I honestly cannot help but feel this song is about sexual abuse of some kind. Possibly even rape. Each heave-ho from the captain is him forcing himself on Tamara. Hush now hush love, here's your gown, there's the bed, lanterns down is him effectively sending her to bed. In all my dreams I drown could be reference to the trauma because this happened when she was sent to bed.
It could be possible that this is one long sequence over time. Initially it may have been something non-penetrative. Oral etc, but he was no longer satisfied so in order to get his way, he ties her down to the bed with sheets. A storm is brewing in the south referencing the nether regions, and "It's time to go to sleep" meaning to sleep with one another.
His berth it rocked heave-ho heave-ho. Pretty obvious,
The next verse, "Hold me scold me I'll be yours to keep" I wonder if she was okay dealing with the abuse up until this point but didn't want it to go to penetration, and was begging them to stop, that she'd happily deal with the abuse, so long as he didn't sleep with her.
The sky it flashed, heave-ho heave-ho the pillow dulled the brink. The instant of penetration, possibly biting the pillow to dull the initial pain The curtains ran between my legs as we began to sink. I'm going with overly lewd answer here. The curtain would be the labia, and they ran between her legs from the blood.
I closed my eyes heave-ho heave ho as the ship was rent and felled. This is as the act continues, she's closed her eyes hoping it will be over soon, hence the next verse being I beg you please wake me up, because she's hoping this is all a nightmare.