2 min read · Updated 27 June 2026
A block is a pulley, and a tackle is a system of blocks that multiplies your pulling force. Together they are how sailors tame the huge loads in a boat's rigging by hand — turning a pull no person could hold into something manageable. Understanding the block and tackle is understanding how a boat's control systems actually work.
Blocks
A block is the sailing word for a pulley: a wheel — the sheave — in a housing, with a rope running over it. On its own a block changes the direction of a pull, leading a line around the deck to where the crew can reach it. Combine several and they do much more.
Tackles and purchase
A tackle (or purchase) is two or more blocks with a line rove between them that multiplies force. By running the line back and forth between the blocks, the load is shared across several parts of the line, so you pull with less force — the trade-off being that you pull more rope.
Almost every sail control is a tackle: the mainsheet, vang, cunningham and outhaul are all purchase systems that let a sailor apply big loads by hand. See sail controls explained for what each one does.
Mechanical advantage
The mechanical advantage is written as a ratio — 2:1, 4:1, 8:1 — and it is the number of line parts supporting the load:
- A 4:1 purchase lets you pull with about a quarter of the force, but you haul four times the rope. A 100 kg load feels like roughly 25 kg in the hand (ignoring friction), but you pull four metres of line to move the load one.
- Higher ratios = less force, more rope.
It is the same trade-off as a low gear on a bike: less effort, more turning. Sailors add purchase where loads are high, and keep it low where speed of adjustment matters more than power.
Why boats are full of blocks
The reason a sailing boat is covered in blocks is simple: the loads are enormous. Wind on the sails runs to hundreds or thousands of kilograms — far more than a person can hold directly. Blocks and tackles multiply human effort to make those loads manageable, and route the lines neatly to where the crew works. Where even a tackle isn't enough, a winch adds still more power. For the vocabulary, see the sailing terms glossary.
Frequently asked questions
- What is a block in sailing?
- A block is the sailing word for a pulley — a wheel (called a sheave) in a housing that a rope runs over, changing the direction of the pull or, when several are combined, multiplying the force. Blocks are everywhere on a sailing boat, guiding the sheets, halyards and control lines around the deck and forming the purchase systems that let a crew handle heavy loads by hand.
- What is a tackle or purchase?
- A tackle (also called a purchase) is a system of two or more blocks with a line rove between them that multiplies the force you apply. By running the line back and forth between blocks, the load is shared over several parts of the line, so you pull with less force — at the cost of pulling more rope. Mainsheets, vangs, cunninghams and outhauls are all tackles, letting a sailor control big sail loads by hand.
- What does a 4:1 purchase mean?
- A 4:1 purchase means you pull with roughly a quarter of the force of the load, but must pull four times as much rope. The number is the mechanical advantage: a 4:1 has four parts of line supporting the load, so a 100 kilogram pull on the sail feels like about 25 kilograms in your hand (ignoring friction), but you haul four metres of line to move the load one metre. Higher ratios mean less force and more rope.
- How does mechanical advantage work in a block and tackle?
- Mechanical advantage comes from spreading the load across several parts of the line. Each additional part of line running between the blocks carries a share of the load, so the force you need to apply drops in proportion — but the trade-off is that you pull more rope to move the load the same distance. It is the same trade-off as a low gear on a bike: less effort, more turning. Sailors add purchase where loads are high and remove it where speed of adjustment matters.
- Why do sailing boats use so many blocks?
- Because the loads in a sailing rig are enormous and constantly need adjusting. Wind loads on sails run to hundreds or thousands of kilograms, far more than a person can hold directly, so blocks and tackles multiply human effort to make those loads manageable, while also routing lines neatly around the deck to where the crew works. The whole control system of a boat is built from blocks, tackles, cleats and winches.