Cum ventus crescat, gubernator clamat: “Remi parentur; velum firmum maneat.”

Because here cum is a conjunction, not a preposition.

• As a preposition with an ablative noun, cum means with:
  cum amico = with a friend
• As a conjunction introducing a clause, cum can mean when, since, or although.

In Cum ventus crescat, cum is followed by a full clause with a verb (crescat), so it means something like when/as/since, not with.

After cum, Latin often uses the subjunctive when the cum-clause gives the circumstances or background for the main action.

So Cum ventus crescat, gubernator clamat is not just a plain time-statement like at that exact moment the wind rises. It is more like:

• when/as the wind is rising
• since the wind is rising
• with the wind increasing

That kind of background idea commonly takes the subjunctive in Latin.

Crescat is:

• 3rd person singular
• present
• active
• subjunctive
• from crescere = to grow, increase

It is 3rd singular because its subject is ventus, which is singular.

Because the sentence is doing two different things.

• gubernator clamat is a straightforward statement of fact:
  the helmsman/captain shouts
  So Latin uses the indicative.
• parentur and maneat are not statements of fact. They are orders or commands inside the speech.
  So Latin uses the subjunctive there.

In other words:

• clamat = narration
• parentur; maneat = command

Latin often uses the jussive subjunctive for this.

English can say:

• Let him come
• Let them go
• Let the sail remain firm

Latin commonly expresses that idea with the present subjunctive, especially in the 3rd person.

So:

• parentur = let them be prepared
• maneat = let it remain

This is very common, because the ordinary imperative is mainly for you-commands, especially second person.

Here it is from paro, parare = prepare.

Parentur is the present passive subjunctive, 3rd person plural of paro.

So it means:

• let them be prepared

Because remi is plural, the verb is plural too.

A learner might confuse it with pareo because the forms look similar, but in this sentence the meaning and syntax point clearly to paro.

• remi = nominative plural
• velum = nominative singular
• firmum = nominative singular neuter

Why?

• remi is the subject of parentur
  Even though the verb is passive, the subject is still nominative.
• velum is the subject of maneat
• firmum agrees with velum, so it is also nominative singular neuter

So velum firmum means the sail [being] firm, with firmum describing the subject.

Because Latin is describing what the sail is like, not how it remains.

• firmum is an adjective: firm
• firmiter is an adverb: firmly

With maneat, the idea is let the sail remain firm, so Latin uses the adjective agreeing with velum:

• velum firmum maneat

If you used firmiter, the sense would be more like let the sail remain firmly, which is not the natural idea here.

Each verb agrees with its subject in person and number:

• ventus crescat
  ventus is singular, so crescat is 3rd singular
• gubernator clamat
  gubernator is singular, so clamat is 3rd singular
• remi parentur
  remi is plural, so parentur is 3rd plural
• velum maneat
  velum is singular, so maneat is 3rd singular

This is one of the most important habits in reading Latin: always match each finite verb with its subject.

Latin word order is fairly flexible, because the endings show the grammar.

This sentence could be rearranged in other ways without changing the basic meaning, as long as the forms stay the same. But the given order is natural and effective:

• Cum ventus crescat sets the scene first
• gubernator clamat gives the main action
• Remi parentur; velum firmum maneat presents the shouted orders clearly

So the order helps with emphasis and flow, even though the endings carry the grammatical relationships.

Grammatically, remi is the subject of the passive verb: let the oars be prepared.

But in real meaning, the command is directed to the people who must do the action — the crew. Latin often expresses this kind of order passively or impersonally:

• not you prepare the oars
• but let the oars be prepared

This can sound very natural in commands, especially in formal, military, or nautical contexts.