The biggest Scandinavian ship was, according to "Aspects of Maritime
Scandinavia" (1991) 155 tons in cargo size. The biggest Venecian ships, of
the 14th to 15th century (end of MA, beginning Renaissance) was 200 to 300
tons in cargo size [1].
My memory was a bit wrong, the biggest ships that were allowed to enter the
harbour were 134 tons in size (not 150 as I stated). See my post on this:
Subject: Re: Evolution and stuff (was: Re: HTML: woes)
Date: Mon, 16 Mar 1998 19:03:39 +0100
Cargo ships of more than 1200 net tonnage (the size of the Roman ISIS, of
which type at least 60 to 80 ships existed, because of the high wheat
requirements of the empire, however, it was probably much more) were only
built again in 1800 (!) in larger series [2].
Nelson's "Victory" had 3000 brutto register tons, the ISIS had 2900 BRT.
Conclusion: The biggest Scandinavian ships would barely have been allowed to
enter the Roman harbour, and the *biggest* late MA / early Renaissance
Venecian ships were still under the *average* Roman size.
[1] Troitzsch and Weber, "Die Technik", 1987, p.146.
[2] H.D.L. Viereck: Die roemische Flotte, Hamburg 1996, p.123.