ferii ga kekkou desu.

が marks フェリー as the subject of the sentence.

So the structure is:

• フェリー = ferry
• が = subject marker
• 欠航 = cancellation of a flight/ferry service
• です = polite copula

A very literal breakdown is something like:

• As for the ferry, it is canceled
• or more literally, The ferry is in a state of cancellation

In natural English, we usually just say The ferry is canceled.

欠航 is a noun, not a regular verb in this sentence. It means something like cancellation of a flight/ferry voyage.

Japanese often uses the pattern:

• Noun + です

to mean is + noun/state.

So:

• フェリーが欠航です = The ferry is canceled
• literally, The ferry is a cancellation / in canceled status

This is very natural in announcements and practical situations.

Yes, you often can.

The difference is mainly about focus:

• フェリーが欠航です: focuses on the ferry as the thing that is canceled
• フェリーは欠航です: presents the ferry as the topic, like As for the ferry, it is canceled

In many real situations, both are possible.
For a simple notice or announcement, が is very common and natural.

欠航 is used for a scheduled trip that does not operate, especially for:

• flights
• ferries
• sometimes other ship services

It is not the most common word for all transport types.

For example:

• planes/ferries: 欠航
• trains/buses: often 運休

So for a ferry, 欠航 is a very appropriate word.

Japanese nouns usually do not show singular/plural the way English does.

So フェリー could mean:

• the ferry
• a ferry
• sometimes ferries, depending on context

In this sentence, it will usually be understood from the situation.
For example, on a sign at a port, it likely means the ferry service or this ferry is canceled.

Because フェリー is a loanword, borrowed from a foreign language, like English ferry.

Katakana is commonly used for:

• foreign loanwords
• onomatopoeia
• emphasis
• some technical terms

So フェリー in katakana is exactly what you would expect.

It is pronounced roughly ferii.

A few points:

• フェ is like fe
• リー has a long ii sound

So the final part is stretched a little:

• フェリー
• fe-rii

The long vowel matters in Japanese, so it should not sound too short.

Yes. It is polite because it ends with です.

This is the kind of sentence you might hear in:

• announcements
• customer service
• signs
• transportation staff speech

A less polite or plain version would be:

• フェリーが欠航だ

But in normal public communication, です is much more common.

Yes, but the nuance changes a little.

Possible forms include:

• フェリーが欠航です = The ferry is canceled
• フェリーが欠航しました = The ferry was canceled
• フェリーは欠航になります = The ferry will be canceled / has been designated canceled

In notices and current-status statements, 欠航です is very common because it sounds like a direct status update.

Japanese often leaves that kind of detail implied.

Here, フェリー can stand for:

• the ferry boat
• the ferry route
• the scheduled ferry departure
• the ferry service

In English, we may prefer to spell out exactly what is canceled, but Japanese often relies on context.
So フェリーが欠航です is short, natural, and easy to understand in the right setting.