Raising / Lowering a 40' aluminum antenna tower

[ak3b]

TL;DR Summary

I've seen some conversations, but I am not sure how they translate to my install.

I have a 40' Universal aluminum tower, which will have antennas, cables, and a rotor installed. Dead weight on the ground will be 225 lbs. The base, which is three 4.5' legs, is set into 5'x5'x5' concrete. The fulcrum is ground level on the concrete base. The lifting cable will attach to the tower at 25' to a pulley that is mounted to the house 12' above the ground. The tower is 4' from the house. The winch is ground-mounted. Like other posters, I'm curious about the weight from horizontal to vertical so I can determine the correct pulley, the surface to mount for the pulley, and the winch.

Thanks,
Chris

 

[berkeman]

73, Chris, and Welcome to PF.

How far away from the base can you place the winch? How long is the winch cable, and what is your winch power?

 

[ak3b]

73, Chris, and Welcome to PF.

How far away from the base can you place the winch? How long is the winch cable, and what is your winch power?

Thanks!

I was planning to put the winch below the pulley.

I've attached a pic. The base was poured on 10/20. A contractor reinforced the attachment point for the pulley since we had to rebuild this side of the house due to a tree that fell in Aug.

The winch cable should be about 25'. The winch power depends on the lift load. I'm looking at the Dutton-Lainson WG2000 Worm Gear Winch | Hex Drive | Std. Reel https://www.dutton-lainson.com/proddetail.php?prod=11001. for horizontal pulling and vertical lifting applications.
2,000 lb. capacity

 

[BvU]

Could have guessed

73 is an old telegraph code that means "best regards". 73, as well as 88 (which means "hugs and kisses") are part of the language of ham radio.

 

[erobz]

Is this the idea?

 

[berkeman]

I was planning to put the winch below the pulley.

Sorry, I'm having trouble visualizing the lifting operation. That looks to be about the bottom 12' of the tower, right? Are the bottom 2 legs that are opposite the pulley hinged? And if so, is the idea to lower that first 12' of tower, build the rest of the tower on the ground, and then tilt it up left-to right using the 2 hinged leg bottoms until it's vertical and then make the 3rd leg connection?

EDIT -- @erobz beat me to it!

 

[ak3b]

Yes. That's the first 10' section.

 

[berkeman]

Can you upload a diagram of the sections of the tower and the weights that are distributed along the length/height of the tower? How much does each 10' section weigh for just the tower itself? How much weight is there in the winch and antennas at the top? About how much will the cables weigh once they are run in the tower?

Do you have flexibility where the cable attaches to the tower? 25' up may not end up being the optimum placement -- we will need to work through the angles once the weight distribution is nailed down.

 

[berkeman]

I'm looking at the Dutton-Lainson WG2000 Worm Gear Winch | Hex Drive | Std. Reel https://www.dutton-lainson.com/proddetail.php?prod=11001. for horizontal pulling and vertical lifting applications.

Are you planning on using the hand-driven lever, or attaching a power drill? Also, I'm not clear how the lowering operation will work. Do you somehow release the ratchet and use hand resistance to try to unwind the winch slowly to lower the tower?

 

[ak3b]

The tower weighs 124 lbs. The antenna is 25 lbs, the rotor is 8 lbs, the cables are roughly 50 lbs. The reel automatically stops turning whenever cranking is stopped, locking the load in place.

 

[berkeman]

The reel automatically stops turning whenever cranking is stopped, locking the load in place.

Yeah, that makes sense. I'm just wondering how to use it to safely lower the antenna mast for service, additions, etc.

 

[berkeman]

The tower weighs 124 lbs. The antenna is 25 lbs, the rotor is 8 lbs, the cables are roughly 50 lbs.

Are you familiar with how to calculate the position of the center of gravity for the tower?

 

[ak3b]

Are you familiar with how to calculate the position of the center of gravity for the tower?

I am not.

 

[berkeman]

Okay, so it's like balancing a teeter-totter. You want the sum of the weights multiplied by the distances from the fulcrum (the center of gravity) to be equal on both sides of the fulcrum. So if most of the weight is near the top of the tower, the center of gravity will also be closer to the top than to the center.

Figuring out the center of gravity of the tower helps us write the equations that show how much tension it takes in the cable at different angles as the tower is raised, which helps us figure out the best point to anchor the cable onto the tower to minimize the tension over the course of the lifting operation.

The tower weighs 124 lbs. The antenna is 25 lbs, the rotor is 8 lbs, the cables are roughly 50 lbs.

So draw a sketch of the tower laying down on the ground. The distributed weight is 124+50 lbs from the mast and cables, and there is an additional 25+8 lbs concentrated at the left end (top of the tower). Does that sound right? If that's right, my sketch shows a weight of 174 lbs concentrated at the center of the tower (representing the distributed weight), and a weight of 32 lbs concentrated at the top (left side) of the tower. We can just find the balance point of these two forces on the laid-down tower to find the center of gravity.

When I do this, it looks like the center of gravity of the tower is about 24' up from the base. How did you decide on the 25' mark as an attachment point? That's pretty close to the CG!

The lifting cable will attach to the tower at 25'

 

[ak3b]

I didn't use any math. It just seemed logical. A good guess, I suppose.

 

[berkeman]

So for a ballpark number, stealing the sketch from @erobz in Post #5:

If I subtract about 2' for the width of the tower (is that about right?), then we can calculate the angle $\theta$ where the cable attaches to the tower when the tower is on the ground:
$$\theta = tan^{-1}\frac{10'}{29'} = 19^o$$
So then we can calculate the tension T in the cable as it starts to lift the weight of the tower (centered approximately below the lift point):
$$T = \frac{206 lbs}{sin(19^o)} = 633 lbs$$

 

[berkeman]

BTW, assuming that that we do still end up with about $633 lbs$ for the initial lifting tension in the cable after some discussion, you would obviously need to size things to include reasonable safety factors. That includes the mounts for the pulley and winch. (Speaking from personal experience here after helping to erect many large and heavy antennas for Field Day and at fellow HAM's homes, sometimes antenna masts bounce as part of the process...)

 

[Borg]

Wouldn't this system need a wire on the backside as well? Once it gets close to vertical, it's going to tend to slam into the ground on the non-pivot side.

 

[berkeman]

Wouldn't this system need a wire on the backside as well? Once it gets close to vertical, it's going to tend to slam into the ground on the non-pivot side.

The 3rd leg touching down should stop the rotation, if I understand the setup correctly.

That said, there are the bounces that I mention above...

I was helping to erect a large and moderately heavy antenna mast at Field Day a few years ago, where finishing the setup involved pushing a locking pin through the base and the mast as it reached vertical. The person with that assignment missed, and the mast came down as slowly as us puny humans could try to manage it. Kind of bent the 10m antenna at the top of the mast, but no puny humans were harmed in the "mishap"...

 

[DaveC426913]

I do this with my 30ft. (boat) mast twice a year. Of course, it only weighs about 100lbs.

I do it by hand using a 4:1 pulley system.

^{This is not me and this is not my boat.}

This anecdote is of absolutely no use to you.

 

[berkeman]

This anecdote is of absolutely no use to you.

Goofball.

You could at least check my math, mate.

 

[berkeman]

I do it by hand using a 4:1 pulley system.

Hey BTW, how does the lowering work? Do you open the ratchet and resist the lowering torque and no problems?

 

[ak3b]

BTW, assuming that that we do still end up with about $633 lbs$ for the initial lifting tension in the cable after some discussion, you would obviously need to size things to include reasonable safety factors. That includes the mounts for the pulley and winch. (Speaking from personal experience here after helping to erect many large and heavy antennas for Field Day and at fellow HAM's homes, sometimes antenna masts bounce as part of the process...)

Yes. The wall where I will mount the pulley was reinforced with 2x6s when they rebuilt the roof. Of course, I missed the opportunity to install the eye bolt before they replaced the porch ceiling with plywood. So I either take the plywood down to get the bolt in place, or I use lag bolts, which makes me nervous. So, I'll probably be taking the plywood down. I will replace the corner post, which was damaged from the tree, with a 6x6. I'm looking for a mount to bolt to the concrete porch and screw the 6x6. I want to install the winch on this post.

 

[ak3b]

Hey BTW, how does the lowering work? Do you open the ratchet and resist the lowering torque and no problems?

The Dutton-Lainson WG2000 Worm Gear Winch only lowers when it's turned. It locks when it stops, so it won't unwind.

 

[berkeman]

The Dutton-Lainson WG2000 Worm Gear Winch only lowers when it's turned. It locks when it stops, so it won't unwind.

I don't really understand that, but that's okay. It looks like it has a 40:1 worm gear ratio, so the hold-back force that you need to use when lowering should be do-able, it seems.

It might be worth doing a trial run with a partial mast (3 sections) and no cables at first to see how hard it feels. Hopefully it is easy and the final mast is do-able. Be sure to have some help and backup when you try this stuff for the first time. That's the medic hat that I'm wearing now...

 

[berkeman]

BTW, you probably already know this, but if you have a couple of helpers who can assist with the initial part of the mast lift while you are cranking the winch, that will lower the peak tension and cranking effort. The hardest part is when the tower is on the ground, because the angle $\theta$ is the sharpest.

 

[ak3b]

BTW, you probably already know this, but if you have a couple of helpers who can assist with the initial part of the mast lift while you are cranking the winch, that will lower the peak tension and cranking effort. The hardest part is when the tower is on the ground, because the angle $\theta$ is the sharpest.

I'll have my wife on the winch. :)

 

[sophiecentaur]

I do this with my 30ft. (boat) mast twice a year. Of course, it only weighs about 100lbs.

I do it by hand using a 4:1 pulley system.

View attachment 334238
^{This is not me and this is not my boat.}

This anecdote is of absolutely no use to you.

Not necessarily.

I had a similar arrangement for raising and lowering my 10m mast (about 80kg) - with an A frame instead of the single lifting post in the image above. On a boat, you have nowhere to place a pulley as in the OP's diagram (could be on a swinging mooring). The shroud fixings on the mast were near the CM, or a bit higher. I used alloy scaffold tubing so it was all do-able single handed but I used mates to help 'cos the rigging would always find somewhere to catch onto. The required force was manageable, using the main sheet blocks.
Can the OP rely on having an available high spot to fix and pulley? If not, the A frame solution would work and the same forces would be involved..

 

[DaveC426913]

You could at least check my math, mate.

Me? Post high-school math??

Hey BTW, how does the lowering work? Do you open the ratchet and resist the lowering torque and no problems?

Yeah. Cam cleat, not ratchet. Maybe when I get older and weaker, I'll use a manual winch but it's not really necessary (except for the last two inches).

I use the 4:1 mainsheet with fiddle blocks and integrated cam cleat.

The 4:1 fiddle blocks provide enough advantage (as well as friction) that lowering it can be done one-handed, and the cam cleat acts as an automatic brake.

 

[DaveC426913]

On a boat, you have nowhere to place a pulley

That's why a Mac comes with a mast-raising pole as standard equipment.

Mine is about 6 feet long, pivots on the mast step plate.

 

[sophiecentaur]

a Mac comes with a mast-raising pole as standard equipment.

I'm wondering where the OP's pulley is attached. Sky hooks would be ideal for sailing but you can find them on the sides of buildings - it's another world on land.

The original Westerly centaur had a massively over-specked mast and it was not intended for bridges or for towing (two massive iron keels) so the mast raising pole was not standard equipment, afaik).

I don't really understand that,

A worm drive is often very inefficient and will only work from worm to pinion. A great example where Velocity ratio is much higher than 1/mechanical advantage - People still insist on using the wrong one, even here on PF.

 

[sophiecentaur]

The hardest part is when the tower is on the ground, because the angle θ is the sharpest.

Lifting it off the ground manually and resting it on a prop (or another person) can take care of the worst case of theta is zero). They can also hold a rope to control rotation when near vertical.
Basically there's no substitute for a few spare muscular blokes for these events.

 

[DaveC426913]

I'm wondering where the OP's pulley is attached.

 

[sophiecentaur]

Sorry I missed that image. Another thing to reduce the extreme of tension the lifting from the ground would be to use a pole or A frame, starting at say 45 degrees elevation - like the boat mast lifting gear. It would make things much less dramatic and stressful on the pulley fixing.

View attachment 334307