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The Callaway
Big Bertha Dimple
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Analysis
& Approaches for the Dimple-Error in PuttingFurthermore, experts tell us that dimple patterns do not affect how a ball rolls on a green. Of course, a smooth ball will roll straighter than a dimpled ball on a perfectly smooth surface, says Maxfli's John Calabria. "On a pool table, yes. On a putting green, no."
On the other hand, Dave Pelz states that a ball wobbles on top of its dimples as it finally slows down to stop, and that on occasion this wobble may cause a ball to miss the edge, especially on tight, fast greens. He therefore advises to deliver the ball with more than just-get-there speed.
D. Pelz's Putting Pible fig. 9.10.5, p 209
The plastic liner inside the golf hole is required to be down below the rim at least 1 inch. This means that there is practically no chance the shape of the dimple would influence whether a putt sinks based upon the dimple impacting the hard liner. Nor should the dimple-turf impact on the rim itself matter much, as the turf is generally resilient and thus neutralizes the dimple's effect.
An additional advantage, at least on short putts, is that if the ball is struck on the seam by the putter, there is no dimple to possibly cause misdirection. As Dave Pelz has shown (see p. 211 in the Putting Bible), when the ball is not compressed, as is the case on very short putts, hitting the edge of a dimple can cause the ball to come off the face at odd angles, odd enough to miss. What Pelz does not say is that the new soft inserts, which allow the face to compress on short putts rather than the ball, takes care of most of this problem. But just to be safe, one could try to strike the ball on a seam or a flat place on the ball's surface between dimples. Pelz advocates marking such a spot on the ball.
Dave Pelz in his Putting Bible (sec. 9.10, pp 208-211) describes dimpled balls as balls with feet that roll oddly when hit with a putter. The chances of hitting a dimple edge at an odd angle to the intended line of the putt increases with dimple size. The chances that the off-line impact on a dimple edge will actually result in the ball starting off on a line not intended (other than the one that results from the putter face movement at impact towards the center of the ball) increases with the hardness of the cover material in that the cover material hardness decreases the compression of the material from the low-velocity impact of a putter face strike. He shows patterns of dimple impacts on impact tape on the putter face for various putterhead speeds at impact (as indicated by distance of putts on the same green speed), and these patterns indicate that edge-only impact survives incomplete compression of the edge during impact up to a 10-foot putt, and the dimple is completely compressed to flush impact by a 30-foot putt or longer. (Pelz does not specify the cover material, dimple shape or size, point of impact on the dimple, putter face material or green speed he used, so his data is merely suggestive.) Pelz shows a chart he made correlating percent of dimple compression against distance of putt as resulting in inches offline at the end of the putt, again without specifying his materials and conditions. Pelz writes that the dimple-error problem only matters on "short or downhill putts on fast greens". His chart indicates more specifically, however, that the only time the dimple impact causes a miss at the hole is when the putt is long enough (3.52 feet) and the percent of compression low enough (37.5 to 50 percent) or for a longer putt (4.94 feet) with the compression percent being 37.5, 50, 0or 62.5 percent. Pelz seems to imply that putts longer than 4.94 feet do not suffer from sufficiently minimal compression to miss, but this is very unclear. The chart clearly indicates that putts under 3.52 feet do not have a big enough error to miss the hole even at minimal compression, but this assumes dead aim and otherwise perfect impact dynamics.
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Dimple-error misses indicated in shaded boxes
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Percent compression of cover dimple diameter (%)
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37.5
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50
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62.5
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75
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87.5
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100
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Putt Length (feet)
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Distance off-line putts have rolled when hole
high (inches)
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0.70
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0.54
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0.44
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0.33
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0.22
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0.11
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0.00
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2.11
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1.64
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1.32
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0.99
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0.66
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0.33
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0.00
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3.52
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2.74
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2.20
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1.65
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1.10
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0.55
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0.00
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4.94
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3.84
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3.08
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2.31
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1.54
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0.77
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0.00
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D. Pelz's Putting Pible fig. 9.10.5, p 211.
NESTA's support is enabling Dr Norman Lindsay to solve the problem of dimple-error in putting and pioneer a breakthrough in the spin-imparting properties of golf clubs, improving ball trajectory and length.
All-TS putters are designed to address this problem, featuring a patented face with fine horizontal ridges that distribute the impact force across the dimples of a golf ball to improve line accuracy.
Norman Lindsay and the Theory of Dwell Time
Dwell time' or contact duration between two colliding objects such as a golf club and ball is a well-understood topic in the science of contact mechanics. The founder of contact mechanics was Heinrich Hertz, a brilliant young German physicist. Heinrich Hertz 1857 to 1894 In 1882, Hertz was only 24 years old and working as a research assistant in Berlin University when he published a paper describing his theory of impact. This theory predicts what happens when objects collide and bounce off each other - how much deformation occurs, how the impact force varies with time and the total duration of contact, or what some putter manufacturers call 'dwell time'.
A recent paper in Science and Golf IV by Professor Ieuan Jones of Flinders University presents convincing evidence that when you hit a golf ball, the force and duration of the impact obey the Hertz theory very accurately. Jones studied ball impacts over speeds corresponding to a gentle 'tap in' with a putter and up to a full drive down the fairway. Over this range of speeds the impact duration varied from 0.85 milliseconds for a gentle tap-in to 0.37 milliseconds for a drive.
So the rule is, the faster the swing speed, the shorter the dwell time. The 'dwell time' for a drive is just less than half that for a gentle putt, even though the ball speed off a driver is about 50 times faster than a tap-in. On the putting green, the variation in dwell time for different putt strengths is very much less. For example, on a level green, with the same putter and the same ball, a 10-foot putt will have just less than 15% more dwell time than a 40-foot putt.
The Jones study focussed on how accurately the Hertz theory predicts impact dynamics of one type of golf ball. The ball-hitting implement used in his experiments was made of stainless steel but was very much heavier than a putter head. Replacing this with an average weight putter head would reduce the values he obtained by about 6%. However, different weight putter heads do not change dwell time by much. The dwell time for a 450 grams putter head is only 3% greater than for a head weight of 250 grams.
The property of balls and putters that makes the most difference to dwell time is their hardness. Balata covered balls and elastomer face inserts give longer dwell time than harder materials such as Surlyn or steel, but even these soft materials do not increase dwell time significantly. The Hertz equations use basic elastic constants (Young's modulus and Poisson's ratio) whereas golf balls and putter inserts are usually specified in 'Shore Hardness' scales measured by a hardness tester called a 'durometer'. This makes it difficult to apply the Hertz equations directly.
What we do know is that with any flat metal-faced putter, the dwell time is almost entirely determined by the ball material so there is no measurable difference between the dwell time from 'soft' metals like aluminium or copper and 'hard' metals like stainless steel. This is because metal putter faces are much harder than golf balls and all the impact deformation occurs in the ball. The Hertz equations also tell us that replacing a metal putter face with an insert made of the same material as the golf ball cover increases the dwell time by only 32%.
Since The Rules of Golf prohibit inserts that are softer than a golf ball, it is very unlikely that 'legal' inserts could increase dwell time by more than 40% to 50% compared to the value obtained with a steel face and a balata covered golf ball. A way of getting round the rules would be to produce a very soft-covered golf ball - much softer than alata - but his would be almost unplayable. To prevent this anomaly, a specification that face inserts must be no less than 85 on a Shore A durometer scale is included in A Guide to the Rules on Clubs and Balls.
MEASURING DWELL TIME
The two traces plotted on the left show the C-Groove accelerometer signals for two different types of ball. Both balls were putted very close to the sweet spot with putt strength of one Stimpmeter¨. In other words, with this putt strength, the balls would roll about 10 feet if the 'green speed' were 10 feet. The top trace is for a Surlyn-covered ball, which gives a short dwell time of about 0.6 milliseconds. The 'ripple' on this trace is caused by putter head vibration. This would disappear if you could get the impact perfectly on the sweet spot, but this is very difficult and the hard covered ball shows up any tiny offset. The lower trace shows the C-Groove deceleration pulse when a balata-covered ball was used. Here the dwell time has increased to about 0.8 milliseconds.
TaylorMade are correct to assume that the 'nubs' on the putter face increase dwell time slightly. It depends on the softness of the insert material and the additional compliance provided by the voids between the nubs. We found that the dwell time for the Nubbins putter was about 0.9 milliseconds, fractionally longer than for a balata ball off a flat steel putter and with the same strength putt (one Stimpmeter¨). However, the claim that this improves ball roll is pure fiction. The nubs in the Nubbins putter are unfortunately similar to dimples on a golf ball and cause line errors. A special groove configuration on Lindsay putters is designed to reduce these line errors, but the TaylorMade nubs will tend to slightly increase dimple error effect. (More details of this error effect will appear in future editions of this website.) As it happens, the Nubbins putter is probably less prone to dimple error effects than some other putters because its soft insert material helps to reduce dimple errors.
So what is the maximum dwell time you can get from a 'legal' putter? This is going to be from a putter with an exceptionally soft insert - probably softer than a standard balata-covered ball. One likely candidate is a Fisher putter. Fisher claim that their putters have more than twice the dwell time of a flat-faced steel putter and quote some quite amazing 'scientifically proved' figures. Undoubtedly, their putters have very soft inserts Ð in fact just within the limits set by The Rules of Golf Ð but their figures for dwell time are highly exaggerated and again, equating dwell time with overspin is simply marketing hype.
Top trace: The Nubbins putter - dwell time just less than one millisecond.
Lower trace: Fisher F-6 putter.
Dwell time marginally over one millisecond.
(Both putters tested against a balata-covered ball at one Stimpmeter¨ putt strength.)
Fisher Golf's claimed dwell time
Measuring the hardness
of the Fisher putter with a durometer. Its hardness measures about 87
Shore A.
This is within the legal limits set by The Rules of Golf but quite a bit
softer than most 'soft-covered' golf balls.
Comparing Shore A and Shore D is not straight-forward.
Comprised of over 23,000 miniature brass balls encapsulated in a polymer substrate, the insert in the Carbite CAP Series putters is designed to hug the dimple pattern of a golf ball at impact, providing better feel and a truer roll. The CAP putters also feature extreme heel-toe weighting (Polar Balanced) for maximum forgiveness on off-center hits. In addition, the CAPs are designed with a precise center of gravity location to encourage a more forward roll.
Also, the PIXL putter, the Taylormade Nubbins putter, and the Ping Isoforce putter
The PUTT RICH System includes our EQUATOR LINER with instructions to mark your ball for useful feedback, but also to find and mark the equator.Ê This marking provides a reference for aligning the ball for putting, plus facilitating striking the ball on the equator which eliminates any inaccuracies resulting from striking the irregularities of the dimple pattern.Ê (Our research delivered evidence that the randomness of the dimple pattern(s) can cause significant inaccuracy, even on short putts.)
http://www.neohioschoolofgolf.com/puttingtrainer.asp
http://www.golfaroundtheworld.com/prich.htm
No dimples on some equators -- so mark the equator with the line and hit the equator -- PuttRich
Many balls today, including the Callaway, have a pattern of dimples that does not have an equatorial or other seam.
There are six small, bald spots on each ball that do not contain any dimples. The rationale to these smooth spots is that the uneven, unpredictable nature of a standard ball's dimpled surface dictates that the contact made with a putter face will cause slight deviations in roll. The manufacturer claims that a more pure roll will result when the putt is struck on a bald spot. We've putted a couple hundred putts into the scoring grid on our trueboard. It did not take long for it to become apparent that that there are some very real differences. We have witnessed many examples of absolutely beautiful roll. The accuracy scores that have resulted are slightly better than with standard issue golf balls, but clearly enough to make the company's claim that 1 to 3 strokes a round can be saved sound reasonable. 1 to 2 strokes saved seems very realistic - provided the balls perform satisfactorily in other regards.
We putted a series of comparison putts with the Taylor Made Nubbins mallet. It was just as we suspected; the tiny little bumps on the Nubbins' face do act irregularly with the tiny dimples on a conventional ball's surface. Even our two testers who saw no improvement when using regular putters with the Bald Eagle did definitely see a marked improvement this time around. The Nubbins, already a fine putter, just plain putts better with a Bald Eagle ball.
Bald Eagle putting balls review
ConclusionsThe magnitude of the line error resulting from dimple-edge impact depends upon a number of factors:
All of the above assumes that the putter face is uniformly flat and oriented square and moving square at and during impact and that there is no twisting of the putter face or change of direction of motion during contact with the ball. (These assumptions are only true in the Ideal world of Plato.) The same observation made by Werner and Grieg in How Golf Clubs Really Work applies here: the likely magnitude of the dimple-error is very minor in comparison to errors that result from such basics as aiming and making a good stroke with good speed control or errors that result from surface irregularities.
The usual assumption that the impact of putter and edge is instantaneous is obviously incorrect, given the dwell time and the time involved in compression of the cover material. The effect of dimple-edge impact is not really fixed solely by the geometry of putter face against edge at initial contact. Other considerations are how the oblique impact imparts spin to the ball with angular momentum about a certain axis, how this angular momentum of the ball reacts to static friction and the inertial properties of the ball (as these influence compression of the edge during impact), and how forward rolling over the grass washes this effect out. If the edge is mostly ABOVE or BELOW the center of the putter face, the effect of dimple-edge impact is presumably constrained in the vertical dimension and has little or no effect on line of travel of the ball, whereas if the edge is mostly off to the LEFT or RIGHT of the center of the putter face, the effect is more directly on the line of travel of the ball. As with an off-center ball, it matters quite a bit HOW MUCH out of the center the imbalanced COG is located AND what is the orientation of the out-of-balance COG to the intended vertical plane of roll of the ball at address. The actual chances of the dimple edge being oriented out of the relatively trouble-free vertical plane (say between 4 and 8 on the clock or between 10 and 2) and inside the troublesome lateral plane (say between 2 and 4 or between 8 and 10) is roughly 1/2 the total, so from this perspective, the problem is half as large as one might suppose.
As with an out-of-balance ball, this orientation can be handled by trying to center a single dimple squarely on the back of the ball to meet the putter face flush, with the intended impact dynamics (level blow, upward blow, downward blow, etc.), or even by trying to position the dimple edge backmost towards the putter face. This process might be facilitated by marking one specific dimple and placing the ball on the green so that this dimple is squarely on the line of the putt and on the equator of the ball in relation to the surface.
Another possible approach is to notice how a ball's dimple pattern makes the ball settle onto a flat surface like a table top. Does this pattern necessarily position a dimple edge in a troublesome way at the back of the ball? How does this sort of pattern settle into the grass of different greens?
In the same vein, does the manner in which the manufacturer imprints the ball with its logo and other writings reliably assist in favorably orienting the back of the ball to mitigate dimple-error? Does the ball have an easily identifiable seam that can be oriented vertically, or a similar regular pattern that can be taken advantage of in positioning the ball? This doesn't appear to be the case in general, but often enough the happenstance imprinting can be helpful.
Turning to the Callaway dimple, the first observation is that the dimples of the Callaway HX and Big Bertha balls are not substantially different from almost all other balls in terms of the chances of striking the edge of the dimple. The two differences -- width and edge shape -- aren't sufficiently BIG differences to matter much. While the Callaway dimples are wider than most, they are not that much wider, as a visual comparison indicates. Paradoxically, a wider dimple has some advantages in reducing line error: the bigger dimple is easier to orient in a less troublesome manner because easier to see and position; and the bigger width means there is less chance that an edge occupies space close to the center of the putter face impact point as a result of chance positioning. (Indeed, if the dimple were really wide enough stretched onto the spherical surface, the putter impact could occur solely inside the bottom of the dimple without contact with the edge.)
The second observation is that the hardness of the cover on the Big Bertha balls is in the mid-range at 63D for Red and 60D for Blue. In comparison, the hardness of the cover for the HX balls is very soft, with Red at 50D and Blue at a very soft 43D. The HX Tour ball cover is also soft at 54D. The Nike TA2 and One balls have covers at 53D. The Strata Ace is at 55D and the Strtat Tour Ultimate is at 51D. The Big Bertha hardness is in the middle of the pack and probably does little to mitigate dimple-error at impact.
Even so, the Pelz data suggests that the only real problem at this hardness level is for putts in the range of 3-5 feet on fast greens. Otherwise, the data suggests that the dimple-error has little influence on the outcome -- on shorter putts because the off-line error is too small to matter by the time the ball reaches the hole, and for longer putts because the putter head speed compresses the dimple edge out of the picture and reduces or eliminates line error. Since Dr Norman Lindsay is in the process of addressing the specifics of this issue, and will doubtless do so in a manner far more detailed and analytically complete than Pelz has, the final word most likely rests with Dr Lindsay.
In the meantime, the main approaches to reducing the somewhat limited dimple-error in putting are:
The recommednation for the Callaway balls is to orient the back of the ball with some care, but don't get too worked up unless you're playing Augusta National facing a kneeknocker in the 2 to 5 foot range, and have a perfect stroke to begin with.
More generally, I would suggest using a soft-cover ball, and perhaps also a soft-insert putter.
ADDITIONAL
RESOURCESCompare Prices and Read Reviews on Callaway HX Ball
eBay item 7108590375 (Ends Oct-25-04) -- 230 golf ball patents compiled on CD-ROM
Closest-Packed Structures: Hexagonal Lattices
Golf Tips Magazine, Distance, feel and Spin: The top new golf ball offerings unveiled, 2003
Titleist.com -- Technology -- Principles of Aerodynamics
Golf Tips Magazine 2003 Golf Ball Buyer's Guide
Frankly Golf -- Q&A about Golf Balls
Discover Engineering Online - Cool Stuff
Andy Brumer, The Technology of Golf: The Golf Ball, Informit.com, 2 Apr 2004
Math & Science: Golf Ball Flight Physics
Golf Digest: Sam's Best Swing Keys - Sam Snead -- Hit the Dimple
Zen Oracle reduced dimple error putter face technology
Rod Cross: Dimple error in putting
Norman Lindsay: dimple-error reducing putter face patent
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