A four-guy mast derrick, or gin pole, supports a hoist at the head of a single mast. Four guy lines connect the mast head to surrounding anchors. Hiscox’s figure 1466 shows this pole arrangement without a separate boom. The calculator illustrates one guy’s force components; it does not calculate a derrick’s lifting capacity.
Four-Guy Mast Derrick Interactive Calculator
Compare a single guy resisting an entered horizontal force in its vertical plane. The angle is measured above horizontal ground. The drawing shows a four-guy mast, but the calculation does not solve the loads in all four guys.
Equation Used
H is the horizontal force assigned to one guy, not the suspended weight. The guy is straight and the force balance is static. Pretension, sharing among guys, mast compression and bending, rope elasticity, anchors and dynamic lifting loads require a complete structural model.
A mast, four guys and a hoist
The mast supports the upper hoisting block. A rope passes through the hoisting arrangement to raise or lower the load. The guy lines restrain the mast head laterally, while the mast and its base carry the resulting forces.
The four anchor directions are shown in perspective. The highlighted guy illustrates the line opposing the entered horizontal force. The other guys remain part of the structure; their actual loads depend on pretension, geometry and deformation.
A gin pole has no separate boom hinged to the mast. That distinguishes this historical arrangement from a guy derrick with a rotating mast and pivoted boom. The animated load movement illustrates the hoist only, not a rated lift.
A compact lifting arrangement with a large support footprint
A guyed pole can position a hoist above a load where the mast and anchor arrangement suit the site. The anchors occupy space around it, so the support footprint is part of the installation.
The figure explains the arrangement rather than prescribing a modern installation. Mast members, ropes, blocks, anchors, foundations and operating limits must be selected together for the actual equipment and task.
Resolve the force along one guy
Let α be the angle between the guy and horizontal ground. A tension T has horizontal component T cos α and vertical component T sin α. If that one guy supplies a horizontal resistance H, then T cos α = H, giving T = H/cos α.
The rope pulls upward on its ground anchor. The vertical component there is V = T sin α = H tan α. At the mast head, the same guy pulls downward and toward its anchor.
For the same H, a steeper guy needs more tension because less of its force acts horizontally. A shallower angle needs a farther anchor for a fixed mast height. Neither observation supplies a universally suitable rigging angle.
Example: a 10 kN horizontal component
For H = 10 kN and α = 45°, tension is 10/cos 45° = 14.14 kN. The anchor’s upward rope-force component is 10 tan 45° = 10.00 kN.
At 30° above ground, the same horizontal component requires 11.55 kN tension and 5.77 kN uplift. At 60°, it requires 20.00 kN tension and 17.32 kN uplift. These are single-line force components, not working-load ratings.
Why one force triangle cannot size the derrick
Four guy tensions cannot generally be found by assigning the whole lateral force to every line. Their directions, pretension, stiffness and the mast’s movement determine how they share the load. The suspended load also creates forces in the hoist, mast and base that are absent from this calculation.
The result therefore does not choose wire-rope diameter, anchor capacity, allowable mast lean or a safe lifting load. Use the equipment’s engineering data and applicable requirements for those decisions.
Frequently asked questions
Does this mast have a boom?
The gin-pole arrangement shown here does not have a separate hinged boom. A boom-equipped guy derrick is a different arrangement.
Where is the guy angle measured?
From horizontal ground up to the guy line. At 45°, its horizontal and vertical tension components are equal.
Why is tension divided by cosine?
Cosine gives the horizontal component when the angle is measured from horizontal. The balance T cos α = H gives T = H/cos α.
Is horizontal force the same as the lifted weight?
No. H is an assigned lateral force component. Determining it from a lift requires the mast, hoist and load geometry and their complete force balance.
Do the other three guys carry no load?
Not necessarily. Pretension, direction and stiffness affect all the guys. This calculator isolates one force triangle and does not calculate the full load distribution.
Does a lower calculated tension mean the setup is safe?
No. The calculation omits structural capacity, anchor behavior and dynamic loads. It is a force-component comparison, not approval of a lifting setup.
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