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Spinnaker Dimensions Every Sailor Should Know

Spinnaker Dimensions Every Sailor Should Know

The two types of spinnakers that we use on our boats (symmetrical and asymmetrical) both have a substantial width (girth), which allows then to propel the boat when reaching/running. It is because of this characteristic that the two types have been placed in the same category. Apart from the fact that they are both very wide, the two types of spinnakers are quite different. A symmetrical spinnaker has no defined tack or clew, while an asymmetrical one has three distinct corners, i.e., the Head, the Tack and the Clew.  Boat owners therefore need to be familiar with specific dimensions for both types of spinnakers. These dimensions are going to be used for ordering a new spinnaker, putting together a selection of spinnakers according to your type of sailing, and complying with racing regulations.

To Order a New One

spinnaker dimensions every sailor should know

If you need to order a new spinnaker, you can simply measure an existing one. All measurements should be taken with the sail under sufficient tension to remove all wrinkles, but you need to make sure that the sail cloth is not stretched. However, you might not have your old spinnaker at hand, or you might want to order more spinnakers in order to have a selection of them on your boat. This will allow you to choose the spinnaker that is best suited for the current weather conditions. The availability and quality of crew is also a factor to consider: for example, using a symmetrical spinnaker will not be possible without sufficient and competent crew.  If you are ordering spinnakers that are different from your existing ones, you will need to provide your sailmaker with the following dimensions.

For a symmetrical and asymmetrical spinnakers:

  • Measure the max hoist.
  • Measure the tack to sheeting block (or bow for symmetric spinnakers)

Read our new spinnaker measurement guide here.

If You Are into Racing

  You need to know the following dimensions of your spinnaker in you take part in races (according to PHRF). The measurements should be taken of your largest symmetrical spinnaker and largest asymmetrical spinnaker.

Three dimensions are needed for a symmetrical spinnaker:

  • Max girth (MG). When the spinnaker is folded in half, the MG is twice the maximum width of the sail measured from the center fold of the sail to the luff and leech.
  • Luff length (LL) is the distance from the projected intersection of the luff and foot with the luff line under moderate tension.
  • Foot (SF) is the distance from the tack to the clew measured in the shortest path on the surface of the sail.

asymmetric spinnaker dimensions diagramFour dimensions are needed for an asymmetrical spinnaker:

  • Asymmetrical spinnaker Mid Girth (AMG) which is measured from mid luff to mid leech under moderate tension.
  • Luff length (SL or LL) is the distance from the projected intersection of the luff and foot with the luff line under moderate tension.
  • Leech length (LE) is the distance from the projected intersection of the leech and foot with line under moderate tension.
  • Foot is the distance from the tack to the clew measured in the shortest path on the surface of the sail.

Dimensions Needed for Calculating Spinnaker Area

Knowing the area of your largest symmetrical and asymmetrical spinnaker is necessary for obtaining a rating certificate. It might also enable you to feel more in control of your sailing and improve the planning of your sailing.

The following dimensions are needed to calculate the spinnaker area:

For a symmetrical spinnaker:

  • SLE, or Spinnaker Leech.
  • SLU, or Spinnaker Luff (same as SLE for a symmetrical spinnaker).
  • SHW, or Spinnaker Half Width.
  • SF, or Spinnaker Foot.

For an asymmetrical spinnaker:

  • SLE, or Spinnaker Leech.
  • SLU, of Spinnaker Luff.
  • SHW, or Spinnaker Half Width (distance from mid-point luff to mid-point leech).

The following formula is used for a basic calculation of the spinnaker area:

(SL x(SHW+SF)/2 x 0.95.

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