"Homemade" is doing a lot of work there, I'd bet for ultra voyagers they had master boat builders (for their time and with their materials) that were prized for the quality and strength of builds

I live on O’ahu. We recently observed the 50th anniversary of the first voyage of Hokule’ia which is the first voyaging canoe built and navigated in the traditional ways, which was sailed from O’ahu to Tahiti and is still active, currently on a worldwide voyage. My kids got to go on board when it was docked as part of their school and there’s been lots of stuff available here about traditional navigation. It’s all truly amazing stuff. I chaperoned a field trip last year where we got to sit with one of the former crew members and it was like meeting an astronaut. Their descriptions of being in the middle of the ocean among the stars on that traditional ship is just breathtaking.

Polynesians were master mariners. Even European explorers were impressed by their knowledge of the sea.

So the thing with exploration is that an overland journey is just as dangerous as long distance sailing. Both have hazards like weather, plants and animals, terrain/waves, the need for shelter/clothing to protect against the elements, and a need to source food and water locally along the way. Seafaring cultures know where food is and isn't just like how land based explorers know. Expanses of open ocean without fish or rain water is like crossing the desert. Plus the seafaring people know how to build ships that can handle the ocean, so sinking isn't a real danger.

Both had their share of losses as they explored new areas, but guidance by the stars and guidance by landmarks is comparable and they just needed to share knowledge.

I'm not trying to minimize seafaring cutltures, just pointing out that is has different challenges and not necessarily harder challenges than the comparably dangerous overland exploration. Both are very impressive in different ways!

And your only map is a stick chart

And that only covers known waters