A firm rotating sky roof must have a central axle, horizontal if viewed from the equator. The rotating motion should cause a whirlpool if the axle was located in the sea. The Polynesians knew that the axle would turn upwards when the viewer moved away from the equator, becoming vertical somewhere far in the north - below the North Star.

"... Snorri Sterluson explains why 'Frodi's grist' is a kenning for gold. Frodi ruled during a peaceful and productive period, contemporaneous with Augustus's Pax Romana and the birth of Christ; hence the kenning. There were neither thieves nor robbers during this period, 'so that a gold ring lay long on Jalang's heath'. Snorri continues his account with the legend of the mill beyond what is told in the song: The girls' grinding produced an army hostile to Frodi. On the very day of the girls' predictions, the sea-king, Musing (Son of the Mouse), landed o the Danish shore, killed Frodi, and took away Grotti and the women on his ship. The girls were bidden to grind out salt on the mill. At midnight they asked for further instructions. 'Keep grinding', he told them. Then they ground with such vigor that the ship sank. Water poured into the eye of the mill, creating the maelstroem of the sea. Therefore the sea was salt. Incidentally, the mill was given a kenning, Serpent's Couch." (Worthen)

Olaus Magnus located a whirlpool outside Helgoland, 'Helalandia, terra nobilium', (ref. Hamlet's Mill):

Curiously it is located in the midst of three islets, just as we would expect a similar whirpool to be found outside the southwest corner of Easter Island. There should be two holes, though, also one at winter solstice.

In the dialect of Easter Island a whirlpool is ure tiatia moana. Moana is the deep sea (in contrast to tai, the shallow sea close to land) and the intensified tia is worthy of a closer look:

Tia

(Tiha G) .To sew. T Mgv.: tia, to prick, to pierce, to stick in. Churchill.

Ta.: tia, the lower belly. Mq.: tia-kopu, pubes. Ma.: tia, the lower abdomen. Tiahonu, to piece together. Mq.: tuhonu, to mend, to patch. Ma.: tuhonu, to join. Churchill.

Mq.: tiaha, drinking cup. Ha.: kiaha, a cup, a mug. Tikao, to dig out, to disembowel. Ma.: tikaro, to dig out of a hole. Churchill.

Fornander:

"KIA. s. Haw., pillar or inner post of a house supporting the roof, any kind of pillar or post, a mast of a vessel; kia-aina, a supporter of the land, a governor of a province.

Marqu., tia, id.

Sam., ti'a, the stick used in tanga-tia, a man's head (abusively); tia-pula, taro-tops cut off for planting.

Sunda, tihang. Mal., tiang, a pillar.

Greek, κιων, a pillar, support of the roof, the identical sense of the Polynesian usage of the word. Liddell and Scott give no etymology or connections of κιων."

The pillar upholding the sky roof would have been called kia by the Hawaiians, I think. A rotating pillar is like a screw and it will fit into the hole of the mill.