416 
FOREST AND STREAM, 
[Nov. 
to about 200 tons, a large fraction of the increase of weight 
due to sheathing. 
The cost ratio being 3.83, the increase of cost in the case 
considered would be about $90,000, or about 3 per cent, of the 
total cost of vessel. 
A 3 per cent, increase of cost is a small price to pay for a 2 
per cent, saving of weight. 
The bottom would still be liable to corrosion from the In- 
side, and until experiments have been made with cement 
and other bilge coverings, it would not be prudent to use 
aluminum even for sheathed bottoms in the parts where 
bilge water is liable to collect. 
(4) For torpedo-boats and small boats considerations of 
stiffness determine the scantlings for shell plating. The 
fiber stress of girder calculation in such cases is less than 
half the stress admissible. To give the same stiffness alumi- 
num plates would be 1.34 as thick as steel, making a weight 
ratio of .48, but the same weight of aluminum plating would 
realize 9 times the stiffness. For stiffness, therefore, alumi- 
num offers pronounced advantages. In cases of grounding, 
however, to which such boats are more or less liable in their 
operations in shoal water, the inferiority of aluminum in 
dynamic resistance would be in evidence as for the case of 
large vessels, debarring its use for keel plates and garboards. 
When navigating in fresh water and when hauled up, such 
craft are removed from the corroding effects of salt water 
and sojourn in these conditions is more or less extended. 
The conditions of corrosion are therefore materially amelio- 
rated, but would still require a suitable coating or paint of 
good resisting (jualities. 
The increase in cost would be similar to the increase in the 
case of large vessels, not at all prohibitory. 
There are, therefore, material advantages to be gained in 
the use of aluminum for the bottoms of torpedo-boats and 
small boats generally, where saving of weight is precious 
and only the absence of a suitable paint stands in the way of 
adaptability. 
(b) For plating above water. 
(1) In conditions of usual service, plating above water 
does not require unusual dynamical resistance found neces- 
sary for the safety of bottom plating, and the pronounced 
greater elastic dynamical resistance of aluminum places it 
perhaps ahead of steel, notwithstanding the great inferiority 
in ultimate dynamical resistance. In battle, however, the 
inferiority of aluminum would again appear in an empha- 
sized form in the increased wreckage and debris and multi- 
plicity of splinters. The use of aluminum is, therefore, ques- 
tionable in wake of gun protection and in the region of un- 
protected spaces occupied in battle. This is an important 
factor for unarmored war vessels and is serious for armored 
vessels, where, notwithstanding isolation of gun positions 
and the high degree of armor protection, the secondary bat- 
tery is largely exposed,, and fragments and splinters are still 
a menace. 
The conditions of corrosion are severe just above the water 
line and would exclude aluminum from two or three strakes 
at least. For the topside above, subject to intermittent 
spray and sea, the conditions of corrosion, though much less, 
are still serious and would require an efficient protecting 
coating. 
The increase in cost is similar to the increase for plating 
below water and is not commensurate with the similar large 
gain or saving in weight. 
(2) Fragments and splinters in battle do not enter the con- 
sideration for torpedo-boats and small boats and for mercan- 
tile vessels. 
(3) There is, therefore, an important field for aluminum in 
plating above water, restricted only by the lack of a suitable 
coating. 
2. Adaptability for framing. 
Requirements of dynamic resistance exclude aluminum 
from use in framing behind armor and in general from all 
association with armor except the support of weight. They 
affect its use in gun positions and in other spaces occupied 
in battle where fragments and splinters are to be feared. 
For framing elsewhere, however, the nature of its resist- 
ance would not incur disadvantage for aluminum, except to 
a certain extent for outer angles of frames and longitud- 
inals. 
Considerations of corrosion are against its use as outer or 
frame angles in the pa,vts liable to collect bilge water, also as 
outer angles on longitudinals in the same regions. The con- 
ditions for the other parts are also more or less severe. 
For the purposes of comparison, assuming the use for all 
longitudinal and transverse framing below protective deck, 
and for half the transverse framing above the protective 
deck, the saving in weight in a 9,000-ton vessel of ample free- 
board would be about as follows, with weight ratio .48 for 
shapes and .43 for plates: 
Tons. Tons. 
Transverse framing below protective deck . . about 58 
In angles and other shapes about 30 
In platework, floor plates, brackets, gussets, etc. ..about 28 
In transverse framing above prorective deck, 
angles and other shapes ,, about 13 
In longitudinal framing , . . about 45 
In plates about 33 
In angles about 13 
Total 116 
Total saving about 116 tons. With cost ratio of 2.9 for 
plates and 5 for shapes, the additional cost would be about 
$98,000; $69,000 additional for shapes, and $29,000 additional 
for plates. 
It is to be noted that the shapes realize only 56 tons of the 
116 tons saved, while they entail $69,000 out of $98,000 increase 
of cost, illustrating the general fact of the smaller advan- 
tage to be gained in the use of aluminum for shapes, than is 
to be gained in the use for plates. 
In the present case, as pointed out, the outer angles are 
additionally subjected to severe conditions of corrosion. If, 
therefore, these remain of steel, the saving in weight would 
be about 16 tons less, and the increase of cost would be re- 
duced by about $20,000. 
Considering the smaller advantage of weight, the larger 
increase of cost, the severer conditions for corrosion, and the 
lesser adaptability of resistance, ib would appear advanta- 
geous to have the outer angles of steel, even in the case of the 
adoption of aluminum for the plates and inner angles. 
For these latter plates and angles, decided advantage is to 
be gained in the use of aluminum when a suitable coating is 
found. Until this time, however, such use would not be 
prudent in view of the conditions of the double bottom and 
difficulty of access. 
For framing below the protective deck forward and abaft 
the double bottom, and for framing above the protective 
deck, where not associated with armor, and where there is 
no special menace in battle from fragments and splinters, 
aluminum can be used with advantage in the present stage 
of progress, provided, as is assumed throughout, that use is 
made of an alloy other than copper, and that due attention 
is paid to preservation. 
For torpedo boats and for small boats generally, the con- 
ditions of corrosion of frames are not severe, and the frames 
are more or less accessible, excepting the lower parts of 
frames of torpedo boats. The nature of its resistance being 
suitable, aluminum is therefore adaptable. General adop- 
tion for this purpose, however, should also be preceded by 
experiments to determine the coating best suited for preser- 
vation, while it should be borne in mind that the gain in 
weight of about one-half entails an increase of five times in 
cost. 
3. Adaptability for inner bottom. 
The nature of aluminum's resistance is suitable for inner 
SEAWANHAKA ONE-DESIGN KNOCKABOUT 
Designed and built by W. B. Steams, 1897. 
