Mechanical Movement 16 — Spanish Burton
How does a Spanish burton quadruple the pull?
Mechanism No. 16 from 507 Mechanical Movements, the first of two “Spanish bartons” (Spanish burtons). Two ropes and three pulleys: rope 1 is tied to the beam, runs down under the pulley carrying the load, up over a second pulley (the runner) and down to your hand. Rope 2 runs over a fixed pulley and joins the load pulley to the runner. Both parts of rope 1 pull the runner down, so rope 2 is twice as tight as rope 1, and it lifts the load too. The load hangs on 1 + 1 + 2 = 4 times your pull.
How it works, step by step
1. Two ropes, three pulleys
Rope 1 runs from the beam under the load pulley and over the runner to you; rope 2 ties the load to the runner.
2. Rope 2 is twice as tight
Both parts of rope 1 pull down on the runner, so rope 2 carries twice your pull: 393 N ideal.
3. Four shares
The load hangs on two parts of rope 1 and on rope 2: 1 + 1 + 2 = 4 times your pull. Pull 223 N for 785 N.
4. Lowering
The runner drops as the load rises, and your hand travels 4 times as far: 59 cm for 15 cm.
The key idea
F ≈ W / 4 — Rope 2 carries twice the tension of rope 1, so the load hangs on 1 + 1 + 2 = 4 shares of your pull.
A second rope turns the runner’s doubled tension into extra lift: one rope and one fixed pulley more give 4 : 1.
Model and assumptions
Ideal mechanical advantage 4: as the load rises 1 cm the runner drops 1 cm and the hand end travels 4 cm. Friction: each of the three pulleys passes on a fraction η of the power, so lifting needs about W / (4 η³). Rope weight is neglected.
Frequently asked questions
What is a Spanish burton?
A sailors’ tackle using two ropes: the second rope links the load pulley to a moving runner, adding lift.
Why is the advantage 4?
Rope 2 carries twice your pull, and the load hangs on 1 + 1 + 2 = 4 shares.
Where is it used?
Ship rigging and cargo handling, where few blocks must give a good advantage.
Part of the 507 Mechanical Movements series
This is Movement No. 16 from Henry T. Brown’s 507 Mechanical Movements (1868), redrawn and simulated by BCRUZ. ← Mechanical Movement 15 — White’s Pulleys · Mechanical Movement 17 — Spanish Burton, Second Form →
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