We are playing a SoB campaign and in the sea combats the Overlord is playing Sharks as a barrier on the first space of tne firecone of Revenge's canons, so that they are useless. Is this allowed by the rules? If so, It should be modified, it breaks sea combat.

Kaiser Karl said:

There is nothing in the rules that says sharks break line of sight. They are never listed as figures nor do they have specific rules which specify how they interact with line of sight. However, most groups (all AFAIK) treat them as figures.

If that's what you're doing you then the tactic is pretty easy to work around: Just move the ship or kill the shark. Which is the better option depends on how easy it'll be to kill the shark(s) and how close you are to the edge of the map. If you can one-shot a shark and it's replacement won't be able to reach the ship next turn, kill it. If it'll take multiple attacks or you're right next to the map edge, just move away from it.

As a consolation prize: sea combat is broken pretty much across the board, not just by sharks able to jump so far out of the water you can't see past them.

If you can't one-shot them with the cannon, then have a melee hero step up to the edge (with fatigue) and Battle to hit it twice. Once the line of fire is clear, have a second hero use the cannon.

Although the point about sharks not being declared figures is a good one. I can't think of any such passage in the rules myself, but unless someone else can find it, technically sharks wouldn't block LOS.

You can't think of it because it's not there. Both shark fins and tentacles fail to mention what kinds of props they are and how they interact with movement or LOS. I don't know of anyone that doesn't treat them as figures, as it's the most likely explanation of how the designers intended them to work (since they behave in all other ways as monsters and every other monster is a figure).