Here we’ll discuss sailing the boat and making decisions on the fly while racing to improve your performance. In this article we are going to keep it simple and focus on upwind sailing. Changes here are more straightforward. Developing good downwind speed in more a matter of developing the right technique rather than boat set up and trim.

Understanding apparent wind

Most of us understand that the movement of a boat through water and in turn through the oncoming flow of the wind creates apparent wind. This is the wind the sails actually “see”. Apparent wind is always forward of the true wind and can easily diagrammed with vectors. The stronger the wind or the faster the boat travels the more forward the apparent wind will be.

Affect of waves and/or puffs

Unless you sail on a very small lake or a very enclosed body of water all boats are affected by waves and more so as the wind and fetch increases. It is important to realize that as the hull moves through the waves the mast and sails that are attached to it are moving too, sometimes by many feet in a very few seconds. All this has a huge affect on the apparent wind the sails see.

As the boat goes up the face of a wave, the tip of the mast will pitch back, in effect slowing the sails down in the view of the wind and decreasing apparent windspeed and hence causing it to come more from the side. Conversely as the boat goes down the back of the wave the mast pitches forward increasing boatspeed as the wind sees it and increasing the apparent windspeed and moving it forward.

Apparent wind from surface to top of mast

Another factor that comes into play is the change that occurs in true windspeed from water level to the top of the sails. The surface friction that occurs between the wind and water at surface level naturally causes the wind at the surface to be lighter than the wind aloft. The taller the mast  the more this difference will be. Since the sails on your boat are moving through the wind at the same speed from top to bottom this causes the apparent wind to be more from the beam at the mast head relative to deck level.  

The importance of twist in sails.

All of this discussion serves to explain the importance of twist in our sails. Twist can be measured and is the increasing angles that the chord lines in a sail take from bottom to top. All sails (and even airplane wings) have twist of some degree.  It is important to note here that twist in sails is one of the main reasons why most upwind sails are fuller in the top than in the bottom. If you are going to twist open the top you need to make the sail fuller there so that it does not get too flat as you add twist. Twist is added to a sail by either easing a sheet, inducing more mast bend or moving a lead aft.

Armed with this knowledge, we can now head out on the race course and start making sail trim decisions on the fly as we encounter different conditions. Let’s take a look at some typical conditions we might encounter.

Keep in mind at all times that we are always looking to set up boat up with balanced or a very slight (4 degrees or less) weather help for optimal performance upwind.

Flat Water/Steady Breeze

The simplest of all conditions and generally the easiest to get good speed in. With no waves to sail through the mast is not pitching. These conditions are all about pointing high. Here we’ll set the sails up to be relatively flat which allows up to trim them harder before stalling. On the main we will have the outhaul tight and main trimmed hard and be going for the backstay early so we can trim the main even harder. For the jib we will look to have the lead aft slightly to flatten the jib and again allow for a trimming the sail hard. Hard trim will mean straight leeched sails with very little twist from top to bottom. We don’t need twist here because the boat is in a relatively steady state and easy to sail.

Bumpy Water/Light Wind

Like the most exasperating conditions and requiring the most patience. To keep the boat moving we will want to the opposite of flat water and always be hedging on the side of sailing low and keeping the boat moving. We’ll have to sail with the sails eased and we need them to be nice a full. Outhaul can be on the looser side, we’ll want to go light on the backstay to keep the top of main as full as possible with the sheet eased. Having a loose backstay will also induce sag  in the forestay which will make our jib or genoa fuller. We will want the jib lead forward to reduce the twist in the jib at the top and keep the head of sail full and powerful.

Bumpy Water/Heavy Wind

In this condition we the conflicting conditions of waves we need power to get over and around combined with lots of breeze which induces heel and helm and overpowers the boat. In general the best solution here is to set your sails up with enough twist to keep the boat flat as the top of mast moves through a wide range of wind angles. Then we will look to power up the bottom of the sail plan. Things that work on a lot of boats are not moving the jib lead back to far (just ease the jib sheet to twist open the top of the sail). Moving the mast butt forward at its base or adding mast chocking in front of the mast to keep the bottom of the main from over flattening. In this condition we will want to be our most aggressive at adjusting trim. Easing boat sheets to keep the boat flat as we hit and foot through a big set of waves and them trimming right back in for the flat spots pays huge dividends here.

Troubleshooting Guide — Common Issues and Potential Concerns

This table is only a starting point. There are many, many factors to consider when evaluating your boatspeed issues. Hopefully by reviewing this table you can develop a sense on your own to diagnose your boatspeed issues.

Dealing with all different challenges Mother Nature throws at us in sailing is what makes the sport such a great challenge. Good Luck!