North Solutions:
Demystifying the Asymmetric Spinnaker by Andreas Josenhans, Special Projects Mgr., North Sails
Before defining what the Asymmetric spinnaker is, and how this sail can add to your boats performance, its important to identify what its not.
1. An asymmetric is not "just like a spinnaker..
2. The asymmetric is not used for running dead downwind.
3. The asymmetric does not have a place in every boats inventory.
The asymmetric is a fast, fun; easytofly sail adding exceptional performance to a boat's reaching and broad reaching speed. Before deciding on what type of asymmetric is best suited for your racing or cruising boat, specific characteristics of boat design, sailing angles, and speed enhancement need to be evaluated individually.
Is it a genoa or a spinnaker?
The asymmetric is not new. Rather it has been around for
a very long time, only gaining widespread popularity in the last five years.
Take a walk through any maritime art gallery and view the photos taken
during the mighty era of JBoats, and you will notice sleek hulls carving
through the water powered by oversized "balloon" genoas. These
are the predecessor of the modern asymmetric spinnaker.
It was during the 1970s that the asymmetric resurfaced onboard Intrepid during the Americas Cup defense trials. It was too small for the heavy displacement 12meter on a light reach, but proved devastating in 25 knots of breeze!
At the same time, the Cruising spinnaker" was introduced.
Based on a symmetrical spinnaker with a shortened leech and the tack attached
to the headstay, the sails were usable on a reach but their symmetric,
draftaft shape kept them from being good performers.
'In the late 1970s, Australian 16 foot skiffs accelerated development of asymmetric design. These high speedplaning dinghies flew wireluff chutes called "flatties" from a spinnaker pole. Champion 18 foot skiff sailor, Julian Bethwaite set out to reduce onboard weight by eliminating one crew member. To simplify downwind sail handling, he flew a large asymmetric spinnaker from a long, fixed bowsprit. With no pole to gybe, the flat chute handled like a genes and was perfectly suited for the 45 degree apparent wind angles common in skiff sailing.
In the 1980s North designer Tom Schnackenberg designed a 12meter gennaker for the Australia IVcampaign which proved a winner in the heavy Perth conditions. Dennis Conner liked what he saw and set North Sails to work experimenting with new designs. The result were true reaching asymmetrics that were draft forward and had leeches and luffs that were more vertical in profile...a true genoa/spinnaker hybrid.
Recently, retractablesprit Sport boats have been winning the hearts of sailors, and also caused headaches for local handicappers. Lightweight, and very fast on a reach, the boats demonstrated a weakness in the medium airs, where they could not match the deeper downwind angles of boats flying symmetrical spinnakers. The 1992 Americas Cup was a key to solving this design dilemma.
The 1992 America's Cup course included runs and reaches of varying angles. The reaches put the apparent wind at 45 degrees and demanded true reaching asymmetric shapes, but the runs required a shape that was totally different. The crossover area between the asymmetric and symmetric spinnakers was the focus of much testing. The narrow, slippery hulls of the new IACC class could sail fast at deeper reaching angles, requiring asymmetries to have more luff projection, sometimes called Luff "positive".
North Sails designer Dave Hirsch, explains: "To get projection, the sail requires a longer luff, shorter foot and leech, widening and adding depth to the upper sections, and moving the draft aft. This allows the trimmers to ease the sheet so the sail can rotate to weather. This development has found its way into the sport boat classes, effectively narrowing their window of vulnerability in medium air".
CHOOSING THE RIGHT ASYMMETRIC
Asymmetrics are designed to boost reaching and offwind performance in both racing and cruising boats. Sailing offthewind faster is fun for everybody. Before you buy, look at your type of sailing.
Racing. The rule you race under will be a determining factor in sail selection. In IMS, one asymmetric is allowed to complement a selection of symmetric spinnakers. Some sport boat classes, such as the Melges 30 allow two asymmetries. The Mumm 30 class allows 1 masthead asymmetric, 1 masthead symmetric and 1 fractional sail (either symmetric or asymmetric). The type of asymmetric you chose will depend on the wind range and points of sail it must cover in consort with the rest of your inventory.
If you race PHRF, consider whether the addition of an asymmetric will alter your rating. If you add a "J+" length pole, expect your rating to change. Equally important are boat characteristics, rig setup and crew handling. If your rig is setup to carry a "J" length pole, check the distance between the headstay and the luff of the asymmetric.
IMPORTANT: The narrower the slot, the tougher it will be to gybe, which places a premium on boat handling and crew work.
The benefits of an asymmetric in your inventory should also take into account how often you would use the sail. Remember, an effective sail is designed for specific wind angles (maximum band is generally 35° AWA) and the choice of sail cloth determines the maximum wind range where it can be flown. There may be specific boats where the tradeoffs are not enough to warrant the addition of an asymmetric. You may be better served by a flatter, reaching symmetric spinnaker (AP Reacher) which may be more familiar to handle and usable over a broader range of wind angles.
Cruising. North's Cruising asymmetries are called Gennakers", and they come in two basic types. First is the all purpose reaching Gennaker, designed to be forgiving, effective over a wide range of wind angles, and easy to fly with a minimum of spinnaker trimming experience. Second is a larger, fuller, "runner" mold called the TrueMax". The TrueMax is designed to perform well at deeper wind angles. With the addition of a Snuffer, a retractable sleeve that pulls down over the Gennaker, setting and dousing is easier and safer, especially for shorthanded crews.
Following are three different shapes (molds) that are the most commonly used racing asymmetries depending on the AWA (apparent wind angle), wind strength and sea conditions.
From the early days of 12 meters to modem sport boats, North has built more asymmetries and invested more resources in asymmetric R&D than any other sailmaker in the world.
RACING ASYMMETRIC SPINNAKER SELECTION GUIDE
· Screacher
Design: The Screacher is a dual purpose asymmetric which can also serve as a heavy air reacher. It is smaller and fairly flat, often used to 'heat up' speed on tight reaches. Area is about 65% of maximum size.
AWA: Starts at 40° to 50°
Recommended cloth: .85 poly or light mylar
· AP Reacher
Design: Slightly fuller and larger than the Screacher. A true reaching asymmetric especially well suited for pointtopoint racing. Area is 8085% of maximum size.
AWA: From 50° to 75°
Recommended cloth: Fabric should be 2 weights with stronger cloth in the luff. For inshore sailing, either .6 /.5 polyester or .85 /.6 poly for larger boats. For offshore sailing where sea conditions are rougher, nylon is recommended
· MaxRunner
Design: Maximum girth
in the head helps sail rotate to windward out from under the main. Can
also be set wingandwing with the main. Well suited for windwardleeward
courses where boats will sail deeper downwind angles.
AWA: 95° to 150°
Recommended cloth: Polyester
for inshore racing and added longevity.