unkousaikai no ato de, hunayoi wo sita.

運航再開 is a compound noun.

• 運航 = operation/navigation of a ship, ferry, flight, etc.
• 再開 = restarting, resumption

So together, 運航再開 means the resumption of service/operations.

It is a fairly formal expression. For a ferry or ship, it can mean that service started again after being suspended.

Because あと is a noun, and here it is attached to another noun phrase.

• 運航再開 = a noun
• あと = after
• Noun + の
  • あと

So:

• 運航再開のあとで = after the resumption of operations

This is similar to:

• 食事のあとで = after the meal
• 授業のあとで = after class

If the first part were a verb instead, you would not use の. For example:

• 運航が再開したあとで = after operations resumed

In this kind of sentence, the difference is small.

• あと = after
• あとで = after, afterward

Both can mark that one thing happens later than another. In many everyday sentences, あとで sounds very natural when introducing the later event.

So these are both possible:

• 運航再開のあと、船酔いをした。
• 運航再開のあとで、船酔いをした。

The で does not drastically change the meaning here; it just makes the time expression sound a little more complete and natural.

船酔い is usually treated as a noun, and the common pattern is:

• 船酔いをする = to get seasick / to be seasick

So:

• 船酔いをした = got seasick / was seasick

This is similar to:

• けがをした = got injured
• くしゃみをした = sneezed

You may sometimes hear shortened forms in casual speech, but 船酔いをした is the standard, safer form for learners.

Grammatically, yes: it is the past tense of する.

But in English, you usually would not translate it literally as did seasickness. In this pattern, する often means something more natural like:

• experience
• have
• get
• suffer

So 船酔いをした is best understood as:

• got seasick
• was seasick

This is a very common thing in Japanese: the grammar may use する, but the natural English translation uses a different verb.

船酔い means seasickness—motion sickness caused by being on a boat or ship.

Related words:

• 車酔い = carsickness
• 乗り物酔い = motion sickness in general

So 船酔い specifically tells you the sickness came from being on the water.

Yes, but it sounds somewhat formal because 運航再開 is formal.

This kind of phrasing is common in:

• news
• announcements
• reports
• official writing

In more conversational Japanese, someone might say:

• 運航が再開したあとで、船酔いをした。

That version sounds less compressed and a bit more like spoken language.

Yes. Japanese often leaves out the subject when it is clear from context.

So 船酔いをした could mean:

• I got seasick
• he got seasick
• she got seasick
• they got seasick

depending on the situation.

If your provided translation says I got seasick, that I is coming from context, not from an explicit word in the Japanese sentence.

Not necessarily.

あとで mainly shows sequence: one event happened after another. It does not by itself say whether it was:

• immediately after
• much later
• somewhere in between

So 運航再開のあとで、船酔いをした。 means that the seasickness happened after operations resumed, but the sentence alone does not tell you exactly how soon afterward.

The comma marks a pause after the time expression:

• 運航再開のあとで、 = after operations resumed, ...

This is very common when a sentence begins with a time phrase or other introductory phrase.

It helps readability, but punctuation in Japanese is often somewhat flexible. The sentence could also appear without a comma in some contexts.

Yes. Some natural alternatives are:

• 運航が再開したあとで、船酔いをした。
• 運航再開後に、船酔いをした。
• 運航再開後、船酔いになった。

These are slightly different in style:

• 運航が再開したあとで = more verbal, more straightforward
• 運航再開後に = compact, formal, written
• 船酔いになった = focuses on became seasick

Your original sentence is perfectly understandable; it just has a somewhat formal feel because of 運航再開.