UMBRINA CRUISING CUTTER SAIL PLAN DESIGNED AND BUILT BY THE MARBLEHEAD YACHT YARD FOR J. P. ELTON, 1900. 
other, the deck-h'ne only being somewhat longer and more 
sharply drawn out. Next, to give an increased moment 
of inertia to the load water-line plane and to form 
sharper sections of entrance and run when heeled, the 
water-line plane was filled out at the ends and brought 
to closely resemble a circumscribed rectangle. Thus the 
horizontal sections of the water-line became absolutely 
square and blunted at the stem and stern, resembling 
those of the ordinary mudscow ; and hence arose the terra 
"scow" as applied to racing craft. It might be thought 
that these square water-lines would be a great factor of 
resistance, but it must be remembered that the profile or 
vertical section lines showed but a slight angle to the 
surface of the water, and thus it was a case of a flat 
plate moving not normally to its line of advance, but 
skimming over and pressing down the water at a very 
acute angle. 
As time went on the desirability was found of filling in 
or squaring the deck-line to an almost equal extent to the 
load water-line itself, for the boat with long overhanging 
square how and stern thus held in reserve above the water 
an immense chamber of buoyancy, which on the smallest 
iicel she could at nv.cc place in the water and at a great 
f'lsfp.-r^ from, and consequently acting with a great lev^r- 
'A<,:v I'pon the centre of gravity. The enormous length 
oi' < untaxed oiit-of-the-water hull was exemplified 
yM~<;^ (.'- tremely in the Quincy cup defender Outlook of 
l-.^t ^!r' ■(;!!. 'I'his boat, whose immersed Iniil when verti- 
cal ine-'sured but 2i feet, was 53 feet on deck. Many of 
I'll' scLnv type of boats, while sailing very fast in smooth 
waier, were found to lose headway and almost stop 
v.iii'ri eiicountering a clicppy set. This was explained to 
■'1 g'-e-'i extent liy their forward overhangs striking the 
writer at an obHqiic angle which tended with each pitch 
I') 'I'-'p the hull backwards. This was overcome by the 
so c'lleil rc\crscd-cur\-e Ixjw. tliat is, a bow whose verti- 
cil (Mnionr and hnttcck lines, while rising somewhat 
ph ■'-'!>• to ihe water surface, quickly reverse and run 
!■! «,r'i Jtt lines over and almost parallel to the water 
s- '-''r;\ Such a boat when pounding struck the water 
w i '1 ! "krming crash, but received no back-throwing 
i i;p -1 When under way in a moderate sea the forward 
p'M-i r. f i'le Outlook's bottom bent like paper with each 
|. !..,,,_,-(:., It sounded like wicker baskets under the blow of 
| ile (!'-iver. To derive the greatest possible advantage 
\-()<:\ reversed-curve bow it is essential to have the 
■jKiriro'-"'! contour line of the deck as nearly as possible 
3 fliv-iol-t lino all along the region of entrance, for other- 
• i-" i! \v\\\ have the effect of a bow with sharply rising 
lines when heeled. This type of craft when 
Ti'f^'i'; 'red by the le'.n:th of immersed hull alone allov^'s 
a!mr--l riulimited sail area, and will exhibit relatively 
nnr^-'Mlous speed as long as she holds together, but she 
s'-.bject to the most unusual stresses, and from the very 
uafn-e of her type must be built with most disproportion- 
lite lightness. Although most exciting to sail on, she must 
be considered rather as an abnormal development of a 
faulty rule than as a useful type of craft. 
Sir William White says that the ablest designer is the 
one who under given restrictions turns out the ship which 
best meets the special requirements demanded, such as 
great cargo capacity, extreme speed, a heavy armament, 
or unusual steadiness in a seaway. As I have already 
said, the one requirement in a small racing yacht is speed. 
Therefore the designer must aim to conform to the re- 
striction under which he builds, in the manner which 
shall least retard the racing efficiency of the yacht. 
The successful yacht in a heavily restricted class is 
often referred to as a "disguised racing machine," and 
it is slightingly pointed out that while she doubtless com- 
plies to all prescribed measurements and weights, she 
really has the greatest proportion of sail area to weight, 
or of overhang to water-line length, or in some real or 
imaginary speed-giving element. 
There is a satisfaction in going to the hmit which may 
be indulged in in a small yacht. Unheard of dimensions, 
hulls whose length on deck more than doubled the load 
water-line and ratios of sail area to displacen:(ent appar- 
ently out of the question. 
I shall try to describe briefly the phenomena that occur 
when a hull is moved a reasonable speed through still 
water. 
If a flat plate is moved sideways through water, the 
fluid ahead will be seen to rise, then sweep arotind die 
edges of the advancing plate, curl in eddies in its irti- 
mediate wake, and pass astern in fanlike, spreading rip- 
ples. To create these waves requires the expenditure of 
work in moviiig the plate, b-t were the moving body of 
such form that the stream lines of a perfect fluid, de- 
flected by the stem were Li'i with their original velocity 
and motion at the stern, ro waves would be set up and 
no force expended. This ideal condition manifests itself 
to some extent under real conditions, for it is an actual 
fact that the stream lines, whose deflection olifer great 
resistance to the advancing forebody, sweep in around, 
and, so to speak, squeeze forward the afterbody. This is 
but little realized, and may perhaps be better stated as 
follows : 
The part of the work done in stream deflection by the 
forebodv is given back in forward propelling impulses to 
the afterbody, just as the energy lost by the slowing 
piston of the steam engir.e is stored in the flywheel and 
given back in the return stroke. 
'I'hus in a boat, if the afterbody is disproportionately 
slioflened, tlie stream lines are unable to deliver their 
forward propelling impulses to the best advantage, and 
instead swerve around the counter in disturbed eddies, 
and waste their energy in useless waves. Or, in the other 
extreme, if the afterbody be too long or a straight mid- 
dlebody of great length intervene, the skin pressure of the 
stream lines can have but a lifting or balanced side press- 
ing effect, which yields a small forward resultant. It is 
also probable that in the case of a long, straight middle- 
body the action of the stream lines is delayed, and so to 
speak, damped out so that its effect when closing around 
the afterbody is partially destroyed. This tendency of a 
long straight middlebody has been demonstrated by tow- 
ing models of steamers, where the wider ship with long 
fore aiad afterbody gave less resistance than the narrow 
hull with straight sides and comparatively blunted en- 
trance and run. 
It was determined at an early date that the resistance 
per square foot of a thin plate moving under water nor- 
mally to its line of direction was a little over 100 pounds 
at a speed of 10 feet per second or 600 feet per minute. 
As the speed increased or deci'eased within reasonable 
limits, the pressure was found to vary as a little less than 
the square of the velocity (with the one and eighty-five 
hundredth power, according to the experiments of Cal- 
vert). It was also thought that for an angle of obliquity 
X of a plate to the line of its advance the normal pressure 
of the afterbody was the square of the sine of the angle 
of obliquity. Many sought to determine the resistance 
of hulls by considering their surface divided into many 
separates plates of unit volume and of varying angles of 
obliquity. However, no satisfactbrj^ results were obtained 
by this reasoning, and it finally gave place to the modern 
stream-line theory, so beautifully worked out by the late 
Mr. Froude. The stream-line theory does not attempt 
any arbitrary division of the immersed hull into separate 
plates or units, but, on the other hand, regards it as a 
whole. 
Long before the advancing hull reaches a given 
spot, the particles of water begin to feel its influence, 
and are set in motion in different directions. As the 
stem approaches the particles on either side are not 
only caused to diverge, but are given a forward mo- 
tion, and a zone or wave of water higher than the 
surrounding surface is formed at the bow, and as a 
given region of particles reaches the middle body, its 
speed sternward is greater than the outlying surface, 
then a depression of water is caused. This again gives 
place to a summit at the stern where the stream's line 
motion is also changed, and they, to a certain extent, 
follow and are urged forward at the hull. Not until 
the hull is well passed do the particles of water as- 
sume their original state. These retardations and ac- 
celerations of particles of water as the ship passes 
give rise to the bow and stern waves. To sum up the 
foregoing a little more concisely, it may be said that 
at the bow and stern the speed of the particles of 
water with reference to the advancing vessel is at its 
minimum and wave crests are formed, while on the 
other hand, amidships, where the relative speed is at 
its maximtim, a wave hollow results; that is, the par- 
ticles of water at the bow and stern are moving in the 
same direction as the ship relatively to the surround' 
