How to keep your boat moving
Tips for keeping a cruising boat moving at an acceptable pace in light airs By Rupert Holmes
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.)
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 air flow 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.
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
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