there's a mob called a shulker that teleports whenever it's hurt
i summoned a shulker and spawned a slab of material on it
since the material overlaps it, it gets suffocated and teleports
then i spawn another slab so it builds a shape
in the first stage of generation i used long flat horizontal slabs
in the second i used the same slabs, but vertically oriented
in the third, i made the shulkers put small 3x3 blocks of glass all over it to smooth it before making them convert the glass into stone
then in the fourth i did the same, but with finer 1x1x1 blocks
then i poured water all over it using endermen, using the same trick but with spawning water on them
then i shifted the water back into stone to smooth the hull out from the jagged mess it was before
then i copied the smoothed parts to a separate shape, and picked the parts i wanted to use in the final ship

after i did that, i converted the entire hull to bricks
then i used the same shulker trick with a small replace radius to make the external hull into stone
then i made the shulkers convert bricks into air in a wide radius to hollow out the interior

once i did that, i used a different trick with a command that spreads entities over xz but not y values to cover the entire top of the hull in snow