by Daniel Martinez and Michael Argyelan
This article is intended to focus on the basics of asymmetrical spinnaker trim once the sail is hoisted and drawing. Each boat will have different requirements for rigging and different considerations for maneuvers, so we will keep this general. If you have specific questions about your boat, shoot us an email and we’ll do our best to point you in the right direction.
Asymmetrical spinnakers are much simpler than symmetrical kites and for that reason are a great option for cruisers and racers alike. For cruisers, sure, you can “set it and forget it,” but you can get to the bar an hour earlier if you put in a little effort. Here are a few tricks to get you out there having more fun and take out some of the guess work.
While there are different cuts of asymmetrical spinnakers, many are cut to be versatile across wind ranges and downwind angles. You may notice a large curved panel along the luff of the sail. That panel is to allow the sail to roll out to windward on a deep downwind reach to escape the wind shadow of the main, but may look ugly when trimming the sail for a hot reach. Sails without such a large luff may have difficulty sailing low, but will have a more efficient flow and more stable curl at higher angles.
Now what angle do we sail? In lighter breeze, boats like to sail higher angles, closer to a beam reach in order to keep the apparent wind moving through the rig. If you sail too low in light breeze, your boat will outrun the sails and backwind the sail. While it may feel counterproductive to sail a hot angle when your destination is downwind of you, consider that using an asymmetrical spinnaker downwind is just like tacking upwind except that you’re jibing. It’s faster to keep the boat moving and throw in a few extra maneuvers than to pinch your way to a standstill.
We now know our general angle, but do we have to sail straight? Absolutely not! Downwind driving with an asymmetrical spinnaker should follow a gentle S-turn. Head up until your rig begins to load up and the luff of the spinnaker begins curling. Then bear away slightly and carry your momentum down until the boat begins to feel light or slow down, then head back up. The sailing in the middle of this S-curve is your “groove”. How wide your “groove” is depends on your trim.
The general rule of spinnaker trim is to ease the sheet until you see a curl in the luff, then hold there. If the curl begins to grow and threaten to collapse the sail, trim in until it stabilizes. How much curl you want to have depends on the sail, angle and speed of the boat. Generally we find that healthy curl is about 1-1.5’ of luff folding in, but if the sail is trying to collapse a lot, reduce the amount of curl by trimming on more sheet.
There are other control lines as well. One of the most often undervalued is the tack line. Tack line adjustment is key to adjusting the shape, and even location, of the sail. On a deep downwind run with healthy breeze, an ease in the tack line will allow the sail to fly up and to windward of the rig, allowing it to catch more breeze and also helping move the center of effort of the kite further to windward to help the boat balance and carve its own path downwind. When reaching hard upwind, the tack line should be completely taut in order to stretch out and stabilize the luff of the sail.
The other control line, and one that should be avoided until necessary, is a twing. Not all asymmetricals are rigged with twings, but when the waves get big and the sail trim gets fluky, a little tension (think an inch or two) on the twing will help steady the sail. Don’t get greedy on the twing, because cranking it all the way down will close the slot between the kite and the main, backwind the main and seriously unbalance your driver.
Try these steps and keep a close eye on your speedometer. Notice the speed differences you see when heading up to the top of your groove and see how far you can continue carrying speed when you press down. Eventually you’ll find exactly how high you need to go to get the acceleration, and just how far down you can push it before you slow down too much.