if you like to see other islands, you must leave Sal by plane. Ships are seldom and normally not regulary.
But try to book (from home) the wished flight, as soon as possible and let it reconfirm after arriving in Sal. It is necessary, also, if there is an “o.k.” written on your print. ❗
From Sal you have nearly all destinations to all the other islands.
Have a nice time on these different and interesting islands. 😛