The Photon-Skiff

In James Blish's The Star Dwellers (London, 1979), the "'...photon-skiff...'" is "'...an interstellar sailing vessel.'" (p. 64) When I googled "photon-skiff," all that came up was two references to Blish's text and no image. When I have published this post, I will have to check whether it comes up as well.

The photon-skiff:

is a very light keel with lugs to hook spacesuits to;

has a mile-long steel cable kept at right angles to the keel by a small inertia-controlled atomic reactor at the far end;

on the cable, a mile-square zirconium foil sail rigged with other small reaction motors by radio control;

in the Coal Sack nebula, will respond to dust squalls, radiation storms, other disturbances, light pressure and slow neutrons.

If that is all that the skiff is, then how does Dr Langer get it to pass the speed of light? (p. 98) Jack, watching, does not understand this and I don't think that he ever finds out?

Later: googling "photon-skiff" with inverted commas brought up only my sentence above, "When I googled 'photon-skiff'..."