A galleon was a large, multi-decked sailing ship.
The design evolved as a result of Royal Charisian Navy captains' willingness to sail onto open water rather than make their way along the shores of Safehold's many landmasses. A number of innovations that improved the design were introduced by Merlin Athrawes around the dawn of the Year of God 891. (OAR)
The galleon as a cargo-carrying ship tended to be deeper-hulled, had higher sides, and possessed a significant tactical advantage in naval combat once the infantry action was joined. Its lack of speed and, especially, handiness in comparison to the galley, however, meant that it would find it very difficult to close with a nimbler adversary and bring its advantages to bear.
In the absence of decisive range-combat capability, the galleon would thus be a primarily defensive design. This was fine for an essentially civilian ship class which was only going to fight when it has to, but was last than optimal for a warship class. (infodump)
Military version Edit
Under Merlin's prompting, the Charisian Navy changed into a galleon navy very rapidly, introducing many improvements and innovations. By the time the RCN became the Imperial Charisian Navy, the most recent galleons were, in essence, overgunned double-banked frigates. (OAR, BHD)
The evolution of Charisian galleon design between 891 and 895 was a follows (source: post by David Weber in www.davidweber.net).
HMS Hurricane: length 108’; beam 35’; 750 tons; gundeck 14 35-pounder carronades; upper deck 14 35-pounder carronades; weight of broadside 490 pounds. (Notes: this is fairly typical of the Royal Charisian Navy's smaller converted merchant galleons. She does not have warship-grade scantlings or planking and carries only carronades to reduce weights, which limits the range at which she can engage. Even so, she has very limited freeboard.)
HMS Gale: length 115'; beam 35'; 840 tons; gundeck 18 35-pounders; upper deck 14 35-pounder carronades; 4 long 14-pounder chase guns; weight of broadside 588 pounds. (Notes: this is fairly typical of the Royal Charisian Navy's larger converted merchant galleons. She does not have warship-grade scantlings or planking, but her greater tonnage lets her carry long guns on the gundeck and gives her slightly better freeboard.)
HMS Dreadnought: length 154'; beam 42'6"; 1,200 tons; gundeck 30 long 30-pounders; spar deck 20 30-pounder carronades; 4 long 14-pounders; weight of broadside 828 pounds. (Notes: the first purpose-built war galleons of the Royal Charisian Navy. Freeboard to lower port sills only about 10' — better than anyone else's, but still about 3'-4' short of what a proper blue-water frigate really needs.)
HMS Empress of Charis (original): length 168' 11"; beam 40'3"; 1,400 tons; gundeck 32 long 30-pounders; spar deck 30 30-pounder carronades; 4 long 14-pounders; weight of broadside 958 pounds.
HMS Empress of Charis (final): length 168'11"; beam 40'3"; 1,400 tons; gundeck 30 long 30-pounders; spar deck 18 57-pounder carronades; 4 long 14-pounders; weight of broadside 991 pounds.
HMS Royal Charis: length 174'; beam 40'; 1,520 tons; gundeck 30 long 30-pounders; spar deck 24 30-pounder carronades; 4 long 14-pounders; weight of broadside 834 pounds. (Notes: 30-pounder carronades later replaced by 20 57-pounder carronades, at which point weight of broadside became 1,048 pounds. She carried her guns higher than the original Empress, and showed 12' of freeboard to her port sills. This was the immediate follow-on class to Empress.)
HMS Sword of Charis: length 178'6"; beam 45'4"; 1,725 tons; gundeck 30 long 30-pounders; spar deck 20 57-pounders; 4 long 14-pounders; weight of broadside 1,048 pounds. (Notes: An improved Royal Charis. Her greater displacement gives her 14' of freeboard to her port sills.)