Lawn Bowl Bias: On the Green and on the Test Table

Introduction

There was a prelapsarian time when all lawn bowls had about the same draw and furthermore, the rules of lawn bowls prescribed a minimum curvature that all legal woods should have. Whether for better or for worse this is no longer the case. Today, you can purchase traditional uniform sole wider swinging bowls or dual sole, narrow running bowls. The purpose of this blog is to better understand these issues concerning bowl bias.

The Present-Day Single Bias Test

There is at present only one test that a set of lawn bowls must pass to be acceptable to the lawn bowls regulators of the world. Each bowl must have at least as much bias as a working reference bowl (WRB) when rolled, without wobble, under standardized conditions, on a flat hard-surfaced table. This was not always the case. Before 2002, all bowls also had to have at least the bias of the WRB on a grass green or they had to pass a second table test which featured an initial 7% cant (tilt) of the bowl which produced an initial wobble on the testing table. In an action whose motives and blame has been in dispute ever since, the manufacturer’s representatives and the bowling organizations’ representatives, either out of guile or ignorance, eliminated these second phases for bowl testing. 

Why Bowls Bend

It is not an agreed fact that bowl’s curve only because of extra weight on one side of the bowl. In the web article, THE ROMANCE OF BOWL MANUFACTURE the late J. P. MUNRO wrote “contrary to the belief of many bowlers-and particularly those of the younger generation-the bias of a bowl is not brought about by extra weight on one side of the bowl, but by the shape of the crown or running surface, which is slightly higher on the non-bias side.” 

Changed Regulation Changes Manufacturing

Returning to the historic evolution of bowling bias, the change in the regulatory test regime had an immediate engineering consequence. Because a set of bowls now only needed to have as much bias as the WRB when released without wobble on the flat, hard testing table, only the curve of a narrow central strip of the running surface, (A) in the Figure, needed to be controlled so that in combination with the overall asymmetric mass of the bowl it would pass the new single-stage test. The two curved strips on either side of this central running strip, (B)s in the Figure, could be varied since they would not make contact with the hard testing surface. Manufacturers recognized that certain combinations of curvature for these edge running surfaces would cause bowls to run narrower on grass than the WRB.  In the diagram below, what I am saying is that the strip B on the left and the strip B on the right need not be mirror images.

How a particular bowl’s curved running surface interacts with different types of rinks would come to depend on what width of the running surface came into contact with that particular rink. If the bowl is rolling, without wobble, on smooth hardwood or linoleum the contact is only a very narrow band in the center of A. If the rink is a carpet, perhaps a wider portion of A is touching. If the surface is grass, the width of bowl touching the rink depends upon the length of grass; but certainly the A and  both B sections of the bowl’s sole would make contact. If the two B surfaces, acting together, have been engineered to subtract bias, then the bowl will run narrower on  softer playing surfaces than it ever ran on the hardwood test table.

How Wobble Effects Realized Bias

There is however a separate factor that, for these engineered non-uniform arc bowls, changes the exhibited bias on the hardwood test table. If such bowls are tilted slightly when they are set rolling down the test table they will wobble from side to side, at least initially, and this will cause both the A and B surfaces to contact the table. When modern era, dual sole bowls are tested with wobbling they do not exhibit the required minimum bias of the WRB bowl. But there is no longer a part B wobble test. Such bowls now pass the modern ‘bias test’ but go down an average grass green more narrowly than the WRB would. Some players who were brought up with the standard regulations of the last century sometimes call these dual sole bowls “cheater” bowls but they are no such thing. They are different because the regulation that tests bowls has changed and that has allowed a wider range of bowl performance than before. The unhappiness is understandable but, from my perspective, we need to play the game as we now find it!

The Pros and Cons of ‘Narrow’ Bowls

Because there are plenty of bowlers who believe that the game is easier to play with very narrow running bowls, such bowls, once they were ruled legal, were soon manufactured. These "variable geometry arc" types go down a green that is faster than 14 seconds with narrower than stated bias. It can be argued that they play the weighted run through (running) shots better, because hitting the head is less weight sensitive. Proponents also say they enable straighter drives, particularly on fast greens and particularly when delivered with an intentional wobble.

These claimed advantages are not without commensurate costs. For example, variable sole bowls may play quite well in the morning, when the greens are fresh but poorly in the afternoon when more tracking marks have been laid down, because when unbalanced sole bowls cross these runs at an acute angle they are more likely to be pulled offline. Even throughout the day, greater drawing inconsistency can be observed; some deliveries may turn into the head while others stay out. This is due to the bias-subtraction, inherent to these models, being disturbed not just by recently created ruts, but by wobble, wind, or general unevenness in the rink. Because of the latter, these dual sole bowls play poorer where green maintenance is an issue. All of these generalizations are more consequential for greens running 14 seconds or more such as most New Zealand rinks outdoors and rinks made with carpet, outdoors and indoors, everywhere. 

In summary, it is fair to say that narrow bowls play best in the hands of an experienced bowler who can consistently deliver bowls without wobble and who plays indoors where there is no wind and where the surface is hard and perfectly flat.

The balanced sole bowl is comparatively more stable because its profile is simpler but it can't be made to take the very narrow line down even the faster rinks that some players seek. It still probably has advantages for new bowlers or in high winds or on rutted or otherwise uneven greens.