Symmetric, asymmetric and code zero
1The lesson in plain words
Downwind sails are big, light and powerful. A symmetric spinnaker flies from a pole; an asymmetric or gennaker is tacked at the bow; a code zero is for close reaching.
Symmetric spinnaker
A symmetric spinnaker is a large, balloon-shaped sail with two matching side edges. It is flown from a spinnaker pole clipped to the mast. The windward corner sits at the pole end, controlled by the guy (US: afterguy). The leeward corner is trimmed by the sheet. A topping lift holds the pole up and a downhaul (foreguy) holds it down. It suits broad reaches and runs.
Asymmetric spinnaker
An asymmetric spinnaker has a longer luff (front edge) than leech (rear edge). Its tack (front lower corner) is held by a tack line at the bow or on a bowsprit, a spar projecting ahead of the bow. No pole is needed. Two sheets trim it, one each side. It suits reaches and broad reaches. When flown to leeward on a dead run, it is usually blanketed by the main. Broad reaches linked by gybes often keep it drawing better.
Gennaker and code zero
Gennaker is a common cruising name for an asymmetric, often a flatter, all-purpose cut. A code zero is a flat, light reaching sail with a tight luff, usually set on its own furler at the bow. It is for close reaching in light to moderate winds, at apparent wind angles from roughly 40° to about 100°. It is not a running sail.
Wind ranges
Use each sailmaker's wind-speed and angle chart, checking whether values are true or apparent. Symmetric and asymmetric spinnakers have different ratings for light, moderate or stronger winds; their shape alone does not tell you the limit. A cruising gennaker commonly suits light to moderate winds; a code zero mainly suits light-air reaching. Stay within your particular sail's chart and drop early in rising gusts.
Choosing
For a cruising crew, an asymmetric in a snuffer (a sleeve pulled over the sail) is often easiest to handle. A furling code zero suits light-wind reaching. A symmetric sails deeper but needs more crew coordination. Choose for your usual wind angles, your sail's limits and the crew available.
2Key data
- Symmetric spinnaker
- Pole, guy, sheet, topping lift, downhaul; best running
- Asymmetric / gennaker
- Tack line at bow or bowsprit, two sheets; best reaching
- Code zero
- Flat, on its own furler; close reaching, roughly 40–100° apparent
- Wind range
- Sailmaker's speed and angle chart; check true or apparent wind
3Key points
- 1
A symmetric spinnaker flies from a pole: guy to windward, sheet to leeward.
- 2
An asymmetric has its tack fixed at the bow or bowsprit and needs no pole.
- 3
Broad reaches linked by gybes usually keep an asymmetric drawing better than a dead run to leeward of the main.
- 4
A code zero is a flat reaching sail on a furler, not a running sail.
- 5
Know each sail's maximum wind speed and drop before it.
4Frequent mistakes
Wrong: An asymmetric always draws well to leeward on a dead run.
Right: The main commonly blankets it there. Broad reaches and gybes often keep it drawing more reliably.
Wrong: A code zero is a light-wind run sail.
Right: It is a flat reaching sail for close reaching. Deeper angles need an asymmetric or symmetric spinnaker.
5Practice case & exam keys
A couple cruising a 12 m yacht want a light-wind sail for long trade-wind passages, mostly at 120–150° apparent wind angle. They have no spinnaker pole and do not want one.
Show the answer
A cruising asymmetric cut for deep reaching, in a snuffer, suits them. It needs no pole, uses two sheets and a tack line, and works well on broad reaches. They can gybe downwind when the wind is dead astern. A conventional code zero is intended for shallower apparent angles.
Exam keys
- Symmetric: pole, guy, sheet, topping lift, downhaul.
- Asymmetric: tack at bow/bowsprit, two sheets, no pole; best on reaches.
- Code zero: flat reaching sail on a furler.
- Respect each sail's maximum wind speed.
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