02 
FOREST AND STREAM. 
tjAK. 30, 1904. 
N. Y. Y. C. Measurement Rule. 
Editor Forest and Stream: 
It appears from Mr. Lawton's communication in 
Forest and Stream Dec. 26 ult. that the writer was mis- 
taken in assuming that D was used as a divisor in the 
formula of the New York Rule in order to influence 
form. Whether that was the purpose or not, the history 
of racing rules shows that without exception they have 
had the practical effect of barring out from successful 
racing all but one peculiar form especially favored by the 
rule. And there seems to be no reasonable^ doubt that the 
present rule will develop its peculiar winning type as the 
others have done. 
Mr. Lawton's letter, coming from one who was a mem- 
ber of the committee that prepared the rule, is especially 
interesting, because it states authoritatively the theory 
on which the rule is based, viz. : 
The principle is accepted that within economic limits 
opportunities for speed vary in different vessels as the 
square roots of their respective lengths (provided they 
have the necessary motive power). Then it is found 
that the necessary power will be supplied, if sail area be 
allotted in proportion to displacement. Under these con - 
ditions speed will be proportional to the square root of 
length. 
There is some discussion of the relations between sail, 
bulk (power to carry sail), and resistance; but there is 
nothing in the letter to explain how the amount of sail 
necessary to produce the required variation of speed was 
determined. Thus the theory is stated, but it is neither 
explained nor justified. Both explanation and justifica- 
tion seem to be required because the theory of the rule is 
apparently a novelty, and in conflict with generally ac- 
cepted theory. 
According to text-books of naval architecture, in theory 
the resistance of a vessel at low speed is wholly due to 
skin friction, and varies (i) as the wetted surface, (2) 
as the square of the speed. 
If, then, a yacht's wetted surface is increased, say, by 
enlarging the model or design, in order to maintain her 
original speed sail would have to be increased propor- 
tionally to the increase of wetted surface. But accord- 
ing to the rule her speed would be increased by reason of 
the added length. 
Nearly the same results would follow if the yacht were 
lengthened without increasing displacement and sail. In 
this case also the theory of the rule calls for an increase 
of speed proportional to the increase of VL; but accord- 
ing to generally accepted theory, there would be not only 
no increase of speed, but a small decrease on account 
of the larger wetted surface due to lengthening the hull. 
If in either case there were to be an increase of speed as 
the rule calls for, resistance would further increase as the 
square of the speed, but the rule provides no increase of 
sail to meet this increased resistance. At low speeds, 
therefore, assuming the water to be smooth, according to 
orthodox theory, speed will not vary as VL as the rule 
requires, but will be constant when sail is proportional to 
wetted surface. 
At higher speeds, when wave-making resistance is en- 
countered in addition to that of skin friction, the only 
theoretical way of comparing the resistances of vessels of 
different length and displacement, at different speeds, 
known to the writer, is by Froude's law of correspond- 
ing speeds ; and then the vessels must be similar in form, 
i. e., made from the same lines, one being simply an en- 
larged model of the other. That law provides that if 
the speeds vary as the VL, then the resistances will vary 
as the cube of the ratio of the linear dimensions. Thus 
if one be 2 times as long as the other and have 4 times 
the wetted surface, her resistance will be (2)^=8 times 
as large when her speed is V2 = i.4i times as great; and 
she would therefore require 8 times as much sail. But, 
according to the New York Rule, she would require only 
4 times as much sail, having only 4 times as much 
wetted surface. 
At all speeds, then, the New York Rule seems to be at 
variance with commonly accepted theory. 
There are some observations which show the variation 
due to increase of length when displacement is kept con- 
stant. Froude towed two yacht-shaped models (that is 
without parallel middle body) representing ships of equal 
displacement, one 318ft. and the other 368ft. long, the 
longer boat necessarily having the larger wetted surface. 
Up to 16 knots the resistance of the shorter vessel was 
the smaller, the saving in skin friction being more than 
sufficient to offset any loss by wave-making resistance. 
According to the New York Rule the resistance of the 
larger vessel should have been the smaller. 
The precise applicability of text-book theories of re- 
sistance to the case of racing yachts is not here urged. 
It is only attempted to show that, tried by those 
standards, the theory of the committee seems to be a 
novelty, and to need further justification. Froude's ex- 
periments were made with models of large vessels which 
would probably be little affected by such waves as yachts 
commonly encounter in racing, whereas every yachtsman 
knows that ordinary summer waves do largely affect the 
speed of the smaller yachts at least. But if any new 
theory is to be substituted for the old; or if that is to be 
modified to suit changed conditions, the changes should 
be explained and justified. The problem requires quanti- 
tative solution; but there is no attempt in Mr. Lawton's 
defense of the rule to prove the quantitative relation set 
forth in the theorem. 
The truth seems to be, as nearly as the writer can 
make it out, that the hydrodynamic relations governing 
the resistance of yachts of different size and shape mov- 
ing at different speeds through waves of varying 
dimensions, are so complex that any measurement rule 
based on theory can give but roughly approximate re- 
sults. Mr. Hyslop, who well understands the theory, who 
has had much practical experience in making rules,_ and 
who, moreover, is a friendly witness, testifies to this in 
his remarks on Mr. Popr's criticism of this rule. And if 
any further proof were needed that the rules of this type • 
are empirical, notwithstanding protestations of their 
scientific basis, it is afforded at once by the fact that they 
who make the rules proceed at once to ; discount their' 
theoretical results anywhere .from 20 tO; 60 per cent, when , 
applying them in practice., ;' 
There is little or no use of refinement in methods when 
the proljability of error yarie? . f row iQ 6q,. per cfent.. 
/ ^ \ 
/ 
/ 
l— — 
15-FOOT KNOCKABOUT SAIL PLAN- — DESIGNED BY E. A. BOARDMAN FOR COLONEL ISAACSON. 
and it would be better to get approximate results by 
smipler methods. If yachts be classified by length and 
taxed for sail area alone, they will soon be built either 
to the head or the foot of their class, and be of substan- 
tially uniform length. This will eliminate all uncertain- 
ties concerning resistance arising from differences of 
length. 
If freak forms be barred by suitable restrictions, 
the difficulties arising from difference of form will also 
be eliminated ; and then SA will be a reasonable satisfac- 
tory measure of speed until yachtsmen decide to abandon 
time allowances altogether. The objection commonly made 
to this plan is that it does not give the designer sufficient 
freedom, and tends to a uniformity of design. The 
answer is that the designer should have no freedom to go 
outside the limits that surround desirable forms; and that 
there ought to be a tendency toward one form ; namely, 
the fastest — the form of least resistance. The more 
nearly yachts are matched in speed, the greater the inter- 
est for spectators, and the sharper the zest of skipper 
and crew which arises from the personal factors in the 
contest. Imagine, for example, the effect of allowing time 
in trotting races for heavy wagons, drivers, or other load. 
Sextant. 
Desigfn for a J5ft. Knockabottt. 
We publish herewith the plans of a isft. waterline keel 
knockabout that was designed by Mr. E. A. Boardman 
for Colonel Isaacson, of Halifax, N. S. The yacht will 
be used as a day boat and for racing in Halifax Harbor. 
The design shows a nicely turned little boat of sub- 
stantial construction that should make a durable and 
satisfactory craft. 
Her dimensions are as follows : 
Length — 
Over all .27ft. 10 in. 
L.W.L isft. 
Overhang — '■ 
Forward 6ft. i in. 
Aft 6ft. 9 in. 
Breadth — 
Extreme 6ft. 6 in. 
L.W.L 6ft. 
Draft- 
Extreme 4ft. 6 in. 
Rabbet ift. 2 in. 
Freeboard — 
Forward . ift. ii^in. 
Least ift. 4 in. 
Aft ift. 6 in. 
Ballast lead 1,000 lbs. 
Sail area, total 304 sq. ft. 
Messrs. H. I. and J. T. Pratt have ordered two motor 
boats built, and it is expected they will develop high 
speed. One will be a rigged screw boat, 6oft. long, with 
a 1 10 horse-power engine, while the other will be a twin- ' 
sci'ew boat 90ft. long, with a 500 horse-power motor. 
Messrs. "Gardner & Cox will design the boats' hulls. 
' - »6 i5 « , 
.■ • . The first club house of the New Yorfc Y. C, which 
:Sf0.od en Elysiatt Fields, Hoboken, for many years,- is to 
hel us^i.m the: future as. the club station ^t 
":Gp?^ei, U 1= ■ ... . v..:.'^. 
The Scale of Time Allowances. 
Editor Forest and Stream: 
I am glad to see that Mr. Lawton has opened up this 
subject. The tables in use, with the various forms of 
the length and sail area rule, are so crude and errone- 
ous that it is impossible to justify them except by 
pleading extenuating circumstances, the commonest 
being that in class racing boats are so nearly of a size 
that the allowances are too trifling to affect the result 
of a race. In some places — Lake Ontario, for instance 
—it has been found quite feasible to abolish time 
allowance in class racing, and there is no doubt that 
such an arrangement, where it can be fairly applied, 
gives better and more interesting sport. But there are 
always events which demand that two or more classes 
must sail together; and so long as conditions exist that 
require the use of time allowance it is only just that 
the fairest and most accurate system should be used. 
The explanation of the "Table of Time Allowance," 
as set forth in the books of clubs using the length and 
sail area rule is not only curt but incomplete; and 
probably few yachtsmen have ever taken the trouble 
to find out what it means. The introduction of a 
formidable looking algebraic expression, and the ex- 
tension of the actual allowances to hundredths of sec- 
onds, convey an appearance of great care and accuracy 
to the casual reader; but these are no better than fine 
polish on rotten timber. But let us go into details. 
The rule books say, "The allowances in this table are 
based upon the rule accepted by naval architects; that, 
within economic limits, opportunities for speed vary 
in different vessels as the square roots of their respec- 
tive lengths." 
Applying this to two yachts, A of 2Sft., and B of . 
36ft. length, we infer that their possible speeds vary 
as 5 and 6. If they are to race together, one way of 
putting them on an equality would be to lay out a 
course of, say, 10 miles for A and 12 miles for B, and 
the first to complete her course would win the race. 
This plan is quite out of the question in practice, and 
is mentioned only as a simple illustration of the prin- 
ciple involved. An alternative is to require each yacht 
to sail, say, 12 miles and to make the allowance to the 
smaller in time. And as time and speed are in inverse 
ratio, the allowance should be one-sixth of the time of 
the larger, or one-fifth of the time of the smaller 
yacht. This involves the selection of one or the other 
as a standard; but with only two yachts, which are 
well matched, the choice is not important, and the rule 
in this form is workable. With more than two yachts 
in a race this method would lead to complications, and 
the calculations would be tedious, although a proper 
table of allowances could easily be arranged to min- 
imize the latter difficulty. In practice both have been 
overcome by the use of the startling assumption that 
Vlength (in feet) equals speed in miles per hour. 
On this basis the allowances per mile are shown in 
terms of time, all of which is very handy and decidedly 
wrong. 
I do not know who first propounded the above speed, 
formula, nor am I able to explain its persistent 
omission from the theoretical explanation of time al- 
lowance published in the books of the various clubs. 
It is an essential link in the chain of reasoning which 
tbfe cyrif us yachtsman is allpiyeS to d§du^ fya^ t^f 
