A few comments about naval warfare as I will be running it:
- I advise investing in a few skills (or seeking items that provide bonuses), if you're planning on primarily making someone who fights on ships:
- Balance -- it's actually quite difficult to run across a sloped or angled floor in armor, which is pretty much always on a ship. If you charge in wearing naught but a look of determination, a +9 is enough to never faceplant while charging someone on a boat. If you wear armor, more is going to be useful. Or planning on getting around only by walking is going to be useful.
- Climb -- even if you're only going to be climbing on the chance that you fall into the water, a damp rope ladder is still a climb check (DC 5). Fellows in light or no armor can expect to get up that ladder without falling back in (you need to fail by 5 or more to fall). Dudes in more armor need to invest in skills to have that security. Also an interesting bit of trivia, if someone injures you while you're climbing, you have to roll climb to hold on. So if you're up on the rigging, "will I also fall onto the deck if I'm hit by an arrow?" is a real question.
- Swim -- as with climb, you need to fail by a margin to start drowning, but water outside of a harbor is pretty much always "rough water," so you need* to be able to roll a 10 reliably to not spend time under water if you end up in the drink. 15 if the weather is bad. And you can't breathe if you're under water**.
- Profession -- two professions worthy of note. Sailor is needed to make sail-operated ships go where you want them to. Seige Engineer is needed to operate pretty much any device capable of sinking someone else's ship.*** These are trained-only checks. So, if everyone on your ship who has ranks in sailing dies, you're in a pretty bad way. If everyone with ranks in siege engineer dies, you're confined to devices light enough to be reasonably comparable to regular weapons.
- Consider a diversity of weapons-- particularly
- A light weapon that can be used in confined spaces. (one might consider a shortsword, a handaxe, a light mace, or a dagger; I am likely to do a little work to handle that scimitars aren't "light weapons" but are our D&D standin for the cutlass, which is a very good weapon for confined spaces on boats)
- A ranged weapon that can be used one-handed. (for the most part, this means throwing weapons-- so that you can keep fighting while hanging from something or anchoring yourself to a point).
- A piercing weapon that can be used without penalty in or under water (spears, shortswords, rapiers, daggers-- amusingly, the rules as they read say a spiked chain takes no penalty. I lol at this, and am glad we don't have those)
- Be careful with armor and with shields. Everything that matters on a ship is affected by your Armor Check Penalty.
- Be careful with fire. Things that are good at keeping water out of a ship are also good at spreading fire on it.
* Unless you're a water genasi. They have a swim speed, and thus only have to roll checks to do backflips through hoops and beg for fish from their trainers.
** This may or may not be problematic for your character. Some spells temporarily cause you to not need to breathe (living undeath, stone body, iron body) or allow you to breathe water (water breathing), and some races don't need to breathe (air genasi) or can breathe water (water genasi).
*** Probably of note that only ships explicitly built for war actually have weapons heavy enough to straight-up sink a ship on them, and I'd thus put this on the "take this if your character has a strong and established background in naval combat" list. Most ships have ballistae, which require no profession check to use, and medium-sized creatures can operate them at -4 to hit. Though they can't really
sink a ship, they can damage one, or its sails, or be fired right in a kraken's stupid face.
I might update this list if I find more stuff about how boats work in D&D. Seems to all be reasonably well handled by the SRD, though-- probably because of D&D's history as a wargame.