25G Rohn tower installation

aliebling · Post by **aliebling** » Mon Aug 03, 2009 10:56 pm

We're planning on utilizing a 35' 25G Rohn tower to mount our camp mascot and would love some feedback from playa-savvy engineers on guying requirements.

According to the Rohn guidelines, a single set of guylines should be enough for that height in any winds the tower is rated for, but we've been considering double guying (20' and top) due to the mascot mounted on top (a large - 6' rotating light up duck made of a covered welded steel framework - total surface area facing the wind ~15'). We have a base plate, but obviously won't be bolting it in to a concrete base in the ground.

Needless to say, the Rohn guidelines don't cover such odd shaped structures or the peculiarities of playa engineering, so I want to get feedback as to whether this should be safe.

Please let me know if more information is required. We want to make this happen, but also want to ensure it is safe. Any engineers (especially with tower experience) willing to provide an off the record opinion would be very welcome.

Thanks!

The Duckpond (9&D)

P.S. if anyone has a gin pole that would fit the 25G and will be bringing it to the playa, we would be deeply in your debt if we could borrow it!

gyre · Post by **gyre** » Tue Aug 04, 2009 1:17 am

I'd check with the factory.
There are a few other towers that go up out there.
Those guys may have suggestions.

It isn't just wind, but gusting and direction changes that shock structures.

Bluemandrew · Post by **Bluemandrew** » Tue Aug 04, 2009 4:19 am

I've got a fiberglass mast going up, but it doesn't look as beefy as that rhon one. I'll be guying it in 3 places, and it only has a camera going on it.

Again though, it's fiberglass, so not sure if you need to go through that extra work. A second set shouldn't really break the bank, and you can't be too careful. Don't want 35 feet of doom tumbling around your camp.

What are you using for anchors?

aliebling · Post by **aliebling** » Tue Aug 04, 2009 8:50 am

Our current plan for anchors is 1" rebar, which we used last year with our 25' tower. Anything less than the 1" was getting bent.

My big concern is the heavy weight/high surface area as these towers were meant for ham radio gear, not huge steel ducks.

Still, I think we'll be fine for the week. Obviously, if this were a permanent installation we would want to use more rigorous guying, but for the stretch of burning man, I *think* we'll be fine.

phil · Post by **phil** » Tue Aug 04, 2009 9:50 am

> Still, I think we'll be fine for the week.

Just so you're more than 70 feet away from me, I think you'll be fine for a week, too.

Do you have homeowners insurance? Any insurance?

Ugly Dougly · Post by **Ugly Dougly** » Tue Aug 04, 2009 9:58 am

How much wind does your mascot catch, and does it have insurance as well?

sputnik · Post by **sputnik** » Tue Aug 04, 2009 10:04 am

If it were me I would use a steel earth screw anchor like this:

http://gmesupply.com/product_info.php/c ... s_id/56002

Bob · Post by **Bob** » Tue Aug 04, 2009 10:11 am

I put up ten 30-ft 25G Rohn towers in 2000 for the "Beaming Man" installation, which had structures on the tops that were about 3'x3' as I recall, for 5-watt laser mirrors and targets. A single tier of guy lines was sufficient -- some of the towers were 2000 ft apart and I don't think the laser beams were off by more than a quarter inch. Used 5/16" wire rope and typical hardware (crosby clamps, turnbuckles etc.) anchored to 40" long screw anchors with 4" helixes, same as the Center Camp Cafe uses. For stability, we tied back the screw anchors to circus stakes (car axle shafts, actually) a couple feet behind, and all were driven flush to the ground surface.

Anyhow, one-inch or larger stakes at least 3' long would probably work for you, or use screw anchors, and two tiers of guy lines might be a good idea with the larger surface area of the thing on top. You could tie the stakes back to one or two other stakes for a little extra security.

Raising was done by hand and with a pickup truck. For lowering, I think we used one of the Cafe's snorkel lifts.

aliebling · Post by **aliebling** » Tue Aug 04, 2009 1:15 pm

Great info all and special thanks to Bob.

I will invest in the earth screws with the one 1" rebar as backup.

How difficult are those earth screws to remove from the playa? We've had some bad experiences with anchoring that we couldn't remove from the ground without serious excavation (great for holding stuff, bad for leave no trace departures).

If your 30' ones weren't a problem with a single set of guylines, I'm sure we'll be fine with doubled guys.

Come by and check out the duck at 9&D and have a drink.

[quote="Bob"]I put up ten 30-ft 25G Rohn towers in 2000 for the "Beaming Man" installation, which had structures on the tops that were about 3'x3' as I recall, for 5-watt laser mirrors and targets. A single tier of guy lines was sufficient -- some of the towers were 2000 ft apart and I don't think the laser beams were off by more than a quarter inch. Used 5/16" wire rope and typical hardware (crosby clamps, turnbuckles etc.) anchored to 40" long screw anchors with 4" helixes, same as the Center Camp Cafe uses. For stability, we tied back the screw anchors to circus stakes (car axle shafts, actually) a couple feet behind, and all were driven flush to the ground surface.

Anyhow, one-inch or larger stakes at least 3' long would probably work for you, or use screw anchors, and two tiers of guy lines might be a good idea with the larger surface area of the thing on top. You could tie the stakes back to one or two other stakes for a little extra security.

Raising was done by hand and with a pickup truck. For lowering, I think we used one of the Cafe's snorkel lifts.
[/quote]

gyre · Post by **gyre** » Tue Aug 04, 2009 1:18 pm

Check with the factory.
They may have specs for differing wind loads.

Bob · Post by **Bob** » Tue Aug 04, 2009 1:55 pm

Re: screw anchors, welded eyes are preferable, but either should work okay. They screw out just like they screw in, eg with a five or six foot length of inch or inch and a quarter plumbing pipe or a breaker bar or somesuch. Screw them in straight down, don't bother with angle.

aliebling · Post by **aliebling** » Tue Aug 04, 2009 1:58 pm

That's perfect Bob. I cannot thank you enough.

Bob, can you comment on this burner's experience with ground anchors:

http://dome.zillabit.com/homedome.html#anchoring

was he just using them wrong or was it playa-condition dependent, or something else altogether?

Bob · Post by **Bob** » Tue Aug 04, 2009 2:15 pm

Not exactly sure what kind of screws he used or what the problem was. The Cafe uses dozens of 40" anchors year after year, and larger anchors are used to guy the Man.

aliebling · Post by **aliebling** » Tue Aug 04, 2009 2:16 pm

Great, I'll go with them and plan on bringing 1" rebar as an emergency backup.

Do you have a reasonably priced source for them in the bay area?

[quote="Bob"]Not exactly sure what kind of screws he used or what the problem was. The Cafe uses dozens of 40" anchors year after year, and larger anchors are used to guy the Man.[/quote]

Bob · Post by **Bob** » Tue Aug 04, 2009 4:08 pm

I used to buy them at Cameron & Cameron, a vineyard supply yard in Santa Rosa, for something like six bucks a piece. They use them up there to anchor grape trellis.

25G Rohn tower installation

25G Rohn tower installation

Re: 25G Rohn tower installation