Light-Air Sailing - Sail Magazine

Light-Air Sailing

Tips for keeping a cruising boat moving at an acceptable pace in light airs
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           Don’t give up in a drifter! Light-air sailing is some of the best sailing there is   

           Don’t give up in a drifter! Light-air sailing is some of the best sailing there is   

Some of the best times aboard a cruising boat are in light airs—those quiet, relaxed sunny days with gentle sailing that just wouldn’t be the same if you were motoring. However, many cruising yachts are not set up to truly fullfill their potential in these kinds of conditions.

One of the problems, of course, is the sheer weight of many cruising yachts. Displacement is still valued by many thanks to the more comfortable motion at sea (and at anchor) that it can confer, not to mention the reassuring assumption that extra weight is synonymous with additional strength. For many owners, it’s also a byproduct of buying an older and therefore more affordable boat. Equally, for those travelling farther afield, a heavier boat is likely to have better load-carrying ability than a lightweight flyer. Of course, a downside to all this is that it can lead to a greater dependence on the engine, bigger fuel bills and arguably less time spent fully enjoying good weather.

This also applies to today’s beamy and broad sterned yachts, which have lots of wetted surface area and therefore a high level of frictional resistance. Nonetheless, with a few tweaks most cruisers can be coaxed to move at an acceptable pace.

The challenges

In many cases, weight is not the only reason cruising yachts struggle to make progress in light winds. They may also have aging and badly stretched sails, inefficient controls for sail shape and a degree of underwater fouling. Older boats may also lack efficient reaching sails, Code 0s, while old-school cruising chutes are nowhere near as effective downwind as modern asymmetric spinnakers, or A-sails.

These factors often lead to owners abandoning any thought of sailing in light airs, which can result in their boats becoming such that it’s next to impossible to do so. However, with enough sail even the heaviest of boats can be made to move at reasonable speeds, especially at wind angles that put the boat on anything between a broad and close reach.

Never forget that when reaching in light airs the boat’s own motion increases the apparent wind strength. It also doesn’t take a great deal of power to overcome the frictional resistance of a clean hull. Speeds approaching the square root of the waterline length in feet (for example, 6 knots for a 36ft waterline) are therefore reasonably easy to achieve. (Although above this speed the boat starts to create a wake and bow wave, which require much more energy to overcome than the frictional resistance that predominates at slower boatspeeds.)

           Ease your outhaul and halyard to create a deep, powerful shape in a drifter: note the wrinkles along the luff of this main    

           Ease your outhaul and halyard to create a deep, powerful shape in a drifter: note the wrinkles along the luff of this main    

What lies beneath

Many cruisers will accept a degree of growth on the bottom of their boats. Often there are sensible reasons for this, since it’s more economical and saves the hassle of organizing mid-season scrubs. In addition, if you’re not looking to win races, where the last 20th of a knot of boatspeed can make all the difference, a thin layer of slime won’t have much impact on passage times.

However, as growth starts to become more firmly established, the frictional resistance of the hull rapidly increases, and will eventually reach a level at which it prevents a boat reaching speeds anywhere near its potential. In fact, in many cases a good chunk of the cost of scrub before a long passage or summer cruise can be offset by the reduction of fuel costs.

Another major source of drag on many yachts is a big three-bladed propeller. Although a more expensive option, a good feathering or folding prop will not only dramatically reduce resistance under sail, but still offer excellent efficiency under power.

Sail shape

Careful adjustment of sail shape is fundamental in light airs, especially when the wind is well forward abeam. The most common mistake is to trim in a similar manner to stronger winds, which invariably results in flat sails and a tight leech. This all but guarantees it will be difficult to establish laminar airflow over the sail, which will, in turn, severely reduce boatspeed.

Instead, ease the main outhaul and both halyards a couple of inches to create a fuller shape that will deliver more power. It’s also generally helpful to set more twist than usual by easing the vang and mainsheet, with the twist in the headsail matching that in the main. If you have a traveller for the mainsheet, haul this to windward to maintain the correct angle of attach. But as you do so be sure you don’t pull the bottom batten of the sail above the boat’s centerline.

In super light airs, unless you have a gas vang there may not be enough apparent wind to lift the weight of the boom, resulting in a hard, straight leech. If so, take up a little on the topping lift to achieve the correct amount of twist.

If the wind is well forward of abeam, telltales on the leech of the mainsail at the batten positions will help considerably with sail trim. Ideally, the lower ones will be constantly streaming, while the upper one will stream around 50 percent of the time. If the top telltale never flies, there’s not enough twist, so the sheet and/or vang should be eased to allow the leech to go outboard a bit. Conversely, if it flies all the time you will gain a marginal benefit by bringing it inboard and reducing the twist.

Steer carefully

The golden rule in light airs is to minimize helm movements to avoid applying too much rudder angle. While oversteering is arguably less of an issue for a 1970s-era fin-and-skeg designs, it’s very important for later boats with big spade rudders. When these are pulled through the water at an angle they create a huge amount of additional drag that’s akin to leaving the parking brake engaged in your car.

If not close-hauled or well downwind in light airs, it’s often more efficient to leave the steering to the autopilot. In these conditions, even a low-spec model will steer a straighter course than all but the most focused crewmembers. This approach also leaves more time to pay attention to trimming the sails and adjusting sail shape to suit the changing wind angles you’re likely to experience.

Upwind progress

It’s often said that upwind performance doesn’t matter when choosing a cruising boat. However, I tend to subscribe to a slightly different view, which is that even if you don’t intend to make passages directly to windward, an efficient yacht should still be able to sail fast and comfortably at a true wind angle of 55 degrees (as opposed to a boat with a less efficient rig, sailplan and keel will be tedious, slow and uncomfortable when sailing close-hauled mode at that same angle).

Sailing directly upwind in light airs can be a slow process, thanks to the rapidly diminishing power generated by the sails and increased drag on the rig as a boat points progressively closer to the wind. Nevertheless, it’s often possible to make good ground on the favored tack before finally motoring upwind to the next waypoint.

Finally, it’s important to resist the temptation to point too close to the wind or to over-sheet your sails, both of which will completely kill speed. In many cases the apparent wind angle will need to be 10 or even 15 degrees lower than in a moderate breeze if you want to keep moving.

Twin Headsail arrangements

When setting up a boat for serious offshore use, there’s a danger that adding equipment for heavy weather will have an unnecessary adverse effect in light airs. Twin headstays with furlers make lots of sense in strong winds, but in lighter airs it can become impossible to tack or gybe the genoa easily.

On boats of less than around 40ft my preference is for a removable Dyneema Solent stay that leaves the foretriangle clear in light airs. On a larger boat, the arrangement adopted by Paul and Sheryl Shard of the Distant Shores TV channel for their new Southerly 480 is ideal: specifically, electric furling for the fore headstay, which enables the genoa to be quickly and effortlessly two-thirds furled for a tack.

Downwind

Sailing deep downwind in light airs is a recipe for going nowhere. The problem is that the faster the boat goes, the more the apparent wind speed is reduced. That’s why racing boats tend to gybe downwind, often doing so through angles of up to 80 degrees. If you use routing software, the solutions it offers should reflect this fact.

Once there’s 10 knots or more of true wind, this is less of a problem for small boats with spinnakers, and a dead downwind course is often the best option for a heavy 30- or 35-footer. However, the speed potential of larger modern yachts means their most efficient course remains a series of broad reaches until the true wind speed approaches 20 knots when a poled-out headsail is usually the best option.

When sailing off the wind try sailing toward wherever there’s breeze, although be aware that gusts, lulls and shifts

are rarely uniform in strength and direction. The key signs to look for are dark patches on the water, with wavelets indicating the true wind direction. Lulls, on the other hand, appear as less disturbed areas that are lighter in color. Also watch for big wind holes and/or gusts in the lee of headlands, tall building, or even just a patch of trees. Often a wind line will be seen, signifying the border between a dead inshore zone and the edge of more reliable breeze offshore.

Sail handling systems

So far, we’ve not talked about modifications to a boat or spending money on additional equipment. That’s because often there are many improvements that can be made without buying more kit. However, if sailhandling systems are not slick and effective you won’t be able to readily respond to changes in the wind strength and direction.

In light airs the most common problems are associated with excess friction preventing a line from paying out when eased. This can arise from a number of factors, including under-specified or seized blocks, lines that are too large in diameter for their deck hardware and deck layouts that route lines around too many unnecessary corners.

Unfortunately, all too many cruising yachts either have layouts based on outdated ideas or have low-grade hardware fitted as original equipment for the sake of economy. Paradoxically, the better systems usually fitted to performance cruisers and cruiser-racers tend to make these boats easier to handle, despite the greater power of their larger rigs when compared to most mainstream cruisers.

It might seem strange to discuss mainsail reefing systems in an article about sailing in light airs, but it is relevant. If a boat is set up in such a way that it takes five minutes to reef, you will have a tendency to drop in a precautionary reef as soon as there’s a hint the wind might start increasing. While this may appear to be a prudent measure, it will often leave you floundering along in 8 knots of wind next to a big dark cloud, making little progress, yet afraid to shake the reef out. However, there’s no reason why any boat under 45ft should not be set up so that one person can tuck in or shake out a reef in the mainsail within 60-90 seconds.

           Today’s cruising A-sails provide the necessary power to keep moving in almost anything   

           Today’s cruising A-sails provide the necessary power to keep moving in almost anything   

Light air sails

Because a boat’s own forward motion increases the apparent wind when reaching in light airs, any increase in the sail area sets off a beneficial circle of improvement. Bigger sails make the boat faster, which further increases the apparent wind making the boat faster still. With this in mind, sail designs that were first refined on raceboats 20 years ago have now been adapted for cruising yachts and can make a huge difference.

One of the most common of these, the asymmetric spinnaker, represents a huge step forward compared to earlier cruising chutes. In particular, the dramatically curved luff on a modern A-sail means it will not be blanketed by the mainsail until the apparent wind is aft of around 150 degrees. By contrast, many older cruising chutes will collapse at an angle of around 125 degrees.

Asymmetrics can also be cut to be used with a top-down furler, which hugely simplifies sail handling. However, this tends to involve a compromise with the amount of luff curve that can be incorporated into the sail, which means they won’t set as far downwind as a sail with a conventional snuffer.

Another common racing sail now used by cruisers is the Code 0, which maximizes the area available for a reaching sail and can be a hugely powerful tool in light airs. On a race boat, Code 0s typically have to fulfil the requirements to measure as a spinnaker, which means they are cut with excess cloth on the leech. However, this isn’t needed for a cruising Code 0. Two other advantages of Code 0s are that they are super easy to handle thanks to their furling systems, and they can can’t form an hourglass or wrap around the forestay, in the same way as a conventional nylon spinnaker.

Although it’s possible to spend large sums of money on these sails, discarded racing sails will often do the job for budget-conscious cruisers. To be competitive, racers need to use their kites even when it’s blowing hard, but the biggest gains for cruising yachts are in gentle conditions, with the apparent wind under 10 knots. The much-repaired big asymmetric spinnaker on my 30ft boat, for example, is a castoff from a J/80 sportboat that cost me less than $200 a decade ago. Similarly, an old racing Code 0 with a damaged leech—the part that invariably fails first—can often have the weakened area cut away for use as a cruising sail.

I also have a similarly sized symmetric kite that makes it possible to make good speed dead downwind, with the main boom appropriately secured using a preventer, in apparent wind speeds of only 7-8 knots. These two sails mean that, even in a region with predominantly light airs, I can cover roughly 1,000 miles in a season without using more than around 15 gallons of fuel.

Routing software

Routing software can shave a significant amount of time off many passages and also help identify the optimum time to leave port. Note, though, that once your GRIB files start showing significantly less than 8 knots of breeze, the accuracy of their routing can be significantly reduced. This is especially true for boats that sail at the same speed as the true wind on a reach in light airs, but are significantly slower on other points of sail.

That said, there are now many fine-grained models that include the effects of shorelines and islands, making them a valuable resource for a passage that will include areas of light winds. This kind of software is also becoming ever more accessible, with companies such as PredictWind, SailGrib and Fast Seas all offering various low-cost, or even free options. 

Light-air Tips

• Don’t pinch, oversheet or oversteer

• Keep the bottom as clean as possible

• Eliminate unnecessary friction

• Adjust your speed expectations

• Analyze the forecast carefully

• Watch for gusts and lulls

• Set up easy reefing

• Buy light airs sails

Rupert Holmes has 80,000 miles of offshore experience, including racing doublehanded around Britain and across the Atlantic. He has also cruised from New Zealand around Cape Horn to the Beagle Channel and on to the Falklands.

For more on sails and sail technology CLICK HERE

June 2018 

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