RIGGING HARDWARE

Block & Tackle

Sheaves and rope combined into a system that trades distance for force — with friction taking its cut.

INSPECT BEFORE LOAD · NEVER EXCEED WLL

Rope, splices and hardware are only as good as their condition. Inspect before every use and retire on evidence.

Block & Tackle — nautical chart line drawing

Specification

Sheave count	Single, double, triple
Bearings	Plain, roller, ball
Materials	Stainless, aluminium, composite
Rope diameter	Matched to sheave groove
Efficiency	≈ 90–95% per sheave
Common error	Sheave too small for the rope

Technical parameters

2-part tackle	Ideal MA 2, effective ≈ 1.9
3-part tackle	Ideal MA 3, effective ≈ 2.8
4-part tackle	Ideal MA 4, effective ≈ 3.6
6-part tackle	Ideal MA 6, effective ≈ 5.2
Sheave ratio	Sheave ≥ 8 × rope diameter
Friction per sheave	5–10%

SelectLoad

Overview

A block is a frame holding one or more sheaves, and a tackle is two or more blocks reeved together. The point of the assembly is mechanical advantage: with the right reeving, a small pull on the fall can raise a load several times heavier, at the cost of pulling several times as much rope.

The theoretical advantage is the number of rope parts supporting the load. A tackle with four supporting parts has an ideal advantage of four, so a 100 kg load needs roughly 25 kg of pull. In practice friction takes a share: each sheave costs something in the region of five to ten per cent, so a four-part tackle might deliver an effective advantage nearer three to three and a half.

Efficiency also depends on the sheave diameter relative to the rope, on the bearing type — plain, roller or ball — and on the rope itself. A stiff line round a small sheave loses far more to friction than a soft one round a large sheave, and the difference shows up as heat and effort.

Safety notes

A block's rating applies to the block, not the assembly. The weakest element — shackle, rope, splice or anchor point — sets the limit.
Sheave diameter should be at least eight times the rope diameter. A small sheave with a stiff rope both wastes effort and damages the line.
Inspect sheaves for cracks, grooves for wear and the frame for distortion. A seized sheave turns a tackle into a chafe point.

Using it well

Reeve so the fall exits in the direction you want to pull; the last sheave decides that.
Use a becket or a shackle to anchor the standing block on the load side so the tackle shortens as it lifts.
Watch the rope where it enters the first sheave — that is where chafe shows up first.

Suited to

HalyardsLiftingTensioningLoad handling

Typical applications

SailingLiftingMechanical advantage

Figures are typical catalogue values for new equipment, quoted for comparison and planning. They are not a guarantee for any specific product or any specific load. Always work to the manufacturer’s stated working load limit and to the regulations that apply where you sail.

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