The bug
You can place a boat about 4 blocks underwater sometimes. When you do you can breath forever. Also your partner can jump in and enjoy the submarine view too. Mobs will not target you as well.
How to reproduce
Use a structure block to load the structure contained in
/setblock ~ ~ ~ structure_block{mode:"LOAD",name:"mc-127322:mc-127322",showboundingbox:1}
Place any type of boat on the lowest water level
Ride into the water current
→ ❌ Observe that the player doesn't lose oxygen
Linked issues
is duplicated by
relates to
Attachments
Comments
Confirmed for 18w32a
Confirmed for 1.13.1, although you'll be teleported out the boat shortly after entering the boat.
This issue relates to MC-96198.
I've found a reliable way to reproduce this and have saved the structure that I've used to reproduce to
[media].
How to reproduce
Use a structure block to load the structure contained in
/setblock ~ ~ ~ structure_block{mode:"LOAD",name:"mc-127322:mc-127322",showboundingbox:1}
Place any type of boat on the lowest water level
Ride into the water current
→ ❌ Observe that the player doesn't lose oxygen

Thanks. I've put it into the description of this ticket.
Confirmed for 1.13.2-pre2.
Unable to recreate
boat could not be placed even with datapack.
boat created with /summon couldn't be entered.
This description does not quite follow the standard grammar. Jason, or moderators would you please change it to something like "Sitting in a boat placed underwater gives the player limitless oxygen"?