eli5 Why some sailing ships have multiple square sails like Clipper? Why not have one continuous sail from top to bottom like Korean Turtle Ship?
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The turtle ships primary mode of propulsion was rowing. The square sail were only used on rare occasions when they were sailing with the wind. Medieval European ships also had the same arrangement of sails and would also primarily use ores for propulsion or have to wait for favorable winds. The concept of tacking and jibbing as a way to sail fast in any direction was not used much until the renaissance and even then it had limited use for war ship and inland ships (turtle ships being both) as maneuvering in close quarters were significantly harder using sails alone. These types of sailing techniques requires you to be able to turn the sails so they face along the hull of the ship, which is what the clippers primarily is designed for. In addition it is harder to find masts that can support the forces of the sail so you need to use more masts to distribute the forces. The turtle ships were able to use huge old trees for their masts but that does not scale to a large industrial mercent marine like the clippers were serving.
There are several reasons you might want multiple sails.
For one thing, clipper ships were large ships that carried lots of sail. Having your sail partitioned up into smaller pieces makes each piece easier to work with…to raise and lower and shift around. This lets a ship respond more quickly.
It also lets a ship carry more sail. A tall ship could have masts 100 feet tall! It’d be difficult to even raise and lower a single sail that tall.
Another advantage of having separate sails is that the amount of sail can be adjusted to match the wind conditions. It’s not always good to have the maximum amount of sail out, especially if the weather isn’t great. With multiple smaller sails, you can take some down to reduce the chance of damage from high winds, while still keeping others up to keep the ship moving.
Big piece of cloth hard to use and costs a lot of money.
Many smaller pieces of cloth easier to handle and you don’t go broke if it brakes.
The biggest factor IMO is that Asian sails use sticks. If the sail has sticks it tends to stay flat in the wind. European sails are just a big piece of canvas, having smaller chunks helps to keep the sail straight.
Other factors are:
you have to man the sail. Lifting a single piece sail requires tremendous amount of force. A turtle ship is very small compared to a ship of the line. Specially if you consider the rigging.
Mast is strong but not invincible: if you do a single very tall sail you have the top of the mast to be subject to all the force. If you split it to 3 vertical sections you can split the force of the sail and the lower sail is gonna load the lower portion of the mast, which is far stronger than the thinner top. And so on going up. The more you go up the mast the smaller is the sail you can fit. The top sail can be smaller and lighter, loading less the top thin part of the mast.
For the same effort, you can fit the ship with a taller mast and more total sail surface.
Western sails are supported only on the edges, and think about it, as your sails get bigger, the energy being imparted on them goes up exponentially. Asian type sails often have rigid reinforcements all throughout like in a Chinese junk type boat. Not familiar with Korean sailboats but probably similar.
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