the form of a circle, 
with the ends welded and strapped. The flange, which is on 
the exterior, sits on a foundation plate of steel. The step- 
ping is stiffened by a partial vertical keel or keelson, and by 
special floor plates on the frames adjacent, with angles 
4in. x4in. on one side and 2in. x 2in. on the other, with verti- 
cal angles 2iu. > 2ia- 
The pin rails are of steel piping. The rigging on each side 
is secured to steel eye bolts attached to live chain plates, 
about 4)-i,in. wide and ,%in. thick, extending down to the 
lower deck, riveted to the shell plating. 
The jibboom is guided by two main straps of bronze about 
1ft. long with flanges at the ends, and by an additional nar- 
row strap of simple bronze plating. 
The fid is of aluminum, in the form of a yoke, which re- 
ceives tie rods which are of one piece bent around the stern, 
and, passing through the ends of the yoke, are set up by 
nuts, which permit of an adjustable strain on the single 
jumper or martingale of steel wire secured to the stem a 
short distance above the water line. There is no lateral sup- 
port of the jibboom. 
The standing rigging and topping lifts are of light steel 
wire Blocks are of Oregon pine or spruce, with straps and 
sheaves of aluminum. Cleats are of hard cast bronze. Eye 
bolts are of steel. The spars are of Oregon pine and spruce. 
The internal fittings are of light wood with minimum thick- 
ness. Partition,? and partial bulkheads are of canva^, held 
by a light wood framiug. The water-closet fittings are of 
alumiuuai, with small pump of aluminum. The bunks for 
the crew are of i^in. gas tube framei, tift. :<33in., covered 
with canvas, hinged lengthwise to the .side, and folding or 
dropping down. They are three tier.s deep, with about 2()iu. 
vertically between the bunks. They are secured in the hori- 
zontal position by straps from the reverse angle bulbs under 
the main deck beams. 
Thua the fittings are of steel, bronze, aluminum or wood, 
according to the requirements. 
3. CoNCLUSiOKS.— The method of construction as above de- 
scribed presents three prominent features, namely: 
1. Simplicity and directness of construction. 
2. The use of new materials and their combiUaLion with 
steel. 
against which they sit back to back: by three rivets of ^oin. 
diameter and by a single strip of aluminum plating 24in. 
long, 4in. wide and -^sin. thick, forming a triangle with the 
frames and bea.m arm, secured by three rivets at each end of 
Min. The two beams between which the mast is strapped 
are of steel, 4}{in. ■ SV^in. 
A bilge stringer, steel angle bulb, SMln xSln., extends 
throughout the entire length on each side, at the height in- 
dicated in the sketch. A corresponding inverted steel angle 
bulb, 33';2in. y. 2in., extends under the main deck beams in the 
position indicated in sketch along the whole length on each 
side about 4ft. from the central line. 
The bilge stringer angle bulb and the inverted angle bulb 
under beams on each side are connected by fourteen struts 
made of iron piping, IM'in. amidships and lVin. forward and 
afb, spaced five frame spaces. These pipes have forgings 
welded in their ends and flattened to lie on the backs of the 
angle bulbs, to which they are secured by three rivets of 
}ijin. diameter. 
A deck stringer plate of aluminum, varying from 28in. to 
24in. in width and 5-16in. thick, extends over the beams 
from end to end. On this stringer plate, alone; its outer 
edge, extends an aluminum angle bulb. Sin, x 2>sin,, which 
receives the upper edge of the phell plating and forms the 
upper ending of the hull at the sides. The deck beams are 
strapped in addition by diagonal plates of aluminum, %m. 
thick, varying in width from Sin. aft to ll-iio-. forward, the 
four converging on the mast being lOin. wide. The length 
of these strapping plates and their disposition are indicated 
in sketch. Fig. 4, 
Thus the skeleton consists of a steel angle stem, a bronze 
keel, with lead underneath, steel angle bulb frames, with 
floor plates of alternating heights, of bronze at the bottom 
and steel above the bronze, with steel angles binding the 
frames on the two sides, wooden deck beams for the lower 
deck, and aluminum angle bulbs for the main deck beams, 
fitted only to alternate frames, steel angle bulb bilge 
stringers, one on each side, inverted steel angle bulbs on 
under side of main deck beams, one on each side, two rows 
of inclined struts between bilge stringers and inverted 
angle bulbs under main deck beams, one row on each side, 
spaced every five frame spaces, aluminum deck stringers 
and angle bulbs at sides of main deck, and diagonal strap- 
ping fore and aft. 
2. The Coyeeings. — The shell plating is on the raised and 
sunken system, with liners behind frames under outside 
plating, secured to frames by a single row of rivets of >sin. 
diameter. All butt straps are double riveted. 
3. Lightness of scantlings. 
The complex nature of the forces to be resisted, the comlji- 
nation of pronounced twisting and a heavy thrust of mast 
with the usual forces, would lead to the expectation of com- 
plexity, whereas examinations show an entire absence of 
redundant parts, and even of parts found in usual construc- 
tion. 
The examination of the parts, in view of theforc;3s to be 
resisted, shows a singular directne.^s of purpose for each part 
or piece that enters the construction. These characteristics, 
simplicity and directness, are so evident from the sketch of 
the midship section that they need not be pointed out in de- 
tail. Notice should be taken, however, of the use of angle 
bulbs instead of simple angles or combinations of angles. 
The sectional moment of inertia being greater for the angle 
bulb, there is a gain in stiffness, or a saving in weight for 
the same stiffness. Notice should he taken also of the sim- 
plicity of fastenings, the economy of rivets. 
Special attention should be gis'en to the system of struts, 
which, thongh exceedingly liglit, give to the transverse sec- 
tion a girderlike nature hitherto unattempted afloat. Special 
attention should be called al.'so to the disposition for insuring 
continuity of resistance in the main deck, to the longitudinal 
angle bulbs under the deck beams, and the combination of 
angle bulbs and wide deck stringers at the sides, but espe- 
cially to the diagonal strapping which opposes itself directly 
to the twisting forces referred to above, note being taken also 
of the fastenings of deck planks to each other. 
It may be added that the characteristics in question appear 
in full relief when the boat is conceived inclined under the 
great localized force=; when the parts are conceived distrib- 
uting these forces and transmitting them to the resisting 
forces without, tlie structure. will be seen to present remark- 
able stiffness of form, remarkable resistance to deformation, 
combined with the simplicity of structure described above. 
In sum, the boat is an architectural departure, and is an 
interesting study for all architects. For the marine archi- 
tect the study is of practical value, for thedejjartureis along 
the line of his constant effort to realize a maximum of resist- 
ance to complex forges with the minimum of weight. 
The realization of this main object, however, is not confined 
alone to the disposition of the material, but extends also, 
with even more marked characteristics, to the selection. The 
lightest strong metal known to architecture is used where- 
ever characteristics other than weight do not prevent. The 
shell plating of the topsides, the main deck beams and strips 
securing them to the frames, the deck stringers and topside 
angle bulb, the deck strapping plates, and various fittings, 
