Thuyền đầy nước.

In Vietnamese, adjectives can often act as the main predicate by themselves, so you do not need a separate verb like is.

So:

• Thuyền = boat
• đầy nước = full of water

Together, Thuyền đầy nước literally works like Boat full of water.

This is very normal in Vietnamese. Compare:

• Nhà lớn. = The house is big.
• Trời lạnh. = The weather is cold.
• Thuyền đầy nước. = The boat is full of water.

Using là here would usually be incorrect.

đầy means full, and nước means water here.

So đầy nước means full of water.

A useful pattern is:

• đầy + noun = full of + noun

Examples:

• cốc đầy nước = a glass full of water
• phòng đầy người = a room full of people
• túi đầy tiền = a bag full of money

So thuyền đầy nước follows a very common Vietnamese pattern.

Vietnamese often expresses relationships like this without an extra linking word such as of.

English says:

• full of water

Vietnamese says:

• đầy nước

So the structure is simply:

• đầy + thing

There is no separate word needed for of.

It is usually best to think of đầy as an adjective meaning full.

However, in Vietnamese, adjectives can behave like predicates, so in a sentence like Thuyền đầy nước, đầy is doing the job that full does in The boat is full of water.

So for an English speaker, the easiest way to understand it is:

• word type: adjective
• sentence function: predicate

Vietnamese classifiers are often used when you want to count something, introduce it clearly, or sound more specific.

For example:

• một chiếc thuyền = a boat
• chiếc thuyền đầy nước = the/a boat is full of water

But classifiers are often omitted in short statements, headlines, descriptions, or when the noun is being used more generally.

So:

• Thuyền đầy nước. = perfectly fine
• Chiếc thuyền đầy nước. = also fine, a bit more explicit/specific

Both are possible, depending on context and style.

By itself, thuyền does not mark definiteness the way English does.

So depending on context, it could mean:

• the boat
• a boat
• boats in a general sense

Vietnamese usually leaves this to context.

In a real situation, if everyone already knows which boat is being talked about, Thuyền đầy nước would naturally be understood as The boat is full of water.

If you want to make it more clearly singular and specific, you might say:

• Chiếc thuyền đầy nước.

In isolation, nước can mean several things, including water and country/nation.

But in đầy nước, the meaning is clearly water.

That is because đầy nước is a common expression meaning full of water.
đầy nước would not normally be understood as full of country.

So here there is no real ambiguity.

Yes, it is grammatical and understandable.

It sounds like a short descriptive sentence: The boat is full of water.

Depending on context, native speakers might also say things like:

• Thuyền có đầy nước. — less common in this exact use
• Thuyền bị đầy nước. — possible, but more marked
• Thuyền ngập nước. = The boat is flooded / full of water

A very common alternative is ngập nước, especially if the boat has taken on water in a problematic way.

So:

• Thuyền đầy nước = the boat is full of water
• Thuyền ngập nước = the boat is flooded / filled up with water

The order is:

• Thuyền = subject
• đầy nước = predicate

So the structure is basically:

• noun + adjective phrase

This is a very common Vietnamese sentence pattern.

You can think of it as:

• Boat + full of water

rather than trying to force it into English word order.

A rough pronunciation guide for an English speaker is:

• Thuyền ≈ twee-uhn
• đầy ≈ duh-y or day with a short gliding vowel
• nước ≈ nook with a shorter, clipped vowel and the correct tone

A few important notes:

• th in Vietnamese is an aspirated t sound, not the English th in think
• đ is like an English d
• each word has a tone, and the tones matter

The tones are:

• thuyền: huyền tone, low-falling
• đầy: huyền tone, low-falling
• nước: sắc tone, rising, with the ươ vowel combination

If you want to say it well, focus especially on:

1. not using English th
2. making đ a normal d
3. learning the tones from audio rather than English spelling alone

Usually no, or at least it sounds unnatural.

đầy nước already expresses a fairly complete state: full of water. Because of that, rất does not combine naturally with it in most normal situations.

More natural options would be:

• Thuyền đầy nước. = The boat is full of water.
• Thuyền ngập đầy nước. = The boat is filled/flooded with water.
• Trong thuyền có rất nhiều nước. = There is a lot of water in the boat.

So if you want to emphasize quantity, Vietnamese often uses a different structure instead of rất đầy.

You can add words depending on what you want to specify.

For example:

• Chiếc thuyền đầy nước. = The boat is full of water.
• Chiếc thuyền này đầy nước. = This boat is full of water.
• Con thuyền nhỏ đầy nước. = The small boat is full of water.
• Thuyền đã đầy nước rồi. = The boat is already full of water.

Useful additions include:

• chiếc / con = classifier
• này = this
• nhỏ = small
• đã ... rồi = already

So the short original sentence is correct, but Vietnamese often adds context words when needed.