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