I proposed similar in another thread. Basically, you set up some basics about Crew Size and Configurations and then just add options within those Tiers. So you get this basically:
1-2 Crew Size, 2 Cannons (1 per side), 1 Sail (Fast Response), Fast Anchor, etc.
Sloop: The current ship of this category.
Cutter: A single Mast/Sail ship that is directly known to have a different configuration from a Sloop in look, and can also be equipped with a Triangle Sail so that this can fall in line with the other alternates that I have suggested so that we have some common themes to work off of when approaching the concept.
2-3 Crew Size, 4 Cannons (2 per side), 2 Sails (Moderate Response), Moderate Anchor, etc.
Brig: A dual Mast/Sail ship that featured a Square Sail setup which would make it a perfect fit to be the next ship type we have released to us in the already confirmed spot (since Square Sails are already a thing, and it sets up a new Crew Configuration). These guys should feature four cannons (two facing each side) and fall somewhere between the small and large ship classes regarding speed and maneuverability and ability to utilize the Sails/Anchor.
Junk: This would be the Triangle Sail variant ship for this size range, and it also has a varied general construction as well for the Hull compared to a Brig. This would make it a nice distinction option for this grade to help add some more variety to the world at large and establishing a style for your Crew.
3-4 Crew Size, 8 Cannons (4 per side), 3 Sails (Slow Response), Slow Anchor, etc.
Galleon: The current ship of this category.
Frigate: These tend to have a design that sits them lower in the water compared to a Galleon, and tend to have a generally flatter main deck (the helm is raised normally, but it doesn't feature that front section like on a Galleon). They can feature either Triangle or Square Sails, but I propose this one go with Triangle since the Galleon uses the Square helping to further visually distinguish them.
Basically the combo of the different looks of these ships mixed with the differences in sail design I tossed in (which doesn't have to be a thing, just adds even more diversity) means we would have 3 main play styles with 6 different potential appearances. Would certainly make the adventures we have more diverse.