- Make a nether portal in the nether.
- Place a boat in it.
- Go though the portal.
- TP to 0 0 0. If there is a lava lake at this position, fill the area around it with stone and make a hollow air chamber at 0 0 0, then repeat these steps.
You find the boat in the OW portal in step (3)
Sometimes you find the boat at 0 0 0 in step (4) or (5). This seems to depend on the location of the destination portal because it happens for some portals and not others when I test. The boat may be invisible until you relog.
Note: this also occurs sending boats from OW --> Nether, but in that case the the boat falls into the void because there is no block below 0 0 0 to support it.