The secret is harpoons.

Go get a second boar of any size, lure it to wherever you have the 2-star pig. Tame it next door. Once tame breed pigs till you have 3 2-star piglets. Recommend you do this in a raised-earth pen with a roof and a second raised earth wall 6m or so away around it to protect the boars. After you have this second boar, go tame a boar of any size at your home base as well, and for preference protect it similarly.

Make a stack of stamina potions.

When you have 2 adult 2-stars kill the non-2-star adult, breed another 2-star piglet, then move 1 2-star adult to the shore. Drop your longship in, harpoon the boar at medium range (you'll need the length of the leash later)

Get on the boat (just yourself, and not the boar), and sail away, towing the pig behind you. If you arent within aggro range of land when you're down to about 30% stamina stop the boat. Watch which way the boar tries to swim and paddle the boat BACKWARDS in the same direction just enough that the boar isnt pulling on the harpoon. When its not pulling you will regen stamina. Once your stamina is full, or full enough, continue sailing towards your base. If you are within aggro range of land (islands too near to each other, near a swamp (which have a larger aggro range), or in a river etc) then keep going and use a stamina potion at 10% stamina. Do NOT stop in those areas- something WILL come and try to kill your boar. Once youre back at your base drag your boar to the one you tamed locally and breed your bacon till you go blind. :)

Do NOT try to get the boar on the boat, harpooned or not- wave action and stuff will likely cause it to explode for... reasons... before you get it home.

Originally posted by Conan:

a animal ALWAYS have the equal (100%) child, a boar has a boarchild, a boar* has a boarchild* and a boar** has a boarchild**, this internet fakenews with 50% is ....fakenews

Not in my experience. I had a boar pen with all 1 star boars and they still produced normal boars sometimes. Its not 100% unless I'm missing something.

on 2* land mass set up a breeding spot.
take /push the new 2* boars onto a boat (use a ramp n fence if u need ..or harpoon
since you have a breeding set on 2* landmass if u lose a boar that aggros a serpent.. u can try again
sail to new land mass by shortest path with moder power in case weather fouls you up.
repeat untill you suceed

a animal ALWAYS have the equal (100%) child, a boar has a boarchild, a boar* has a boarchild* and a boar** has a boarchild**, this internet fakenews with 50% is ....fakenews

I believe it is very difficult to transport boars from one landmass to another. Not impossible but might not be worth the trouble. maybe secure the boars in a safe breeding shelter on original landmass and portal to cull them every now and then.
Breeding a 2 star boar with a non star boar has a chance to produce a 2 star boar. Best practice is to remove the no star when a 2 star boar is produced so you have two 2 star boars to breed.