Canister
Grapeshot
As you say, ship’s guns, especially those on Ships of the Line, were heavier than field pieces. The Victory for instance had 30x 32pdr, 30x 24pdr and 45x 12 pdr.
The guns could be charged with a heavier load of powder and thus their throw weight and range would be greater. The balls in grapeshot were larger, less tightly packed than in canister and would burst from the muzzle so their spread would be wider. Being larger and heavier they would damage the ships as well as their crews – the effect of a broadside of grape on a smaller vessel must have been devastating. Canister wouldn’t have the same effect, so therein lies the answer. Probably.
Everything else is semantics.
Obvious contrarian and passive aggressive old prat, who is taken far too seriously by some and not seriously enough by others.