[UK-CONTEST] Pulleys and rope

[Dave Lawley]

Hi Steve

Last things first, if the masts are only used a handful of times a year, 
for field day, then polyprop rope will be ok provided it is kept out of 
sunlight for the rest of the year. If the ropes are going to be out in 
the open all the time then go for pre-stretched polyester but it is more 
expensive.

We use two London Pattern double sheave blocks. Sheave diameter is about 
3inches. It's important to use the right size rope, to minimise friction 
and rope wear. 12mm rope is right for 3in sheaves (love the 
metric/imperial mixture!). On VHF FD at the weekend we put up a monster 
7el for 6m on 60ft of scaffold mast, and with the 4:1 mechanical 
advantage it was easy for one person to pull up. Make sure the stake 
that the block is tied to is firmly in the ground, if in doubt back it 
up with another one about 3ft behind and lash the top of the front one 
(nearest the base of the mast) to the bottom of the second one.

The end of the rope is attached to the upper block, then the other end 
that you pull also comes from the upper block. Keeps you out of the 
danger zone.

Finally a plea - it horrifies me when I see people putting up a mast 
with a gin pole and someone insists on being at the fulcrum, at the 
base. Even on a hard surface the base isn't going to move anywhere and 
on grass it will tend to dig in so there's no need to fix it, but if 
anything should fail then the base of the mast is the most dangerous 
place to be. Never ever let anyone stand at the base while a mast is 
going up.

Hope that helps

Dave G4BUO


Steve Bunting wrote:
>  
> Hi Folks,
> 
> Having relied for a number of years on brute force to pull a portable 
> mast upright using a gin pole, it seems that it is time to use a pulley 
> to provide some mechanical advantage. I guess a marine pulley is the 
> grade to look for? I looked at several websites and there is a baffling 
> array of pulleys available. Can anyone advise me on the type required? 
> Also, I am looking for opinions on how many times should one go back and 
> forth between gin pole and anchor stake to form a usable system? I guess 
> this could be calculated from first principles, but I am too lazy to do 
> that!
> 
> Finally, I have been told that some contest groups use marine grade rope 
> for their portable masts. The plan is for this to "last a lifetime" so I 
> wonder which of the plethora I should choose. Any comments?
> 
> 73
> Steve
> M0BPQ