21a - Is without a small amount of support (5) ?O???
11d - Startle when vehicle is caught in a strong wind (9) I though this could be Galvanise, with "van" being the vehicle and Galise as a wind....but I'm thinking I'm making that up as I can't confirm it, I have ?A?V?N??? (second last letter is also second last letter of 21a
20d - A small amount of fish (3) I think the middle letter is A!!