They were two Riverine, either Command or Patrol, Boats. I’ve seen them described as both. Sweden designed them, FWIW.
They were transiting from Kuwait to Bahrain. Why, I dunno, and the links I’ve cited don’t really say. Ferry transit to another operating area is my guess. Depending on which port they were leaving and arriving at, it’s a haul of about 250 to 275 nautical miles. Which is a bit of a hike for those type of craft. And, while we’re not exactly talking about the Mouth of the Columbia River in a storm, the weather’s not supposed to be pleasant on the Gulf this time of year. I’ve read 5-6 foot seas with 15-25 knots of wind at the time of the seizure.
Further, it’s a route that should have taken them along the western side of the Persian Gulf, well away from Iranian territorial waters. The island they were taken to, Farsi Island, is roughly in the middle of the Persian Gulf, between the west and eastern shores. Nonetheless, even if you draw a 12 mile circle around Farsi, that still leaves a roughly 35 mile corridor of international water between the Kuwaiti, then Saudi, then Bahrainian shores. Since Farsi has a Iranian Revolutionary Guard Navy base on it, and per rumors I’ve read from people who’ve served in the Gulf, the Iranians are supposed to be rather pissy about planes and ships getting near it, you’d think the planning for the transit would have emphasize staying away from that place. But who knows?
Playing around in Google Earth, it looks like the water is anywhere from 50 to 175 feet deep. You’d want someone like Princhester or Sniipe70E (?) to confirm, but I’d think you can still anchor in water that deep. IOW, even with one of the two boats suffering an engine failure, (never mind that both boats were videoed sailing away under their own power after the Iranians released them and their crews), you’d think they could have anchored, or called for assistance before blundering into Iranian waters. Especially as I’ve read the currents tend towards the south in that area, not easterly towards Iran or Farsi Island.
Add that the French Navy’s aircraft carrier Charles De Gaulle was supposedly near by, along with its escorts, yet for some reason they weren’t able to lend assistance to the two boats, I don’t think we’re getting the whole story on what happened and I doubt we ever will. It’s strange.