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B5

Points to note on fencing

  • Jock Simmonds, "Rowan Park", NSW
  • Kym Hannaford, "Kinross", Adelong, NSW

It is an interesting fact that a very large number of blokes who live in, or have spent some time in, the country claim expertise in farm fencing, and they cannot refrain from airing their "expertise" to the new chum. Unfortunately, the advice given is rarely the best advice available, and this is especially the case where individual circumstances are not considered. The lesson here for newcomers to farm fencing is to read the most up to date material on fencing available, from technically qualified sources, and to apply common sense to adapt this information to the specific situation. Friendly advice can be included in this process, but it should not taken as the primary source.

Recommended reading would be the most recent agricultural department publications or pamphlets and the "Waratah Fencing Manual" which can be obtained through your local rural products supplier. Much of what follows has been taken from the "Waratah Fencing Manual", which at the time of writing was the most up to date publication available.

Strainer Posts

Strainer posts are the most important components in any fence. If any of these fails, the fence fails, therefore, it is most important that they are erected correctly and are strong enough for the job. The functions of strainer posts are to provide:
  1. An immovable anchorage.
  2. A structure for straining the fence wire.
  3. The start and finish of the fence.
  4. A point at which major changes of direction and/or topography occur.
  5. A structure from which to swing gates.

It is very important to consider engineering principles before embarking on a fencing project. Research undertaken in the United States into the best method of fence erection found that vertical movement of the strainer post is the most frequent type of failure. Some important findings of this work are discussed in the following paragraphs.

The following table shows exactly what sort of results occur the deeper the post is set in the ground.

0.75m deep0.9m deep
Total load carried20kN50kN
Horizontal movement at 13kN (3000lb)40mm25mm
Vertical movement 13kN15mm10mm

These results show that by increasing the depth, in this case, by 150mm (6in), the total load carried by the fence is more than doubled while the horizontal movement has been reduced by nearly 50%, and the vertical movement by 33%. This is a lesson that should never ever be forgotten.

This next table illustrates the benefits of driving the strainer post into undisturbed soil versus placing it into an oversized hole, back filling with earth and ramming.

DrivenRammed
Total load carried26kN18kN
Horizontal movement at 13kN40mm100mm
Vertical movement at 13kN10mm50mm

It can be seen that where the post was driven into undisturbed soil, it withstood a higher load, the horizontal movement was reduced by 60%, and the vertical movement by 80%. Another valuable lesson. Where driving is not an option, the next best approach would be to drill the post holes. In this case, however, the auger size should be noted and posts  obtained that are only slightly less in diameter than the auger.

These findings disprove a commonly held belief that the greater the size and weight of the strainer post, the less the chance that it will move. In fact, it is quite possible a 15cm post driven 100cm into the ground to out perform a 75cm post dug into the ground. Thus, considerable savings in time and material costs can be achieved, as well as better performance, by following these engineering principles.

The US research also found that "the horizontal stayed or boxed assembly was 25% more effective than the diagonally stayed unit. However, on a material cost basis, the box assembly could be expensive and it is more time consuming to erect". One could infer from this that, if diagonal stays are used, the depth that the post is sunk in the ground is an even more important consideration. It is also important that the diagonal stay be attached about 2/3rds of the way up the vertical post, whilst the other end of the stay be placed on a base plate that is itself is bearing on undisturbed ground. The positioning of the diagonal stay is important because, unless it is correctly positioned, it can act as a fulcrum and increase the likelihood of vertical movement of the post.

Some Fencing Tips

When building new fences use the gripple system on all sections, including short sections of the fence. This system was introduced by Waratah and is described in the Waratah Fencing Manual. With this system, the fence sections are tensioned after the fence has been erected. This saves considerable time in fence construction and in long term maintenance of the fence because the fence can be readily retensioned at any time. The up front material costs are soon repaid by the long term savings.

As far as possible, use steel posts between strainer posts. Attach live wires with the appropriate insulators on electric fences, and on all fences attach non-live wires with steel clips. This makes it easy to adjust fence heights and wire widths down stream.

Never use the 15cm picket spacing when fencing for goats with prefabricated fencing, because they can get their horns caught in the fence. Furthermore, do not fix droppers on prefabricated fencing centrally between 30cm pickets as this creates local 15cm spacing.

On electric fences, always connect all non-live wires to make the whole fence an earth matrix, as this improves the performance of the fence. Do not omit to run earth connections as well as live connections under gates.

In lightening prone areas, do not have a live line as the top wire on the fence. Always have a plain or a barbed wire on top to act as a lightening arrester by earthing through the steel posts. This helps to protect the energiser.

Do not use less than 2.5mm diameter wire, including lead in wire, on electric fences to minimise voltage drop along the fence.

Finally, keep a checklist of the tools required for various fencing tasks and use it before going out on a job. Otherwise, you will not have all of the tools with you that you need until you have finished the task, and you will probably have wasted a lot of time.

Upgrading Old Fences

There are a number of ways of upgrading old fences, and a few are shown in the following diagrams. Care should be taken when adding offsets to old netting fences to ensure netting cannot be pushed against the offset wire by kangaroos, wombats etc. Generally an offset ground wire is all that is required to deter goats.  Additional wires would only be required in special circumstances (See Figures 1 to 3).

Figure 1. Offsets holding wire 25 to 30 cm from the ground and the same distance from the fence.

Figure 2. Short post for wire offset. Wire about 30 cm from ground and fence.

Figure 3. For maximum security or very old fences.

© 2000 ACGA