A tackle is an arrangement of blocks and rope that lets a person move a load greater than they could pull directly. The line passes back and forth between a fixed block and a moving block, and each part of the line that leaves the moving block shares the load, so a four-part tackle lets you lift or haul roughly four times as hard as you pull. Sailors traditionally pronounce it “tay-kle”, and the word purchase is used for the same thing. A beginner meets tackles on the mainsheet, the vang and the backstay adjuster; an experienced sailor knows that every extra part costs speed of adjustment and adds friction, and chooses the ratio for each job accordingly.
How a tackle works
Imagine a single block fixed to the boom and a line running from a fitting on deck up through the block and back to your hand. Pulling one metre of line moves the boom one metre; there is no advantage, only a change of direction. Now fix the block to the deck and put a second block on the boom, with the line dead-ended at the deck block: two parts of line now support the boom, so each carries half the load, and you pull two metres of line for every metre the boom moves. Add another sheave at each end and you have four parts, and so on. The mechanical advantage of a tackle is, in theory, the number of parts of line leaving the moving block. In practice each sheave adds friction, so a 6:1 purchase might deliver 5:1 at the hand.
Anatomy and vocabulary
- Standing block: the block fixed to the boat or spar that does not move with the load.
- Moving block: the block attached to the load; the number of parts leaving it sets the advantage.
- Standing part: the end of the line made fast to one of the blocks.
- Hauling part or fall: the end you pull, often led to a cleat, cam or winch.
- Becket: the eye on a block to which the standing part is tied.
Common tackles on a sailing boat
The mainsheet is the most familiar. A dinghy may use 2:1 or 3:1 so the sheet can be played quickly; a cruising yacht of ten or twelve metres typically has a 4:1 or 6:1 mainsheet, often with a fine-tune added by a second small tackle on the end. The kicking strap or vang is nearly always a tackle, 4:1 to 8:1 on a cruiser, or a rigid vang with an internal purchase. Backstay adjusters on boats without hydraulics use a cascade: a 2:1 wire over a block feeding a 4:1 rope tackle gives 8:1, and a further stage doubles it again. Cunninghams, outhauls, jib car adjusters and traveller controls all use tackles, and many are led below deck to keep the cockpit clear.
Why tackles matter to trim
The right tackle turns a control the crew avoid using into one they use constantly, and that changes how a sail is trimmed. A vang a crew can adjust by hand controls leech tension downwind; one that needs a winch handle stays where it was set at the start of the day. A cunningham on a 4:1 purchase lets the trimmer move the mainsail’s draft forward in a gust without asking for the halyard winch. UK Sailmakers design mainsails expecting these controls to be used, with luff and leech shapes that respond to vang and cunningham, so a boat with tackles too weak to move them is not getting the sail it paid for.
Practical tips
Use ball-bearing blocks where the line moves a lot, such as mainsheets, and plain bearings where it is mostly static under high load, such as a vang. Size the line for grip in the hand rather than strength; a tackle divides the load so the line is rarely the weak point, but a thin line hurts to pull. Keep the parts from twisting by ensuring the blocks are free to align, and check the beckets and shackles, which carry the full load, more often than the sheaves. Flush salt out of bearings with fresh water.
Related terms
A block is the pulley itself; a sheave is the wheel inside it. Purchase means the same as tackle, and ratios are written 4:1 and spoken “four to one”. Ground tackle is unrelated: it is the anchor, chain and rode.
Frequently Asked Questions about Tackle
How do I work out the mechanical advantage of a tackle?
Count the parts of line that leave the moving block, including the hauling part if it comes off the moving block. That number is the theoretical advantage; subtract a little for friction at each sheave.
Is a higher ratio always better?
No. More parts mean more line to pull and more friction, so the control becomes slow and the line piles up in the cockpit. Choose the lowest ratio that lets the crew adjust the control comfortably in the wind the boat will sail in.
A tackle is the quiet machine that makes sail controls usable. Give each control the ratio it needs, keep the blocks running freely, and the crew will trim the sail the way the sailmaker intended rather than leaving it where it was when the day began.