They both look after the Twins:

The Twins that drive her to do her best
Where the Roaring Forties rage
From the Fastnet Height to the Liberty Light,
And the Customs landing-stage.

Where the crank-shafts pitch in the iron ditch,
Where the main-shaft swims and glides,
Where the boilers keep, in the sullen deep,
A master-hand on the Tides;

Where the reeking shuttle and booming bar
Keep time in the hum of the toiling hive,--
The men of the deep, while the travellers sleep,
Their steel-clad coursers drive.

And Davy Jones' locker is full
Of the labour that moves the world;
And brave they be who serve the sea
To keep our flags unfurled:

The Union Jack and the Stripes and Stars,
Gallant and free and true,
In a world-wide trade, and a fame well made,
And humanity's work to do.

Now list, ye landsmen, as ye roam,
To the voice of the men offshore,
Who've sailed in the old ship Never Return,