How many long beats do you hear in "Sea Fever"?
"Sea Fever" by John Masefield is certainly a lyrical poem whose lines vary in their meter. Moreover, the shifts in beats in the lines appear to imitate the irregular flow of waves. As an example, the first line, written here to demonstrate the stressed syllables, varies in its meter:
i MUST/ down TO /the SEAS/ a GAIN,/ to the LONE ly SEA /and the SKY
This line is 4 Iambic rhythms through the word again (in boldface), and ends with 2 anapestic rhythms. So the longer "beats" are at the end of the line.
Of course, there are irregularities in the line, unlike many poems which have a set pattern. But, the first two lines are quicker in beat and rhyme with each other, while the second two of the quatrains are longer in beat. Therefore, there are 6 lines that have "longer beats" as asked.
Here is an example of the meter in the last lines of two quatrains:
And QUI/et SLEEP/ and A/ sweet DREAM/ when the LONG/ trick’s
2 Iambs anapest