My boat is kept in a marina and although I don’t have any shore or on board power the boats either side of me do. Do I need to worry about having an anode? Can de-zincifacation(?) be active from boats along side?
Almost definitely yes! The purpose of the anode is to protect the boat from corrosion due to the existence of metals in the craft itself. It works by having as an anode a metal more likely to corrode than other metals on the craft thus protecting the other metals through sacrificial corrosion. An anode should be wired up to these bits. eg Engine, propeller shaft
If it's a rowing boat or anything that has no metal in the water (prop, rudder, skin fitting etc.) then you don't need an anode, but if your boat has any metal that touches the water you need an anode to protect it.