144 
FOREST AND STREAM. 
[Feb. 15, 1896. 
YACHT DESIGNING.— V. 
BY "W. P. STEPHENS. 
[Continued from page 80, Jan. 25.] 
Matter is found in three different forms, of a solid, a 
liquid and a gas; and the naval architect is compelled to 
take cognizance of all, the solid being the vessel herself; 
the liquid, water, being the medium in which she floats; 
while the gas is the propelling power, either directly in 
the form of wind (air) on the sails, or more remotely in 
the steam or other vapor which animates her engines. It 
will be directly in order to consider briefly the medium 
before attempting to deal with the body which floats and 
moves in it. In a solid the force of cohesion is stronger 
than all the repellent forces, and therefore the body does 
not easily change its t form. In fluids the attractive and 
repellent forces are either in equilibrium, producing 
liquids, or inelastic fluids; or the repellent forces are 
wholly in control, producing gases or elastic fluids. To 
the scientist and investigator water is what is termed a 
* 'perfect" fluid, the attractive forces of cohesion and the 
repellent forces of heat being in exact balance, so 
that the particles of the fluid move upon each other 
with absolute freedom. To the yacht designer, how- 
ever, in his actual practice, it is not a "perfect" 
fluid, as the cohesive forces are very slightly in 
excess, and it possesses the quality of "viscosity," or, in 
plain language, stickiness, due to the presence of foreign 
substances — solids. While the viscosity of salt water is 
greater than that of fresh, both may to all practical pur- 
poses be considered as perfect fluids so far as the friction 
of their particles upon each other is concerned; were it 
otherwise the Gulf Stream and other ocean currents 
would be impossible; the law of tides, which has been 
reduced to exact mathematical formulas, would also be 
impossible, and many of the established laws of physics 
would be overturned. "While friction does exist to an 
appreciable extent between the water and solid bodies 
immersed in it, but little exists between the particles of 
the water itself. Water, then, is a fluid, incompressible 
and inelastic, and of course capable of imparting equal 
pressure in every direction. The weight of a cubic foot 
of fresh water is 6<J.39lbs., and a ton measures 35.905 
cubic feet. Salt water weighs 64.051bs. to the cubic foot, 
and a ton measures 34.973 cubic feet. The weight of 
fresh water equals the weight of salt water multiplied by 
.9740. In all ship calculations the weight of fresh water 
is taken at 62. 25, and of salt water at 64lbs.; while the 
former is estimated at 36ft. and the latter 35 cubic feet to 
the ton.* 
The whole subject of the mutual relations between a 
perfect fluid and a solid body immersed or submerged in 
it or moving through it (or, as the assumption commonly 
is, of the fluid moving by the fixed body) is a most fas- 
cinating one, and has engaged the attention of some of 
the most eminent scientists of this century, such as Prof. 
W. J. Macquorn Rankine, John Scott Russell, the late 
William Froude and his son and successor, R. E. Froude; 
and the ' 'form of least resistance" has been sought almost 
as eagerly as the philosopher's stone by the alchemists of 
old. While many important and practical truths have 
been obtained and much has been done to advance the 
science of naval architecture, the form of least resistance 
has not yet been discovered, and only the most general 
deductions have been reached on many important points. 
As far as the actual advancement of yacht designing is 
concerned, the matter for regret is not the failure to dis- 
cover the form of least resistance or the exact degree in 
which water, fresh or salt, falls short of the attributes of 
a perfect fluid, but rather that the most absurd and mis- 
leading theories have been so generally prevalent until 
recent years among the men in whose hands rested the 
progress and advancement of designing, the practical 
builders. These theories, most of them directly contra- 
dicted by the elementary laws of physics as taught to boys 
in the public schools, have been seriously advanced as un- 
assailable arguments for the old-time skimming dish 
model and against the introduction of greater depth and 
more effective systems of ballasting in yachts. The worst 
of these, as well as the most widely prevalent, was that 
which accepted the mere increase of hydrostatic pressure 
due to increased depth of submersion as influencing the 
"dynamical conditions incidental to motion" of a sub- 
merged plane. 
Through the fall and winter of 1881 the wonderful 
victories of the deep cutter Madge over the shoal New 
York yachts was the absorbing topic of dispute among 
yachtsmen, builders, sailors, fishermen and 'longshore 
characters in general; and the writer has had many a 
bout over the vexed question with those who believed in 
extreme light displacement and draft — of a vessel en- 
tirely on top of the water. The general theory of resist- 
ance then accepted, not only by ignorant fishermen and 
boatmen, but by successful builders, was about on the 
same high plane of intelligence as that of savages as to 
the nature of an eclipse — that some great fish was about 
to swallow the moon. As formulated to us at different 
times, accompanied by the familiar saying, "the nearer 
the sun the faBter she goes," it was of this nature: the 
upper layer of water, to the depth sailed in by the aver- 
age yacht or smack, some 4ft., was water pure and simple, 
with no resistance; the next layer going downward, say a 
foot depth, was as viscous or "sticky" as strong brine, the 
next foot was as stiff as molasses, the next as stiff as black 
mud, and beyond that, where the broad lead keel of the 
cutter must force its way, the water was a body of great 
but unmeasured density, sufficient to retard the speed of 
any deep yacht. These varying densities, according to 
this theory, were all due to the increase of hydrostatic 
pressure with the depth. The performances of Miss 
Madge showed that something was wrong with this beau- 
tiful and ingenious theory of resistance, as she cut the 
deepest strata with her broad lead keel more rapidly than 
the sharp, thin centerboards of the sloops could divide 
it; but even such proof failed to convince her opponents. 
Indeed it was a hopeless task to reason with a man who 
instanced the established fact of the blood gushing from 
the mouth and ears of a diver at great depths as an argu- 
ment against the speed of a cutter drawing 8ft. 
The subject of resistance, in its entirety, is one that per- 
tains to naval architecture rather than to yacht design- 
ing,and we shall touch on only a few of the most important 
and strongly established facts; those who wish to pursue 
it further will find it fully and ably discussed by the 
* Wherever the word ton is used throughout these srtlcjeg the "long 
toe 1 ' ot ?,24Plbs. to to be understood. 
authors named later on. As to the viscosity of water, 
fresh and salt, no reliable data has yet been given to the 
world, and no specialist has yet devoted himself to the 
subject. That salt water is decidedly more viscous is 
generally recognized, as is the fact that greater speed is 
obtainable in fresh than in salt water, whether partly 
immersed or fully submerged. In all investigations it is 
assumed, as already stated, that the water is a perfect 
fluid. 
That the hydrostatic pressure increases with the depth 
is quite true, the rate of increase being directly propor- 
tional to the depth, as in the following table: 
PRESSURE OF WATER AT VARIOUS DEPTHS. 
Depth in Feet. Pressure per £fq. Inch. Pressure per Sq. Foot. 
1 0.43IOS. 62321bs. 
2 0.86Ibs. 124 641 bs. 
3 1.301bs. 186.97108. 
4 1.731bs. 249.291DS. 
5 2.16)08. 311.611bs. 
6 2 60Jbs. 373 941 bs. 
7 3 031bs. 436.26lbs. 
8 3.461D8. 498 581bs. 
9 3 891bs. 560.91 lbs. 
10 4.331bs. 623.23108. 
As far as the motion of a fish or a yacht through the 
water is concerned, this increased pressure has no effect 
whatever, nor should it have, as it is balanced, or the 
same in all directions; if the yacht is pushed astern by a 
pressure of 6231bs. on the fore end of her keel, she is at 
the same time pushed ahead by the same amount of pres- 
sure acting on the other end of the keel. T;he rudder 
turns as freely at a great depth as at the surface, the 
greater pressure still being balanced on its two sides. 
Contrary to a generally accepted idea, pressure has no 
effect whatever on the friction of -the water upon the 
solid, which is the same at all depths. As a matter of 
fact, so far from the resistance being in any way in- 
creased by deeper immersion, it is materially diminished 
by the change from a partial immersion, the body being 
just at the surface of the water, and the complete submer- 
sion to a considerable depth; a much higher speed being 
possible under the latter condition, owing to the entire 
absence of one element of resistance, wave-making. 
The idea formerly accepted, that there was a direct re- 
sistance proportionate to the greatest area of transverse 
section, and called head resistance, has been rejected in 
view of the demonstrations of Scott Russell and Rankine, 
and it is now positively known that there are but three 
elements of resistance: 
First — Skin resistance, or that due to friction. 
Second — Eddy-making resistance. 
Third — Wave-making resistance, 
There is, it is true, a small element of resistance due to 
the viscosity of water, not in the form of friction, but of 
resistance to change of shape of the particles as they pass 
by the hull; but this only comes into play in the case of 
small models moving at slow speeds. In the actual vessel 
it need not be considered, nor need the "air resistance" of 
the air on the hull and upper works. 
The method generally followed in investigating the 
phenomena of resistance and friction between a perfect 
fluid and a floating solid is as follows: The body, of a 
symmetrical, fishlike form, pointed at both ends, is con- 
ceived as submerged to a considerable depth, and not as 
in motion through the fluid, but as stationary, the fluid 
flowing past it on all sides. At some material distance 
ahead of the body the water flows in parallel streams or 
lines, of normal velocity and pressure; but as the numer- 
ous streams approach the he.:d of the solid they are de- 
flected from their straight course, with a consequent loss 
of velocity. As they near the head of the solid, however, 
the velocity begins to increase, and continues to do so 
until abreast of the greatest breadth, when the velocity is 
greatest and the pressure least; from this point the veloc- 
ity decreases as the tail of the solid is neared, until at a 
more or less remote distance the stream lines become per- 
fectly parallel again, and with their normal pressure and 
velocity. It is capable of demonstration that the vari- 
ations of velocity and pressure are inversely proportional, 
the one decreasing as the other increases, and vice versa. 
By this method of investigation, involving what is called the 
"stream line" theory first enunciated by Prof . Rankine, 
many important facts have been discovered. These 
assumed conditions, it will be perceived, differ widely from 
those found in actual practice, in which the water is not a 
perfect fluid, the surface of the solid is by no means free 
from friction, and the solid, being only partly immersed, 
the water in contact with it is subject to the pressure of 
the air on its upper surface, a constant pressure; in place 
of the pressure of adjoining stream lines, which, as has 
been noted, constantly varies with the velocity. This 
interchange ' of velocity and pressure which takes place 
about a completely submerged body finds expression 
about the actual ship in a new form; the pressure about 
the bow, for instance, is now unbalanced by equal pressure 
from adjoining stream lines, and as soon as it exceeds 
that of the atmosphere, 151bs. to the square inch, it be- 
comes visible in the form of an elevation of the surface 
of the water or of waves. Interesting as this portion of 
the subject is, we can barely allude to it here, as it is 
entirely too extensive to be discussed at length. 
It is to the elder Froude that we are indebted for nearly 
all the facts now in the possession of naval architects 
concerning friction, the results of long and elaborate ex- 
periments conducted by him under the auspices of the 
British Admirality. The special experiments on friction 
were made about 1870 by the towing in an experimental 
tank of boards ■jfoin. thick, 19in. deep and of varying 
lengths up to 50ft. The results are summarized in the 
following table as quoted from Taylor's "Resistance of 
Ships." 
LENGTH OF SURFACE! OR DISTANCE FROM CUTWATER. 
Nature of 
Surface. 
Varnish 
2ft. 
8ft. 
20ft. 
50ft. 
A B 
.2.00 .41 
Parafflne 1.95 .38 
Tinfoil 2.16 .30 
Calico 1.93 .87 
Fine sand ..2.00 .81 
Medium sand.2. 00 .90 
Coarse sand, .2.00 1.10 
C & B C A B 
.390 1.85 .325 .264 1.85 .978 
.370 1.91 .314 .260 1.93 .271 
.295 1.99 .278 .263 1.90 .202 
.725 1.92 .6<6 .504 1.89 .531 
.690 2.00 .583 .450 2.00 .480 
.730 2.00 .625 .488 2.00 .534 
.880 2.00 .714 .520 2.00 .588 
C A 
.240 1,83 
.287 .... 
.244 1.83 
.447 1.87 
.384 2.06 
.465 2.00 
.490 .... 
B 
.250 
!246 
.474 
.405 
.488 
C 
.226 
'Mi 
.423 
.387 
.456 
Column A gives the power of the speed according to 
which the resistance varies. Column B gives the mean 
resistance in pounds per square foot of the whole surface 
for a speed of 600ft. per minute, Column C gives the re- 
sistance in pounds at the same speed of a square foot at 
the distance from the cutwater stated in the heading. It 
will be observed that the resistance of the last foot in 
length in each of the four examples is decidedly lees than 
the mean resistance per square foot for the entire plane, a 
circumstance attributed by Mr. F r <>ude to the fact that a 
certain amount of motion in the direction of the plane 
had been already imparted to the water about the end of 
the plane by the preceding portion. The value of the 
"coefficient of friction," as determined by Mr. Froude, is 
dependent on: 
1. The nature of the surface of the solid. 
2. The nature of the fluid, varying directly as the 
density for small variations, such as between salt and 
fresh water. 
3. The length of the surface, decreasing as the length 
increases. 
4. Temperature, decreasing as the temperature in- 
creases. 
The coefficient of friction is entirely independent of the 
pressure of the water and the depth below the surface. 
This is a point which we would impress upon our readers, 
and another is the conclusion of the elder Froude, whioh 
is now generally accepted, that the friction upon the im- 
mersed skin of a vessel is equivalent to that upon a flat 
rectangular' surface of equal length in the line of 
motion and area of equivalent to the vessel, and moving at 
the same speed. 
Another important point that is not as generally known 
as it should be is that while in bodies moving at the sur- 
face of the water the bow should be longer than the run 
in the proportion of 3 to 2, in bodies which move entirely 
under water, such as the lead bulb of a modern yacht, 
the bow should be the shorter and blunter, about two- 
fifths in place of three-fifths of the whole length, as in 
fishes. This same fish form, with a bow but two-fifths of 
the length, is also the correct one for the cross section of 
any projection or brace moving entirely under water. 
The researches of the Froudes are detailed in the vari- 
ous annual volumes of the "Transactions of the (British) 
Society of Naval Architects" since 1860; other valuable 
works of reference are: 
"Resistance of Ships and Screw Propulsion," D. W. 
Taylor, Naval Constructor, U. S. N. 
"Manual of Naval Architecture." Sir Wm. H. White. 
"Yacht Architecture," Dixon Kemp. 
"Ship Building, Theoretical and Practical," W. J. M. 
Rankine. 
"Forms of Fish and Ships," |Prof. R. H. Thurston, 
Trans. Soc. Nav. Arch., 1887. 
YAM PA'S VOYAGE— III. 
New York to Gibraltar, 1 895. 
On landing at the steps at the Custom House, we all 
found it rather hard work to walk, as we had been on the 
jump for so long. Knocked about the town for a while 
and then went to see the American Consular Agent, 
Sefior Moreria, who is also Consul for Hawaii. There is 
a very large emigration from the Azores to Hawaii. While 
we were there a steamer left for Hawaii loaded with 
emigrants. All the friends and family connections of the 
emigrants came down on the Custom House wharf to bid 
them farewell, and the crying and screaming could be 
heard for miles. 
On arriving on board Yampa again found she had been 
moored alongside of a dirty little Portuguese bark. She 
was just about large enough for one to sail on the lake 
in Central Park. We were securely moored with l^in. 
chains, capable of holding the largest ship afloat. At 
night we went ashore and saw a play at the Opera House. 
As it was in Portuguese we found it rather tame, but the 
400 of Ponta Delgarda who occupied all the boxes were 
very interesting. 
Next morning we hired a boatman for $1 a day to do 
all the ferrying to and from Yampa, so that the crew 
would not be kept from their work. T. and I started to 
take the terrier ashore for a run; but the boatman said it 
was against the law and that we would have to get a 
permit from the Custom House before we would be 
allowed to land the dog. Went to the Custom House and 
they refused to issue a permit. From there we went to 
the American Consul and in fact pulled all the wires we 
could; but it was no go. The dog was quarantined on 
board ship during all our stay at Ponta Delgarda, and all 
because years ago a dog from some vessel had gone mad 
onshore and bitten several others. 
Crew at once started in giving the ship a general over- 
hauling. We had two boat builders on board for several 
days fixing our life boat. Spent about eight days alto- 
gether straightening things up, etc. Also gave her a new 
coat of white outside, which improved her appearance 
wonderfully. We also fitted out with fresh provisions, 
water, etc. Everything was very cheap and fruits and 
flowers galore. Oranges, for instance, were 40 cents a 
hundred and delicious. There are several beautiful coun- 
try places on the island that belong to rich Portuguese. 
St. Michael's is really worth visiting and the climate de- 
lightful. 
Feb. 9. — Turned out this morning at 8 A. M., fine N.W. 
wind blowing, but rather cloudy. At 9 A. M. the pilot, 
with a gang of about twenty boatmen, came aboard to 
unmoor us. They were about the slowest people in the 
world, and the pilot, who was bossing the job, only 
seemed to have one idea at a time, and when that was 
carried out by the whole twenty, when two could have 
done it, he would think of something else and all hands 
would rush off to do that. As our second mate remarked: 
"They weren't fit to feed chickens." By 10:30 A. M. we 
were ready and Btarted out under f orestaysail. Soon after 
we set jib. When we were clear of the breakwater the 
pilot Bhook hands all around, and wishing us "bon voy- 
age" departed. 
There was quite a sea on outside the harbor, as it bad 
been blowing from N.W. for a week. 
At 11 A. M. set maintrysail and headed her for Gibraltar. 
At 11:15 A. M. put£bonnet on squaresail and set it — we 
were dead before the wind, so downed headsails. Crew 
started in at once to rig life lines and coil away hawsers, 
etc. ; also got both anchors on deck and lashed them to 
the windlass. Unrove chains and sent them below and 
put the plugs back in the hawsepipes. We were rolling 
quite a bit and the pup was seasick again. It rained a 
little off and on in the afternoon and set in rather thick. 
At 3 P. M. wind hauled more to the south'ard and we set 
jib, which steadied her somewhat. At 5 P. M. wind 
shifted to W.S.W., so we downed squaresail and set fore- 
sail and topsail. It started in to clear up soon after and 
we had a chance to see the sunset. T. felt rather squeam- 
ish and did not turn up for dinner, so I had mine alone. 
