No, you do not need a passport to travel on the ferry from Portsmouth to the Isle of Wight. Since the Isle of Wight is part of England and the United Kingdom, the journey is considered domestic travel. You are not crossing an international border, so there are no passport control or immigration checks at the ferry terminals in Portsmouth, Ryde, or Fishbourne. While a passport is not required, it is always a good idea to carry some form of photographic identification (such as a UK driving license), especially if you are using a discounted senior or student ticket, or if you need to collect pre-booked tickets from a manned window. For international visitors already in the UK, your passport is your primary ID, but you do not need it to "enter" the island. The crossing is treated much like a bus or train journey within the mainland UK.
No, you do not need a passport to travel from Portsmouth to the Isle of Wight, as both are located within the United Kingdom. The Isle of Wight is an island off the south coast of England, and Portsmouth is a city on the mainland. You can travel between the two by ferry, hovercraft, or catamaran, and passengers typically only need to purchase a ticket for the crossing. However, it’s always a good idea to carry some form of identification, such as a driver’s license or other ID, in case it is required for any reason.