science

Three-mile limit

Three-mile limit is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Three-mile limit rather than just read about it. In short: The three-mile limit refers to a traditional and now largely obsolete conception of the international law of the seas which defined a country's territorial waters, for the purposes of trade regulation and exclusivity, as extending as far as the reach of cannons fired from land. In Mare Clausum (1635), John Selden endeavoured to prove that the sea was in practice virtually as capable of appropriation as terrestrial t…

Key takeaways

Three-mile limit belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Three-mile limit to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Three-mile limit from memory before moving on to harder problems.

Reference excerpt

The three-mile limit refers to a traditional and now largely obsolete conception of the international law of the seas which defined a country's territorial waters, for the purposes of trade regulation and exclusivity, as extending as far as the reach of cannons fired from land. In Mare Clausum (1635), John Selden endeavoured to prove that the sea was in practice virtually as capable of appropriation as terrestrial territory. As conflicting claims grew out of the controversy, maritime states came to moderate their demands and base their maritime claims on the principle that it extended seawards from land. A workable formula was found by Cornelius Bynkershoek in his De dominio maris (1702), restricting maritime dominion to the actual distance within which cannon range could effectively protect it. Most maritime nations adopted this principle, which developed into a limit of 3 nautical miles (5.6 km). It has also been suggested that the three-mile limit derived, at least in some cases, from the general application of the league (a common unit of measurement at sea) rather than from the range of cannon. It is also close to the distance to the visible horizon as observed from sea level by a person about six feet tall, so is the limit of what is visible from land. Since the mid-20th century, numerous nations have claimed territorial waters well beyond the traditional three-mile limit. Commonly these maritime territories extend 12 nautical miles (22 km) from a coastline, and this was eventually established as the international norm by the 1982 United Nations Convention on the Law of the Sea. As a result, the three-mile limit has become largely obsolete. As of 2021, only the Coral Sea Islands, Gibraltar, Greenland, Jordan, and Singapore retain it.

See also Admiralty law Gambling ship Hugo Grotius Territorial waters

References

Worked examples

Example 1 — a first encounter with Three-mile limit

Start with the simplest possible case. Write down what Three-mile limit claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Three-mile limit before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Three-mile limit ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Three-mile limit

In research: Three-mile limit appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Three-mile limit in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Three-mile limit is common in secondary-school and first-year university syllabi. It links to neighbouring topics Law of the sea, Maritime boundaries, so understanding it makes those chapters shorter.
In everyday life: Look for Three-mile limit outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Three-mile limit in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Three-mile limit means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Three-mile limit out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Three-mile limit in simple terms?

Why does Three-mile limit matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Three-mile limit?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Three-mile limit.