Przybijemy do brzegu, jak tylko dopłyniemy do przystani kajakowej.

Yes. They are future in meaning.

Both verbs are perfective:

• przybić → przybijemy
• dopłynąć → dopłyniemy

In Polish, perfective verbs do not have a true present tense. Their present-looking personal endings are used to talk about a completed action in the future.

So:

• przybijemy = we will pull in / we will come ashore
• dopłyniemy = we will reach by water

That is a very common difference between English and Polish.

In Polish, if both actions are in the future, both verbs are normally put in the future:

• Przybijemy do brzegu, jak tylko dopłyniemy...

English usually uses a present form after time words like when, as soon as, after:

• We’ll pull in as soon as we reach...

Polish does not usually copy that pattern. So the Polish sentence is completely normal.

Jak tylko is a fixed expression meaning as soon as.

It does not literally mean how only in this sentence. You should learn it as one unit.

Very similar alternatives are:

• gdy tylko
• kiedy tylko

So:

• jak tylko dopłyniemy = as soon as we reach / as soon as we arrive

Przybić do brzegu is a boating expression.

It means something like:

• to pull in to shore
• to come alongside the shore
• to make landfall
• to dock at the shore

Even though przybić can literally suggest hit/strike, that is not the idea here. In this context it is an idiomatic verb used for boats.

The imperfective partner is:

• przybijać do brzegu = to be pulling in / to pull in regularly

Because dopłynąć means to reach a destination by water.

Compare:

• płynąć = to be swimming / sailing / going by water
• dopłynąć = to get there by water, to reach the destination

The prefix do- often adds the idea of reaching an endpoint.

So:

• dopłyniemy do przystani = we will make it to the marina / kayak landing

Using płyniemy would focus more on the fact that you are moving on water, not that you have reached the place.

Because the preposition do takes the genitive case.

So the nouns change form:

• brzeg → brzegu
• przystań → przystani

And the adjective must match:

• kajakowa → kajakowej

So:

• do brzegu = to the shore
• do przystani kajakowej = to the kayak marina / kayak landing

Because it has to agree with przystani.

The base form is:

• przystań kajakowa

But after do, the noun goes into the genitive singular:

• do przystani

The adjective must also go into the genitive singular feminine:

• do przystani kajakowej

So the ending -ej shows the adjective matching a feminine noun in the genitive singular.

It is understood from the verb ending.

In Polish, subject pronouns are often omitted because the verb already tells you who the subject is.

The ending -emy means we:

• przybijemy = we will pull in
• dopłyniemy = we will reach

You could add my, but usually only for emphasis:

• My przybijemy do brzegu...

That might sound like we specifically, as opposed to someone else.

Yes.

You can also say:

• Jak tylko dopłyniemy do przystani kajakowej, przybijemy do brzegu.

That means the same thing.

Polish word order is more flexible than English word order, though different orders can slightly change emphasis. Starting with jak tylko... puts the time condition first.

Not quite.

• do brzegu = to/toward the shore
• na brzeg = onto the shore / onto dry land

In this sentence, przybić do brzegu is the normal expression for a boat pulling in to shore.

If you wanted to talk about people getting out onto land, you would more naturally use something like:

• wyjść na brzeg = to go out onto the shore

So do brzegu fits the boat’s movement, while na brzeg fits being physically on the land.

Because jak tylko dopłyniemy do przystani kajakowej is a subordinate clause.

In Polish, subordinate clauses are normally separated by commas. So when the main clause comes first, you write:

• Przybijemy do brzegu, jak tylko dopłyniemy...

If you reverse the order, the comma is still there:

• Jak tylko dopłyniemy do przystani kajakowej, przybijemy do brzegu.