This post will contain, in as much detail as I can muster, instructions for building a hoist to allow top-down construction of a 16′ or smaller dome. 16′ tall domes fall into a gray area: too big to conveniently build with ladders, to small to be worth renting a crane. That’s where this hoist comes in. If you’ve got a 16′ dome or thereabouts and you’re sick of wrangling struts while perched precariously on a ladder 15′ in the air, this is for you.

The advantages of top-down construction are, first, that you can do all the work on the ground. This is obviously safer than doing the work on a ladder. It’s also faster, since you don’t spend time climbing up and down, and moving, a ladder. It’s also easier on your legs. The main advantage, however, is that you can have multiple people help with the build, which means that the more helpers you have, the faster the build goes. This is not possible with a bottom-up build, where you can only do as much work as you have ladders, and given how much tall ladders cost, you probably don’t have very many ladders.

Before I get to the parts list, let me insert a disclaimer: These instructions should NOT be assumed to be complete. Do not just follow them by rote. You should have experience building this kind of thing, working with rigging, and so forth, or enlist the aid of someone who does. Implementing this will probably require some creative problem-solving on your part. You’re welcome to ask questions, and I’ll be happy to answer them, but you assume all risk for following these instructions.

If you want more information on why I think this is reasonably safe, see this post. In fact, you should probably read that either way, so that you are better able to judge the safety margin of your own project.

Before you proceed, you need to know how heavy your dome is. We estimated the weight of our dome by weighing a bundle of 10 pieces of the EMT conduit that we used to build the dome. Since we know how many total sticks of EMT conduit went into building the dome, we could just multiply out. The total weight of our dome is between 600 and 700 lbs. This is important, because you need to make sure that all the parts are rated to take the weight of the dome–the parts that have weight-ratings, anyway. Add in the weight of the bolts too.

Now, the parts list. Total cost for these items was about $300.

• 2x steel plumbing pipe, 10′ long x 2″ diameter. I selected 2″ diameter pipe because it was the smallest diameter I couldn’t easily bend by hand, and because I have used it before in erecting impromptu RF antenna masts.
• 1x pipe coupler, 2″ to 2″.
• 1x pipe coupler, 2″ to 1.5″
• 1x pipe “nipple,” 6″ long x 1.5″ diameter
• 1x pipe end-cap, 1.5″ diameter

These parts are used to build the mast. The 2″-2″ coupler connects the two 10′ pieces of pipe into one long 20′ piece of pipe. Then the remaining parts are put onto the top of the pipe as shown here:

This assembly is to allow the attachment of the guy lines. I considered various alternatives such as eye bolts, but I didn’t like having to drill holes in my mast any more than necessary, and eye bolts are actually not very strong, especially when force is applied in any direction except along the direction of the bolt.

• 3x 50′ of rope. This will be for the guy lines. I like 3/8″ nylon sheathed poly rope, which is rated for 250 lbs and can be had for $10-20 per 100′. The guy lines don’t need to be able to take the dome’s whole weight, since the mast will be very close to vertical.

The guy lines attach to the assembly at the top of the mast as shown above.

A figure-8 knot with a large loop is tied at the end of the line. For instructions on tying this knot, see here: http://en.wikipedia.org/wiki/Figure-eight_loop

Then it is wrapped around itself as shown here and slipped over the top of the mast, where it is cinched tight. I like this method because it allows easy and secure attachment of the guy lines without having to tie and untie a knot or buy hardware like carabiners. This is, of course, absolutely not how a “professional” would do this, but I find the risks to be acceptable.

• 3x “corkscrew” style stakes. These are also for guying out the mast. The ones I bought were rated for 100 lbs. Again, this is plenty, because the mast will be very close to vertical, so there won’t be much lateral force on the lines. I like the corkscrew stakes because they are very easy to put in and take out, and are very secure.

Whatever you use for stakes, the rope must be able to slide past the stake, because you will be cinching the guy lines tight. If you want to get fancy, you can buy ratcheting line tensioners at the hardware store, but I prefer a good old trucker’s hitch:

Tie a loop about 10′ from the stake using a figure-8 knot. Then pass the free end of the line through the loop in the stake, back to the figure-8 loop, and through the figure-8 loop. This creates a block-and-tackle effect, allowing you to tension the line easily. Once the line is tensioned properly, tie it off. For many applications, I use a simple slip-knot, as shown in the photo above. For more security, I use a doubled half hitch. The point is simply to prevent the free end of the line from moving.

For instructions on how to tie a trucker hitch, see here: http://en.wikipedia.org/wiki/Trucker’s_hitch

• 50′ of wire rope, of sufficient diameter to hold your dome up. When you buy wire rope, it will have a weight rating. It needs to be at least strong enough to hold up your dome, of course. You must also consider that your winch will have a certain maximum diameter of cable that it can take, so first figure out what diameter of cable you need, then buy a winch that can support it. The winch will also have a certain maximum length of cable that can be spooled on its drum. Since the mast that you’re going to build is 20′ long, you only need 40′ of cable at most, so I recommend buying a pre-made 50′ cable (I got mine at Home Depot). Just look at the weight rating on the package and select the diameter that can hold up your dome. If you’re on the edge, I’d say go larger. Better safe than sorry! The cable that you buy should have a loop pre-inserted in one end, and the other end should just be cut off. If you can only find bare cable, you will need to buy a “thimble” and clamps to put the loop in the cable’s end. This is kind of a pain in the ass and you can screw it up, so better to find pre-made cable.
• 1x slip hook. This is just a hook that goes on the end of your cable. They come in various sizes and weight ratings. Pick one that can hold up your dome. It should have a shaft held in by a cotter pin, or something similar, to allow it to be affixed to the loop at the end of your wire rope.

• 1x dual-direction, brake winch. Needs to be rated to take the weight of your dome. Actually, needs some safety margin, since you lose 10% of your winch’s rated strength for every complete wrap of cable around the drum. My winch is rated for 1200 lbs. After I am on the second wrap of cable around the drum, I’m down 10% (120 lbs) to a rated weight of 1080 lbs. On the third wrap of cable, I lose another 10% (972 lbs), then 874 lbs for the 4th wrap, 787 lbs for the 5th wrap, and so on. The winch should be dual-direction so that you can both raise and lower the dome. It should have an automatically-engaging brake, for hopefully obvious reasons. You can find winches at Northern Tool and Equipment, most boating supply companies, and, of course, Amazon.com. The winch needs to be able to take the diameter and length of cable that you bought. A nice-to-have feature on a winch is a “freewheel” setting, that allows you to freely play out the cable without having to crank the handle backwards (slowly). Some people view this as a safety hazard, since engaging the freewheel feature when a load is on the winch can have disastrous results.
• Misc. hardware to attach the winch to the mast. The details of this will depend on the bolt pattern of your particular winch. Some creativity was required. If you can’t solve this problem on your own, consider yourself un-qualified to attempt this project. I installed the winch 4′ up from the base of the mast because that seemed to be a comfortable height.

• 12″ of chain, rated to hold up whatever your dome weighs. At the store, have them cut three links off the end of the 12″ section. Keep both sections of chain so that you have one that is 3 links long and one that is 12″ minus 3 links.
• 1x quick-link, rated to hold up whatever your dome weighs. This will be used to make a loop out of the chain, to attach the dome to the slip hook. So the quick-link needs to be sized so that it will fit through the chain.
• 1x carriage bolt, 3/8″ x 3″.
• 2x nuts for the carriage bolt.
• 2x 3/8″ flat washers.
• 1x snatch block. This is basically just a pulley, with a high weight rating. It is installed at the top of the mast and the wire rope runs from the winch, through the snatch block, down to attach to the dome. The snatch block needs to be weight-rated to take your dome, but the lowest-rated snatch block I found could still take 8,000 lbs, so this was not a problem. It also needs to be able to take the size of cable you bought, but this is not likely to be a problem either. Do not just buy a pulley at the hardware store because they are rated for 150 lbs or so, and they will not work.
• 1x quick-link or some other device to connect the snatch-block to the chain. I bought a quick-link, but it was actually a tight fit to get the snatch-block onto the quick-link, and I kind of wish I had bought something else. Whatever you use needs to fit through the chain and then have the snatch block put onto it easily. It needs to be weight-rated to take your dome (duh).

The assembly of the above-listed parts is shown above. The carriage bolt has been installed in a hole drilled through the top of the mast, with a nut and washer on either side. The carriage bolt is 3/8″, which was the largest diameter I could get that would also fit through the chain that I bought. This keeps the chain from sliding off the head of the bolt and gives as much strength to the bolt as possible. I chose a carriage bolt because it is full-threaded and has a larger head than a hex-bolt. The first nut provides spacing between the mast and the chain, to allow the chain to swing a little more freely. You could accomplish something similar with a washer and a hex-bolt, although hex-bolts are often not full-threaded.

You might be wondering why I ended up with this silly setup. I originally was going to use an eye-bolt to hold the pulley at the top of the mast, but eye bolts have pathetic rated working loads–in the range of 100-150 lbs. Even solid forged eye bolts couldn’t reach the 700 lbs I needed, especially because the load was going to be 90° from the direction of the shaft. This was the simplest thing I could cobble together from hardware-store parts that would accomplish what I needed.

I don’t have a picture of this, but the final step is to use the remaining section of chain and a quick-link to attach the dome to the slip hook. Basically, you build the very first section of the dome, then loop the chain around the top-most vertex and put the chain in the hook. Also, as you get started, you have to build the first section of dome around the mast so that as the dome is raised, it slides up along the mast. Here is a photo of the early stages.

One thing we learned when doing this the first time is that the weight of the dome can drive the mast into the ground. The ground was relatively soft when we did this and the mast ended up about 12″ in the ground–no lie. I suggest setting the mast on a cinderblock to prevent this.

Installing the corkscrew stakes at the perfect 120° angle to each other can be tricky. To provide enough clearance so that the dome can be raised to its full height, the stakes need to be 26′ out from the mast. At this radius, the distance between any two stakes is 45′. What I do is mark the center of the circle, then measure 26′ in any direction and set the first stake. Then I measure 26′ out from the mast and 45′ from the first stake. The place where those two lines cross is the correct location for the 2nd stake. The mirror image of that setup is the place for the 3rd stake.

The most effective way we have fount to raise the mast is to set the base close to the desired center-point, then have one person start at the top of the mast and raise it while walking towards the base. Around the halfway point, this will become impractical. Another person should be pulling on a guy line from the exact other direction. Around the time that the “walker” gets to the halfway point of the mast, the guy line puller will get mechanical advantage and will be able to help. Two people should be holding the remaining two guy lines to keep the “puller” from pulling the mast all the way over. Once the mast is generally vertical, the three guy lines can be loosely tied off and the base of the mast can be tweaked. If needed, it can be lifted onto a cinderblock or moved to the exact center of the circle. Following this, tension on the guy liens can be adjusted using a level or inclinometer to bring the mast as close as possible to perfect vertical.

When adjusting tension on the guy lines, resist the urge to tighten them too much. Unless you’re using steel cable, you’re not going to keep the mast from jiggling entirely, and that’s okay. My calculations suggest that the system can go at least nine degrees out of vertical (with a 700 lb dome fully assembled) and not exceed it planned operating margins (notice I did not say “safe” operating margins). If you tighten the guy lines too much, they will just be pulling on each other and using up their working load. Get them taut, but don’t worry about getting them piano-string tight.

Once the dome is fully assembled, you will probably want to take the mast out. Even if you don’t consider it to be in the way, it is a tempting target for mischief, and it’s not designed to be climbed upon and so forth. I found the easiest way to do this is to leave the slip hook attached to the chain at the top-most vertex, then simply “kick out” the bottom of the mast so that it is hanging by the hook. Do this gradually and take as much tension out of the cable as you do it to keep things under control. Once the mast is hanging by the hook, simply reverse the winch to lower the mast to the ground. Finally, use a ladder to climb up and disconnect the hook from the chain at the top of the dome. Oh: disconnect the guy lines before doing any of this. They will simply follow the mast down as you lower it. Reverse this process to re-erect the mast when it’s time to take the dome down.