My definition of non-coastal sailing is sailing beyond sight of land. The Portuguese were far far later.
Um, no, a trireme is very different in size and construction to a penteconter. The two ship types are very different. I'd be wary of using 'Men of the Sea' as a reference, as much of its material about ancient ships is inaccurate.
A trireme has a full ram, often three-bladed; a Wolf Pirate has a a fore-ram and cutwater. The use and operation of the two are very different: the former is intended to hole the enemy; the latter to hold an enemy for boarding.
Roughly true: neither are cargo vessels; a trireme is much larger.
And neither were operating very far from friendly ports. There are reasons why the Athenians waited until Salamis - restricted waterway where their tactics and operational capability could overcome the superior number in the Persian fleet.
The Spanish Armada is a good example of a fleet being scattered by a storm; the exploits of Zheng He are the subject of considerable debate.
According to the Guide, long-distance trade routes out-of-sight-of-land are minor, even those taking 'seven days.' The majority of shipping is coastal.
And neither are ordinary sailors.
There's little room on a penteconter, and pirates throughout history have captured the cargo vessel, not sunk it. It's pretty tricky to offload a cargo from one vessel to another at sea, especially when the pirate vessel lacks a hold. If a pirate holes the cargo vessel, it will take its cargo and crew to the bottom.
Unfortunately, on these small vessels, collecting rain to refill casks isn't very practical.
Trailing nets acts as a drag, slowing the vessel. I'm afraid you seem to have misapprehensions about how triremes operated, and how they were supplied. A few fish are not going to feed a crew of more than two hundred. These are not long range sailing vessels.
Speculation. And latest evidence indicates the Black Sea filled very very slowly, and Doggerland was so far away in time and distance as to have no bearing.
It would be very unusual for a trireme or penteconter to carry enough food or water for more than three or four days.
The main thing to draw from this is that penteconters are capable of remarkably quick bursts of speed and rapid maneuvers. Their battle tactics are customarily ramming and holding fast to the enemy vessel and then boarding – with the number of warrior rowers giving a numerical advantage. Bear in mind that a trireme rarely carries more than 14-20 marines, and a cargo ship very few if any fighters, but a pirate penteconter has fifty rower/warriors. The pirates swarm the target, and intend to capture the ship, its crew and passengers, and cargo whole. The vessel is then manned by some of their rower/warriors and sailed to where it can be offloaded at port. This tactic worked in the ancient Mediterranean and in the Caribbean, where pirate ships sailed with larger crews not only to overwhelm defenders, but to then sail the captured vessel.