Rigg

... vpon springe tydes, or after great riggs of the sea, at which tyme the sea will cast the same in more aboundance together into great heapes.

Source: wiktionary

to take no better company with you than Michaelmas Riggs? If you do not make haste, I profess I cannot tell what to say to your journey. You may find more danger in a ship to Ireland, than over the Thames in a skuller.

Source: wiktionary

[…] that uncertain season, before the riggs of Old Michaelmas were yet well composed, and when the inclement storms of winter were approaching, began to flicker over the seas, and was as busy in building it's halcyon nest as if the angry ocean had been soothed by the[…]

Source: wiktionary

... returne before the Michaelmas Rigg, as they call it, those seas beinge very daingerous about Michaelmas, neuer faile of stormes.

Source: wiktionary