I’ve been running sample calculations for trade ships, and I’m having trouble figuring out how to take advantage of the extra shipping capacity of a large ship.
To start, let’s assume we have a Class II market. This is a pretty sizable market, and is probably loading dozens of ships a month, so I figure it’s large enough that it should be sensible to send a large trade ship there, or even a small fleet of trade ships.
A market this size is going to yield 2d4+1 merchants (let’s call that about 5), and each of them will have about 4d6 (average 14) loads. If each load weighs an average of 70 stone, then I get around 4900 stone of cargo, assuming that all the reaction rolls fall my way (not impossible, with a good CHA bonus, but still optimistic).
That about half-fills a small sailing ship. I can fill the other half with an equal number of shipping contracts, plus a few odd passengers. This works out nearly perfectly to match the listed 10,000 stone capacity of my small ship. Great!
Now I’m ready for the big leagues. I buy a large sailing ship, with 30,000 stone capacity. But I’m still making all the same rolls above. So now my large ship is only 1/3 full. How do I find the cargo for the other 2/3rds of the space? I’ve already saturated the markets for that month!
Even if I run the same calculations for a Class I market, I still only about half-fill the ship. Worse yet, really good traders tend to be able to procure cargo that consists mostly of valuable luxury goods that have very low weight. That gives them even less need for a large trade ship.
I can avoid this whole problem by running two small ships, and having them arrive on alternating months. But it seems like cheating to get twice as much available cargo this way, and I don’t see why it should be necessary from a simulation standpoint. Showing up with two different small ships rather than one large ship shouldn’t change any need for transportation services, from the perspective of a selling merchant!
Large sailing ships are only meant for routes that make lots of stops, not just running between two ports.
Large sailing ships stick around in port for multiple months, building up a full hold. (While any perishable goods are protected by some kind of food preservation cantrips?)
Large sailing ships hire additional traders and procurement specialists to fan out around the city and locate more local merchants faster. (In game terms – you can split up your party and have them each locate the full number of merchants, using the best CHA character in each sub-party.)
I suspect that historically the answer was usually #3, so I think that’s the way I’m going to house-rule the problem. But I want to make sure I’m not overlooking some mechanism already in the rules that solves this problem.