What Are Blocks and Tackles?
The silent physics behind every rope on deck: blocks that change direction and tackles that multiply power.
A block (pulley) is deck gear that changes the direction of a line while keeping friction to a minimum. A tackle is a purchase system built by rigging blocks in sequence: a 4-sheave mainsheet tackle roughly reduces the load in your hand to a quarter, at the cost of hauling four times the rope.
It is the hidden backbone of onboard comfort: mainsheet, vang and halyards feel 'manageable by hand' because of tackle ratios. Ageing is subtle; salt works its way into the sheaves and friction builds quietly.
Maintenance
Heavy, stiff running: salted bearings; regular fresh-water rinsing plus the manufacturer’s recommended dry lubricant. Grease is not used on most modern blocks as it holds dirt.
Cracked sheave cheeks: UV fatigue; older blocks with plastic cheeks are retired once they’ve had their day.
Running out of line: a block working at the wrong angle not only wears itself out but also chafes the line; fit a swivel or correct the lead.
The feeling that 'this sheet used to run much easier' is often less about muscle and more about a dirty sheave. A block failing under load is one of the most dangerous moments on deck; blocks are selected to match the line and working load (SWL). At the end of the season, turn every block by hand and note any that are sticking.