According to the Oxford Companion to Ships and the Sea, "A Burton is a special *purchase using three single blocks or two single blocks and a hook in which one *whip is needed to haul on the fall of the other, thus multiplying the power gained.

In sailing ship days it was used mainly to set up the shrouds of the mast so as to get them as taut as possible. It's not much used today except where a strong haul is required in a restricted space."

*Purchase - A mechanical device to increase power or force whether by means of levers, gears or blocks or pulleys.

*Whip - A single rope rove through a single block.

Now all we need to do is to find the definition of "Archway" as mentioned in the shanty, Down Trinidad.

But that's a bit above me, I'm afraid!!