The principle behind the antihail cannon is to prevent the damage cost by hailstones by eviting their formation and growth by melting all together. Thanks to shockwaves which emanate from the hail guns, the supercooling water situated on the external layer of hailstone is transformed from liquid state to solid state. Therefore the hail nuclei are not able to melt anymore and remain at a small size which thus prevent them from inflicting damage when they hit the ground.
On the early 1900s, hail cannon shockwaves were generated by gun powder, which was both dangerous and take a long time to reload. At those days, a much greater number of cannons needed to be deployed in order to adversely impact the formation of hailstones.
Today, hail cannons generate their hail disruptive shockwaves through the use of acetylene or butane gas which allows for the emission of a more powerful shochwaves and a greater rate of frequency which greatly improve their efficiency in the prevention of hailstone formation and growth.
An antihail gun is not effective against an already formed hailstone, so the most important requirement in the use of a hail cannon is its timely startup. A hail cannon operation must be initiated 20 minutes before hail storm formation or storm arrival. The efficiency of the cannon decreases in proportion to startup delay. If the antihail device is activated when the storm is directly above, its efficiency will be very low because a cannon has little effect on an already formed hailstone. It is strongly recommended therefore to use this means of protection in conjunction with either weather radar equipment or a at a weather alert subscription service.
As compared to the anti hail guns, silver iodide rockets are not effective against already formed hail because antihail rockets influence hailstones formation by adding nuclei (silver iodide particles) inside the cloud.
“By injecting many extra ice-forming nuclei into the cloud at the right time and at the right place, where in weak updrafts hail formation is beginning, it should then be possible to reduce the average size of fully-grown hailstones. Small hailstones may melt on the way down and are less damaging anyway.”
(Meteorologische Zeitschrift, 15, issue 3, June 2006 – Wieringa and Holleman)
Anti-hail nets are the only means of protection which is recognized by the insurance companies and which could reduce your policy.
However, this protection is rarely installed to protect some important farms because its installation and handling costs are very expensive for large-area farms.
For instance : a 50-hectare orchards will pay about 250 000€ for an installation of anti-hail nets on the entire farm (5 000€ / hectare) and for both handling operations (unroll nets in springtime and roll up in winter) yearly costs will be around 60 000€ (1200€ / hectare / year)
As with other anti-hail protection equipment, the antihail nets are not efficient in the event of strong hail storms. Consequences are potentially even worse than for a completely unprotected farm because if the nets structure collapses on the crops the grower will often be forced to replant the entire afflicted areas.
Very expensive, reduction of sunlights for crops under the nets, problem of stains on vehicles under nets when raining.
Crop insurance can initially be an effective means to protect your farming interest in the event of hail storms. However, the grower must always take into account the insurance deductible which is subtracted from the total of any loss or damage claim filed. Crop insurance however, is not a viabale ongoing solution for those growers who are located in regions that are typically affected by hail on the seasonal basis in which case most insurance companies will eventually refuse to offer/underwrite continued coverage.
