Tower Lift Failures - Are You Prepared?

First the good news. My new 140' tower is complete. At the time the adjacent photo was taken the only thing left to do was to tighten the top set of guys and realign the tower. There are no antennas on the tower at this point. A few of the yagis for the 15 and 20 meter stacks can be seen on the ground biding their time.

The reason I delayed completing the tower was to build the mast and rotation system which required keeping the top two sections on the ground. With that job completed the tower sections could be raised. More on that in a subsequent article.

Unfortunately the final lift was not without mishap. No matter how carefully you plan and execute an operation of this scale there is an ever-present possibility that something will go wrong. It is never routine.

Several of the hams who have generously given their time to this project have commented that I make these big jobs look easy. Of course they are not easy. It helps to have experience but that is no insurance policy. What experience does provide is a bag of tricks to avoid or recover from many of the things that can and do go wrong.

No one was injured and the toll on tools and equipment was minor. I enforce safety practices on site. By describing what happened and what may have precipitated the mishap I hope to instill a sense of respect in readers for towers big and small. Mistakes can be very costly.

Photo credit: all but two of the pictures in this article are courtesy of Alan VE3KAE who was assisting me that day.

Lift procedure

Like most hams I don't do tower lifts the way professionals do it. The cost of tools, equipment and manpower is too high and unjustified for a ham. For those without the ability to do the work it is worthwhile to hire those professionals. I won't say more about how they do these jobs.

Hauling 150 lb loads 150' vertically upward is not a job for a few muscular hams. A manual winch with a 4:1 or greater advantage isn't as easy as you might guess, and it takes a long time. Power is required. A vehicle or tractor comes in handy and I've used both over the years.

A pulley at the tower based turns the downward rope from the gin pole horizontal. Find a suitable attachment point (tow hook, trailer hitch, etc.), hook up securely and without risk to the vehicle and away you go. The biggest problem is that you have more power than needed. An automatic transmission with a hydraulic clutch helps modulate the power. A rope rather than steel cable provides elasticity that allows a safe and graceful recovery when the load inevitable snags a guy or other tower protrusion.

Failure

When the tower section was up about 90' the rope seized. The load would not move up or down. A brief inspection discovered that wheel on the bottom pulley had split in two. The rope was caught in between the broken halves and was partially severed.

No disaster at that point but not an easy problem to resolve. The axle kept the rope from popping out and dropping the load. Had it broken through the load would have dropped at least 40' and possibly hit a guy at the 65' level. Damage to the car was likely. Had the rope been severed the load would have gone into free fall, an even worse outcome.

Since the situation was stable I had a few minutes to consider the problem. We took care to stand to one side of the tower while doing this. Had the rope or axle broken we would have had time to jump away from ground zero. Hard hats and steel toe boots are no match for a free falling load.

Unfortunately there is no picture of the seized and broken pulley since we were fully occupied dealing with it. The picture shows the split wheel and axle after being extracted from the pulley during the recovery procedure.

Recovery

As the saying goes: necessity is the mother of invention. The come-along (hand winch) and a bunch of old guy grips were at hand in preparation to pull in the top set of guys. While a poor fit the grip was wrapped on the top side of the rope, a thimble inserted and the the come-along hooked to the tower bottom.

Once the tension was transferred the load was safely suspended. The pulley was then broken apart and the rope freed.

A new and larger pulley was attached next to the old one on the same cable wrapped around the tower base. The rope was wrapped around the pulley wheel and the pulley was reassembled. Only then did we pause to have a close look at the rope cut.

No more than 25% of the rope fibres were severed. It still had ample capacity to support the load. The car was backed up to take up the tension and test this assessment. Had it broken through the come-along would have held the rope.

The rope was again inspected under load. We decided to continue the lift with the damaged rope and new pulley.

Completion

The lift was completed without incident. Before climbing up the come-along was reattached to the rope. This eliminated further risk from the damaged rope. My helper used the come-along to lower the tower section into place when I was in position.

The two pictures were taken at almost the same moment. Alan took the one on the left -- one of the rare pictures of me in this blog. You can see me retrieving or replacing my phone for the picture on the right.

Notice that the gin pole has taken some abuse during this problem plagued lift. It looks bad but all that happened is that the pole rotated and pivoted on the top pin so that it is no longer perfectly vertical. This has happened before and is not a risk. All that said it is safer for the rigger to be at the top before the lift, staying above the load rather than climbing below it. On that day the ideal wasn't attainable.

After clearing the tower top the load typically dangles on the far side of the gin pole, only occasionally drifting in the breeze to where you see it in the pictures. The tower has only one climbing face so I cannot climb another face as the load drifts. We monitor it in case something untoward occurs.

A few minutes after reaching the top the section was lowered and bolted in. The guys were then lifted and attached to the segments on the top section. Success at last. After a break we pulled the guys to the anchors and called it a day.

Aftermath

Equipment doesn't come with a best before date. Everything should be inspected before an operation. Had I looked closely at the pulley it's possible I'd have seen something. Often the damage isn't visible so you must rely on the quality of the hardware.

The pulleys have seen lengthy service: lifting 300' of tower; tramming yagis; and a variety of other heavy lifts. Each has passed many thousands of feet (or meters) of rope and cable. No equipment lasts forever, not even when the working load capacity is never exceeded. Since an identical pulley is on the gin pole I brought it down and inspected it. Unlike the broken one there is no evidence of stress. Despite that the pulley will no longer be used at critical locations for heavy loads.

The 100 meter long polypropylene twist rope is approaching end of life, and that's okay since I planned to discard it once the tower was up. There is UV damage (polypropylene is very sensitive to UV) and fraying. Considering what I paid for it I have no complaint. I'll can buy another reel of it or a better product.

I subsequently spoke to a local tower pro. He showed me the rope and pulleys they use. These are very expensive and look awesome. I found it interesting that they never use steel cable, only rope. I will hunt for suitable products at a better price point.

For critical lifts I will be more diligent about using keepers. These are loosely bound ropes or cables that "catch" lifting ropes should the hardware fail. For example, a keeper for the recent failure would be a cable around the tower pillar that passes on the outside of the pulley. Even if the rope comes completely free the load will not fall. Unfortunately the mechanism to recover from a severed rope is not so easy to implement. The answer to that is to use better rope.

As to why the pulley wheel failed I have a likely failure mode. These pulleys are made for rope. As the loaded rope passes over the wheel it compresses and spreads the load over a large cross section of the wheel surface. Steel doesn't behave this way. Since it is thinner (for the same capacity) the force is focused on a narrower area of the wheel.

Second, aircraft cables are hardened steel that abrade the wheel surface, thinning it and reducing its load capacity. Steel cable should not be used on rope pulleys or the pulleys should be discarded sooner and inspected before each use. In future I will try to avoid steel cable for lifts and tram lines. The former I haven't done for a long time anyway.

None of us is perfect. By dissecting this mishap I hope to provide a lesson to myself and to others. Learning by direct experience alone can be deadly. Be safe out there.