May a ship still turn after doing the adjust speed manoeuvre?

Because if yes it makes the adjust speed & bearing a bit useless in the case of slowing down, because a ship could slow down to 0 and turn on the spot. While if it is using the combined manoevre, the restriction of both parts apply, wich as far as I understand means the ship has to move atleast 1VU before turning.

If it may not move, would a failed roll still default to the basic move maneuvre?

Thanks for any answers!

This is a good question. The way we play it is that you always get to turn after your movement, but your question made me wonder if this is true with the adjust speed. But reading the adjust bearing it says that you need to move 1 UV before turning, so I would say that if you choose not to move at all with the adjust speed, you shouldn't be allowed to turn either. That much is clear to me.

And a failed roll always default to either version of the default manoeuvre.

With Adjust Speed you can indeed turn on the spot, but you cannot move after turning. With Adjust Speed & Bearing you must move at least 1 VU, may turn then and may then move the remaining numbers of VU according to your speed which may again be modified by your success on the Piloting test.