Sonnet LXXX

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,
He of tall building, and of goodly pride:
   Then if he thrive and I be cast away,
   The worst was this, my love was my decay.

 The questioning of the rival poet's position continues. Here the poet portrays himself as a foolish boat sailing in the shallows, whereas the rival is a stately galleon on the wide open sea, foreshadowing the exclamatory question of 86, Was it the proud full sail of his great verse? However the content of the poem militates against itself, for the marine imagery gives it a sort of buoyancy which overturns its declared humility. In addition there are subtle innuendoes which undermine the worthiness of the rival, not least of which are the half hinted sexual meanings which give a touch of ribald mockery to the descriptions of the new poet. 'Perhaps he is a proud galleon sailing on the sea of your generosity', it seems to say, 'but he has a big mouth, a big arse, and for all I know, a big dick'.

The 1609 Quarto Version

OHow I faint when I of you do write,
Knowing a better ſpirit doth vſe your name,
And in the praiſe thereof ſpends all his might,
To make me toung-tide ſpeaking of your fame.
But ſince your worth(wide as the Ocean is)
The humble as the proudeſt ſaile doth beare,
My ſawſie barke (inferior farre to his)
On your broad maine doth wilfully appeare.
Your ſhalloweſt helpe will hold me vp a floate,
Whilſt he vpon your ſoundleſſe deepe doth ride,
Or (being wrackt ) I am a worthleſſe bote,
He of tall building,and of goodly pride.
   Then If he thriue and I be caſt away,
   The worſt was this,my loue was my decay.

Commentary

1. O! how I faint when I of you do write,
I am overcome with faintness and diffidence when I write of you (because a better spirit, person, poet, praises you, and makes my efforts look weak by comparison).
2. Knowing a better spirit doth use your name,
a better spirit = a better poet. But in view of what is stated in Sonnet 86, (which also uses the ship imagery), the spirit also refers to the supernatural influence which 'nightly gulls him with intelligence', 'him' being the rival poet. The rival poet is a spirit who is possibly using demoniacal powers.
use your name = uses you as inspiration, has you as patron. See Sonnet 78: As every alien pen hath got my use, and the note thereon.
3. And in the praise thereof spends all his might,
in the praise thereof = in praising your name.
spends all his might = expends all his energies.
4. To make me tongue-tied speaking of your fame.
It is not clear if the speaker or the rival poet is speaking of the youth's fame. Both meanings are acceptable, for the syntax allows either 'He makes me tongue tied when I attempt to publish your fame', or, 'He makes me tongue tied when he starts publicising your fame and qualities'.
5. But since your worth, wide as the ocean is,
The next two quatrains use a metaphor from the sea, comparing the poets' flights of fancy and creation to ships sailing on the ocean - either small inferior barks, which the speaker modestly and humbly claims as an adequate description of himself, or else massive galleons, lofty and proud (and perhaps riding for a fall as the Spanish ships of the armada). But the ocean is the symbol and metaphor of the worthiness of the beloved and of his capacity to inspire his poets and admirers. It is on that ocean that these metaphorical ships of poetry set sail.
6. The humble as the proudest sail doth bear,
sail = ship, vessel. See OED n.(1).4.a.
7. My saucy bark, inferior far to his,
My saucy bark = my impudent, foolhardy boat. Continuing the sailing metaphor which depicts, or pretends to depict, the poetry of both contenders for the post of poet in residence. The poet claims that the ship he sails is nothing more than a ketch in comparison with that of his rival.
8. On your broad main doth wilfully appear.
your broad main = the vast open sea that you, figuratively, are, for a poet looking for subject matter.
main = open sea.
wilfully = stubbornly, provocatively.
9. Your shallowest help will hold me up afloat,
I only need the shallowest water to remain upright, which you easily can supply.
10. Whilst he upon your soundless deep doth ride;
He, being a ship of much deeper draught, sails upon your open deep water.
soundless = unable to be sounded. So deep that the lead plummets which the mariners use for taking soundings do not reach the bottom, hence such waters are effectively bottomless.
11. Or, being wracked, I am a worthless boat,
wracked = wrecked. An old spelling, but still occasionally used today. Being homophonous with racked it does suggest the torture the writer undergoes in his quest for the youth's loyalty.
12. He of tall building, and of goodly pride:
His is a stately boat, built very tall, and consequently worth saving from shipwreck. There was a huge increase in shipbuilding in the Elizabethan period, so these references would have had immediate relevance for many readers.
13. Then if he thrive and I be cast away,

Then if he should thrive and I should be cast away.
thrive = prosper, come off safely.

be cast away = be shipwrecked, thrown onto the strand or shore. As in Merchant of Venice:
.......................Antonio
Hath an argosy cast away coming from Tripolis.  MV.III.1.105.

14. The worst was this, my love was my decay.
The worst was this = the worst aspect of the calamity would be this (that I now describe).
my love was my decay = my love would have been the cause of my fall from grace, my ruin.
decay = decline, loss of power, ruin. Used 11 times in the sonnets (including decayed etc), of which typical is Sonn 13. Who lets so fair a house fall to decay?