[TowerTalk] Question on mast height above tower

[Roger (K8RI) on TT]

On 8/21/2013 10:51 AM, RShirbroun at newportlabs.com wrote:
> I didn't get any comments or suggestions to my previous post, so I'll try again.
> If this is a dumb question, feel free to tell me!
>
> I have just erected a new HDBX 40 in place of my 30 year old HBX 48,
> sacrificing 8' of height to gain some strength and load capacity (and peace of
> mind!).  The stock rotator plate allows 2' of mast below the top plate and I
> will be using the heavy duty Yaesu thrust bearing (along with the Yaesu heavy
> duty 2800 rotator plus the absorber plate).   I have added steel angle braces
> to reinforce the rotator plate.

My opinion...The mast is plenty strong, (far more than needed) but I 
have my doubts about thr tower to reliably stand that much load. That 
series of towers are designed for relatively light loads and low torque 
conditions.  They are stamped metal that is riveted and I believe the 
load plus leverage of the mast exceeds the tower ratings by a 
substantial margin.

The 10' boom limitation is to limit the torque.

73 and good luck,

Roger (K8RI)
> I'm looking at using a 15' chrome/steel 2" mast (in place of my previous 9'
> mast), so 13' of the mast would extend above the tower.  The mast would support
> a TX38 tribander just above the top plate, a 6 m beam half-way up, and a 40m
> rotatable dipole near the top, 12' above the top tower plate and the thrust
> bearing.  The mast, of course, is very heavy, weighing around 75lbs.  The
> tribander weighs 40lbs and with 5 ft2 surface area; the 6 m. beam weighs 10lbs
> with 1.5 ft2; the dipole weighs 10lbs and is 0.5 ft2.
>
> Is this too much mast for this tower?   (BTW - I'm aware the boom length
> exceeds the 10' maximum for this tower, but the HBX 48 handled a similar
> tribander for 30 years, with occasional severe ice-loading, without any
> problems.)
>
> Thanks and 73,
> Randy, ND0C
>
>
>
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