Manipulating the Draft

As already pointed out, spinnakers can be viewed as large, inefficient headsails and as such you might want to manipulate the location of the draft. Again, you can do this by raising or lowering the pole. If you lower the pole it stretches the luff of the sail and in effect pulls the draft forward. Raise it and the draft moves aft. This is a

Figure 115

By bringing the clews of the spinnaker closer together, you can dramatically increase the overall chord depth of the sail. Conversely, moving the clews apart flattens the chord depth.

SPINNAKER FROM THE TOP OF THE MAST

Figure 116

When the apparent wind is aft of 120 to 130 degrees off the bow, keep the pole at right angles to the apparent wind.

Spinnaker Flatter-better for reaching

Pole Angle Less Than 90

Spinnaker Flatter-better for reaching

Pole Angle Less Than 90

Figure 117

When the wind is forward of 120 degrees the angle between the pole and apparent wind direction should be less than 90 degrees in order to flatten the spinnaker.

Figure 117

When the wind is forward of 120 degrees the angle between the pole and apparent wind direction should be less than 90 degrees in order to flatten the spinnaker.

very important adjustment because you are not only moving the point of maximum draft in the sail, but changing the shape of the leading edge of the sail. Earlier in this chapter we discussed how much easier it is to sail with a draft-forward head-sail since the wider angle of entry makes for a much more forgiving sail. The same is true for spinnakers. When you are reaching, having the draft pulled forward by lowering the pole makes it easier for the helmsman to steer the boat without the spinnaker collapsing, although you have to be careful not to put too much fullness in the luff causing it to stall. On the other hand, having the draft slightly aft might allow for better attached flow across the sail (remember that when reaching most of the flow is attached). It might cause the leading edge to be a bit unstable and require more sheet tension to stop it from continually breaking, but if the conditions warrant it, consider raising the pole and dealing with a finer angle of entry.

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