As Gary's Student has pointed out, in the simplified example

• Maneuvering the tanker is a challenge.

the subject of the sentence is maneuvering the tanker;
in order to be a subject, this must be a noun. But it doesn't look like a noun.
It looks exactly like a verb phrase, with a verb maneuvering
and a direct object noun phrase the tanker.

And that's what it is. A verb phrase, acting as a noun phrase. But not just any old verb phrase.
Maneuvering the tanker is a Gerund verb phrase -- that's what the -ing suffix marks.
This verb phrase is all that's left of the subject gerund complement clause

• Indef's maneuvering the tanker is a challenge for Indef

after removing all the references to the indefinite subject
("Indef", the person who's doing the maneuvering and experiencing the challenge).
This has the effect of making the clause generic, true for any agent subject.

So, to answer your question about grammatical name and function:

1. maneuvering the tanker is a transitive verb phrase (verb + direct object)
2. maneuvering the tanker is a gerund verb phrase (with an -ing suffix)
3. maneuvering the tanker is a gerund clause (with a missing subject)
4. maneuvering the tanker is a complement clause (with a grammatical relation to the verb)
5. maneuvering the tanker is a gerund subject complement clause (subject of be a challenge)
6. maneuvering the tanker is a noun clause (with a missing subject)
7. maneuvering the tanker is a noun phrase (because it functions as the subject)

These are all true, simultaneously, depending on which aspect of the sentence you're talking about.

Note:

• that a clause is any constituent with a subject and a verb
  (though the subject may only be implied in context, as here),
• that a verb phrase is just a clause with a missing subject,
• that a clause can be the subject or the object of a verb  (and therefore a clause), and
• that a noun phrase is anything that behaves like a noun in a clause.

As Gary's Student has pointed out, in the simplified example

• Maneuvering the tanker is a challenge.

the subject of the sentence is maneuvering the tanker;
in order to be a subject, this must be a noun. But it doesn't look like a noun.
It looks exactly like a verb phrase, with a verb maneuvering
and a direct object noun phrase the tanker.

And that's what it is. A verb phrase, acting as a noun phrase. But not just any old verb phrase.
Maneuvering the tanker is a Gerund verb phrase -- that's what the -ing suffix marks.
This verb phrase is all that's left of the subject gerund complement clause

• Indef's maneuvering the tanker is a challenge for Indef

after removing all the references to the indefinite subject
("Indef", the person who's doing the maneuvering and experiencing the challenge).
This has the effect of making the clause generic, true for any agent subject.

So, to answer your question about grammatical name and function:

1. maneuvering the tanker is a transitive verb phrase (verb + direct object)
2. maneuvering the tanker is a gerund verb phrase (with an -ing suffix)
3. maneuvering the tanker is a gerund clause (with a missing subject)
4. maneuvering the tanker is a complement clause (with a grammatical relation to the verb)
5. maneuvering the tanker is a gerund subject complement clause (subject of be a challenge)
6. maneuvering the tanker is a noun clause (with a missing subject)
7. maneuvering the tanker is a noun phrase (because it functions as the subject)

These are all true, simultaneously, depending on which aspect of the sentence you're talking about.

Note:

• that a clause is any constituent with a subject and a verb
  (though the subject may only be implied in context, as here),
• that a verb phrase is just a clause with a missing subject,
• that a clause can be the subject or the object of a verb 
  (and therefore a clause can itself be the subject, or object, of another clause), and
• that a noun phrase is anything that behaves like a noun in a clause.