Dear Larry,
Great question!
I consider a "snake" putt one that has different breaks.
The critical break in a series of different breaks is really the last one nearest the hole, as this break determines whether the rolling ball sinks or misses. So my advice is to focus most intently on getting this break read astutely, and then work backwards from this curve to discern the earlier breaks.
All breaks are read by accurately envisioning the realistic speed of the ball as it rolls over the specific region of the green surface, intuitively imagining the way surface tilt and green speed and condition interact to alter the course of the ball's path. The three elements of reading a putt are 1) ball's speed pattern over the course of the putt; 2) surface contour in relation to gravity; and 3) surface playing condition and speed. There's plenty of science here for those interested, but almost all golfers have to rely upon intuition and experience to be able to envision gravity's effect on a rolling ball accurately.
There are two main principles for accurate visualization of breaks: 1) work from the known to the unknown; and 2) respect the required continuity that integrates the known and the unknown.
The known: The speed of the ball is best known only as it approaches the hole with good touch. Golfers with good touch deliver the ball to the hole on ALL putts with the same end-speed at the lip (e.g., 2 revolutions per second of rolling speed when the ball arrives at the front edge of the hole). Golfers never know the speed of the ball right after the moment of impact, and really don't know the speed during the middle stages of the putt, either. The speed only comes into the realm of the known once the ball rolls to within about 2-3 seconds of the hole, and over this final part of the path of ALL putts, the speed of the ball of a golfer with good touch always looks exactly the same. So the golfer most accurately can visualize the break nearest the hole. The point is that the golfer needs to visualize any sort of breaking putt backwards from the hole, reversing the movie of the putt to start from the finish of the roll, the known.
The continuity: There are no corners or angles in putting, and all curves have continuous radiusing. Some segments of a putt may have a "sharp" or "tight" curve, while some may have a "smooth" or "gentle" curve, but there are no sudden changes in the direction of rolling. The ball changes direction in a continuous shifting of the "tangent" to the path. The "tangent" is the line perpendicular to the radius of the curve, like pressing a ruler flat against an orange. The radius line runs perpendicular from the flat ruler to the center of the orange, which in the case of the contour of a sphere is also the center of the radiusing.
To understand the smooth way the "tangent" to the putt path changes at different points along the course of the path, the reference for the putt path (like the center of an orange) is the "baseline." The baseline of a putt runs straight from the ball to the center of the hole. A straight putt runs only along the baseline, but a breaking putt starts away from the baseline aimed at a target other than the hole. At the very beginning of a breaking putt, the path appears relatively straight, and the "tangent" of the path at the starting point is aiming pretty much the same way the start line of the putt is, and both the startline and the tangent at the starting point make some specific angle with the baseline. (For a straight putt, the baseline, startline, and tangent at the startline all make a 0 degree angle, so they are the same.)
Take a 10-foot putt with 1 foot of break from right to left for a right-handed golfer as an example. The startline aims at a point 1 foot to the right of the center of the hole. The baseline runs straight from ball to hole. The startline is angled off to the right from the baseline at a specific angle that corresponds to the very particular proportions of the triangle: A=baseline (10'), B=line connecting aim target and hole (1'), C=startline (over 10', the hypotenuse). From the standard trigonometry, the angle between baseline and startline at the ball at address is 5.7 degrees = arctan(B/A). If the hole is a clockface with 6 o'clock closest to the ball, the baseline runs to the hole at 6 o'clock and the line from aim spot to hole runs to the hole at 3 o'clock.
What does the curve of the total putt path look like in this example, where exactly is its "apex" off the baseline, and where on the clockface of the hole does the path enter the hole? We don't really have enough information yet, since we haven't fully assessed the surface contour and the playing condition of the surface. Assume that the surface is flat-but-tilted and all the tilt is right to left thru the hole from 3 o'clock to 9 o'clock, so that there is no elevation change between the ball and the hole along the baseline. That is, the fall line thru the hole and indeed everywhere on the green between ball and hole runs perpendicularly to the baseline downhill from right to left. Also assume that the green speed is normal or about 9 on a stimpmeter and that the condition of the surface is also normal -- no big spike marks or ball marks or ant hills or foot prints or pronounced grain to contend with. We still don't know just HOW tilted the surface is, but whatever the tilt, this final element will have to be such that the resulting break is correct, and that aiming 1 foot to the right of the hole results in a path that breaks into the center of the cup. (It's possible to figure out the tilt from physics and math, but let's just say we have the right tilt for this break and leave it at that.)
Following the ball as it rolls up the startline and then takes the break, the tangent to the curving path right at the ball will smoothly shift from the maximum 5.7 degree relation to the baseline at the beginning, rotating counterclockwise until the tangent parallels the baseline at a 0 degree angle. This point is the "apex" of the putt, which is the highest point of the ball along the path above the baseline. The tangent here, or the immediate direction the ball is then rolling, is parallel to the baseline only at the apex. After this point, the rotating of the tangent or direction of the roll continues to shift counterclockwise, aiming downhill more and more at the cup. Eventually, the forward motion of the ball delivers it to the hole so that the tangent of the path right at the ball aims to the center of the cup, right when the ball is on the lip. The exact final angle of the tangent of the path to the baseline at this time (ball on lip) corresponds to a clockface position where the ball will enter the cup (say, for example, 5 o'clock). If the tangent is aimed into the hole at 5 o'clock at the end, the angle with the baseline is 30 degrees (each hour of angle on a clock represents 30 degrees of a 360-degree circle, and 5 o'clock is 1 hours or 30 degrees off 6 o'clock, the baseline). The tangent from the apex to the lip has rotated 60 degrees counterclockwise in order to form this final angle with the baseline at the lip.
The REAL key to seeing the shape of the curving path accurately is to see the "changing rate" of shifting of the tangent at the ball as it rolls along the path. The tangent shifts smoothly the whole way, but not at the same rate of rotation hole-ward or right-to-left (counterclockwise). The slower the roll of the ball, the faster the counterclockwise rotation of the tangent of the curve. At the beginning of the putt, when the ball is rolling quickly, the force of gravity does not have as much effect on the shape of the path of the ball. More exactly, gravity always has the same effect on a ball at all moments of time on the same surface tilt and same direction of roll, but the speed of the ball is such that this gravity effect does not show in the changing shape of the path as much as it does when the ball is rolling more slowly. The slower the ball rolls, the faster the tangent rotates counterclockwise since gravity is more radically affecting the shape of the path.
This is why a clear understanding of the total pattern of speed of the rolling ball is needed for accurate reading -- the rate of rotation of the tangent along the path has to correspond to the exact speed at every given point along the path. Without this, the envisioning of the breaking path will not correspond to reality with a smoothly changing curve, but one that changes more rapidly in curvature nearer the end as the ball slows down approaching the hole with your characteristic same-every-time drop speed from your touch.
Now suppose that near the end of the putt, the surface breaks left-to-right, so the putt has a double break in opposite directions. What does this mean for accurate envisioning of the total curvature of the putt and where to aim the startline?
First, this means that our assumption of a single tilt in the green cannot be the case. The tilt must have changed from downhill right-to-left to downhill left-to-right. Let's assume that the surface tilt changed evenly, like an airplane banking smoothly first right-wing up then over to left-wing up -- there is no fitful or start-stop motion in the transition. Somewhere in there, the plane has to level out its wings, and the surface has to return to untilted, or flat and level. (Really, the attitude of the plane has to return to flat, even if still tilted.) Spotting this flat section of the green along the putt path and knowing how it connects the two breaking paths is the key to reading this sort of multiple breaking putt accurately.
Following the changing tangent at the ball along such a double breaking path, the tangent will first be rotating counterclockwise right-to-left until the ball passes thru the apex, where the ball is furthest uphill (to the right) from the baseline. After this, the ball will roll downhill until it enters the transitional zone where the surface tilt changes. Since we assume the change is "smooth" on the surface, there is really on one spot along the path where the surface is flat and level without tilt. Just before then, the tilt was downhill right-to-left but decreasing from 1 percent slope smoothly to zero percent slope right at this changeover spot, and thereafter the slope is increasingly tilted downhill left-to-right. Let's assume that the increasing tilt stops increasing when it gets to 1 percent slope. This means that the tangent of the ball right when it crosses the changeover spot will cease rotating counterclockwise, as on this level spot the influence of gravity no longer affects the path. That is, thru the transitional zone, coming into this spot and going away from it into the new tilt, gravity's influence lessens to zero and then picks back up. This means that thru the transition zone and across the transition spot where the surface levels out, the ball's roll tends to straighten out a little, and then the tangent starts to rotate the opposite way (clockwise now).
Also, the tangent right at the transition spot is aimed perpendicular to a line that defines the relationship of the two oppositely-tilted areas of the surface. To see this, imagine a letter envelope with corners A and B at one end and C and D at the other held at diagonally opposite corners A and C, with each corner twisted up -- the "gulley" between the two oppositely-tilted sections of the envelope runs diagonally athwart the two raised corners along a line from B to D. The transition spot where the surface is perfectly flat is on this "gulley" line and all along the bottom of this gulley there is no elevation change from B to D.
The exact angle of the tangent to this gulley line and the speed of the ball over the transition spot at the bottom of the gulley has to be such that what happens on the far side of the transition is exactly what is needed to deliver the ball into the cup with your touch's characteristic drop speed.
This brings us right back to working backwards from the hole to see the break. First read the last break into the cup with the ball's end speed, then read the same final path in a reverse movie with the ball running backwards out of the hole along this path. When the reverse-movie roll reaches the bottom of the gulley, this spot is critical, and the speed and direction of the ball at this point has to be respected. The reading of the path of the first section of the putt has to be such that it delivers the ball to this transition spot with the appropriate speed and direction for the final part of the putt.
The problem of multiple-break putts always ends up being reading separate putts -- the final putt being the key one. Once the starting spot of the final putt, with its starting speed and starting direction, is identified, the problem shifts to reading the preceding putt. The only difference between simply reading the first putt to deliver the ball to the transition spot as if it were the hole and reading this putt to deliver the ball to the transition spot with a specific speed and direction needed for the next section of the putt is the speed of the ball at the transition spot. It's very similar to trying to putt with more than your characteristic drop speed in order to "take some break out" of a single-break putt. The ball arrives with more speed and on a more acute angle to the baseline.
Bottom line:
1. read the last section first to identify the transition spot.
2. estimate the startline and start speed of the ball at the transition spot for the final section of the putt to work out correctly.
3. read the preceding section of the putt so that the ball arrives at the transition spot rolling on the correct line with sufficient energy to finish up in the hole.
Usually, if you take the first putt's path at the address position and plan the putt just to deliver the ball to the transition spot as if it were a hole, then this staring aim line (tangent at address) sets the out limit on the startline -- this startline is too high and the ball will just reach the transition spot without enough juice to finish thru the next section, and on too steep a line. So regarding the first putt as akin to taking some break out and following a straighter startline at the transition spot means starting the putt more downhill. Exactly how much you come down off the too-high startline really depends on the slopes and the manner in which they change -- abrupt changes versus gradual changes, steep slope one way to mild slope the other way, etc. Once you have a sense of the startline, it is very often the case (but certainly not always) that extending the startline from the ball all the way to hole-high (to some spot on a line perpendicular to the startline out from the center of the hole) gives you a distance or touch reference that will work well for the total double-breaking putt. This at least gives you a ball park reference for the total distance of the putt. Begining with this hole-high aim spot for the initial startline of the putt and for the initial sense of how much energy the total putt will require, and then turning to the specific contours of the green along the path for a fine-tuning of the sense of touch, is the plan I follow to inform my intuition as accurately and richly as possible.
At least this way, there is a ball park too-high starting line in relation to the transition spot, a way to identify the transition spot, and a way to sense the needed line and speed of the ball across the transition spot, and a general plan for coming down from the too-high startline to a startline that sends the ball over the first slope in a manner that delivers the ball across the transition spot with the right line and energy to find the cup. It's all pretty intuitive, within this general framework. Once you have a startline and a sense of the required energy, you're right back to the same-old, same-old empty-headed time to pull the trigger with a nice, smooth, steady-tempo putt with solid contact that rolls the ball straight away out of the setup, without regard to results.
Cheers!
Geoff Mangum
Putting Theorist and Instructor
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The other day, I had a slightly downhill 35 footer...the first 20-25 feet or so, looked to me like the ball would break left just a little, 7-8 inches, but then I noticed the elevation of the green changed again and the ball would break right, back toward the hole at about 10 feet out! I have to admit that I had to take a little more time reading this putt and walked to the other side of the putt and looked back at the contour from the opposite side of the hole. Well, I guessed correctly and made the putt to save par.