Pesachim 50b-52a
When and why is boat travel prohibited due to Shabbos? \u2022 When and why is there a correlated custom to refrain from traveling by ship before Shabbos? \u2022 Why and on whom is this custom binding? \u2022 May one substitute a custom of leniency to embrace a custom of stringency? \u2022 When must one conform to the local custom? \u2022 When may one maintain and encourage a leniency against the broader custom, for themselves, their family and their followers? \u2022 Why is the custom of Yom Tov Sheini so strict?