Ako imamo mirno more, podignut ćemo jedro i isploviti.

Because Croatian usually uses present tense after ako for a real future condition.

So:

• Ako imamo mirno more... = If we have calm seas / if the sea is calm...
• podignut ćemo jedro... = we will raise the sail...

This is normal Croatian structure. English often uses present after if too, so the logic is similar: If the weather is good, we’ll go.

It is understandable, but many speakers would probably find other versions more natural, such as:

• Ako je more mirno, podignut ćemo jedro i isploviti.
• Ako bude mirno more, podignut ćemo jedro i isploviti.

The given version sounds a bit like English if we have calm seas, which is possible, but ako je more mirno may sound more idiomatic in everyday Croatian.

Because more is a neuter singular noun, and the adjective has to agree with it.

So:

• masculine: miran
• feminine: mirna
• neuter: mirno

Since more is neuter, you say mirno more.

This is the future tense form.

The infinitive is podignuti. When the future auxiliary ću, ćeš, će, ćemo, ćete, će comes after the infinitive, the final -i of the infinitive is dropped:

• podignuti + ćemo → podignut ćemo

So podignut ćemo means we will raise.

This is a very common pattern in Croatian future tense.

Yes. Both are possible.

• Podignut ćemo jedro
• Ćemo podignuti jedro

The first version is more standard and common in neutral written Croatian. In both cases, the meaning is the same.

A useful rule:

• if the auxiliary comes after the infinitive, the infinitive usually loses final -i
• if the auxiliary comes before the infinitive, the infinitive stays whole

So:

• podignut ćemo
• ćemo podignuti

Not necessarily. In Croatian, one auxiliary can be shared by two coordinated verbs.

So:

• podignut ćemo jedro i isploviti

means:

• we will raise the sail and set sail

The future auxiliary ćemo applies to both verbs. Croatian often avoids repeating it when two future actions are linked with i.

No. Here it is not a participle and not an adjective. It is the shortened infinitive form used before the future auxiliary.

That can confuse learners because podignut can also exist in other contexts as a participle-like form, but in this sentence podignut ćemo is simply the future tense of podignuti.

It is in the accusative singular because it is the direct object of podignuti.

We are raising what?
→ jedro

For many neuter nouns in Croatian, the nominative and accusative singular look the same, so:

• nominative: jedro
• accusative: jedro

Because Croatian has no articles like English a / an / the.

So:

• more can mean sea or the sea
• jedro can mean a sail or the sail

The exact meaning depends on context.

Because they describe single completed actions:

• podignuti = to raise, as one completed act
• isploviti = to set sail / sail out, as one completed act

That fits the sentence well: first the sail is raised, then the boat sets off.

In Croatian, perfective verbs are very common in future sentences when you mean a complete future event.