You know, I don’t have a clue… Didn’t write that chapter, Morg did. (I think have to go an confirm that… 
Personally, I think the naval rules need to be seperated from the army combat rules at the two are just not the same thing. Also the relative speeds of vessel needs to be looked at very harshly, there was not a huge difference in travelling times of most sailing vessels of the period at least in the long term. Also missile combat, ships did not sit there slinging catapult stones at each other, aside from the difficulty of actually hitting an enemy ship, that sort of ship combat didn’t really come about until ships were packed with cannon and used them to blast each other to bits. IMO most naval combat would involve boarding enemy vessels and cutting down their crew.
I’m working on a new system for naval combat as part of my Adurian Campaign setting. It is still in its early stages, but is very promising so far. I don’t have a lot of time to develop it right now, but it is something I’ll consider one day. Basically, it sets naval combat on a hextagonal grid and gives ships a speed rating in knots. Ships have a manueaverability class that effects how easy they can turn, and turning too quickly can cost you speed, while takes time to pick up again.
So as an example, lets say an Anuirean Galleon is sailing off the Serpent’s Isle bound for Suiriene. It is a foggy morning, but the Galleon’s captain has still ordered full sail, and the favourable conditions give the galleon are good speed of 8 knots. Then, out of the fog loam the shapes of two serpent galleys. They are running under oar only, and are at their maximum speed of 4 knots into the wind. The Gallleon is travelling NE, and the two galleys are coming in from the north and east in a classic pincer movement to strike at the galleon. Using the hex system, the galleys are 3 hexes away from the galleon, within striking distance with their rams if the galleon captain keeps his heading and speed as the galleon cannot move quickly enough to avoid them. So he order a turn hard to port (to change his heading to the NW). His ship has a MC of D, so this 90 degree turn costs him 6 movement pts (out of 8) and reduces his ship speed by 2 for the next turn (as a penalty for making such a sharp turn). He then moves 1 hex NW (movement cost of 2). The two galleys each respond differently. The one coming from the north turns SW (movement cost of 2 for oared vessel) and moves 1 hex (movement cost of 2). This puts it 1 hex away from the galleon, so the galley fires its heavy catapult, but the shot goes wide. The other galley coming from the E moves forward 2 hexs, putting it in the same hex as its companion (although on a different heading) and it also fires its catapult, scoring a hit on the galleon. The galleon responds with its two forward catapults, but misses with both.
The next turn, the galleon captain is faced with a choice. If he continues on his current heading, then he could be rammed by the 2nd galley, but if he turn to the port again he is moving into the wind and will lose most of his speed. So he decides to run for it. After his maneuver last turn he now has a speed of 6 knots, so he can move 3 hexes, potentially escaping the trap, but not before the 2nd galley can make a ramming attack. The galley picks up speed, but is unable to ram the galleon, however it does get off another catapult shot and is lucky enough score a critical hit and smash the main mast of the galleon, immediatly cutting its speed in half. The galleon can still move, but only has 2 movement pts now instead of 4, so can only move 1 more hex. The 1st galley turns to starboard and moves into the hex to the rear of the galleon, while the 2nd galley now turns to follow the galleon.
The next turn, the galleon continues to try and escape, while its crew hustle to cut the broken mast free. The galleon now has a movement rate of 4 (7 divided by 2, rounded up) and continues to the NW, trying to outrun the galleys. It moves 2 hexes. The second galley continues to follow the galleon, firing its cataputl as it does, scoring another hit. The galleon responds with its two rear catapults, scoring 1 hit on the galley. The 1st galley turns again, this time to the NW and moves 1 hex, but it is still a hex away from the galleon, so its captain decides to raise sail, while will increase its movement rate to 6 knots.
Subsequent turns will be a catupult battle between the 2nd galley and the galleon while the 1st galley picks up speed. Once it is up to speed (in 2 turn), its movement will increase to 3 hexes/turn, compared to 2 hexes/turn for the galleon, so it will eventually catch its prey and this battle will most likely be resolved in a boarding action or ramming attack, where the trading ship’s inexperienced crew will stand little change against the bloodthirsy sons of the serpent.
Obviously I have vast amounts of work to do on this, but initial test is promising. I need to do a lot more research into how sailing ships actually sail first, as well as into maximum speeds under certain wind contidions, that sort of thing. It is a system that will require some sort of counter or miniture to work, but just a square of paper with an arrow to indicate heading would do. I’m using the little paper ship thingys that came with one of the Spelljammer boxed sets myself.
