[TowerTalk] Question on mast height above tower

[john at kk9a.com]

I won't comment on the tower, however using a 4130 mast seems like
overkill for that windload.  Also 2 ft in and 13 ft out does not seem like
a good ratio.

John KK9A


To:	 <towertalk at contesting.com>
Subject: [TowerTalk] Question on mast height above tower
From:	 <RShirbroun at newportlabs.com>
Date:	 Wed, 21 Aug 2013 10:51:25 -0400

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.

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