Fortøyningstauet er langt.

Because Norwegian very often makes compound nouns by joining words together.

• fortøyning = mooring
• tau = rope

So fortøyningstau means mooring rope.

Then the definite ending is added:

• fortøyningstau = a mooring rope
• fortøyningstauet = the mooring rope

This is very normal in Norwegian. Where English often uses two words, Norwegian often prefers one compound word.

The ending -et is the definite article attached to the noun. Instead of putting a separate word like the in front, Norwegian usually adds the definiteness to the end of the noun.

So:

• et tau = a rope
• tauet = the rope

And with the compound:

• et fortøyningstau = a mooring rope
• fortøyningstauet = the mooring rope

This is one of the biggest differences from English.

Because the adjective has to agree with the noun’s gender and form.

The noun tau is neuter:

• et tau

When an adjective comes after er and describes a singular neuter noun, it usually takes -t:

• tauet er langt = the rope is long

Compare:

• en bil er lang = a car is long
• et tau er langt = a rope is long
• biler er lange = cars are long

So langt is used because fortøyningstauet is singular neuter.

The head word of the compound is tau, and tau is a neuter noun.

That means:

• et tau
• tauet

In Norwegian compounds, the last part usually determines the gender of the whole word. Since tau is neuter, fortøyningstau is also neuter:

• et fortøyningstau
• fortøyningstauet

That is also why the adjective is langt.

Er is the present tense of å være = to be.

This sentence is a simple description:

• Fortøyningstauet er langt.
• The mooring rope is long.

So the structure is:

• subject: fortøyningstauet
• verb: er
• adjective: langt

This is the standard way to say that something has a quality.

It is the normal Norwegian sentence pattern for a simple statement:

• Subject + verb + complement

So:

• Fortøyningstauet = subject
• er = verb
• langt = adjective/complement

This is very similar to English:

• The mooring rope is long.

Nothing unusual is happening with the word order in this sentence.

Yes, absolutely. Tauet er langt means The rope is long.

The longer noun fortøyningstauet is just more specific: it tells you that it is a mooring rope, not just any rope.

So:

• Tauet er langt. = The rope is long.
• Fortøyningstauet er langt. = The mooring rope is long.

Fortøyningstauet by itself already means the mooring rope, because the definite ending is built into the noun.

So in a simple sentence, you normally just say:

• Fortøyningstauet er langt.

You might use det fortøyningstauet in a different context, for example when pointing something out more specifically:

• Det fortøyningstauet er langt. = That mooring rope / that particular mooring rope is long.

So det is not needed just to mean the here.

The indefinite version would be:

• Et fortøyningstau er langt.

That means A mooring rope is long or A mooring rope is a long rope, depending on context.

Compare:

• et fortøyningstau = a mooring rope
• fortøyningstauet = the mooring rope

The adjective still stays langt because the noun is still singular neuter.

A rough guide is:

for-TØY-ning-stau-et

A few helpful points:

• ø is a vowel sound that English does not have exactly
• øy sounds somewhat like the vowel in French œil or German eu, not like English oy exactly, though that is a rough approximation
• au is usually pronounced roughly like the vowel in English how
• the definite ending -et is usually unstressed

You do not need perfect pronunciation immediately, but it helps to notice that Norwegian compounds are usually spoken as one unit.

Because lange is usually used for plural nouns or certain definite noun phrase patterns.

Here are the basic forms of lang:

• lang for singular common gender
• langt for singular neuter
• lange for plural

Examples:

• en vei er lang = a road is long
• et tau er langt = a rope is long
• tauene er lange = the ropes are long

So fortøyningstauet er langt is correct because the noun is singular neuter, not plural.