Tradecraft topics: Heavy air technique

Next in a series of postings on sailing tradecraft, offering various tips on technique, is the timely topic for spring of 2025 (!) of heavy air technique.  When the true windspeed exceeds about 15 knots, Volant and most sloops are overpowered and cannot use all the wind force for propulsion.  It's critical to keep the boat on her feet, that is, manage weather helm (limit the amount of speed-robbing hydrodynamic drag), and heel angle (excessive heel causes leeway and compromises upwind performance).    

Ummm, might not want to go sailing!

A few definitions we need:

• Apparent wind angle - The angle between the wind direction and the boat's longitudinal axis when the boat is moving.  If you were traveling at 2 knots and the wind was blowing directly from your right at 15 knots, you would feel the wind almost directly from the right.  If you sped up to 15 knots, the wind would feel about 45 degrees to the right.  If you sped up to 100 knots, the wind would feel almost directly ahead, not from the right.  You are feeling apparent wind, the combined vector of windspeed and boatspeed.   
• Weather helm - The amount of force on the helm to keep the rudder turned to leeward to prevent the boat from turning up into the wind.
• Heel angle - The amount of tilt from horizontal.  Note that as heel increases, more of the leeward side of the boat is in the water compared to the windward side.  This increases the waterline length on the lee side, which induces turning force to windward.  Try this in your kayak or canoe when moving ahead in a straight line - lean to the right and your boat turns to the left.
• Leeway - The amount of distance that the boat slips downwind as the keel and rudder lose lift.  The slippage means that your course is not the same as your heading - the direction the boat is pointing.  
• Chordline - Straight line from luff to leech of a sail.
• Draft - The curve of a sail from luff to leech.  The deepest draft is the point of maximum camber, typically located 40-50% aft of the luff of the sail's width at that point.
• Angle of attack - Angle between the chordline of a sail and the apparent wind angle.
• Twist - The difference in angle of attack in a sail's shape from top to bottom.  Tighter leech = less twist;  looser leech = more twist.
• Center of effort - The point on a sail plan where the wind forces are balanced forward and aft.  On a sloop, this point is generally in line vertically with the center of the keel, just aft of the mast. 
• Broach - Sometimes called a round-up or wipe out, the boat loses rudder authority for steering and turns up into the wind out of control.  This can be caused by mainsail sheeted too tight, spinnaker momentarily collapsing, rudder exposed from overtaking waves, or a big wave pushing the stern downwind.
  
  

The goal in heavy air is to depower the sail plan, open the angle of attack to handle waves, induce twist in the sails, and keep the boat balanced.  Here's how...  

HEADSAIL TRIM

Wind force on the jib or genoa forward of the center of effort pushes the bow down and helps prevent the boat from turning up into the wind.  So, while the mainsail trim moderates weather helm and heel angle, the headsail needs to work hard.  Flatten the sail and move the draft forward with tight halyard.  Tight backstay will reduce sag in the headstay and flatten the headsail.  Sheet very hard, but don't push the sail into the spreaders.  The inhaulers should generally be eased because reduced angle of attack is more important than pointing ability.  If wind force is too strong, moderate the power in the jib by moving the fairleads aft to open the leech, twisting off the top of the sail to spill some wind.  The top telltales will then break before the middle and bottom telltales. 

MAINSAIL TRIM

Flatten the mainsail aggressively with tight halyard and cunningham, tight outhaul, tight backstay, tight mainsheet.  If the mainsail is reefed, the cunningham and outhaul cannot be used.  There should be no horizontal wrinkles in the luff, and no angled wrinkles from luff to clew that indicate excessive mast bend.  Move the traveler to leeward to open the angle of attack and depower the sail.  Top telltale on the leech should be stalled behind the sail 75% of the time.  Manage constant heel angle of less than approximately 22 degrees with traveler and then sheet.  If wind power is still too great, induce twist in the mainsail by bringing the traveler slightly up to windward and easing mainsheet.  Do not let more than one-third of the sail luff from the force of wind off the headsail.  When sailing downwind, the challenge is to ease the mainsail without the material folding around the spreaders.  Ease the outhaul to reduce sail area.  Tension the boom vang to prevent the boom from rising and dumping air.  If the rudder gets light and a broach is imminent, spill the boom vang completely.  As you can see, the mainsail trimmer basically drives the boat upwind in heavy air.  

SPINNAKER TRIM

Surfing down waves in a sailboat flying a kite in big breeze is exciting, and a bit risky!  The spin trimmer and helmsperson must be a tight partnership.  Spin trimmer communicates the degree of pressure in the sail and directs the helm to head up when light and head down when heavy.  Trimming to a nearly constant luff curl is fast.  Another crew should be looking aft and report oncoming waves.  Helmsperson communicates when the rudder is losing authority, often when it lifts out of the water from overtaking waves, and steering down can avoid a broach.  When steering down, spin trimmer eases the sheet; when steering up, trimmer trims the sheet.  If the boat seems to be rounding up, resist the temptation of easing the spin sheet.  Trim instead.  The spinnaker is the only force forward of the center of effort keeping the boat from broaching.  If the true wind angle is fairly high, set the tweaker on the spinnaker sheet and bring the clew down to near the deck.  This reduces exposure of the spinnaker and keeps it better in control.   

STEERING

Steering is by reference to the headsail telltales, as usual, but also in reference to waves.  Pointing mode is rarely effective in heavy air.  Adopt press mode to power through big waves, with windward and leeward telltales streaming.  See this post about shifting gears.  Steer up the crests to minimize time climbing; steer off the troughs to stay on the wave downslope longer and build speed back up.  To get extra height and moderate the wind power, it may be necessary to feather up into pinch mode, with windward telltales lifting 75% of the time. 

BALANCE

Crew weight placement is very significant in heavy air.  Sailing upwind, crew should be hiking hard and positioned somewhat aft of amidship so that the bow is not diving into the waves.  Sailing downwind, crew should be all the way aft to keep the boat from submarining, and on whichever side keeps the boat relatively flat.  In preparation for a tack, only the jib trimmer should come off the rail and be ready to release the jib sheet from the leeward primary winch.  If more crew come to the middle of the boat before the boat turns, heel could increase by 10 or even 20 degrees, risking a big build-up of weather helm or even a broach.