Resultant Forces in Tower Rigging: Why Your Anchor Is Seeing More Than You Think

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When lifting on a cell tower, you must know the total weight of the load, according to Kathy Gill President and founder of Tower Safety in Phoenix, AZ. 

“But the tower doesn’t ‘feel’ weight the way we do,” Gill said. “It feels ‘directional forces’ vectors that combine at every anchor point, pulley, and structural member. Every pulley, tag line, heel block, offset lift, or gin pole redirect creates a ‘resultant force’ that can significantly exceed the actual load weight.”

Understanding vectors turns guesswork into engineered safety because we are lifting in 3 dimensions and using physics, she said. If you lift a 100 lb./45kg antenna straight up vertically, Gill said the anchor sees roughly 100 lbs./45kg (plus rigging weight and dynamic factors). 

And if you change the rope angle with a redirect pulley, tag line, or offset? The same 100 lb. /45kg lb. load can produce:

  • 140 lb./63 kg
  • 173 lb./78 kg
  • 200+ lb./90kg on the anchor or structure

Forces are vectors, Gill said. They add geometrically, not arithmetically. The resultant is the single combined force acting on the anchor.

A resultant force is defined as the net single force created when two or more forces (vectors) meet at a point. In tower work, this happens with the following:

  • Rope passing through a pulley (two legs pulling)
  • Tag lines adding horizontal control
  • Heel blocks redirecting haul lines
  • Offset lifts (load not perfectly vertical)
  • Gin pole operations (multiple directions at tip/base)
  • Static lines for positioning

Gill said her “Simple Rules for Every Rigger” mean shifting the mindset from “it worked last time” to professional engineering awareness. Commandments she goes by are:

  1. Rope changes direction → Anchor force increases
  2. Second rope controls the load → Anchor force increases
  3. Load moves off vertical → Anchor force increases
  4. Always evaluate the resultant, not just the scale weight.

Mastering resultant forces helps crews:

  1. Select stronger/more appropriate anchor points
  2. Minimize unnecessary multipliers
  3. Communicate clearly with ground teams
  4. Plan lifts with proper safety factors

“Every rope, sling, pulley, carabiner, shackle, gin pole, and anchor has limits. When vectors combine, those limits are reached faster than the load weight suggests,” Gill said.

The load may weigh 100 lbs./63 kg, but the tower (and your anchors) always feel more.

  • Forces Are Not Hidden.
  • Calculate them.
  • Plan them.
  • Respect them.

Gill advised to always consult a qualified person/engineer for site-specific lifts and use proper dynamic factors/safety margins. Field calculations, she said, should use angle factors from recognized tables (e.g., ~1.41–2.0 for common block angles).