Effective has nothing to do with finding anything. Remeber the rules were put in place to prevent unreasonable dissruption to trade. Countries had found that they could claim they were blockading whoever and then radomly raid ships. This was bad for trade. Instead the requirement was introduced that a blockade be effective. That basicaly meant that they deployed enough force to have a decent chance of stopping the vast majority of ships. There was no requirement that they actualy find anything relivant. For example at least towards the end of WW1 Britian's blockade of Germany was legal.
Israel and Hamas, the ruling party of Gaza, are in a state of armed and under international maritime law under this state of armed conflict Israel can impose a blockade of all maritime traffic, including both civilian and non-civilian traffic.
Official Israeli foreign affairs position:
The Gaza flotilla and the maritime blockade of Gaza - Legal background
This flotilla had stated its intentions to break this blockade so there's nothing 'random' about it.
Comparing the ability to stop most traffic on the scale of Britain against Germany was not feasible based on the manpower and the resources required to fully block all traffic coming in and out of the country/territory in question. With the limited amount of coastline Gaza has, this is completely feasible in addition to advances in technology.
Not using the term effective in terms of finding anything. Its to minimize the ability to Hamas to wage war against Israel and to severely limit their supplies and financial lifelines regarding this ability.
Thus blockades could be used as a tactic of war without causeing widespread dissruption to trade which I'm sure we can all agree is the important thing. All this long predates Isreal however.
Its not a tactic of war if one is already in a state of war. Both you and I know the difficulties in applying international rules of engagement and war in general when dealing with asymmetrical warfare, so I would appreciate that we stop drawing parallels between warring countries like WWII era Britain and Germany and that of Hamas/PLO and Israel.
In addition, the blockade by Britian on Germany hurt Germany's overall campaign of war. This is not necessarily true when it comes to Hamas's asymetric campaign where even one vessel with several tons of military equipment will allow it to drag on this conflict for years to come. For Hamas, its not about timing, for Germany and their axis allies, it was.
The only real disruptions in trade between Israel and Gaza occurred and continues to occur when trade/humanitarian convoys are diverted to Hamas and other terrorist factions posing as working governments and when the trade hubs themselves are attacked closing them down.
Attacking the UN misses the point. If you are going to make the argument that something is de jure legal and therefor fine it had better be de jure legal which means meeting every de jure requirement no matter how objectionable you find them.
How does it miss the point? The UN itself states that ch VII art 41 is their call based on a vote. Judging by their past abilities to enforce the brunt of their initiatives worldwide, the lateness, and once they receive a charter to act on any conflict, I completely think its relevant since its the international body in the world that is looked upon for clearance and its ability to act in areas of armed conflict and humanitarian functions.
Point out where this is not de jure according to international maritime law regarding a state of armed conflict between two (or more) parties.