In sailing, a block is a single or multiple pulley. One or a number of sheaves are enclosed in an assembly between cheeks or chocks. In use a block is fixed to the end of a line, to a spar or to a surface. Rope or line is rove through the sheaves, and maybe through one or more matching blocks at some far end to make up a tackle. – Wikipedia
And if you understand any of that you are a better man than I am.
I took this because it looked like a little surprised face.
It is on the last surviving Severn Trow boat ‘Spry’ on display at Blists Hill Museum near Ironbridge Shropshire (UK)
Down by the Sea
New FUJI FINE
A Love of Boats
Not What it Seems – This That and the Other Thing
WOODEN BITS ON BOATS – A Love of Boats