Why Are Sails Made In A Triangular Shape?

Why Are Sails Made In A Triangular Shape?

If you’ve ever seen a traditional sailing boot, then you’ll already be aware of the shape of the boat’s sails. Of course, the shape of a traditional sail is triangular.

But for many people, this might then pose the question, how come most sails are a triangular shape?

If you’ve ever simply been curious about why a boat’s sail is this shape or you have an interest in boats and are wondering why exactly they are that shape, then read through our guide on why sails are a triangular shape to learn more! 

So, Why Are They Triangle Shaped?

Well, the simplest way of explaining it is that sails are triangle shaped because it makes it much easier to navigate when making use of a half wind, which in turn helps the boat to be able to manoeuvre.

So, when the airfold has wind passed around it, negative pressure is then induced out of the front and then onto the leeward side of the sail. As a result of this, a rush of air is then pushed into the sail, which is what helps to move the boat forwards. 

In comparison to other different shapes of sails (see also ‘Everything You Need To Know About Sailboat Jibs‘), by using a triangular sail, boats are able to garner more speed than they would with other shapes.

For example, a square sail would not provide the same propulsion that a triangular sail does, in fact, square sails are much more difficult to use on boats, especially if they happen to have a push-button system. 

We have all the experience and knowledge you need to understand this sort of thing better, especially when it comes to which of the shapes of sails work best and why.

Which is why we will teach you all about lateens, which is where a triangular-shaped sail is mounted on an angle on the mast (see also ‘Sailboat Mast: Everything You Need To Know‘) which runs in a fore and aft direction on the boat. So, what are we waiting for? Let’s start learning! 

Why Are Triangle-Shaped Sails Used?

It might sound slightly crazy, but in order for us to better understand why triangle-shaped sails are so much more effective than other shaped sails, we need to start by looking at the wing of an aeroplane. 

Yes, we know this sounds weird, but when you think about it, an aeroplane’s wing is also triangular shaped, and this is for good reason. The triangular shape is what helps to create the force which is what helps to propel the boat whilst it is in the water.

This all started when shipbuilders began using sails in a triangular shape fore and aft to the main sails, all because they were actually incredibly more efficient at catching wind whilst further out at sea, which meant the boat was able to travel longer distances much faster than usual. 

So, with these additional triangular sails, the normal sails on a boat would be able to make better utilization of the wind from many more angles than it previously could.

The main advantage of these new triangular sails was that it meant that the ship could work upwind much easier, all because it could be braced around, and would therefore face more forward.

Plus, the lateen sail created less drag, which made it much better to use in lighter winds also. 

A lot of sailors will prefer sailboats with triangular sails mainly because it means that the boat can move faster than boats that have square shaped sails affixed instead.

Plus, when it comes to the blue water cruising style sailboats, a boat with square sails tend to be much more difficult to operate as a result of the push-button system that they will have installed, purely because rigs featuring square fits haven’t yet been developed to turn smaller cruisers into a more viable option. 

For the most part, cruisers tend to be ketches or sloops, which means that they’re an easy rig to deal with for beginners and new sailors.

In addition to this, most people who has spent a reasonable amount of time out on the water will be able to propel a loop forward, but when it comes to those who only have experience with square rigs, it can often be baffling when it comes to figuring out how to sail a boat of this type. 

How Do Triangle-Shaped Sails Work?

How Do Triangle-Shaped Sails Work?

So, to reiterate, the wind inflates the lateen, which then takes on an airfold shape. As the wind then passes around this airfold, negative pressure is then induced out onto the front and on to the leeward side of the sail itself.

Therefore, the air surrounding the sail is then rushed into the sail, which in turn helps to propel the boat forwards. 

In theory, this sounds much better than a square-shaped sail, however, it is worth mentioning that triangular sails aren’t always the best when it comes to sails. 

Lateens: What Are They?

Sails are a complicated topic, as you can tell, and are divided into two groups, with an additional seven subcategories on top. As for the two main groups, square and triangular sails make up the two groups.

Square sails tend to be located along the main axis in order to make use of the wind pressure that powers the boat, and then the rear (after side) of these square sails is then facing the wind. 

Triangular sails tend to follow the same axis as the boat does, which means that there are fore sails at the bow, as well as aft sails at the stem.

These sails are designed to help increase the propulsion of the boat in a forward direction and can be found on both sides. It isn’t uncommon for these sails to be modified in some way, which is done to take full advantage of the force of the wind. 

A lateen sail is a type of sail that was developed initially by the Arabs, before then becoming widely adopted by many sailors in the Mediterranean, particularly in the east.

As a result of their popularity in the mediterranean, they were given the name “lateen” by some of the Northern sailors that frequented these routes. 

A Carvel was a type of ship that saw frequent use from the 15th century to the 17th century, and was a light sailing ship capable of long distance journeys used by both the Portuguese and the Spanish.

One of the most distinct features about a Caravel was that it featured three masts, featuring lateen sails.

This is because the lateen sail had very quickly become regarded as a more efficient sail than other designs that existed at the time, in fact, it made boats like the Carvel much easier to sail when close to the wind, and it ultimately changed the way that sailors sailed in rougher weather. 

Bermuda Rigs

Despite their immense popularity in comparison to other sailing rigs, then there is another reason why we’re discussing Bermuda rigs, and that’s because of their prominent use of triangular sails!

A Bermuda Rig typically consists of one particularly large sail that in most cases will extend its way right to the top of the mast. Bermuda rigs also usually feature one singular headsail.

Bermuda rigs also have some other common names, including a Macaroni rig, or a Sloop.

This type of rig has a lot of benefits in comparison to sailboats (see also our article on two-mast sailboats) that feature a square rig, mainly because they are a lot easier to maintain if you only have 1 or 2 people onboard, then again, most sailboats for recreational use don’t tend to be bigger than 45 meet, with the average size being between 20-35 foot.

As such, it makes it easy for a small crew to hoist as well as trim the headsail. Depending on the weather, different sizes of headsail might be used. 

What’s so great about Bermuda rigs is their ability to sail well even in upwind, which makes them excellent at sailing in most directions (apart from straight into the wind).

Originally, boats were only able to sail with the wind behind them, which meant trade routes were initially established in conjunction with seasonal winds in mind, which is why the triangular sail became so popular. 


As you can see, triangular sails are commonplace amongst many sailboats and for good reason, their ability to be maintained by a small crew, as well as being able to sail close to the wind is why they became so popular by sailors in the 15th-17th century, and nowadays are favored by recreational sailors. 

There’s a lot of interesting physics that goes into making triangular sails so effective, but even if you don’t understand it, it’s clear to see just how much of an impact triangular sails have had!