724. A Rock in the Sea

Shabbos 16:2

If a surface is raised more than ten handbreadths (about 30”) above the ground and its area is the size necessary to plant two seah of seed (seven gallons) or less, one may carry on the entire surface. If the area exceeds the space need to plant two seah, one may only carry within four cubits (six feet). If a rock in the sea is less than ten handbreadths high, one may carry from it to the water and vice versa because it is all a carmelis. If the rock is ten handbreadths high and its area is from four handbreadths by four handbreadths (1’x1’) to a space sufficient to plant two seah of sea, one may not carry between the rock and the water. This is a rabbinic safeguard because it is permitted to carry on the rock itself. If its area is larger than needed to plant two seah, one may not carry more than four cubits on the rock even though it is a private domain. One may, however, transport items between the rock and the sea; this is such an unusual situation that the Sages did not legislate regarding it.

Shabbos 16:3

The area in which a seah of seed can be planted is fifty cubits by fifty cubits (about 75’x75’). Therefore, the area to plant two seah is 5,000 square cubits (about 11,250 square feet). The same measure is used whether the area is a square a little over 70 cubits on each side, a circle, or any other shape. Any area this size is deemed sufficient to plant two seah of seed.