I have installed several of my towers this way, but no Rohn 55 or 65
experience. Weight is not usually an issue, but kinking the tower in the
first moments of the lift is. Once more vertical the stresses reduce
greatly. I can't imagine putting up 180' feet of 55 in one length without
extensive trussing and/or multiple pick points. 55 is only an 18.5" face
tower with hollow legs. I'm not sure what the dimensions of 65 are, but
picking up 200 feet of anything isn't trivial.
My experience (initially using a Grove 18 ton crane with only about 95'
lift) Typical pick point is .6 to .7 of the height.
- 160 feet of 40" face bolted/angle construction - no bending problem
-160 feet of 33" face bolted/angle construction - pretty limp, decide it
would kink so put an "truss" on it, to support until it got more vertical.
150 feet of 24" solid rod tower - very very rigid and no concerns at all
(now using a 135' crane)
Other towers I could only partially install because of bending concerns. A
very common tower up here is L&R 20, a 20" welded angle construction. Very
solid stuff but I felt 120 feet of this in one lift was about max. Then
gin poled the rest on the top.
Other towers I have are 16" face solid rod - solid but being only 16" face
it felt that 110 to 120 feet was about max, then gin poled the rest.
When you build the tower on the ground, pick it up with a front end loader
or something at the 2/3 point and see what the sag is. That should give you
a feel for what the max length is that will survive.
Trussing can get you some more length, but it is a lot more work and if
anything fails you have a wreck. A crane with 2 hoist lines could hook one
on lower to support the tower until it gets more vertical. Two cranes would
be better, of course.
A taller crane is not always more $ - they generally charge by the tonnage.
For light work such as these towers, specify a crane with a 2nd jib or
stinger. These are becoming more common. Getting something with 200 feet
plus could be tough but you should be able to get around 175' of lift from a
35 to 45 ton crane, which is certainly a low to mid range sized unit. For
the one I'm familiar with (P&H 40 tonner) at max angle and 173 feet above
ground, a payload of 5000 pounds is still permitted. This is enough for most
ham towers and antennas.
Another way, if you are determined to put up 200 feet, get the crane with
as much reach as possible - 175' or so, and lift up the first however many
feet is comfortable - 120 or ? and then build it from the bottom. I have
considered doing this, but haven't so far.
Around here, the crane company reps know what is possible and safe and may
have other solutions as to how to handle your situation. And up to that
point, it won't cost you.
----- Original Message -----
Sent: Friday, May 02, 2003 22:32
Subject: [TowerTalk] Erecting Rohn 55 and 65
> I have had the good fortune to come across some really nice inexpesnsive
> 65 as well as some decent 55. Rohn 65 of course is pretty
> industrial-strength sized tower to erect by the average ham and is beyond
> capacity of the ordinary gin pole.
> I would like to erect as tall a tower made of 65 as I can up to 200 feet.
> However, I do not intend to put up the tower piece by piece. What I I
> like to do is put it up in one total piece by crane. One of the locals
> up a 180 foot tower of Rohn 55 this way. I was amazed that he was going
> do this but he did it....all 180 feet. Incredible! No way am I going to
> replicate that feat with Rohn 55. However, I am curious as to what the
> who have worked with 65 think.
> What is the maximum height that one continuous length of Rohn 65 tower
> be 'walked up' and set by crane on top of the stub sticking out of the
> ground? We're assuming of course, a crane would have no problem with the
> total weight of the tower. The guys would be attached to the tower ahead
> time and taped to the sides during lifting and put in place before the
> was climbed to release the hook. The reason I don't want to do it in two
> pieces is that it would require a much taller crane....more bucks! LXC
> others, any ideas?
> Bill K4XS