CA Hoop Tests 2014 – Full Report
The following is the full report of the tests undertaken in April 2014, and is aimed at those particularly interested in croquet equipment – shorter versions are being prepared for wider audiences. The report also draws in places on the inconclusive CA Equipment Committee tests of March 2013, a report of which can be found at http://www.oxfordcroquet.com/tech/hoops.
Table of Contents
The search for a more challenging hoop for top-class AC events - especially in typical damp UK soils – has continued for some years. These tests were undertaken as part of that continuing search.
The primary goal of these tests has been to tease apart the factors that seem to make a difference to the inherent 'runability' of a hoop, leaving aside the external factors of soil type, weather, and setting.
Additionally, the tests looked at some specific hoops of novel (as far as the UK is concerned) design – from Egypt, New Zealand and Canada, also assessing their suitability as an Elite Hoop in UK conditions.
The tests revealed the following conclusions about the factors investigated:
It was also evident that despite the novel and varied design of hoops tested, in fact the differences in 'runability' were surprisingly limited. All the hoops – except the Trimmer test Hoops #7 and #8 - had a 'critical angle' (maximum angle from which they could be run) of between about 40 and 45 degrees. This is a disappointingly small range – it would be useful to have an elite hoop which was far less tolerant of poor approaches than a normal hoop, not just a few degrees.
Previous CA tests with hoops with facetted or even square uprights (and other tests of a double-depth hoop, with two sets of uprights welded back to back) confirmed this view that even what appear quite extreme design changes make only modest 'runability' changes in practice.
The Egyptian hoop worked very well. It doesn't meet the formal hoop specification – being too tall and the crown and uprights over-sized (and you couldn't use a normal scoring clip on it). It resisted poor hoop shots well, was easy (compared to some of the other novel designs) to set and adjust, and seemed to keep its setting well. Carrying six around a lawn would be quite a task!
The NZ Atkins Quadway worked very well. The square parsnips and the unfinished stainless steel uprights contributed to its good results. Given how much any hoop springs in or out in UK soils, once the hoop clamp is removed (usually due to stones underground), it is unlikely its 'adjustable width' feature is useful in practice, and only adds to the manufacturing costs.
The Canadian Oakley 4-fin hoop performed much like any normal UK hoop, despite its very different design. It was significantly harder to drive into the ground or to remove from it.
A final conclusion is that we should reconsider the specification for a hoop given in the AC Laws, GC Rules, and WCF Equipment Regulations, as it may be that there are good designs out there (such as the Egyptian hoop) which are technically illegal. Can the specification be written in such a way as to allow more flexibility and innovation?
There are three options it seems for arriving soon at a CA Elite Hoop, for top-class AC events such as the Opens, Mens' & Womens' and President's Cup:
It could also be worth widely inviting suggestions for how to make uprights grippier while still being practical, non-ball-damaging and long-lasting, and then having a further round of tests to select the best solution and including this in the Elite Hoop recipe. This may delay securing an Elite Hoop by a further year, but may yield improved performance.
Hoop difficulty is governed by the design of hoop, how narrow and firmly it is set, the type and dampness of the ground, the kind of stroke and the make of ball. It is very difficult to get meaningful results other than by comparing different designs against each other, when in new holes in the same ground on the same day. Conclusions drawn here may not be valid to different soil types, or soil that is much drier or wetter, or with different balls, and so on.
It is also evident that players have all manner of hoop strokes, some imparting top- or back-spin to varying degrees, and at all kinds of pace. These tests for practical reasons are limited to testing hoops with one standard strength stroke delivered with a similar spin in all circumstances. So it is possible that in actual play, real players may have quite different findings about the relative merits of these hoops and features.
Discounting for now ideas that would require different engineering in the turf, there are 3 factors which seem worthy of systematic investigation:
1). Carrot Shape – square 'parsnips' have already been found to provide some more resistance in damp ground. Do fins instead of carrots work well in UK soils? Egyptian GC hoops stand up to much abuse very well.
2). Friction of the Upright – we have already found some powder coating is akin to Teflon™ ('non-stick hoops') and that unfinished steel and stainless steel uprights seem to pose more of a challenge. Dave Trimmer has now suggested some intriguing alternatives in this direction: not just a move to unfinished stainless steel, but knurled or rubber coated uprights to 'grip' the ball. The 'grippiness' of the upright might also explain why anecdotally, older hoops with thin uprights often seem harder to run then new hoops with thicker uprights (as the ball may deform around these less?).
3). Mass Above Ground – previous experiments seemed to show that, perhaps surprisingly, more mass below ground did nothing to make the hoops more difficult (see the results for Hoop #6). Some crude and quick experiments with adding mass to the top of a hoop seemed to suggest a potential benefit. The Egyptian hoops also seem to benefit from this effect (30mm square mild steel crown, plus taller and thicker uprights). Colin Irwin has suggested a refinement - using this extra mass to also increase the resistance to deflection of the uprights – for example by having extended uprights and welding say 2 or 3 cross-bars in the top few inches to stiffen up the hoop.
A reason to defer – at least at this time - other ideas which involve engineering the turf, is that a desirable goal of a new more difficult hoop would be one that could be used 'everyday', or at least was interchangeable with 'everyday' hoops.
Our 2013 tests also investigated square uprights – but the smallest of chamfers on the edges of the uprights (~1mm) was enough to radically alter the playing characteristics. This might suggest these could be too variable in practice – there was also a concern about potential ball damage longer term. It may be the un-chamfered edges were in fact just digging into the ball and causing the 'grip' that knurling or rubber might provide instead. Tests a few years earlier had also shown that uprights with wide facets milled into them at an angle (35 to 55 degrees were tried) did make a discernable difference to difficulty, but not enough to justify the investment in re-equipping.
In our 2013 tests, we eliminated the US Superhoop as being a usable or effective hoop in UK soils, despite its reported good characteristics when in a stratified sand court. We also wanted to complete the tests of NZ Atkins Quadway this year, and to undertake testing of the recently-acquired Egyptian hoop. So the hoops required for the tests are as shown below.
Individual photos of all the hoops are included at the end. The photo below shows the new "Tonker" used in all these tests to deliver a standard hoop stroke.
Hoop #1 is our 'reference hoop' – a perfectly standard Aldridge hoop, albeit selected at the nominal 1/16" gap rather than 1/8" gap. Aldridge and Hopewell (cast iron but similar dimensions) are the two top-selling club and tournament hoops in UK at this time.
Comparing Hoops #3 and #4 with #1 will allow us to establish the merits of square 'parsnips' over round carrots. Hoops #2 and #5 let us consider other below-ground shapes.
Hoop #2 – and the use of a clamp and lead totalling 1320g fixed to other hoops – will allow us to see the effect of more mass at the top of the hoop.
Systematic tests on Hoop #6 will enable us to check whether the anecdotal findings a few years ago that a much more massive hoop overall, with huge carrots, is strangely easy to run.
It is difficult to eliminate other factors when trying to decide whether one hoop with unfinished metal uprights is better or worse (i.e. more difficult or easier to run) than one with powder-coated uprights – but a simple test will be to trial a good stainless steel hoop then immediately spray-paint the uprights and re-test it. This will show what effect surface finish has, and complements the 2013 test when the powder coating was removed from the uprights on some hoops to see the effect.
Taking this last point further, increasing the 'grippiness' of the uprights by either knurling them or covering with thin rubber tube will see if this is an area worthy of further exploration.
Unfortunately, that still leaves some factors which are too difficult to tease apart with our level of resources, such as degree of flexion of the uprights – is there a difference between different types of steel? Is the 'smoother radius' of a 20mm upright ('bad'?) shielding the greater rigidity ('good'?), for example. We did a late supplemental test (see later) which confirmed rigidity was a positive
In a perfect world, a set of test hoops would be constructed which were all exactly the same height, mass and balance (between crown and carrot), in which specific different variables could be examined – but that is beyond our resources. Instead, we have done our best to interpret the results from test hoops available to determine what factors help, hinder, or make little difference. The full results are presented in [Result sheet April 2014.xslx] – you might make different interpretations from them.
The Pidcock Peeling Plank. An MDF plank which clips around the near wire and allows shots to be played at increasing angle to the hoop. Each stroke is played with a pair of balls initially in contact and resting against the side of the plank. Shims allow various offsets to be set with respect to the near wire. The plank has two problems:
The Ramp. A 2.4m long ramp made of a pair of timber rails 44mm apart. The ball is deposited onto the lawn about 350mm in front of the hoop. This also has two problems:
A new tester was made which would allow more relevant and objective testing of both angled hoop strokes and of straight on (but off centre) hoop strokes. The first seeks to find the maximum angle at which it is still possible to run the hoop (a smaller critical angle would be good, given the goals of our tests). The second seeks to measure how tolerant the hoop is of badly-hit straight hoop strokes (a smaller offset at which it became impossible to run the hoop would be good).
The Tonker (see photo earlier) was designed and built to swing a mallet head as a pendulum, dropped from a controlled height, to strike a single ball aligned to just miss the near wire. This seemed to produce more meaningful results than previous test but it should still be noted:
Ipswich Croquet Club lawns are open all year so the grass is kept representatively short. The testing was undertaken in mid-April, after a couple of weeks of dry weather. The soil is typical of many English clubs – a clayey loam with only a few large stones but more small stones, and a sandy top few inches. It drains quite well. The speed wasn't measured, but was a reasonable, medium pace. It was found that dropping the mallet head from 300mm produced a stroke where the ball travelled about 750cm across the open lawn. That was then taken as the standard hoop strokes for all tests.
Each hoop to be tested was driven into new holes, without any cores being taken, using an Oakley hoop clamp and set to a gap of 1/16" using the same Black ball. All tests were conducted with Dawson balls.
Tests to determine the critical angle relied on a group of at least 4 strokes to ascertain the critical angle beyond which a ball would not run the hoop. The distance through the hoop each ball ran was measured (in cm), and an average for that angle determined. If the results were particularly noisy, then the group was extended to 8 or even 12 strokes. The Tonker was hooked around the near wire and set at increasingly acute angles to the hoop until the critical angle was found. Tent pegs were used to keep the Tonker in position.
Tests for tolerance to off-line straight hoop strokes used a group of at least 4 strokes to measure how far through in centimetres (= how cleanly) they ran a straight hoop at increasing amounts of offset from the centre line. The Tonker was set up perpendicular to the hoop plane and pegged in position. A series of shims were added to the sighting-plank on the left side to offset the ball further and further to the right.
See [Result sheet April 2014.xslx] for the full results – only the averages are discussed further here.
The first test with each hoop was to fire balls at it with the Tonker at increasing angles to the perpendicular, until the angle was reached at which few if any balls ran the hoop (the 'critical angle'). A more difficult hoop would have a smaller critical angle, which would penalise poor hoop approaches.
Critical Angle Results for All Hoops
Although hard to read, this chart shows a number of useful findings:
About a kilo of lead was added to the crowns, held in place with a metal clamp (total = 1320g) to see the effect of more massive superstructure, then the critical angle re-tested.
The effect for many hoops was indistinct – this particularly was the case for hoops which were already massive above ground – such as #2 and #6.
Of those where there was a noticeable effect:
Hoop #1 (our reference – a standard Aldridge) became more difficult to run sooner – so hoop running was more difficult even at 'easier' angles, and the Critical Angle was reduced. Likewise the Critical Angle of Hoop #5 (Oakley 4-fin) became about 2 degrees less.
With Hoop #7 (Trimmer test hoop – rubber coated uprights) the effect was significant – probably due to the relatively insubstantial superstructure and carrots compared to the rest of the test hoops (see chart over page).
There is no obvious explanation for why Hoop #8 didn't also share this characteristic.
It has been suspected for the past few years that modern powder coating is like Teflon™ and helps balls slip through. Strangely, even quite shiny bare metal (#4 and #5) seem to 'grip' the ball better than powder coated or painted uprights. This has now been confirmed in two tests:
It had 'magically' become much easier to run! This was doubly strange as the stainless steel felt almost polished and very smooth, while the spray paint finish wasn't very smooth to the touch – and yet let the balls slip through more easily.
Ideally, we would like to systematically test the effect of different kinds of cast iron, steel and stainless steel uprights, of different diameters, to properly understand the effect of increasing the rigidity of the uprights. Unfortunately, this is beyond our current resources.
We have already noted that it maybe we see two competing effects with the move towards thicker (19 or 20mm) uprights, instead of the “traditional” 16mm: the greater rigidity (“good”) is offset by the smoother radius (“bad”) of the uprights.
One simple test we added at the end of preparing this report was to fix an Oakley hoop clamp about 15cm above the ground between the uprights. This had the effect of binding the two uprights together and increasing the rigidity of the hoop. (It was checked that the clamp hadn’t altered the width setting of the hoop.)
As can be seen, this method of making the uprights more rigid has reduced how easily balls run as the angle approaches critical – though it doesn’t seem from these few measurements to have greatly altered the critical angle itself.
So a method of making the uprights more rigid, without ideally making them a larger diameter, could well be beneficial.
For these tests, the Tonker was set up perpendicular to the plane of the hoop (= straight in front) but by varying amounts offset to the right. When the offset was zero or 1.6mm, not surprisingly, the balls would run through by up to 800cm, while with offsets of about 9mm, many balls were sticking in the jaws. Some balls even got through when 12.4mm off-centre! The results from these tests are less clear cut than the critical angle tests, but we can still draw some conclusions:
While all seem quite similar, it can be seen that those two with 'grippy uprights' (#7 and #8) allowed the balls to travel through least distance at any given offset, and prevented all shots at 9mm from running, while most hoops allowed some balls to run at 9mm offset and even a few at 12.4mm.
So grippy uprights seem to resist inaccurate hoop strokes best.
Again, spray-painting the shiny stainless steel uprights of hoop #4 (Atkins Quadway) produced an interesting result:
Despite the apparent slipperiness of the bare stainless steel compared to the not-very-smooth-to-the-touch paint finish, more balls ran through the hoop further after the uprights had been painted.
So bare metal uprights seem to be more 'grippy'.
Adding the lead weight clamped to the crown made little difference to how well balls ran the hoops at various offsets – it's hard to draw any conclusions from the small differences here and there in the raw data.
CA Equipment Committee
Link: CA Hoop Tests 2014 - Supplement (June 2014)
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