O! how I faint when I of you do write,
Knowing a better spirit doth use your name,
And in the praise thereof spends all his might,
To make me tongue-tied speaking of your fame.
But since your worth, wide as the ocean is,
The humble as the proudest sail doth bear,
My saucy bark, inferior far to his,
On your broad main doth wilfully appear.
Your shallowest help will hold me up afloat,
Whilst he upon your soundless deep doth ride;
Or, being wracked, I am a worthless boat,
“Wilfully” here means that the speaker’s boat is persistent and strong-willed in addition to its more usual meaning of “free-willed”.  The rival is  determined to get himself noticed. 
 The noun “main” means ocean or sea.
Sonnet 80