Downwind Technique (by Michael Johnson)

It is my opinion that sailing downwind fast is mostly a function of finesse (anticipation, body mechanics, steering, wave placement, S turning, …) combined with the proper setup of the rig and sail trim to provide maximum power. Because of the huge importance of finesse, much has been written about this and not much (that I could find) has been written about downwind rig tune and sail trim. This article will attempt to lay some groundwork for proper rig setup and sail trim for maximum power downwind. It is by no means authoritative and I believe there are many debatable topics in this area.  

Rather than try to cover all wind and wave conditions, I’ve decided to focus only on conditions where surfing or planning is possible (>12 knots of wind and >1 ft sea). Many of the concepts discussed also apply in light wind, however going through all the exceptions would dilute the central theme.  Please keep this caveat in mind. There are several commonly used terms that I feel require a definition so when they are used the context is clear.

Twist

Twist is the curve the leech takes when the sail is under load. Twist is sometimes measured by a comparison in the angle of the top batten relative to the boom. For example, zero twist is when the top batten is parallel to the boom. Twist can also be measured by comparing the relative angles of each batten to one another. When going downwind the twist is mostly controlled with boom vang tension.

Active Leech

As the sail loads up due to a puff or added resistance from stuffing the bow into a wave, the upper roach will fall off and create twist. When the sail unloads after the puff, the roach oscillates back to the neutral position. When the leech is said to be “active” it will easily oscillate about the neutral position without any help from body kinetics or pumping the main sheet. Michael Blackburn uses these words to describe the concept: “The leech should move 2 to 3 foot of its own accord”.  Andy Vance says the leech should be “springy”. This natural action can be easily mistaken by a judge as “leech flick” if the motion appears to be rhythmically timed with body movement or mainsheet pumps. Watch the following video clip to see Robert Sheidt demonstrating this concept (fast fwd to 2:15).    

Velocity Made Good (VMG)

When sailing a course other than straight downwind your boat speed vector can be broken into two components: (1) dead downwind; and (2) perpendicular to dead downwind. VMG is the magnitude of component (1). If you luff to a beam reach, your VMG drops to zero. This concept is important when considering whether to momentarily sacrifice VMG to go after a wave that may result in a ride that provides double the VMG if you just remained on the downwind course.      

Sail Trim

Remember the caveat that this guide only applies when surfing conditions exist. When approaching the windward mark it is most common to adjust the cunningham, outhaul, and vang for the conditions expected on the next leg. Once on the run it is uncommon to adjust the trim of any control other than the mainsheet and the tiller. The only exception to this is after a significant change to the wind (velocity or direction). Given this assumption, it is critical to set the cunningham, outhaul, and vang properly to get the maximum thrust from the sail. Here is a discussion of each setting along with my rules of thumb.    

Cunningham

Pretty simple. All the way off in all but very high wind. End of story.

Outhaul

The outhaul and vang settings share a symbiotic relationship. If the vang setting is left alone as you ease the outhaul, the foot moves toward the mast and the leech tension will decrease and create twist. To achieve an active leech, it is critical to match the outhaul setting with a correct vang setting. At the 2000 Cancun Master Worlds I arrived two days early and watched the finals of the Senior Worlds. Scheidt, Ainsle, Blackburn, Suneson, Mendleblatt, Stoffelsma and many other downwind maestros were 4 months away from the Sydney Olympics and we had 12 to 18 knots with 2 to 3 ft seas in water that looked like a very clean swimming pool. It was downwind heaven. I walked around the beach one morning and noticed that almost every boat had a similar outhaul rig. This was in the days when the outhaul was cleated on the boom and the purchase was achieved by wrapping the tail around the mast and back to several thimbles. I noticed that when every outhaul was eased all the way to the knot (handle) the clew grommet was always about 9 to 10 inches from the fairlead on the boom. Watching the Gold fleet round the weather mark, every boat eased the outhaul so the knot went all the way to the thimble and thus the 9 to 10” setting. After seeing this I conclude the optimum setting for almost all times when surfing and planning conditions exist is having the clew grommet 9 to 10” from the fairlead. When in Rome…

Boom Vang

Similar to the symbiotic relationship described above, the vang and the mainsheet also share a symbiotic relationship. Given a standard outhaul setting as stated above, the optimum vang setting to achieve the active leech concept will vary slightly depending on the wind and sea state. It has been said that the top and middle battens should be kept parallel to one another and also kept 90 degrees to the boats centerline. Not enough vang tension will create a situation where the top batten is slightly more twisted than the middle batten. Too much vang tension will create a situation where the leech will not react to a load / unload and therefore will be “inactive”. The optimum vang setting to achieve an active leech is somewhere between these extremes and necessitates finding the optimum amount of twist.

My theory is that between 8 to 18 knots of breeze, one vang setting can do the job. This “one size fits all” setting is probably not what the pro sailors would subscribe to, however I have found it to be just fine for providing an active leech through this wind range.  This theory assumes that the main sheet performs the fine tune and the vang the coarse tune, thus the symbiosis between these two settings. For those that do not subscribe to this theory, I’d like to hear yours.  Most of the sailors who are much better than I rely on “time in the boat” and “feel” which is not very helpful to us weekend warriors. 

I recommend placing a stopper knot in the vang tail so at the windward mark all that is required is to un-cleat it and let it run to the stop knot. In the upper wind ranges (> 18 kts) it will be necessary to pull the line in a few inches to limit twist. To determine where to put the stopper knot here is a procedure I use:

1. Attach the vang to the mast and boom. Put the boom in the gooseneck and lift the end of the boom until the vang purchases goes tight.
2. Put the sail on the mast.
3. Grab the clew in one hand and the end of the boom in the other.
4. Pull down and aft on the sails leech (without bending the mast) and lift up on the boom (without bending the boom).
5. The vang stopper knot should be adjusted so the clew grommet is about 4-5 inches above the top of the boom.
6. When you get a new sail (not yet stretched) it may be necessary to adjust the stopper knot if you have previously been using a relatively blown out sail.
7. Steps 1 to 6 should get you in the ball park and may require some fine tuning to achieve the ultimate “active leech”. This procedure sets the position of the stopper knot so that when fully eased the vang is in its loosest setting.  This vang setting is much looser than most people sailed with in the 80’s and 90’s so if you are returning to the Laser you may want to keep this in mind.  

Mainsheet

As stated earlier, the mainsheet trim shares a symbiotic relationship with the vang setting. While the vang is set to achieve an active leech, the main sheet is used to keep the top two battens perpendicular to the boat centerline. As wind speed increases the average load on the sail increases, and therefore the twist increases. This requires that the boom always be trimmed at an angle less than 90 degrees to the centerline.

To keep things simple and allow the majority of focus to be on the finesse aspects of downwind sailing, I placed a mark on my main sheet that is 25 ft-6 in. from the end that ties to the becket block on the boom. When this mark aligns with the forward boom block I am at my neutral position for sailing dead downwind in the 8 to 18 knot wind range. This is only true given the previous discussion of the outhaul and vang settings and the symbiotic relationships. While this is another “one size fits all” theory, it is not something that I think should be rigidly adhered to. Since the main sheet is in your hand, the mark is helpful to keep the sail at near its optimum trim and not be grossly out of trim.

When sailing by the lee the mark is eased 8 to 12 inches and similarly when heating up it is tighter by 8 to 12 inches. The mark may need to be moved slightly to match your style; however I suggest the 25’6” as a starting point. My hope is that this guide will stimulate some experimentation and fine-tuning of your own style. There are many theories on what is fast and what is not. One irrefutable fact is that time in the boat (TIB) will do the most to improve your downwind performance. Sailing the 27 mile downwinder from Cascade Locks to Hood River, OR is an excellent experimental area. 

Good sailing — Michael Johnson.