Just to test the construction system, I decided to try out a giant merchantman. It’s loosely based on the Roman grain ship Isis.
Our starting point is that the ship was 180 feet long, over a quarter that in width, and had a cargo hold that was 44 feet deep from the main deck to the keel.
So, to start, we’ll use a 180 foot length and a 3:1 beam, which gives us a rather tubby 180x60 ship, with a 15 foot draught. That’s probably not enough to be 44 feet from the main deck, so we’ll add a second deck to drop the draught to 22.5 feet. The ship has a seaworthiness of 5, and as a giant merchant ship, no rowers will be added. Isis is a 2068 ton ship, with a base capacity of 413,600 stone. Her base shp are equal to her tonnage, which is 2068. Because the Romans used mortise and tenon joining, she’ll be considered a clinker ship. This give +10% shp and +1 seaworthiness, but means rowers or artillery cannot be carried on any deck except the top deck. This means Isis has 2275 shp and a seaworthiness of 6.
At 180 feet, she could have up to six masts, for a total of 13 sails, but that’s far more than what the Romans actually did. Instead, we’ll go for a modest 3 masts and 5 sails. With square sails and the beaminess of the ship, that will require 66 crew to handle the sails. This also gives her a speed of 2 hexes per round when sailing with a fresh breeze (0 modifier) from an aft quarter (also 0 modifier). Given that the base turn rate for Isis is 11 (one 60 degree turn every 11 rounds), we’ll also add a bowsprit (which requires 2 more crew), to improve the turn rate to 10. It’s not much, but it makes her a little less of a wallowing pig. The total weight of masts, sails, and rigging is 5400 stone. Carrying a full spare set of sails and rigging adds another 1800 stone, so the total rig is 7200 stone.
With 68 crew needed to run the ship, an additional 7 crew (captain, navigator, bosun, and 4 spare sailors) are added to make an even 75 crew. At an average of 15 stone weight for a human, the crew weighs 1,125 stone. For the sake of this example, each crew member has 200 stone of personal gear and rations for the voyage, for another 15,000 stone in crew weight. The total crew weight is 16,125 stone.
Adding crew weight plus rig weight, the ship could sail with equipment taking up 23,325 stone, which would allow Isis to theoretically carry up to 390,275 stone in cargo, or about 1950 tons. However, a ship like this would also have marines aboard, and the real Isis also carried artillery on her top deck. These would reduce cargo space accordingly, but it shows the massive amounts she could theoretically carry.
For cost, the hull of Isis alone costs 227,500 gold pieces. The masts cost 36,000 gold pieces. Rigging costs haven’t been figured yet, but I anticipate they’d be somewhere around the cost of the masts, maybe a bit more. A normal crew would be 563 gold per month. So, it would cost approximately 300,000 gold to have the ship built, and a minimum of 563 gold a month to have a competent crew handle her. She can haul large amounts of cargo, but only at a speed of 4 knots in a moderate breeze, and she’ll pretty much only be used between Class I markets because of the amount of cargo she needs to haul to be profitable.