Golf balls

A golf ball has a surface pattern of dimples arranged to provide at least 12 symmetrically disposed bald patches, a bald patch being defined in terms of its ability to accommodate a spherical rectangle of specified minimum width and area relative to the dimple size.

The present invention relates to golf balls, and is particularly concerned 
with the surface configuration of golf balls. 
Golf balls have, for many years, been provided with dimples -- i.e. 
depressions or indentations -- in their surface since it is found that 
this gives superior aerodynamic properties compared with a smooth ball. 
Many efforts have been made to vary the size and depth of the dimples and 
the disposition of the dimples on the surface ("dimple pattern") to obtain 
optimum aerodynamic properties and hence flight performance. 
Hitherto, it has been thought that the dimples should be closely packed and 
arranged as uniformly as possible over the surface of the ball. 
We have now discovered, however, that it can be advantageous to provide 
certain dimple-free areas on the surface of the ball. 
Thus, according to the present invention there is provided a golf ball in 
the shape of a sphere having in its surface a plurality of dimples or 
depressions and which has at least twelve bald patches symmetrically 
disposed on the surface of the ball. 
A "bald patch" is defined as any region on the surface of the ball on which 
it is possible to draw a spherical rectangle having a width of at least 
half of the mean dimple diameter and a surface area of at least twice the 
mean dimple area, the rectangle not enclosing any dimple or part thereof. 
By a spherical rectangle we mean a radial projection of a rectangle on to 
the surface of a sphere, the sides of the rectangle thus being arcs of 
great circles of the sphere. By "length" and "width" we mean the larger 
and smaller arc lengths respectively, although it is not intended to 
exclude the case where they are equal -- i.e. a square, and by "surface 
area" we mean the area of that part of the surface of the sphere bounded 
by the rectangle. By "mean dimple diameter" is meant the average of the 
diameters of all the dimples on the ball, while by "mean dimple area" is 
meant the area of a dimple having the mean diameter -- i.e. (mean dimple 
diameter).sup.2 .times. .pi./4. 
Preferably the width of the rectangle is at least three-quarters of the 
mean dimple diameter, while the area of the rectangle is at least four 
times the mean dimple area. 
It is preferred that the bald patch size shall not exceed a maximum defined 
by the following conditions: 
(i) it should not be possible to draw on the bald patch a square having 
sides whose length is greater than twice the mean dimple diameter; or 
(ii) it should not be possible to draw on the bald patch a rectangle having 
a width of at least half the mean dimple diameter and an area of more than 
eight times the mean dimple area. 
In a preferred embodiment the configuration of the dimples or depressions 
is substantially the same in each of those twelve regions of the surface 
of the sphere which are defined by lines formed by projecting on to the 
surface the edges of a regular dodecahedron whose vertices lie in the 
surface of the sphere. 
In the case of a dodecahedron there will be 12 substantially identical 
pentagonal regions. Thus the preferred number of bald patches to maintain 
symmetry for such a system is 20, 12 or 30 according to whether the 
patches are located at the vertices, at the centers of the faces or the 
mid-points of the edges. 
However, the invention is not limited to use in a dodecahedron system of 
dimple arrangement but can be utilized in other systems, e.g. any of the 
more conventional dimple arrangements that have been proposed. These 
include spatial arrangements derived by projecting into the surface of the 
sphere the edges of an icosahedron or octahedron. 
For an icosahedron, having 20 triangular regions the preferred numbers will 
be 12, 20 or 30 for patches at the vertices, centers of the faces or 
mid-points of the edges respectively. 
For an octahedral arrangement the preferred number will be 12 (8 or 6 are 
of course theoretically possible from geometrical considerations, but fall 
below the minimum number required in practice). 
There may be dimples provided on the boundary lines of the regions, or the 
lines may be free from dimples, but preferably the dimples arrangement is 
symmetrical about any boundary line. 
The dimples may all be of the same size and shape, but it may be convenient 
to provide some dimples of differing size and/or shape. The dimples may, 
if desired, have rounded edges. 
The dimples are preferably of circular appearance in plan view, their shape 
being that of a solid of revolution generated by the rotation of a plane 
curve about a radius of the ball, such as a segment of a sphere or of an 
ellipsoid, but other shapes may be used, e.g. dimples may be provided 
whose appearance in plan view is oval or polygonal. 
The dimple diameters may vary according to the size of the ball but are, 
for dimples circular in plan preferably in the range 0.085 inches to 0.150 
inches, especially 0.090 inches to 0.145 inches. Preferably the largest 
dimples have diameters in the range 0.110 inches to 0.150 inches. 
The ratio of the maximum depth of the dimples to the diameter may be 
between 1:6 and 1:15, e.g. 1:10. Thus it is preferred that the dimple 
depths are in the range 0.009 inches to 0.014 inches. 
By "dimple depths" or "maximum dimple depths" in this specification is 
meant the measurement along a radius of the golf ball which passes through 
the lowest point of the dimple, the measurement being from that lowest 
point where the radius crosses the projection above the dimple of the 
great circle of the surface of the ball. 
While any desired number of dimples may be provided, it is preferred that 
there should be at least 240 dimples, preferably not more than 480, for 
example, the ball may be provided with 360 dimples. 
The optimum number of dimples will, of course, vary according to the dimple 
size(s) used. Most dimple arrangements result in a total dimple area of 
about 50- 60% of the ball surface -- e.g. 240 .times. 0.150 inch dimples 
on a 1.62 inch ball gives approximately 51% coverage, while 480 .times. 
0.110 inch dimples gives a figure of about 55%. These figures are not 
quoted by way of limitation but merely as a guide. 
Golf ball covers are conventionally moulded in a two-part mould, which 
results in a seam line being visible at the joint between the two mould 
halves. In practice the mould halves are hemispherical and this seam line 
is therefore a great circle of the sphere -- indeed, to construct a mould 
so as to provide a seam line of any other configuration presents severe 
practical problems. The seam line should preferably not pass through any 
dimples on the ball surface. Thus it will be appreciated that, in 
practice, it will generally be necessary to arrange the dimple 
configuration to allow for this. 
The dimple configuration of the present invention may be applied to the 
surface of any conventional golf ball whether of 1.62 inch, 1.68 inch 
diameter or any intermediate or other size. The construction of the golf 
ball also may be any conventionally used. For example, the ball may have a 
unit-construction, i.e. be in a single piece moulded from a suitable 
rubber or plastic composition. It may be a two-piece ball having a 
unit-construction core encased in a cover or it may have a 
multi-construction core encased in a protective cover, and the present 
invention is eminently suitable for use with such balls. 
Where the ball is of the type having a separately-applied cover around a 
core, the cover may be moulded from any conventionally used material, e.g. 
balata; gutta percha; synthetic trans-polyisoprene; polyurethane; 
polyethylene, the cover materials of the assignee's British Pat. No. 1 087 
566 or any desired blends thereof. The cover may be formed by any 
conventional means. For example, it may be moulded as two separate 
hemispherical half-shells which are then compression moulded around the 
core. Alternatively it may be injection moulded around the core in a 
single operation. 
The dimple configuration will normally be applied to the ball during the 
moulding of the cover around the core (or during the moulding of the 
unitary sphere in the case of a single-piece ball) by use of 
appropriately-shaped negative moulds containing the dimple pattern in 
reverse, this being quite conventional in the field of golf ball 
manufacture. Accordingly in another aspect the invention provides a golf 
ball mould whose moulding surface contains a pattern to give the golf ball 
dimple configuration of twelve symmetrically disposed bald patches. 
The moulded golf ball having the desired dimple configuration may then be 
painted in the conventional manner. 
Alternatively, painting may be rendered unnecessary by suitable compounding 
of the composition used, this being a well-known practice particularly for 
the above-mentioned one piece golf balls.

A golf ball 1 (FIGS. 1 and 2) is provided with dimples 3, the arrangement 
of the dimples in each of twelve surface regions defined by twelve 
contiguous regular spherical pentagons (indicated in the drawing by dotted 
lines 2) being identical. Each dimple is a depression in the shape of a 
segment of a sphere. 
(A spherical pentagon is defined as the figure on the surface of the sphere 
which is bounded by five great circles inscribed on the surface of the 
sphere. A regular spherical pentagon is a spherical pentagon whose 
internal angles are equal and whose sides are equal in length). 
The arrangement of the dimples is such that the ball is provided with bald 
areas 4, indicated in the drawings by chain-dot rectangles, on the 
mid-points of the sides of the spherical pentagons, so that there is a 
total of thirty such areas symmetrically disposed around the ball. 
The arrangement of dimples in each pentagon is a projection of the planar 
arrangement shown in detail in FIG. 3. The pentagonal outline 10 encloses 
dimples 11, 12, 13, 14 of different sizes. The dotted lines 15 show 
possible positions for the seam line of the ball: there are ten such great 
circles on the surface of the ball -- i.e. ten planes of symmetry. 
It will be appreciated that the dimple pattern shown on the drawings is but 
one example of many different possible arrangements. 
The invention will now be illustrated by means of the following examples. 
EXAMPLES 
Golf balls according to the invention were manufactured having the dimple 
pattern shown in FIGS. 1, 2 and 3. The dimple depth was 0.011 inches, 
while the dimple numbers and diameters were as follows (dimple reference 
numbers refer to FIG. 3): 
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Dimple Diameter(inches) No. on Ball 
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11 0.135 120 
12 0.125 120 
13 0.120 60 
14 0.110 60 
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The total number of dimples was thus 360, the mean dimple diameter was 
0.125 inches and the mean dimple area (as hereinbefore defined) was 
0.01228 square inches. There were thirty bald patches, as shown in the 
drawings. The largest rectangle which could be fitted into the bald patch 
-- i.e. with sides tangential to the six adjacent dimples, measured 0.107 
inches .times. 0.46 inches -- i.e. a width of 0.856 dimple diameters and 
an area of 4.01 times the mean dimple area. 
Comparative flight tests were carried out to evaluate the performance of 
these balls in terms of distance of travel through the air (carry) when 
the balls were tested on a flight test machine. The standards for 
comparison were balls made with a dimple pattern based on the octahedron. 
Such a pattern has long been established as `conventional` and the 
majority of golf balls currently manufactured in the world are made 
incorporating such a pattern although variations occur from one 
manufacturer to another with regard to the total number of dimples, dimple 
depths and dimple diameters. 
For the purposes of the comparative test referred to here the standard 
balls had a conventional pattern composed of 336 dimples of which all but 
32 dimples were of diameter 0.130 inches (the 32 being of diameter 0.110 
inches). In the case of one standard ball the depth of each dimple was 
0.011 inches and in the case of the other the depth of each dimple was 
0.013 inches. The 0.013 inches depth is the one most commonly used for 
golf balls currently made in the world with the conventional pattern. 
All balls were of 1.62 inches diameter and were made using liquid centers 
wound with a highly stretched thread based on a blend of natural rubber 
and cis-polyisoprene. The covers were moulded from a 90/10 blend of an 
ionomer and EVA (see British Patent Nos. 1 087 566 and 1 383 422). Normal 
manufacturing procedure was used in each case. 
The compression of the balls was measured -- i.e. the deformation of the 
ball (in thousandths of an inch) under a load of 100 lbs weight. The balls 
were then subjected to flight tests. This is carried out using a flight 
machine specifically designed for comparative testing of golf balls. 
Basically this machine simulates the driving action of a No. 1 Wood club 
and enables a consistent and accurately reproducible impact to be given to 
a succession of golf balls. The speed of the club head as it impacts the 
stationary ball can be varied by means of weights: the speed used in the 
tests was 158.5 ft/sec. 
The Carry was measured visually by noting where the balls landed relative 
to a number of prepositioned markers placed down the flight patch. 
The results of the tests are shown in Table I. It should be noted that 
external factors -- i.e. wind, etc., will vary from one series of tests to 
another so that, for example, the results of test I are not directly 
comparable with those of test II. 
TABLE I 
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FLIGHT TEST RESULTS 
TEST I Weight Compression Carry 
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Golf ball of the 
invention, example I 
45.4 gms 59 232 yds 
Standard Ball 
0.011" Dimple Depth 
45.3 gms 58 230 yds 
(Mean of 4 flights on 4 balls of each type) 
Test II 
Golf ball of the 
invention, example 2 
45.2 gms 54 237 yds 
Standard Ball 
0.013" Dimple Depth 
45.5 55 235 yds 
(Mean of 3 flights on 12 balls of each type) 
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It can be seen from the above results that an improvement in carry of 2 
yards was obtained by means of the invention.