无论有无引航员，船舶均可自由航行、拖带或被拖带。
The Vessel shall have the liberty to sail with or without pilots, to tow and to be towed.
有一些与船只绑定，另一些则如同微型潜水艇一样自由航行，但也是需要有供给船只服务的。
Some are tethered to ships, whereas others are cast free to operate like miniature submarines, although these too need the services of a support vessel.
至此，离子通向太空的单程旅行前的最后一步开始了，这就是沿着地球磁场自由航行。
This is when the last stage of their one-way trip into space begins: sailing along the magnetic field of the Earth.
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