DDD SYSTEMS & Dr. Dan Diaper.  Cricket Writings - The Hover-Roller and Additional Hover-Cover Functionality.




The Hover-Roller and Additional Hover-Cover Functionality.




It was during commentary of the County Championship match between Worcestershire and Durham at New Road, 24th. – 27th. May, 2015, that one of the commentators, probably Dave Braddley, had a slip of the tongue.  He meant to refer the heavy roller, which, it was being discussed, could only be used once during a Championship match.  What came out was reference to a “hover-roller”. 


There was a little hilarity in the commentary box.  I doodled in my mind how a hover-roller might work.  The commentators mentioned it a few hours later and, a couple of days later, in the final session of Day 3 (Tuesday, 26th. May), the hover-roller got a third mention.  Martin Emmerson jokingly suggested one “could probably already buy one in Japan and that it would shoot ions, or something, into the ground to flatten it.”  Enough!  Having thought about it already, I dashed off the following email:




I’ve been amused by your discussion of a Hover-Roller.


This might just be a heavy hovercraft which would press down evenly across it’s footprint.


But what would it do to the wicket?


1                   It would clean all dust and debris;

2                   While pressing the wicket it would erode any cracks;

3                   It would dry the wicket.


Excellent digressions during your commentary.  Thank you.


                        Dr. Dan <>


Read out on the radio almost immediately, I was just pleased I managed not to get too technical, proudly avoiding mentioning plenum pressure (the plenum is the space between a hovercraft’s body and the surface on which it rides).  Reading Science Fiction (SF), I’ve several times noted that how hovercrafts work isn’t always well understood.  Hovercraft are actually one of two types of GEMs (Ground Effect Machines), the other is an ekranoplan.


To be clear,  a hover-roller would not work because it would have to be extraordinarily extremely heavy as a hovercraft distributes its weight fairly evenly over its ground footprint. In contrast, a traditional roller does just the opposite, it concentrates its weight onto the very small surface area in contact with the ground.


Between first and third mentions of the hover-roller concept on the radio, my mind had turned to more practical things, not about rollers but about hover-covers.  At present, the hover-covers I’ve seen are single units a bit bigger than a wicket.  The are pulled out on ground effect and then the engine is turned off and the cover lands.  The critical point is that it is not operating for very long as a hovercraft when over the wicket.  Thus, while a hover-cover will blow around dust and light debris, on the other two numbered points in my email, there will not be time for crack erosion or wicket drying to take place.


Bingo!  A practical idea, i.e. one that is engineering feasible in terms of both functionality (what it usefully does) and at minimal cost.  Working entirely from theory, hovercraft must dry the solid ground surface below them.  This is so because a lot of air escapes the plenum chamber and moving air will pick up a lot of water; a good drying day for one’s washing is one that is windy, even if not sunny.


An important part of design is requirements analysis, identifying what is needed, and often a creative part of this is recognising real problems.  Here’s a real cricketing problem:


After a rain interval it is often the case that, even with extensive covers on the outfield, that areas are damp and, most worryingly when this is so in the areas of the bowlers’ run-ups.


Why not use a hover-cover’s hair-dryer effect to dry the outfield, or at least parts of it?  The ground staff’s procedure would be to remove the covers and then start up the hover-cover as usual, but instead of just taking the hover-cover off they manoeuvre it around the outfield, either in a set pattern or concentrating on areas of greater dampness.  They should, of course, keep it off the wicket to avoid the undesirable effects numbered in my email.


What’s the alternative?  Up to now it’s involved passing a rope over the outfield grass, which will spring water droplets into the air, dispersing them as smaller ones which will evaporate much more rapidly (evaporation depends on surface area and drops of smaller volume have much bigger surface areas relative to their volume – it’s a non-linear or power function to the mathematically literate).  I’ve never been impressed with this rope trick and I’ve heard plenty of cricket commentators sound equally dubious over the years, even if they aren’t really sure of the basic physics.


Being long and thin, and heavy, a full wicket hover-cover will not be that easy to manoeuvre.  Again SF is useful as the proper concept is not weight but mass, which is a problem for spaceships trying to change direction in the frictionless environment of interstellar space.  A hover-cover has low friction, it glides across the ground and, once in motion, it will go a long way as there is little ground braking effect (which is another way to say “low friction”).  Thus it is difficult to manoeuvre because nearly as much energy is needed to stop it in any direction it is first moved (see Newton’s Laws).


As I usually do with my engineering designs, I see in my mind’s eye, just as I watch cricket on the radio, here a team of husky groundsmen hauling the hover-cover around the outfield.  In dryer mode, the hover-cover would be moved sideways (long axis going forward), slowly, in straight lines.  Steering is done by spinning it only when it is stationary as hovercraft are notoriously difficult to steer.


Hover-covers are expensive bits of kit.  Finding a desirable, additional, practical use for something that costs so much must be a good thing.


Finally, if I were to design future hover-covers, I’d consider a two unit system.  Two separate hover-covers only half the length of a wicket would be much easier to manoeuvre when used to dry the outfield because their individual mass would be less (but more than half) of the existing single wicket sized hover-covers.


It was an excellent cricket match with an excellent, entertaining and enjoyable commentary, as I’d said in an email to the commentary team.  Just as might mighty oaks from little acorns grow, so a little slip of the tongue has produce a useful, practical idea, if not an oak of a one.  Unfortunately, I can see no way to make money from the idea, which will disappoint the beautiful Japanese wife, so I offer it free on the internet.



    [ TOP OF PAGE ]


© Dr. Dan Diaper, 2015.  DDD SYSTEMS version 9.0 – updated May, 2015.