I read that this sentence is incorrect:
Because of the accident, he arrived at the dock an hour late. As such, he missed the boat and forfeited his deposit.
Why is it wrong? What is the correct usage of "as such"?
As such means "by virtue of being such" or "in such a capacity":
He is a Justice of the Peace. As such, he is empowered to perform marriages.
Such refers to the preceding noun phrase Justice of the Peace and as such applies to the following noun phrase he.
As a Justice of the Peace, he is empowered to perform marriages.
In his capacity of Justice of the Peace he is empowered to perform marriages.
In your example, as such is taken to modify he; but in what capacity, or by virtue of being what did he miss the boat? There is no preceding noun phrase to which such may refer.
And even if you rewrite the clause as a noun phrase: The accident caused his arrival an hour late, the noun phrase arrival an hour late is not a role or an office by virtue of which he missed the boat, it is the cause of his missing the boat.
What is meant is in consequence or as a result—implicitly, in consequence of that or as a result of that, where that has its referent the entire preceding clause— phrases which modify the entire following clause and not just he.