Everybody with the Nilejamming NWP ( General, Dex-1, 1 slot) can sail a ship.
Nilesails only work in the Nile area, not in the desert sargasso and not in
the outer parts of the sphere.
Planets are of size A, B or C. Most of them earth bodies, round or irregular. Only Ra's planet is larger: E. Both Ra's Manjets are not planetary bodies but avatars of Ra. The nightnile, apparently inside Ra, is extraplanar. The crystal sphere is to half its radius filled with desert sargasso. Only the Nile and some small oasis are normal space.
Desertsargasso has dehydrating effects: all water will be lost in 3 months. Magic will cost 10 liters of water per spell-level located within ten metres. Speljamming cost one ton cargo full of water per day. There are places in the sargasso, so called deep sargasso where the loss of water is even worse.
A Nilesail can move a ship less than 30 tons. A nilesail will cost about 1000
Selket (1 Selket = 1 gp). Nilejamming speed is 1/4 Spelljamming speed when sailing
to the crystal shell and 1/8 when sailing to the centre.
Everybody with the Nilejamming NWP ( General, Dex-1, 1 slot) can sail a ship.
Nilesails only work in the Nile area, not in the desert sargasso and not in
the outer parts of the sphere.