A super-yacht is by far the best refuge in which to weather a zombie apocalypse. Super-yachts are upwards of 150 feet long and easily sleep 50 people. But this is based on the tricky assumption that you can acquire a super-yacht before the apocalypse breaks out, or make it to, and de-zombie the super-yacht of its newly zombiefied oligarch owner, entourage, crew and dancing girls after the dead rise. Assuming that you can, you will have a great place to chill while the world tears itself apart.
A super-yacht of sufficient blinginess can make its own fresh water with on board desalination and can run for months on end on the gargantuan fuel tanks - provided you don't move around too much. At anchor you would only need fuel to run the generators, not the main engines themselves, and the only weak point in your luxury fortress would be your anchor chain.
Zombies can walk on the seabed and may spot the lights and hot tub antics of your crew of survivors from the shore. So you would need to be prepared in case any head over and try to climb up your anchor chain. But the larger your yacht, the more easily defensible this point will be. The chain usually enters the boat through a smallish hole some distance down the side of the hull, if this is too small for a zombie to squeeze through, your'e golden. If not, you may have to put someone on watch with a spear gun. If the chain gets swarmed, simply raise the anchor using your yacht's powerful electric windlass, the zombies will get mashed to a pulp in no time at the touch of a button.
Most yachts in this category come equipped with remote controlled submersibles designed to examine the seabed for good anchor holding, (I have seen one of these first hand) so you could put your sub to good use spotting zombies.
Super-yachts are by nature extremely self sufficient, and are designed to spend extended periods at sea with all mod cons. All your needs for power, light, heating, cooling, refrigeration, entertainment and ice-making would be taken care of as long as you have enough fuel to run the generators.
Fuel – you would need to invest some time identifying a suitable fuel barge from which to refuel, these are often found moored near commercial shipping hubs, or deep water harbors suitable for super-yachts. Alternatively you could refuel from a fueling pontoon – in both cases you may need transfer one of your yacht's portable generators (believe me, your boat will come with everything you could want), connect up the power to the fuel pumping apparatus and fill up. Your tanks will be huge though, so this could take some time. On a pontoon you will have a single gangway ashore to defend, these are often already equipped with impregnable security gates that your determined zombie (and let's face it – there is no other kind), will find difficult, though not impossible to overcome. Not the worst situation to be in, but be prepared to beat a hasty retreat and/or defend your position with your yacht's water cannon.
Food, your super-yacht will be equipped with a stunningly well appointed galley, including all electric appliances under the sun, hobs, ovens, industrial fridges and freezers to store food, either pilfered from shore or, more promisingly fished fresh from the sea. Your yacht will be equipped with all manner of fishing equipment, don't worry. So get used to living off the fruits of the sea, far easier, more nutritious and tastier than trying your hand at farming in an apocalypse, or eating army rations.
Your yacht will also have a fearsome supply of booze already on board, you might want to try growing a lemon or a lime tree somewhere because what is a superyacht without sundowners? Oh, and to ward off scurvy.
Piloting and communications. Superyachts are designed to be operated safely by very few personnel, everything is done at the push of a button, however it’s possible GPS would be offline during the apocalypse, although it's quite possible the that GPS satellite network would be unaffected – unknown. In any case knowing your exact position could be an issue, so I'd suggest moving the boat around as little as possible or digging out the emergency sextant (your yacht will have one), finding the relevant book in your yacht's library and learning to take star sights – it's not easy but you'll have plenty of time to figure it out. Should the apocalypse come to an end and humanity restore itself, you will have all the comms equipment on board you can shake a stick at to monitor and communicate. No chance of you missing the end of the end of the world, and staying locked up in you bunker unnecessarily.
Laundry. Yes superyachts have washing machines and tumble dryers, also ironing boards and shoe polish. No need to look like a zombie if you don't have to.
Maintenance. Inevitably your yacht will go wrong at some point, this might be minor, or if it's the main engine, generator or air-conditioner - major. On the plus side, superyachts are maintained to an exquisite standard by armies of engineers, technicians and deckhands in normal use, so disrepair should take a while to set in. When this happens - move to the next superyacht in the harbour, kill the zombie skipper for his keys and fire up the engines. I would suggest that St. Tropez or Monaco would be good places to do this, and preparing some sort of yacht transfer drill for your 50+ survivors will be the best way to minimize casualties.
Creature comforts. This is where the superyacht approach really owns it over your disused mining structure, or underground missile silo approach. You will be sleeping in 1000 thread-count Egyptian cotton sheets, you will have a commanding view of your surroundings from your various, comfortably appointed relaxation decks, you will wash in one of many heated, lit and surround-sound equipped hot tubs, or gold encrusted bathrooms, you will have, a gym, a dining room, books, movies, music, expensive cutlery, lead crystal glassware, vintage brandy, Cuban cigars – in short, every luxury you can think of, as well of plenty you didn't even know existed. The apocalypse will be a blast.