>They certainly are!
Some are, some aren't. GURPS is meant to be "universal" after all. Rules from the various Vehicles books can provide more detail. Did you check out "Swashbucklers"? ISTR it had somewhat more detailed rules than "one die throw".
>>Basically, I could define ships by historical class, define wind direction relative to both combatants and assess their ability to scud and tack, then work out the modifiers referred to above (there's tons, and I don't care about the exact number and poundage of cannon on board) OR I could not.
OR you could find a sweet spot between those two extremes. Life isn't binary. You have more than two choices. After all, you want your players to be able to upgrade their ships to gain some advantage in combat. That means you'll have to take into account in some manner stuff like class, tonnage, agility, weapons, and the like.
>>I did want ramming because it's cool. Also, because it's featured in the media I've seen about sailing ships
I don't now what media that was but it was shit. Forget you ever saw it.
>>I also want them to be able to pick up abstract amounts of the key resources to upgrade their ship in a reasonable timeframe, instead of commissioning a shipwright to create a warship for their kids.
Again, because you know nothing about ship construction or upgrades, you're assuming both require years of work. The truth of the matter is that wooden warships had remarkably long lives and were quite often modified/upgraded during them. The type and number of guns changed, sail plans changed, sail types changed, mast & spar arrangements changed, hull sheathing was added, rearranged, or removed, the list is endless. (continued)