It's not like Israel boarded a ship that just happened to be in the area,

That's exactly what happened, blockade borders have to be announced and ships have to be allowed time to leave the area. Israel left their blockade and kidnapped people aboard a ship they did not allow to leave an area they weren't in.

these freedom flotilla yahoos very publicly declared they were bound for Gaza, which under Maritime Law permits Israel to board it.

Once they breach the blockade yes arguably though with only aid that gets more complex. Essentially aid entry is allowed so long as you agree to security arrangements that are both reasonable and lawful. That could mean Israel could board and search, or doesn't mean they can blockade all aid to starve a population which is specifically and in multiple very very illegal.

https://casebook.icrc.org/a_to_z/glossary/blockade

Their sources section is awash with good relevant information and specifically findings on the last Israeli famous Israeli blockade and subsequent boarding (and death of iirc 9) which was found to be a legal blockade so long as the purpose was not starvation and aid could enter with security arrangements.

they very publicly declared they were bound for a blockaded port.

Not illegal.

which under Maritime Law permits Israel to board it.

Not detain and seize, maritime law is very specific in that a blockade cannot block aid unreasonably. A super famous ship you've searched that's filled solely with celebrities and aid is something you shouldn't turn away so long as they accept security arrangements like boarding and searching. This isn't star wars nor are they the trade union and total blockades like your implying are very illegal as defined by the law you're sourcing.

Maritime Law (the oldest of international law)

Source?

freedom flotilla yahoos [...] doing things that will hurt your feelings. [...] sovcit [...] pretend

Ew.