As we had no wind today, Ben Kimbell gave us all some top techniques for sailing an asymetric boat downwind. Here are some of the notes that I took from the day (if I've missed anything do let me know and I'll add them in - firstname.lastname@example.org)
Normally the corners of the spinnaker are marked with the Head, Tack and Clew. If they are not then bring all 3 corners together and the head will be the one with the most acute angle of the corner, the tack will be the next and the clew will be the one with the widest angle.
Launching / Dropping:
Launch and drop in the depowered zone (normally about the training run)
When approaching the leeward mark, and you are going to drop the spinnaker, always steer a course that will bring you just short of the mark. This way you can then turn the boat onto a run to efficiently drop spinnaker.
Don’t leave the drop too late, give yourself time so as not to overshoot the mark whilst still dropping the spinnaker.
Apparent wind, spinnakers and sail setting:
Principles to factor: Apparent wind is a factor of induced/head wind (created by the boat moving forward) and true wind (the direction from which the wind is coming).
As the boat increases speed forward the induced wind increases and therefore the apparent wind direction moves forward (closer to the induced wind). As the boat slows down the apparent wind direction moves back (closer to the true wind). Therefore, as the boat increases in speed the sails need to be adjusted, i.e. pulled in, and as the boat slows down the sails need to let out.
However, if we are sailing down-wind then the better option is not to adjust the sail rather adjust the course to cover a shorter distance. Round the mark, set course into the depowered zone and launch the spinnaker. Now head up on to a reach and set the sails. As you gain speed start heading down wind. As the apparent wind has moved further forward with the speed you should not need to adjust the sails. When the boat starts to lose speed head back up to regain the speed. Repeat this keeping speed and minimising the distance sailed to the mark.
The key to a good spinnaker gybe is a factor of speed, small ruder movements, flat boat and slow manoeuvring.
Make sure the boat is travelling quickly, this will minimise the forward pressure on the sails (as the boat is moving its fastest away from the wind direction)
Make sure the boat is flat to ensure the balance is maintained whilst gybing.
Slowly move the tiller with a small amount of movement so the boat turns slowly and smoothly.
As the boat turns let the spinnaker sheets out as the wind moves further to the rear of the boat. When the gybe happens, the spinnaker will now be as far forward as possible (Important: this will ensure it does not get caught on the front of the jib/forestay) now pull on the opposite sheet to bring the spinnaker over to the new side. In the meantime, the helm gybes the main sail when the pressure on the sail drops. Come out of the gibe on a training run then move up wind to gain speed as described in the apparent wind section above.