Advance
Dhow
A common trading ship in the Indian Ocean, the Dhow is a capable vessel for trading in the region, despite its small hull size.
Advance tree
The game files don’t say where this goes: it has no requires, so the game places it in the 
Traditions tree itself.
Definitionin_game/common/advances/2_ship_unlocks.txt:176
179potential = {
180original_capital ?= {
181OR = {
182region = region:arabia_region
183region = region:persia_region
184region = region:somalia_region
185region = region:egypt_region
186region = region:nubia_region
187region = region:ethiopia_region
188region = region:swahili_coast_region
189region = region:deccan_region
190region = region:western_india_region
}
}
}