i used 2 trapezium tread 12mm (don`t know it is proper english) and a nut but is has to be perfect in line ,otherwise it eat eachother.
after 2 trials i decided to use a as you call a boat winch and works perfect.
on the last 2 pics you can see them, i didn`t remove them at that time.
but in the future i will just use a winch,it is cheaper also
i i`m dutch (ons ben zuinig)