I currently have about nine. I tried using a boat to cross the ocean, but when I hit land the wolves were in the first spot they got in the water. I have to travel about 4k blocks.
A tamed wolf will teleport to you if are out of his reach. However, a tamed wolf will not teleport to you if:
- It has been ordered to sit.
- You are not touching the ground (flying, using elytra's, using boat's).
- It is in a mine cart or boat.
- You go trough a portal in which case it will wait for you to return.
- It is in a chunk which unloads, where it will wait for you until that chunk is loaded.
The best way is to use a Lead on it and then go slowly with your boat. Your wolf will be forced to follow you.
My personal favorite way is to use boots enchanted with Frost Walker. Frost walker makes a path of ice under your feet when you walk across water. Tamed wolves will follow you across the ocean on the ice.
Be aware that it does melt rather quickly during the daytime, so it's easier to go at night, especially if you're planning on stopping for very long while you're crossing the ocean.
I'm afraid this is going to take some time, regardless of method. If you travel far enough away, the chunks the wolves are in are unloaded so they won't teleport. However, there might be a way around that:
- Set your render distance as high as your computer can handle
- Carry several large stacks of cheap blocks with you and hop in a boat. I would recommend wood, since you can craft them into wood planks for 4x the number of blocks vs. inventory space.
- When you're about to reach a point where the shore chunks are unloaded, jump down into the ocean and make a stack of blocks to the surface. Make a small artificial island that your wolves can teleport to
- Continue to travel by boat a fair distance, creating small artificial islands for your wolves to teleport to until you reach your destination.
Adding to Gigazelle's answer: Before a chunk is unloaded (basically before it fades from view), you can use a lily pad to start a platform at the surface, rather than swimming down and building a column every time. Once you have a 4x4 platform, stand on it and the dog will teleport to you.
Edit: I just discovered dogs can ride in a boat with you...
Maybe try Using a boat and getting you're wolf in there, and then hold a Bone or something to make him follow you. (I see you already tried this so...) Or you can build a Bridge and get there safely. Or you can just.. You know... Go inside the water and Swim... XD. But that will make the wolf Grey, So the best option is to build a bridge if possible. Sorry if this didn't help. I tried though.. I hope this helped you.