Ef ég sit inni í bátnum, verð ég ekki eins sjóveikur.

This is because Icelandic is a verb-second (V2) language in main clauses.

When the sentence begins with a subordinate clause like Ef ég sit inni í bátnum (If I sit inside the boat), that whole clause takes the first position. Then, in the main clause, the finite verb comes next:

• Ef ég sit inni í bátnum, verð ég ekki eins sjóveikur.

So the order is:

• first element: Ef ég sit inni í bátnum
• second position: verð
• then subject: ég

If the sentence started directly with the main clause, you would say:

• Ég verð ekki eins sjóveikur.

Both are normal; the word order changes because something else comes first.

Yes, verða basically means become, but it is also very commonly used where English would say will be.

So:

• verð ég ekki eins sjóveikur
  literally: I do not become as seasick
• natural English: I won’t be as seasick

Icelandic often uses verða for a change of state or result. In this sentence, the idea is that if I sit inside the boat, the result is that I end up less seasick.

Icelandic often uses the simple present where English might use either sit or am sitting, depending on context.

So:

• Ef ég sit inni í bátnum
  can mean
• If I sit inside the boat
• or, depending on context, something close to If I’m sitting inside the boat

Icelandic does have ways to express an ongoing action, but the plain present tense is very common and natural here.

Inni í emphasizes being inside something.

• í bátnum = in the boat
• inni í bátnum = inside the boat

The extra word inni adds a stronger sense of interior location. In this sentence, that matters because being inside the boat is probably being contrasted with being outside, on deck, or in a more exposed spot.

Because í takes the dative when it expresses location.

Here, the meaning is in/inside the boat as a place, not motion into it. So you get:

• í bátnum = in the boat
  dative singular definite

Compare:

• í bátinn = into the boat
  accusative, showing motion/direction

So the case changes depending on whether you mean:

• location → dative
• movement into → accusative

Icelandic and English do not always use the same prepositions in the same situations.

In English, we often say:

• on the boat

But in Icelandic, if you specifically mean inside the boat, then inni í bátnum is natural.

There is also:

• á bátnum = on the boat

That would usually suggest being on the boat more generally, often more like aboard the boat, and sometimes possibly on deck depending on context.

So this sentence chooses inni í because the speaker means inside the boat, not just on board.

Eins is part of a comparison meaning as ....

• eins sjóveikur = as seasick
• ekki eins sjóveikur = not as seasick

This is like English not as seasick. The second half of the comparison is often understood from context and does not need to be stated explicitly.

You could think of it as:

• I won’t be as seasick (as I otherwise would be / as if I were elsewhere).

Because the adjective agrees with the subject ég in gender, number, and case.

Here it is:

• singular
• nominative
• masculine

So the form is:

• sjóveikur = masculine singular nominative

If the speaker were female, you would usually expect:

• Ef ég sit inni í bátnum, verð ég ekki eins sjóveik.

And for neuter:

• sjóveikt

Predicative adjectives in Icelandic must agree with the person or thing being described.

Usually, a female speaker would change the adjective:

• masculine: sjóveikur
• feminine: sjóveik
• neuter: sjóveikt

So a woman would normally say:

• Ef ég sit inni í bátnum, verð ég ekki eins sjóveik.

The rest of the sentence stays the same.

This follows normal Icelandic sentence structure.

After the initial ef-clause, the main clause begins with the finite verb:

• verð

Then comes the subject:

• ég

Then the negation:

• ekki

So:

• verð ég ekki eins sjóveikur

This is a very typical Icelandic order in main clauses after something else has been fronted.

Not necessarily. In a normal real or likely condition, Icelandic often uses the indicative, as in this sentence:

• Ef ég sit inni í bátnum...

That is a straightforward if-clause about a real possibility.

Subjunctive forms can appear in other kinds of conditional or less factual situations, but there is nothing unusual here. The indicative is exactly what you would expect.

Yes, in standard Icelandic writing, a subordinate clause like this is normally separated from the main clause with a comma:

• Ef ég sit inni í bátnum, verð ég ekki eins sjóveikur.

This is standard punctuation.

Here are the main forms:

• ef = if
• ég = I
• sit ← sitja = sit
• inni = inside
• í = in
• bátnum ← bátur = boat
• verð ← verða = become, will be
• ekki = not
• eins = as, equally
• sjóveikur = seasick

This is useful because Icelandic words often appear in forms that look different from the dictionary entry.