Moving around while not at speed is killing for boatspeed.
With light wind it is important to always move around very carefully (like walking on eggs!), probably even more so on the F16 than F18.
Although that counts mainly for going upwind it is something to keep in mind in general.

Try to get as much weight forward, when crewing I usually sit on the frontbeam (same goes for the helm).

On the Tiger the spin blocks are on the tramp between the shroud and the frontbeam.
Generally that position is fine for most conditions but in light winds I keep the sheet in
hand and push it down on the front beam, that way there is less twist but quite a bit more pressure.
You could also try experimenting with an adjustable barberhauler like some F18s have.