Aim Line with Mat Up at Lawn Bowls

Imagine that, when the mat was on the back T, you found that the correct aim line runs to a point on the front bank a particular number of meters to the side of the rink number.

On this theoretically perfectly flat rink, with the jack now sitting on the forward T and the mat brought forward, what fraction of that distance should you now use to deliver your bowl with the mat up?

This is an important question for players who want to actively move the mat. The change from bowling about 30 meters from T to T to bowling 21-23 meters from a mat drawn up to the Hog line changes several things simultaneously.

First, the curve of your bowl is going to pass over completely new areas of the rink. This is important because ( spoiler alert ) rinks are not actually flat over their entire surface!

Second, if you take an aim line running from the center of the mat to a point on the forward ditch, that point on the forward ditch moves closer to the rink number.

Then, third and most obviously, the required weight becomes markedly less.

That fraction  = {d.sin(tan^-1 W/L)}/W 

Where:

d is the distance to a jack on the forward T

W is the distance in meters from the rink number to the aim point on the forward bank and

L is the distance from the back T to the forward bank

This fraction turns out to substantially vary as a function of the full length of the green. Perhaps surprisingly, there is little variation as a function of the rink’s width.

I have prepared a table below showing the fractional change in aim point.

Notice that for small changes in mat position around the back T, any aim point on the forward ditch changes by an amount less than the likely error in delivering your bowl! Practical result— small changes in length around the back T are not pertinent for aiming.

Distance to jack For a 34 meter rink          For 40 meter rink

d=21 meters         0.65  ( ∿ 2/3 )                  0.55

d=23 meters 0.72  ( ∿ 3/4 )                  0.61

d= 27 meters 0.84  ( ∿ 5/6 )                 0.71

d= 30 meters 0.94  ( ∿ 20/21 )                 0.79