I like the navy ship idea. A nuclear ship would be nice as far as near unlimited electricity. The only problem I see would be where on a metal ship to grow a garden. I think you should set sail for some island. Then use your ship to defend it from other groups looking to raid your supplies.
Here are some of the major, major pluses why I would go after a Navy ship as a long term defense shelter if I didn't have another suitable one to use. I would go for a non-nuclear ship personally, for a few reasons. Most of them are older and would not be prime targets for military attention.
Solid metal- The hull of most Navy ships are several inches of solid steel, very hard to penetrate with anything except high explosives, missiles, etc.
Tactical height- There's a reason why it's a very good idea to be on the high ground in dangerous situations. If I had the choice I would pick a ship that sat rather high in the water, which requires more height than a gangplank to access. There are plenty of ships that large. Get rid of the gangplank or ladders, and the only ways onto the ship are the mooring lines which can be guarded, or the seaward side (which is how I'd get on board the ship in the first place). If I had a group, I would post guards and rig up the .50 cal mounts. If I didn't, I'd just keep more toward the belly of the ship and attempt not to be discovered.
Storage- Obviously ships are quite large which means you have a huge amount of room to stockpile things as well as relatively high physical security once you get the ship locked down and properly guarded. More so than that though, an average ship has a crew of more than 300 people, and there is always a stock of food and fresh water in the
tanks even when the ships are in port. Properly rationed, that food could last for quite some time until it was just zombies to deal with.
Easy exit- It would be safe to jump on and off the ship on the seaward side, just lower down a lifeboat and you can motor or row your way to shore at another location where the zombies are thinner. Scout for supplies, get back to the boat and you can get them back on board the ship. The water would be deep enough that the zombies wouldn't be able to reach you. If your ship was compromised by other hostile humans you can still possibly escape to the sea and try to acquire another one.
Water purification and power generation on board- Every ship has 2 (or more) enginerooms. Within each engineroom there are at least 1 saltwater evaporator, usually 2 (or more) high power turbogenerators, and a large amount of auxiliary equipment which could be scavenged/repurposed. There are usually also at least 2 diesel generators in separate areas of the ship for emergency power backup. I know how to use most of this equipment well enough.
Tools, weapons, other useful gear- I doubt a lot of people would be raiding Navy ships for supplies, it seems unlikely that many people would even think about it. On a pretty standard smaller Navy ship (frigate, troop transport, destroyers) there is usually a small medbay but one that is reasonably stocked. There are weapon lockers and ammunition storage which would provide some weaponry in the form of pistols, shotguns, and carbines. There is usually also some relatively high-grade body armor and tactical helmets. Not top of the line, but alot better than nothing. Also, most ships have .50 caliber mounted guns which can be set up. Within the engineroom and other areas of the ship you'll find all the wrenches, pliers, welding tools, safety gear that you'd need to be able to work with and build almost anything. My ship even had a small machine
shop with lathes and dies and such.
Gym- Most ships have a small gym for the sailors to stay in shape with. Free weights, treadmills, etc. Nothing particularly fancy, but unless you are in tip top shape prior to the zombie apocalypse...having a steel shelter with some weights that you can use to work out and get stronger with along with a limited storage of food and water....gives you the chance to get in much better shape in swift order thus making you more capable.
It would be very easy to build a raised gardening setup of a sizable nature using the welding tools and spare metal parts/deckplates/whatever that you could use to grow plenty of plants in. Getting the seeds would be the harder part unless you brought those with you. You could also fish quite easily from the ship, and assuming that the fish were safe to eat and not impacted by the zombie virus...between the stocked food, fishing, growing veggies....you could last a pretty long time.
File:US Navy 030117-N-2069B-002 USS Anchorage (... 36) departs San Diego Bay .jpg - Wikipedia, the free encyclopedia
This was the ship that I was on when I was in the Service. She was pretty old at the time I served but mechanically was still in pretty good shape. She got decommissioned and then used as missile target practice a couple of years ago, apparently. But as you can see a ship like that is BIG and easy to hide in while still not being terribly difficult to secure IF you can secure the pier and keep guards on the seaboard side.
