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G8MNY  > TECH     20.06.18 07:00l 293 Lines 14729 Bytes #7 (0) @ WW
BID : 25904_GB7CIP
Read: GUEST
Subj: Gin polling up large masts
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 180620/0454Z @:GB7CIP.#32.GBR.EURO #:25904 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                      (Updated Jun 18)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

A 20M MAST
Over the years I have tried several aerial systems. But settled on a well tried
& tested gin pole system.

The biggest used to date uses 3x 21' (3x 6.5m) aluminium scaffold poles with
reinforced Jaybeam joiners & a 42'(2x 6.5m) steel gin pole. (as we are getting
older a 2nd gin pole is used for putting up the gin!)

                                            .:,Pulley
3 tiers of 4 guys @ 90                  ,'.;' \
ensures stability.               Tight,' .',    `\
                             3 Guy ,'  ,' ,'      `\
This design is the          Sets,'   ,'  ,'   Gin   `\
mainstay of nearly           ,'    ,'   ,'    Pole    `\  Gin
all my contest &                   ` Pull up
/P activity.                20m Mast      Ground^ Pivot      Rope

Structures higher than 66' (20m) have been attempted, but computer calculations
showed this to would be unstable, & these were borne out in practice when
unstable attempt proved it, i.e. they tend to buckle the mast on lifting with
any head load at all!

METHORD
The mast is always put up with NO aerials first, to make sure all the mast bits
work properly & are in the right place before, the mast is loaded up. With the
aerial load the mast should be raised slowly & a spotter person used to sort
any snags out. Generally you can tie off the gin up rope at any angle up to the
point of balance, above that someone should slowly pay out the rear 3 mast guys
to stop any sudden shock on the mast as it comes vertical & the rear gys
tighten.

If there is to be any length of unsupported mast above the too guy ring, like
in a 17el over 17el on 2m, then an extra top guy is needed during gining up the
mast to stop the top of the mast bending away from the gin (when total collapse
failure is possible!). And this is then untied from the gin & allowed to rap
around the mast when in use.

REINFORCED JOINTS
            ________________
           o  o  o  o  o  o
-----------~~~~~~~~~~~~~~~~---------
Mast Poles ͳWebbing
-----------________________---------           []
           o  o  o  o  o  o                    /  \
            ~~~~~~~~~~~~~~~~            WebbingĴ    
            _.-~~~~~~~~-._Webbing              \  /
-----------~~~~~~~~~~~~~~~~---------           []
           ================
-----------________________---------
            ~-.________.-~

To stop the joiners tearing along the perforated centre line, extra steel
webbings (0.4 x 2 x 25cm) were welded over the weakness both sides. To lighten
it a bit the webbing ends can be cut down.

SLIPPING JOINTS
If the joints stretch & start to slip           []
(aerial poles rotate), then put a               /  \
thin wire (coat hanger) under one of          Ĵ   .
the sides & clamp up, this will bite            \  /\Wire
into the smooth pole & stop slips.              []

GUY BEARINGS
Made from either plate or tube collars, resting on a large 2" (50mm) greased
ally washer above the joiners. The top set of guys will rest on an exhaust U
clamp, it also has an enlarged guy spacer is needed to stop the steeper guys
rapping around the pole.

        Plate                 Tube                   Top
    == ==        Or      ,o o,               oĴ o
  .'  `.            .'     '.           .'       '.
.'   | |   '.        .'  /~~   '.       .'    /~ ~     '.
                     Washer| |              Washer  \
                                                       Exhaust U Clamp

Never use a long unguyed pole (e.g. 10ft) above a guyed joiner, as the wind
loading on your aerial & the pole leverage will try to sheer the joiner in two!
Always use a top guy set & U clamp close to the aerial as possible.

Halyard pullies for wire aerials etc. can be put on the top guy set to, so they
do not rotate with the mast.

CENTRE GROUND POST
(plan views)

    Gin   Ground                    Ground             Ground
    Pole  Post                       Post               Post
           (_)___Swivel     Mast      (_)                (_) Swivel clamp
ĴĿ Clamp     Ŀ         Mast-( )
Ĵ_=           =             
Mast  90Clamp                     (_)\Tight              
       lose                   Gin pole  Clamp          90clamp  Gin Pole

  All on the ground           Gin up in air                 Mast up

The gin pole clamp is initially left slightly lose on the mast, so that when
the gin is errected from the side it can rotate on the mast.

GROUND LAYOUT                           o
All guy ropes use                       | (5x 5x 80cm)
a safe "clove hitch"                    |   stakes
knot on the bottom of                   |
the angled stakes.       Front   Ground |   Gin
                         Stake     Post |--goes down--->   Back
Once the mast is     =======o==========`8<-----12m----->o Stake
up & no further               Mast'     |           -~
adjustment is needed                    |        _-~
the clove hitch can                Hinge|      17m
be locked with a.                   Line|    -~
simple over knot.                       | _-~
                                        o~  Side stakes

A short 1m x 49mm steel ground pole is put it the middle (after making a hole
with the spare 5th stake first) to take all the hinge forces.

ROPES
A full mast rope set of 3 tiers of 4 guys & a gin pole pulley system + 2 guys,
takes 1,024' (312m) of rope. Using mainly 8mm polypropylene for strength &
cheapness, caused a storage problem, as the rope is ultra-violet light
sensitive. For speed we do not detach the measured ropes from the guy bearings
for neat rope hank storage, so a single guy tier of 4 ropes with its bearing is
chain-laced together (3x shorter then) to give quick & untangled storage. The
bulky & UV free storage was solved using 2 large dustbins (for 3 mast sets).
One for the 1st mast & Gin pole, & the 2nd for the rest of the masts.

GIN PULL ROPE
            ĿThick
          ~~hook                 The pull up rope is a
         _ Ropes               thicker 20mm for hand
Mast  _-~_ (clove hitches)     hauling & uses a 2:1
top_-~ _-/ | o\                   pulley on the gin pole
     _- /  | \/\Strong            that hooks on the pole
middle / G |  \ \Pulley           with the mast ropes tied.
      /  i |   \/\                over the steel hook & eye.  
     /   n |    \\\Gin Ropes
bottom     Side    \\\
           Guy      \\\

The gin pole will need 2 side guys, these need not be @ full length 2/3 is OK.

GUYS
The top guy to the gin needs to be low stretch & pre-tightened, so that the top
of the mast ALWAYS bends (curved up) towards the gin pole. This avoids the
unstable failure mode, when the top guy ends up in parallel to the mast & the
very high compression forces on the mast WILL cause a collapse.

                  .:,                                    .:,
               ,'.;' \                                ,'.;' \
            ,' .',    `\                           ,' .',    `\
   3 Guy ,'  ,' ,'      `\                3 Guy ,'  ,' ,'      `\
  Sets,'   ,'  ,'   Gin   `\             Sets,'   ,'  ,'   Gin   `\
.._,'    ,'   ,'    Pole    `\            ,'__...:_  ,'    Pole    `\
   ~~~---...:.____          `\       _.:-~~       ~~-..__          `\
 Good Curved Mast    ^ Pivot           -~Unstable Mast Fail!  ^ Pivot

COAX TIES                                             Beam Boom
With a rotary mast system, reusable      ==================
coaxes ties were used on the coax &            ~==_____-~Support
reused to attached it to the mast          Coax/   ~~> coax
above the top bearing. Then 1 or 2                  <  loops
lose turns/loops & then attatched               Tie.''.U clamp
to one of the top bearing guys with              .' |  '.bearing
a cable tie threaded through the rope.         .'   |    '.
(stops it slipping down the rope)            .' Coax|      '.
This is then repeated at each lower        .'   Tie.''.joiner'bearing
bearing to take each section of the      .'      .' |  '.      '.
coax's weight, & also keep the coax    .'      .'   |    '.      '.
away from the bearings.              .'      .'     |      '.      '.
                                   .'      .'       |        '.      '.
TRANSPORT
With the large poles, only roof racks could be used, this caused noticeably top
heavy problems with the vehicles. After some research we solved the problem,
with a designed for a dismantleable pole trailer. The UK law on the length of
long trailers is simple, the trailer other than it's drawbar, must not be
longer than the divisible load.
                                            ______
                                  Welded  (__[]__) Arm & rubber      []
Tow         .']              Wheel frame suspension         
Hitch    X====X==========================X========X==================X=
      .'                                                          Tail
   0<'|                    Centre pole()XBrace                     X Board
     '.                                                           
  Welded`X====X==========================X========X==================X=
  Draw A    '.]   2x steel poles (gin)                      
  Frame                                   (__[]__)                   []
                                          Wheel unit
X = scaffold clamps.                      & mud guard
 poles
[ forward lights                      _.-X-.._
] rear light                   _..-''~        ~`.._
                       _,.-''~4m      1m     []    3m``-.._
                _..-''~     Pole     Pole  /~~~~\  Pole    ~``-.._ o []
    _    =X====X=========================X /~~\ X=================X===
   (_\_________                         {} 
    ~~~~~~~~~~~~~                            \__/Mini
                                                Wheels

We welded up the design, added the trail arm rubber block suspension & axel &
wheels. The upper framework adds essential stiffness for bounce free ride.  It
lived up to all expectations, regarding cornering & loadings etc. The only
problem has been the requirement to manually drag the rear & around tight
corners like into the contest site entrance. With experience the wheel unit can
be clamped at a position to set the hitch load to 50kg, dependent on the
planned trailer load. As well as the tail board there are 6 additional running
lights to make the trailer conspicuous as well as being painted in bright
colours. The wiring loom is rapped around the poles & plugs in the fixed lights
etc.

There are 2 shorter bracing poles, that form 2 triangles & are tensioned up
before moving by standing on the long steels & doing up the top swivel camps,
this then forms a very ridged trailer.

The trailer can handle 6 Ally scaffold poles clamped on plus loads more on top.
So it can carry poles for 3 masts using the 2 steels as the shared gin.

The pole trailer is completely dismantled for storage.

AERIALS USED
Mainly concentrating on VHF contests, I have used quite a collection...
 BAND
 160m       100m random wire to halyard to trees, many other dipoles too!
 80m        Insulated 66' mast as 1/4 Wave vertical
 80m/40m    Trap Dipoles, inverted Vs & also plain QRO dipoles
 20/15/10m  3el TH33 Mosley beam with QRO traps
 6m         3el Coax & Bamboo Quad
 6m         5el yagi beam
 4m         2x 5el yagi & phasing harness
 2m         5el, 7el, 11el small beams, 17el & even 2x 17el 11ft apart
 2m         4x 17el yagis Box, 11ft apart stacking frame & power splitter
 70cm       9el, 19el, 23el yagis, 88el multibeam
 70cm       27el quad loop yagi
 23cm       24el, & 65el loop yagi
 13cm       40el with tranverter on 10ft extention pole

For 2m we used to use a box of 4x 17el, stack/baying frame & 4 way power
splitter, but due to its weight it could only be put up at 42' & took a good
hour to assemble onto the mast. This gave a theoretical 20dB gain or 40kW ERP!
However the simpler, 2x17el staked at 10'(3m) apart with a coax splitter works
as well in practice at 20m with is wider beam width.

On 4m we stacked 2x5el at 10'(3m) apart as well.

ROTATORS
Generally I use mast ground rotation, avoiding putting the heavy rotators at
the top of the mast. The slightly faster arm strong methods, have been
superseded with bottom of pole rotators, mainly because of access to the mast
under all contest weathers. But I have seen direct drive gearboxes & shaft into
the shack used on simular masts.
                                         _______________________________
To put a heavy mast on                  |__________________________ Gin Pole
the rotator, either have                         
several helpers to lift a                 /\      
tiller bar with the guys                       __ Jack
fairly loose. Or use a car             Ŀ    
jack under the horizontal              ROTATOR    Ŀ
gin pole to lift the load    Bracing ___ 
while you assemble the          Feet     U   U   
rotators clamp on the pole.         OR  Bolts in
                                         ground

EARTHING                                 Ŀ____ 
A when the whole mast is rotated         X~~~~ )
I put a flexable 1-2 turn earth               ./
strap from the ground post to the             /\
mast rotator clamp.                            
This earth will take some of the           Ŀ
nearby lightening current safely           ROTATOR
to earth & not via the shack.              
N.B. Any direct strike will do               U   U
lots of damage!                           

WINDAGE
Generally this is not a problem as the gining up process puts much higher loads
on everything than the wind will. Do check guy tensions & knots at least once a
day & after/during any storms. If there are problems & you have the extra rope
it is possible to add an additional guy in situ by lassoing a mast guy set at
ground level & slipping the new guy up the others & stake out windward etc.

In strong wind raising & lowering, should ONLY be done side on to the wind! So
the only effect it has is to keep one side set of guys tight, & not help/hinder
the mast raising & lowering.


Y Don't U send an interesting bul?

73 de John G8MNY @ GB7CIP


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