Is there a grammatical difference between "heart of oak" and "hearts of oak" in the British patriotic song "Heart of Oak?" [closed]

A British patriotic song titled "Heart of Oak" has two versions that are widely sung.

The chorus in the first version goes like this:

Heart of oak are our ships,
Heart of oak are our men,
We always are ready, steady boys, steady,
To charge and to conquer again and again.

The chorus in the second version reads as follows:

Hearts of oak are our ships,
Hearts of oak are our men,
We always are ready, steady boys, steady,
To charge and to conquer again and again.

Is there any grammatical difference between using "heart of oak" versus "hearts of oak" in the song? Are both versions grammatically correct?

In addition, is it grammatically correct to use this construction in other contexts? Can I use "heart of aluminum is my car" for "my car is made of aluminum?"

I recently read the lyrics of this song online and I have never seen this grammatical construction used before, so I am wondering about the grammatical aspects of it.

Solution 1:

The song involves countable and uncountable noun phrases and a pun:

"Heart of oak" is an uncountable noun phrase in which "heart" = "heartwood" and describes the literal construction of the ship.

OED

Heartwood: 2. The dense, inner part of the wood of a tree trunk, yielding the hardest timber, often darker in colour and more resistant to decay than the surrounding wood due to higher gum or resin content.

Oak is a material noun and also uncountable ("The chair is oak" cf "The chains are steel.")

In "Hearts of Oak" "Hearts" is countable and refers to a respected person:

OED

22. Originally: a person considered in respect of his or her bravery, courage, or other admirable qualities (usually with preceding modifying adjective). In later (esp. Nautical) use also in plural [...], esp. as my hearts (now archaic; cf. hearty n. 2).

1626 J. Smith Accidence Young Sea-men 25 Courage my hearts for a fresh charge.

1834 T. Hood Storm iv, in Comic Ann. 103 Come, my hearts, be stout and bold.

1988 Cincinnati Mag. Mar. 81/1 Those stout hearts who are paid to predict the Bulls and Bears of a market gone berserk.

In Hearts of oak - the Oak is a reference to England/Englishmen. The oak tree (through its association with strength and nobility - and also the navy) is the generally accepted (jingoistic) metaphor for the quality of an Englishman.

Thus Heart of oak are our ships, = our ships are of the strongest wood

Heart of oak are our men, = our men are as strong as the strongest wood.

Hearts of oak are our ships, = our ships are greatly respected

Hearts of oak are our men, = our men are our dear and courageous friends