chuán zài shuǐ shàng.

在 is the word that marks location here. In this sentence, it works like at / in / on in English.

So the basic pattern is:

Thing + 在 + place

• 船在水上。
• The boat is on the water.

In other sentences, 在 can also act as a main verb meaning to be located at.

Chinese often uses a localizer after a place noun to show the exact spatial relationship.

Here:

• 水 = water
• 上 = on / above / on the surface of

So 水上 means on the water or on the surface of the water.

This is very common in Mandarin:

• 桌子上 = on the table
• 椅子下 = under the chair
• 房子里 = in the house

English often uses just one preposition, but Chinese frequently uses place noun + localizer.

In this sentence, it is best understood as:

• 水 = the water
• 上 = on / on top of / on the surface of

So grammatically, it is noun + localizer.

That said, 水上 can also appear as a fixed expression in other contexts, such as:

• 水上飞机 = seaplane
• 水上运动 = water sports

But in 船在水上, a learner should think of it as water + on-surface.

Mandarin does not have articles like a, an, or the.

So 船 can mean:

• a boat
• the boat
• boats

depending on context.

In this sentence, the exact English translation depends on the situation, but the Chinese itself does not need an article.

Because 是 is usually used to connect two nouns, like A is B:

• 他是老师。 = He is a teacher.

But for location, Chinese normally uses 在, not 是:

• 船在水上。 = The boat is on the water.

A sentence like 船是水上 is not correct.

So a good rule is:

• identity/classification -> often 是
• location -> often 在

Mostly yes in this sentence.

Chinese:

船 在 水上。
boat + at/on + water-on-surface

English:

The boat is on the water.

A useful way to think about it is:

Subject + 在 + location

Examples:

• 我在家。 = I am at home.
• 书在桌子上。 = The book is on the table.

So the structure is very common and important.

Yes, but it means something different.

• 船在水上。 = The boat is on the water.
  This suggests it is floating on the surface.

• 船在水里。 = The boat is in the water.
  This can sound like the boat is in the water more generally, possibly submerged or partly submerged, depending on context.

So if you mean a normal boat floating, 水上 is the better choice.

Yes, here it is pronounced shàng with the fourth tone.

Full pronunciation:

• 船 = chuán
• 在 = zài
• 水 = shuǐ
• 上 = shàng

So the sentence is:

chuán zài shuǐ shàng

Tone pattern:

• chuán = 2nd tone
• zài = 4th tone
• shuǐ = 3rd tone
• shàng = 4th tone

Yes. 在 itself is often a general location marker. The more specific meaning usually comes from the word after it.

Compare:

• 在家 = at home
• 在学校 = at school
• 在桌子上 = on the table
• 在房间里 = in the room

So in 船在水上, the sense of on comes mainly from 上, not from 在 alone.

Yes. Native speakers might also say:

• 船在水面上。

Here:

• 水面 = water surface
• 水面上 = on the surface of the water

This is a bit more explicit. But 船在水上 is simple, correct, and very natural for learners to understand.

No, not as a normal sentence.

You need 在 to connect the thing and its location:

• 船在水上。 ✓
• 船水上。 ✗

Chinese location sentences usually need that location marker.

船 is a general word for boat / ship / vessel. The exact size depends on context.

For example:

• 小船 = small boat
• 大船 = big ship / large boat

So in this sentence, 船 is just the general noun boat or ship.