Ship based combats

What are the best resources for ship to ship and underwater combats?

This sounds weird, but Mage Hand Press's Dark Matter sci-fi book has EXCELLENT ship combat rules that could be adapted to ships and subs easily.

I believe Ghosts of Saltmarsh has ship combat rules.

As for underwater, I don't know of anything besides the stuff in the DMG.

Here's a good place to start 

Appendix A: Of Ships and the Sea

I’ve heard some criticism regarding the GoS RAW was just wondering if anyone had a go to resource they use for players invested in sailing the open seas, seeking sunken treasure and fending off hostile crews or islanders or monsters…

I use the GoS, was just curious.