Making Waves On Shabbos
The Gemara in Shabbos makes an undisputed statement: Less than three days before Shabbos, one is not allowed to board a boat that will travel on Shabbos unless the travel is for the purpose of a mitzvah.
Shabbos
Boarding a Boat Before Shabbos in the Gemara
Why the Gemara forbids setting sail less than three days before Shabbos, with the Rishonim's reasons of seasickness, foreseeable Shabbos desecration and techum.