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By Paul Wood

I imagine most of you have experienced walking up to your ball on the course and seeing a big patch of mud on it. After bemoaning your bad luck, you may start to think about how to make the best of the situation. What does mud on the ball actually do?  Is the effect random or is it predictable?  This is the story of the science of “mud balls”.

One of our engineers had encountered a significant amount of mud on the right side of his ball in a tournament earlier this year. Unsure what the effect on ball flight would be, he aimed for the middle of the green and watched his ball fly into the rough, well left of the green. This spurred a debate as to whether the effect of mud on ball flight could be consistently predicted.

We used our knowledge library to conduct some theoretical analysis, which led to a prediction that mud on the right side of the ball should almost always cause the resultant ball flight to curve to the left. The answer lies in the physics of aerodynamics –during flight air flows around the ball causing lift and drag forces which both slow the ball down and create curvature in the flight (see Figure 1). Our analysis predicts that mud in the dimples will affect the air flow, causing the turbulent wake to be bent toward the mud side. This in turn will cause the ball to curve in the opposite direction. The big question is – in the real world, with a chunk of mud on the ball, is this effect measurable and repeatable?

To test our hypothesis, we set up a 4-iron on our PING Man robot and set the swing characteristics to mimic a fast swing-speed player. The club speed prior to impact was set to 95 mph, leading to center hits carrying a little over 220 yards. We then teed up several balls with mud caked on different areas. Some had mud covering the entire surface of the ball, while others had mud applied to one area – either the front, back, top, bottom, left or right side of the ball.

For our testing, we used a lot of mud to try to maximize the effect and get the most measurable results (Figure 2). However, our high-speed video analysis of impact showed that much of the mud fell off the ball immediately, regardless of how much mud we applied (Figure 3) so we have confidence that our results will hold for smaller amounts of mud.

Our PING Man robot is extremely consistent when delivering the club. With no mud on the ball, the variation in carry and offline distance is not much more than 1 yard from shot to shot. This is reflected in the “error bars” in the charts below. The bars themselves represent the average values from all the shots taken, while the error bars give a visual representation of the consistency of the data.
 

Does mud on the right of the ball cause it to bend consistently in one direction?

The answer is categorically yes. Figure 4. shows that balls with mud on the right side landed around 25 yards left of the target on average but with much wider variation in results. Likewise, with mud on the left, the ball landed almost 30 yards right of the target. With mud all over, the balls went mostly straight but with a similarly wide variation in results. The mud is making the ball flight less consistent, which is no surprise. However, the take home message is that if you find your ball on the fairway with mud on the right side, aim right of your target and you can be confident that the ball will curve a long way to the left. This was tested by one of our engineers in competition not long after we conducted the test and he was able to aim right with confidence and find the middle of the green.
 

Does mud on the ball cause it to fly shorter?

Figure 5. shows the carry distance of all the configurations we tested. There was a significant drop in distance for all the mud balls, but the most dramatic drop by far occurred when mud interfered with the club-ball interaction. With mud on the back or bottom of the ball, the club impacts mud before the ball and — no surprise — mud is not great for energy transfer. Even when mud does not get in the way of the club, ball speed is lower, which is a result of some of the energy in the club head going towards accelerating mud rather than the ball. The message here is: mud on your ball can lead to a loss of carry distance, depending on how much mud gets between the club and ball, so take an extra club, or two, if there is a lot of mud on the ball. Our test shows the extreme case because we used a lot of mud, but the effect will exist whenever there is an impediment on the ball.

This kind of little experiment reminds me how fortunate I am to work in an engineering department where if we have a question based on observations during a round, we have all the tools at our disposal to answer that question in a systematic and reliable way. I hope this helps shed a little light on what you can do if you’re unfortunate enough to find mud on your ball during a round.

 

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