sled, sleigh, (kokuji)
艝 centers on a vehicle that slides over snow: a sled or sleigh. It is a kokuji created for Japanese use, so its meaning is tightly tied to that specific object.
艝 is a kokuji, a character created in Japan. It combines 舟 (boat) and 雪 (snow) to represent a sled or sleigh, a snow-going vessel.
A boat (舟) on snow (雪) is a sled. Picture a wooden boat-shaped sled gliding over snowy hills.
For そり, imagine a sled soaring down a snowy slope: the English word 'soar' sounds like そり, and the sled soars over the snow.