You should check with UK Passports but it looks as though a photocopy of the back page and your seapass is all that is required. As to how many copies one for at least each port you call at and maybe one or two spare just in case, but don't carry more than two copies at any one time and keep them seperate.
Forgot you are a first time cruiser and your seapass will be given to you when you arrive at the ship for accessing your cabin and for use when you purchase drinks; items from the duty free shop on board, in other words a cashless society whilst you are on the Norwegian Jewel or any other ship in the future.
If you are able to laminate your copy of your passport page you need only have the one copy for each person and it will stand you in good stead for many trips and looks very official. Laminating machines and the plastic pouches needed are comparatively cheap now and so useful for so many different things. Ida.
Thank you for all your help. "Ida", I have a laminator at home so will get onto that today. Thank you also to "Blyth" for your help.
Quite often the ship will take your [asssport from you and only return it to you at the end of the cruise or if you actually need it at a particular port.
Assume you are talking about Russia - on the first day there you hand in a copy of your passport page - not needed when you get off the ship on the 2nd day. I hope you are taking a private tour rather than the ships tours. I recommend http://alla-tour.com/.