science

Leeboard

Leeboard 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 Leeboard rather than just read about it. In short: A leeboard is a form of pivoting keel used largely by sailboats, very often in lieu of a fixed keel. Typically mounted in pairs on each side of a hull, leeboards function much like a centreboard, allowing shallow-draft craft to ply waters inaccessible to fixed-keel boats.

Key takeaways

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

Reference excerpt

A leeboard is a form of pivoting keel used largely by sailboats, very often in lieu of a fixed keel. Typically mounted in pairs on each side of a hull, leeboards function much like a centreboard, allowing shallow-draft craft to ply waters inaccessible to fixed-keel boats. Only the leeward side leeboard is used at any time, as it submerges when the boat heels under the force of the wind. A disadvantage, where there is an inadequate fixed keel, is that leeboards typically ship (bear) little ballast, and being on the far (lee) side delays the onset of unballasted craft's heeling, that is, inhibits the effect of putting up a good, constant resistance against the wind. The classical, archetypal definition of ballast is a low, central weight to optimise centre of mass, to reduce turning moment and therefore resistance to the boat keeling over; however, the centre of gravity tends to be higher in self-righting vessels. Modern developments allow leeboards to act as a speed-enhancing lifting foil (hydrofoil).

History

Leeboards existed in China from at least the eighth century on warships that "held the ships, so that even when wind and wave arise in fury, they are neither driven sideways, nor overturn". Leeboards for stabilizing junks and improving their capability to sail upwind, are documented from a book by Li Chuan. The innovation was transmitted to Portuguese and Dutch ships around 1570. "The Portuguese experimented with caulking their vessels in the Chinese manner and the Dutch probably added leeboards to their craft that were copied from Chinese models." Leeboards have been used by relatively large inshore and coastal sailing vessels used for transport since 1570, such as Dutch barges, Thames barges, and American gundalows. For these boats, leeboards provided the advantages of shallow draught for working close inshore and an unobstructed hold for cargo. In particular, they allowed gundalows to take the hard to load and unload cargo in unimproved tidal areas, as well as readily conduct maintenance on their hulls. Leeboards were also easier to build than a large centreboard would have been.

Today Leeboards are no longer common in commercially-built boats, because many people consider them inelegant and awkward. They are far more common in home-built boats, especially the Puddle Duck Racer and stitch and glue type sailboats. Leeboards simplify construction of the hull, as they are attached to the outside and do not require holes in the hull, which can leak. Since centreboards are retractable, they require a large, watertight trunk to hold them in place when retracted, and this occupies what otherwise might be useful space in the cabin or cockpit of the boat. Use of leeboards, while it adds complexity to the process of tacking, leaves the floor of the boat unobstructed. According to traditional design principles, a boat utilizing a leeboard either needs to have two retractable leeboards, one on each side, or a method of removing the leeboard and attaching it to either side while under way, because nearly all sailboats tack to work their way upwind (with the exception of the proa). However, some small sailboat designers claim to have created seaworthy vessels with only a single, fixed leeboard. On a traditional two-leeboard (or non-fixed leeboard) design, the boards are designed so that the windward board can be retracted, to reduce drag. Unlike centreboards, which are symmetric along the boat's axis, leeboards are often asymmetric, so that they more efficiently provide lift in one direction. Some fast racing scows use bilgeboards, which are mounted between the centreline of the hull and the sides, so they can use a pair of asymmetric foils for maximum lift and minimum drag.

Illustrations

Worked examples

Example 1 — a first encounter with Leeboard

Start with the simplest possible case. Write down what Leeboard 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 Leeboard 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 Leeboard 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 Leeboard

In research: Leeboard 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 Leeboard 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: Leeboard is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chinese inventions, Sailing rigs and rigging, Sailing ship components, so understanding it makes those chapters shorter.
In everyday life: Look for Leeboard 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 Leeboard in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Leeboard 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 Leeboard out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Leeboard in simple terms?

Why does Leeboard 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 Leeboard?

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 Leeboard.