[Woesinger]

IF you assume the South Province was slumbering at the time, then a squabble between Nyrond and Onnwal is possible. The dates you mention straddle the end of the reign of Ivid III and the beginning of the reign of Ivid IV. We know that the middle Ivids were little concerned with the outside world, except occasionally almost ritually attacking Nyrond and Almor and we hear little or nothing about the Hertzogs of the South in this period.

If you contrast this to the ascention of Ivid V in the 550s, who appoints the Chelors with the express orders to reclaim the south, it is possible that the South Province was on the nod in the early decades of the 500s. In that case, if an imminent threat was absent, then its possible that Onnwal and Nyrond would have squabbled over trade.

That said, I think that raising tolls is likely to hurt Onnwal more than it'll hurt Nyrond. Nyrondese ships heading towards Hardby would simply bypass Onnwalon ports entirely. Trade through the Straits is little more tricky. The Onnwalons would be foolish to try to impose a toll on passage of the straits, since ships would simply ignore it, refuse to heave to or fight if boarded, which will piss off Keoland AND Nyrond AND Ulek AND Greyhawk and the Urnsts. Where they could have an effect is on excises to berth at Scant - which would be an important stop over for ships plying the routes between the Azure and Gearnat (esp. the Gradsul/Gryrax to Gearnat ports route). Even so - again I'd think it'd hurt the Onnwal exchequer - since all ships have to do is lay in more food and water and sail right by.

[Samwise]

[Woesinger]

Which is not to say that a foolish szek mightn't have tried it out as a policy, but he wouldn't have needed the Nyrondese to sail in and destroy his fleet to realise it was a bad idea - his own merchants and nobles would probably have done Nyrond's work for it and given the Platinum Diadem to someone more "reality-based".

[mortellan]

[Samwise]

And I hate to ruin a casual appeal to magic, but a wizard's spell capacity is more limited than a warships stores of gunpowder and shot.
Yes, magic will cut down on getting lost and storm damage, but its overall effect on combat is not going to be that decisive unless completely unmatched.

[Crag]

Have to disagree but magic in a naval context could and should be decisive;

Fire-based magic
Water-based magic
Weather control
Transmutation
Communication
Invisibility
Underwater Operations
Illusion
Summoned Monsters
Undead

Should all prove devastating in Naval combat, without considering the uses of the underwater races.

Keep your cannons samwise; give me magic.

[Samwise]

Given the duration of most spells, and the number a low level caster can be expected to have access to, they might be decisive in a particular instance, but they won't be decisive on a regular basis.
One fireball won't destroy a ship. And it would take at least two missiles if not all three from a 5th level caster to kill even an average 1st level warrior with magic missile. Other spells that would be useful won't have the range.
So barring 9th+ level casters on every single ship, magic is going to enhance combat strength, not define it. And at the point that you've got dozens of such casters running around on your ships, you've not only eliminated any concept of mundane combat, but left yourself open to explaining why long distance trade isn't just dominated by teleportation. Sure those 9th level wizards mess up 6% of the time (3% of the time if they have private pads to teleport too in each market area), but 13th level wizards are always safe, and it just takes 1 overachieving 17th level wizard to set up a permanent teleportation circle network. Control of sea trade routes becomes irrelevant at that point.

[mortellan]

Mages on every boat, fireballs, magic missiles, etc. I wasn't going to go that far, demographics of mages is what I planned on avoiding. My main intention is that magic enhanced vessels and or items in possession of senior crewmembers is effective enough to coordinate the standard naval group. The original intent of Sam's quote that I came in on, was 'closing a strait' not naval combat per se. Detection, Communication and Intercepting is key in this case and from the items I listed many can help avoid a blockade too.

[Samwise]

[Prochytes]

[Samwise]