Type 73 Sectional Mast Systems
You do not experiment when you choose type 73. Thousands, world-wide, guarantee the success of each further application. With every product, in every activity, there emerges a supplier and model which meets many different customer requirements and which becomes classic.
The Clark Masts Type 73 mast is one such example. From its conception in 1970 until today, it has played many roles as a vertically erected, manually operated sectional mast which is fully controlled by guys during erection. Easy change in height or headload has been a key factor in its success.
Type 73 versatility
It's the sound versatility of Type 73 which makes it so attractive to users.
There are other more sophisticated options, for example a 10 metre mast with antenna stabilisation by means of special guys.
These give a torsional deflection, under load of less than 0.15°.
Type 73 Standard Components
|Kit||18130||10 Metre mast kit complete||1|
|This Kit contains the following components:|
|1||18205||Mast guide box||1|
|6||13973||Hoist support bar||1|
|9||5373||Foot adjustment brace||1|
|10||18021||Guy winch kit (leg mounted)||1|
|13||18034||Picket driving cap||1|
|16||18022||Guy collar set||1|
|18||14522||Mast section carrier (3 sections)||1|
|19||14524||Mast section carrier (4 sections)||1|
Some Typical Type 73 Mast Components
The first item of the system is the guide box and 3 legs which form the base of the erection gear. The guide box has a long, turnable sleeve with a brake and is PTFE lined. A bubble level is fitted during erection.
The second item is the mast section. It is made from a special billet of high strength aluminium alloy for reliability. The method of section joining, by means of a simple long spigot and key, ensures that the connection functions correctly in dirty or muddy conditions. It is anodised and dyed green or desert sand being the usual colour.
The mast section is positioned in the mast guide box, in which it is lifted up by a manual hoist and lifting block. The geared hoist is a special item which is wound up, secured by driving rachets and can be reversed only when a push-button brake is operated. In addition there is a centrifugal brake which limits the free running winch to a speed of approximately 150mm per second, regardless of load.
After raising the first section which is secured with a crosspin, the lifting block is lowered and the second section inserted, the crosspin removed and the section raised. A guy collar is fixed to the first tube section using the crosspin hole for security.
Guys are part of the mast structure. During the vertical erection of a sectional mast, it is essential that guy tensions are continuously controlled. The Type 73 Guy Winch Unit, innovated by Clark Masts in 1970, is the manual device that does this.
As the mast is extended the guy wires are paid out together from the winch unit, or adjusted individually in the case of sloping ground. Safety at all times is maintained. For mast retraction the guys are similarly wound in. Each winch unit is fixed to an erection gear leg or to the ground.
Pickets pose a problem. Length generally should be according to the ground; short pickets for hard ground, long for soft. However, type of ground is not known until erection is required on a particular site. Type 73 uses a 1 metre long tubular picket with a toughened tip.
An exceptional feature is the picket clamp which sets the guy attachment point at ground level however deep the picket is hammered into the ground. Use of a Picket Driving Cap, protects the picket from damage by the hammer. When it becomes necessary to withdraw the picket, an extractor does the work efficiently and quietly. A Type 73 picket becomes a long-life component.
All bags are made from decontaminable, coated, textile base material with simple buckles on nylon straps. Normal colour is military dark green although white and desert sand can be available. Bags are reinforced with removable plastic panels.
The guy wires are attached to guy collars which are fitted to any mast section as required. A nylon lined bearing makes mast rotation easy and which once set in the right direction is held with the screw operated brake on the Mast Guide Box.
The method of attaching the antenna depends on the type of antenna. The Type 73 has two basic methods. A Top Flange Fitting provides the top of the mast with a flange to which antennas or rotators can be attached. Alternatively a side Mounting Adaptor allows a 40 mm male antenna adaptor to be placed at any height on the mast.
Clark Masts always concerns itself with the interface between mast and antenna, mounting of which can give a physical problem due to antenna bulk.
A hinged antenna adaptor enables the antenna to be mounted at ground level and then swung into the operating position. Alternatively, a crane kit is available for even heavier headloads, to lift them from ground level to the retracted mast head.
Sometimes military equipment will go straight from delivery into User stores where it can stay for a period. With this possibility, effective final, functional works inspection becomes vital. After manufacture, every Type 73 mast set of components are fitted to each other and functionally tested to ensure that no snags arise when it is required for service.