Can I book a trip for someone else?
Yes. Book it under your own account and put the name and phone number of whoever is actually going in the note to the captain.
Trips booked as gifts or by one person for a wider group are common here. The booking stays under your account and you remain the contact for payment and changes, so tell the captain who will be at the dock and how to reach them on the day.
If you are booking as a surprise, say so in the note. Captains will avoid ringing the recipient directly if they know.
The deposit is charged to your card and the receipt comes to your email, so the person going does not need to hand over any card details or create an account. They do need to know the balance owed to the captain on the day and the departure point, both of which are on the confirmation — forward it to them, or print it for the gift.