Roman ships at 1st century?

The rowing types were galleys , basically in two sorts , a smaller type used for swift scouting , with single sets of oars ,
and a heavier set of types , Biremes ( oars on two levels ) Triremes ( oars on three levels – a modern interpretation is the ” replica ” called Olympias , lays in the Hellenic Navy’s Historic ships museum at marina Flisvos , south end of Phaleron bay , Athens ) and ( allegedly ) Quinqueremes ( oars on FIVE levels — only god knows how that worked ! )
Those were all Warships .

Sailing types evolved from a single masted small trading type , very like a modern Greek Caique
( timber built fishing boats , 20 foot to 90 feet long ,)
To the Giant Roman ” Round-ship ” types that carried grain from the Egyptian ports at the mouth of the Nile to Ostia , Rome’s seaport .

The galleys all averaged 5 mph , with higher sprint sppeds for battle – for a ridiculous recent interpretation , watch the naval battle bits from the film ” Ben Hur ” . Galleys also had masts and sails and could run downwind , given a fair breeze .

The smaller sailing traders could , just , beat to windward to some degree against a foul wind , but the huge grain haulers would have all the windward ability of Kon -Tiki ,and relied of predictable seasonal fair winds to make their journeys .

Again , an average of 5 mph would be fair going .
– Chosen by Asker

There where a wide variety of both war ships and merchant vessels during this period. There where thousands of ships (not hundreds).

See: http://www2.rgzm.de/navis/Themes/Commerc…

and

See: https://www.google.com/search?q=roman+wa…

As to average speed something under 5 knots. A replica which was rowed by a crew who trained for several weeks only reached that as a maximum speed……for a relatively short distance. Since ramming was the principle weapond “Ramming speed” was reserved for the final attack.