Help needed about Stevenson's "The Merry Men"

[serhanbener]

‘Na, na,’ he said, ‘no as bad as that. I had been drinking, though. And to tell ye the God’s truth, it’s a thing I cannae mend. There’s nae soberer man than me in my ordnar; but when I hear the wind blaw in my lug, it’s my belief that I gang gyte.’
‘You are a religious man,’ I replied, ‘and this is sin’.
‘Ou,’ he returned, ‘if it wasnae sin, I dinnae ken that I would care for’t. Ye see, man, it’s defiance. There’s a sair spang o’ the auld sin o’ the warld in you sea; it’s an unchristian business at the best o’t; an’ whiles when it gets up, an’ the wind skreights — the wind an’ her are a kind of sib, I’m thinkin’ — an’ thae Merry Men, the daft callants, blawin’ and lauchin’, and puir souls in the deid thraws warstlin’ the leelang nicht wi’ their bit ships — weel, it comes ower me like a glamour. I’m a deil, I ken’t. But I think naething o’ the puir sailor lads; I’m wi’ the sea, I’m just like ane o’ her ain Merry Men.’

1-What is the meaning of "There’s a sair spang o’ the auld sin o’ the warld in you sea; it’s an unchristian business at the best o’t; an’ whiles when it gets up, an’ the wind skreights "?

2-What is the meaning of "I’m thinkin’ — an’ thae Merry Men, the daft callants, blawin’ and lauchin’, and puir souls in the deid thraws warstlin’ the leelang nicht wi’ their bit ships — weel, it comes ower me like a glamour."?

3-What is the old sin? What is the relation between "the old isn" and "the sea"?

[Whifflingpin]

3) This is open to interpretation. Given the previous sentence ("Ye see, man, it’s defiance") and the following sentence ("I’m a deil, I ken’t") I would say that "the old sin of the world" is Satan's pride that led to his rebellion against God. The sea is also untameable and does not submit to rules.

1 & 2)
There’s a good measure of the old sin o’ the world in yon sea;
It’s an unchristian business at the best of it;
and at times when it gets rough, an’ the wind rages — (the wind and the sea are like brother and sister, it seems to me) — and the Merry Men, the daft rogues, blowing and laughing, and poor souls in their death struggles wrestling though the livelong night in their little ships — well, it comes over me like a spell.
I'm a devil, I know.
But I don't care about the poor sailor lads;
I'm on the sea's side,
I'm just like one of her own Merry Men.

[serhanbener]

Many Thanks for your explanation.