Morska struja nas nosi, ali skiper drži kormilo.

Because morska has to agree with struja in gender, number, and case.

• struja is feminine singular nominative
• so the adjective morski changes to morska

This kind of agreement is very important in Croatian. The basic adjective form you often see in dictionaries is usually masculine, but in actual sentences it changes to match the noun.

Here, struja means current, specifically a sea current because of morska.

A useful thing to know is that struja can also mean:

• electric current
• electricity / power

So on its own, struja can have more than one meaning. In this sentence, morska struja clearly means sea current.

Because nas is the form for us, while mi means we.

In this sentence:

• morska struja = the subject
• nas = the direct object
• nosi = carries

So the structure is basically The sea current carries us.

Grammatically:

• mi = nominative = we
• nas = accusative/genitive = us

Because short pronoun forms in Croatian often go in second position in the clause.

So Morska struja nas nosi is very natural Croatian word order.

You could also hear Morska struja nosi nas, but that usually sounds more marked or more emphatic. The version with nas before the verb is the more neutral one here.

Nosi is present tense, third person singular, from the verb nositi.

Why third person singular?

Because the subject is morska struja, which is singular.

So:

• ja nosim = I carry
• ti nosiš = you carry
• on/ona/ono nosi = he/she/it carries

Here it has an ongoing sense, something like is carrying / carries depending on context.

Yes. Nositi is imperfective.

That fits well here because the sentence describes an ongoing situation: the sea current is carrying us along.

In Croatian, imperfective verbs are commonly used for:

• ongoing actions
• repeated actions
• general descriptions

So nosi sounds natural for this kind of scene.

Yes, skiper is commonly used in Croatian, especially in sailing and boating contexts.

It means skipper, the person in charge of the boat or the person steering it. It is a masculine noun.

You may also see other nautical words such as kapetan, but skiper is very normal in modern Croatian, especially in informal or practical maritime use.

Yes, literally drži kormilo means holds the helm / wheel / rudder, depending on context.

But in natural use it often implies more than just physically touching it. It can also suggest:

• steering
• keeping control
• maintaining direction

So drži kormilo works well both literally and a bit idiomatically.

Because kormilo is a neuter singular noun, and for many neuter nouns, the nominative and accusative singular are the same.

So:

• nominative: kormilo
• accusative: kormilo

In this sentence, kormilo is the direct object of drži, but its form does not change.

Because ali means but, and in Croatian it is normally preceded by a comma when it joins two clauses.

So:

• Morska struja nas nosi, ali skiper drži kormilo.

This punctuation is standard and expected.

Yes, Croatian word order is fairly flexible, but different orders create different emphasis.

The given sentence is very natural and neutral:

• Morska struja nas nosi, ali skiper drži kormilo.

Possible alternatives include:

• Nas nosi morska struja, ali skiper drži kormilo.
• Morska struja nosi nas, ali skiper drži kormilo.

These are grammatically possible, but they sound more marked or emphatic. For a learner, the original version is a very good model.

Because Croatian does not have articles like English.

So Croatian does not normally use separate words for:

• a
• an
• the

Whether something is definite or indefinite is usually understood from:

• context
• word order
• the situation being described

So morska struja can mean a sea current or the sea current, depending on context.

A rough English-friendly guide:

• struja ≈ STROO-yah
• drži ≈ DR-zhee

A few helpful sound notes:

• j sounds like English y
• ž sounds like the s in measure
• i sounds like ee
• Croatian r is usually more tapped or rolled than in English

So drži has that zh sound, not a hard g or j sound.