“Sea Fever" by John Masefield is considered to glamorize the language with rythmic constructions, and compund resources that project a beautiful imagery.
Answer:
This is a fixed structure because it keeps the last two lines of each stanza in a rhyme, and not only that but also in the first two lines.
This structure is kept throughout the text in a masterful way and repeated several times this is considered "a fixed" way to rhyme even though it uses different combinations of letters in each stanza.
As an example:
Stanza 1 AABB
Stanza 2 CCDD
Stanza 3 EEFF