4 steps to sail downwind like a pro
Okay, really there are 5 but the first one is more like homework, you do it before you go sailing; Know Your Targets! If you want to sail downwind efficiently you have to know the target speed and target wind angles you should be sailing for different wind speeds. With luck you can get these numbers from the designer of your boat or from US Sailing if your boat, or one of the same design, has been rated for ORR. Without one of those options you may be able to find targets for a very similar boat you can use as a starting point and modify over time as you collect real data from sailing your boat; or you may have to totally develop your own by observing and recording your performance over time. In the absence of tactical decisions you will ALWAYS sail downwind faster if you sail your targets!
Step 1: Choose the side of the course you want to sail towards initially before you get to the weather mark. If the wind is oscillating you should know if the wind is in a left phase of a right phase as you approach the weather mark. If the wind is to the left of average you will be expecting the next shift to be to the right, so with a normal port rounding on starboard tack you will be sailing towards the left side of the course (I always look at side of the course relative to upwind so downwind you may be sailing towards your right side but it is still the left side of the course, this makes it easier and more consistent to view the wind shifts). This means you will be sailing towards a lift which will allow you to gybe over sooner and sail a header to the leeward mark. Once you have chosen which way you want to go after the weather mark that will make your decision on what type of spinnaker set you want to do. The options are a normal bear away if you want to continue on the same tack, or a gybe set if getting to the other side of the course is called for. If you want to get to the other side you have two options; the classic gybe set or a normal set followed quickly by a gybe. A normal set and gybe are quicker than a gybe set if there aren’t other boats close by that could gybe inside of you, or if it isn’t necessary to get to the other side of the course immediately.
Your rounding leads into Step 2, Controlling you Competition. On a downwind leg the tactical advantage goes to the boat behind, the wind shadow and its use are powerful tools. In a bear away set, if there are other boats around, you usually want to get deep quickly by sailing very low during the set. This will gain you control of boats that have rounded just in front of you because they won’t be able to gybe until you do, and it will defend your lane from boats behind so that they can’t get inside and prevent you from gybing when you want to. If you are behind and can keep the boat in front from gybing you can hold them there until you are on the layline for the leeward mark. When you both gybe for the mark they will be behind your wind shadow and you will be able to sail down in front of them. To make this most effective you have time your gybe to get maximum benefit from your wind shadow. If possible you want to sail just slightly passed the layline so that the boat in front has no chance to gybe back away to find clear air. As you approach the leeward mark if there is other traffic around it is best to plan your approach to be on the inside at the mark rounding, with port roundings this will also set you up to be on starboard tack at the mark. As when sailing upwind there will be crossing situations with other boats. In each case you want to force the other boat to sail towards the un-favored side of the course while you sail towards the favored side
Step 3: Sailing downwind the rule is the opposite of sailing upwind, you always want to be sailing on the headed course towards the next lift. Upwind you tack on headers, downwind you gybe on lifts. Just like sailing upwind you also have to be aware of persistent shifts, current, and wind pressure in making your decisions. After sailing the initial upwind leg you should have a good feel for what the wind and current are doing; is the wind oscillating back and forth or is it consistently shifting in one direction. In oscillating shifts you want to gybe on the lifts so you are always sailing on the header. In a persistent shift you want to sail towards the lift but sail into it far enough so that when you gybe you will be close to the layline and will still gain on any further shift as you get headed down to the mark. If you sail too close to the layline and there is any further shift you will risk overstanding and losing distance to the boats that gybe inside of you.
Step 4: For a downwind finish pick the favored end of the line for finishing and sail dead downwind the last few boat lengths to the finish line. If the race committee has not changed the line since the start you can calculate which end is favored by comparing the wind direction to the wind direction prior to the start. Since you knew the wind direction and compass heading of the line before you stated you can now check to see if the wind is to the left or to the right of perpendicular to the line. If the wind is to the right you want to finish at the starboard end (on your left as you look at it approaching downwind) of the line because it will be further upwind, if the wind is to the left of perpendicular to the line you want to finish at the port end. If the finish line is different than the starting line the best technique is to gybe so that you are heading directly for the weather end of the line while sailing your optimal angle. As you approach the point where you could gybe and just lay the leeward end you can judge which end is closer to you at that moment. In a downwind finish the same end that would be favored for a start is favored for the finish. Unless you are sailing dead downwind your boat speed through the water will always be greater than your optimal VMG. As you approach the finish line you will generally be sailing at some angle to it. Set up your final approach so that as you get near you can turn down directly perpendicular the line to shorten the distance you have to sail. This will allow you to sail shortest distance to the line and you will initially be sailing faster than your optimal VMG. Your boat speed will bleed off slowly so you want to time your turndown so that as you cross the line your boat speed has slowed to the point that it matches your optimal VMG.