Tips for more effective farm fencing

By: Graeme Quick

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Most weather problems associated with fences are lessened by clearing wide fence lines that simply don’t have trees or anything but grass nearby. Most weather problems associated with fences are lessened by clearing wide fence lines that simply don’t have trees or anything but grass nearby. Most weather problems associated with fences are lessened by clearing wide fence lines that simply don’t have trees or anything but grass nearby.

Good fencing makes a property more efficient, safe and marketable, and indirectly can be a reflection on its owners. Dr Graeme Quick offers a totally fresh approach to the physics of farm fences.


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The main purpose of farm fencing is to keep livestock in and keep undesirable elements (persons or animals) out.

Fencing is also used to subdivide areas and make the farm attractive and presentable.

This article deals with both conventional wire fences and electric fences.

A strong case can be made in favour of electric fences in many situations but there will still be others where a conventional or ornamental fence is needed.

Animals will test the limits of a fence. They have 24 hours a day to think about it.

Floods, wind, fire, sun and rain all work against a fence. Flood crossing fences should allow excess water flow, should only get damaged by the extreme events and should be repaired after flooding.

Fence materials should be selected for minimal damage by fire.

Most weather problems associated with fences are lessened by clearing wide fence lines that simply don’t have trees or anything but grass nearby.

Grass can be controlled by annual spraying with the right chemical.

 

FENCING CONSIDERATIONS

The physics of a fence is considered in light of these factors:

  • What does this fence need to do — will it be impacted by what species of animals? Will it be affected by machinery?
  • Are there unusual landscape contours or soil challenges over the long-term?
  • Have there been any failures with previous fence work? If so, what was learned from those failures?
  • What is needed to make the fence stand up to normal reasonable loads and even abuse?

 Usually a fence shouldn’t need to be made like a fortress — there are even times when it would be a good thing if the fence gave way under exceptional circumstances.

For example if your most valuable prize bull goes on a rampage, it would be far preferable for the beast to be humiliated or only slightly injured rather than be castrated by the fence in the rampage.

If racehorses are being contained or animals are grown and sold for their skins, then barbed wire may be out of consideration.

In some jurisdictions, due to its dangerous nature, razor wire, barbed tape and similar fencing/barrier materials are illegal.

Some local jurisdictions regulate or prohibit barbed wire altogether.

Unless your place is a high security prison or jail, razor wire is an unlikely contender.

In Norway, barbed wire is prohibited on farms except in combination with other fencing; this is to protect domesticated animals from harm.

The Dingo Fencing Machine set-up in action. Image by Dingo Australia.

FLOODS AND FIRE

Special considerations are needed if a creek nearby over flows and the fence is not to be swept away. In fire prone areas the fence needs to be made of less flammable or resistant materials.

After a conflagration, animals need to be kept in the property, it’s bad enough to lose property assets to a fire but if the livestock get out on roads or are loose to roam into neighbouring farms, the misery is magnified.

Suitably designed and well-constructed fences are essential infrastructure on any property.

Property owners are legally obliged to fence their property.

Local councils can provide some basic guidelines and minimum fencing requirements.

 

STRAINER POSTS

Strainer posts are the most important components in any fence.

If a strainer assembly fails, the fence fails, therefore, it is most important that end assemblies are erected correctly and are strong enough for the job.

The functions of strainer posts are to provide:

  • An immovable anchorage and a structure for straining the fence wire
  • The start and finish of the fence
  • A point at which major changes of direction and/or topography occur
  • A structure from which to swing gates. As for failures, vertical movement of the strainer post is the most frequent type of failure.
Top: Sinking a 150mm fence post from 0.75mm deep versus 0.9mm deep. Bottom: This table illustrates the benefits of driving a 150mm strainer post into undisturbed soil versus placing it into an oversized hole that is back filled with earth and rammed.

These results show that by increasing the depth, in this case, by 150mm, the total load carried by the fence is more than doubled while the horizontal movement has been reduced by nearly 50 per cent, and the vertical movement reduced by 33 per cent.

Usually single strainer posts are substantial.

In the days when timber was plentiful, it wasn’t uncommon to see end posts of 600mm diameter sunk 1m into the ground.

Installation was hard yakka — a single post could take a day’s work to install. With a powered post driver, a 150mm post can be punched into firm soil in minutes after set-up.

The stay must be at a shallow angle to reduce the tendency for the wire strain to make a large vertical lifting force component and also rotate the post.

The vertical component would lift the end post if the post isn’t firmly embedded.

Soil resistance has to counter Fv, the vertical force component (and that over the long-term).

The box end has superior holding strength compared with a diagonal stay assembly so is suited to sandy or moister soil.

A box assembly can be a single box with two posts or a double box, which is three posts and two rails.

The diagonal wire or chain brace is crucial in the box assembly.

This should start at the bottom of the end post, finishing at the top of the subsequent strainer post.

Top: A plain end post. Note soil reaction forces, this is how the soil reaction forces would look if the post was punched in tight or earth rammed firmly around post. Bottom: Diagonal stay assembly. The diagonal should be placed at two-thirds the end post height and angled as shallow as practicable. Bed plate must be immovable.

A WORD ABOUT WIRE

‘Soft’ wire — low carbon mild steel of 0.06 to 0.08 per cent carbon — is malleable and nice to work with and tie, but it stretches under load and in heat.

Soft wire is best for horses as it will do the least harm to the animal.

Number 8 Imperial gauge (4mm) plain soft wire has a breaking load of 513kg; 9 gauge (3.65mm) plain wire has 470kg breaking strength, and 10 gauge plain wire has 390kg breaking strength.

By contrast, high tensile (HT) wires have 0.28 per cent carbon and are stronger but stiffer and uncomfortable to manipulate.

Ten and a half gauge (3.1mm) HT wire breaking strength is 732kg; and 12.5 gauge (2.5mm) HT 611kg.

The same weight of HT wire will be far longer and cheaper per unit length.

In summary, light gauge wire (e.g., 2.5mm) made from HT steel has the superior strength yet far greater elasticity than the softer, heavier gauge wire (4mm).

A properly installed HT fence will stay tight for years — it will not stretch with heat or cattle leaning against it; but springs back and stays tight. It therefore requires little maintenance.

A conventional six HT wire strained fence can accordingly place a horizontal load of more than 2 tonnes on an end assembly.

Droppers rather than in-line posts should be used to strengthen a fence.

Droppers help keep the wires spaced, and transfer the load from an impact on one wire to the rest of the wires in the fence.

 

THE UBIQUITOUS BARBED WIRE

Plain wire was used for fencing in England as early as 1840, but woven and barbed wire products were not developed until after 1860.

Initially, the wire was modified with attachments so that livestock or native animals could see it.

The aim was to give animals the ability to see the fence or barbed wire without the use of separate warning devices.

Initially, twisted wooden blocks, metal strips, tin plates, balls etc. were contrived and incorporated into the wire to warn the stock the fence was there.

These warning devices saved a lot of animals from accidents that would have left them crippled or severely injured.

The blocks let the animal see the fence before discovering it by running into it.

These warning devices were sometimes added at the factory or were put on by the rancher or farmer himself. Wire was subsequently developed with large plate barbs, or more commonly, twisted wires with evenly spaced barbs.

The first barbed wire patents came out of the United States western prairie country in the 1860s, but it was not until 1874 that Joseph Glidden of De Kalb, Illinois, invented a machine to manufacture it that barbed wire became usable to any great extent.

Such names are ‘barbed wire signals’, ‘indicators’, ‘warning strips’, ‘warning plates’, and ‘cattle protectors’ were attached to wires — until the so-called ‘devil’s rope’ was available inexpensively.

After the stock became used to the presence of the barbed wire fence, those warning devices lost their importance.

Barbed wire brought a speedy end to the era of the open-range cattle industry. Since the US western grassy sod plains were largely treeless, a farmer who wanted to construct a fence had little choice but to buy expensive and bulky wooden rails shipped by train and wagon from distant forests.

Even if a landowner could afford wooden fencing, he had another problem. Livestock push through or often lean against fences in order to graze along fencerows.

In time, that pushing can result in a break in the fence.

There are specialist collectors, clubs and swap meets. There is even a museum in La Crosse, Kansas where there are 100 barbed wire collectors alone.

Patented in 1881, Dodge’s spur wheel cattle wire was considered more humane.

If an animal leaned against this cattle wire, the six-point sheet metal barbed wheels would roll with the animal.

The ends of the wheel would stick it just so far, but not enough to harm the beast.

For collectors, a 450mm length of this rare wire could fetch more than $1,000.

Samples 450mm long are considered the standard length in the collecting fraternity.

But barbed wire is not the only kind used in today’s farm fences.

In Australia there is a trend away from barbed wire; electric fencing has everything to do with that.

There are several suppliers of packaged assemblies. This diagonal stay set-up is designed to hold the bed plate in position. Image by Clipex Fencing and Stockyards.

THE ELECTRIC FENCE

Traditional fencing is a highly labour intensive task.

Electric fencing is far less laborious and can be more cost-effective.

An electric fence energiser delivers a high voltage pulse down the conductors, typically 8,000 volts, every one to two seconds.

This high voltage is required because the thick skin, fur or wool of animals has a high electrical resistance and cloven hooves are poor conductors.

Although that voltage is high, the pulse is very short, typically 20 to 300 microseconds depending on the size of the energiser.

This short pulse in itself will deliver a painful shock, but does not last long enough to arrest bodily functions.

Modern ‘low impedance’ fence chargers use a capacitor that is charged by a solid-state circuit.

When contacted by a grounded animal or person, the charge is released using the solid-state componentry.

Voltage is consistent due to electronic output controls, within the limits of output power. Pulse width is much narrower, often about 10 microseconds.

This design works for either battery or mains power sources.

Note that electric fences must not be run parallel to or near overhead power lines. Hot tape and polywire can be used effectively for lengths up to 400m from the energiser.

Use galvanised fencing wire for longer distances.

In lightning-prone areas, it is recommended not to have a live line as the top wire on the fence. Instead have a plain or a barbed wire on top to act as a lightning arrester by earthing through the steel posts.

This helps to protect the energiser.

Top: This shows how the vertical force (Fv) component of the force in the stay increases. If the stay is assembled at too steep an angle there is a higher lifting force when the fence wires are strained. Bottom: A single box end assembly. Double H assemblies are feasible for extra load resistance in soggy or weak soils.

DINGO FENCING MACHINE

In Australia we’re well-endowed with some very clever commercial fencing products and fencing tools.

Some were designed here and adopted elsewhere.

The Dingo Fencing Machine (DFM) is a classic example.

Developed by Gary Briggs in Dalby, Queensland, this system is a patented combination of several labour saving ideas.

The DFM allows two men to install up to 6km of multi-wire fence in a day, a task that would traditionally take a dozen men.

The DFM can run woven electric, tape or plain wire, and with a modified set of roller-tensioners, it can run most fabricated wires as well.

With a Dingo mini loader on board to provide all the mechanical and hydraulic power needed, the DFM is a neat operation.

Incidentally, the Dingo itself with auger is probably the best fencing tool for placing and sinking tight end timber posts.

According to Briggs the DFM is intended for large acreages that can "capitalise on the advantages of long runs.

Besides the bigger properties can provide enough work to justify the time and amortise the contractor’s capital investment.

"It would be more prudent to get more productivity out of your acreage [with effective fencing] than buying more land," Briggs says.

He says the key advantage of the DFM is the ability to erect a fence in one-fifth of the time.

The DFM uses reels of wire instead of coils so it is less troublesome and can cover greater spans — up to 1.5km — in one go.

Unit costs for the wires are similar.

"The DFM deploys stackable aluminium fence posts that will outlast the traditional star post by many times, and are cheaper over time," Briggs explains.

"Since the system installs a fence consistently and is ‘hot’ it requires little wire tension thus lighter end assemblies.

The actual material cost per kilometre is very similar to a four-barb traditional fence."

In addition, nothing ever leans on an electrified fence, so there is no need to tightly strain.

"Therefore lighter and lower cost end assemblies are needed, because there’s absolutely no stock pressure on an electric fence," Briggs says.

"A DFM electric fence is a real fence enhanced with electricity to make it absolutely animal proof.

"It’ll make your property into an ‘island’ free of feral animals.

"On a big property for example boundary fencing 40,000ha, costs can be down to $12.50 per hectare. That is a cheap paddock."

 


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