For that matter, how is Iran "closing" the Strait of Hormuz at all? Is this all just a big PR stunt? Deception from both sides?
Speed boats with an automatic weapon on the bow.
Effective on coastal traders.
Merchant ships aren’t armed. Naval warships which are obviously armed, need permission to enter the harbors of foreign countries.
If you remember the Somali pirates when active they were using small boats and small arms to capture ships for ransom.
Iran still has small boats armed with machine guns, possibly larger caliber guns/cannons and maybe torpedoes.
It’s three guys in an inflatable speedboat with an RPG.
Could be easily solved with a few soldiers with sniper rifles on the cargo boats.