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Sailing downwind

Oct 31, 2016
A mainsail secured with an adjustable sheave boom brake.

A mainsail secured with an adjustable sheave boom brake.

Under the right confluence of conditions, sailing dead downwind can be as bad as catching it on the nose. It can be slow, uncomfortable and dangerous. A short-handed crew often doesn’t want to fly a spinnaker or gennaker, and asymmetrical spinnakers don’t fly very well downwind. The common response is to furl the headsail and turn on the motor. However, with the right system, including a poled-out headsail on one side and a main with a preventer on the other, sailing downwind can be fast, comfortable and safe.

Setting the mainsail
The saying I learned while racing dead downwind was “dead down, heads up.” Nobody wants to catch a boom hurtling across the deck in an accidental gybe. The force of an uncontrolled gybe is substantial and is stressful on the hardware, lines and the boom itself, often resulting in broken equipment. Anybody caught in the way can be severely injured or thrown overboard.

There are a number of systems developed to reduce the risk associated with uncontrolled gybes. These systems are called gybe preventers, or simply preventers. Boom brakes are a type of preventer and allow the boom to cross the centerline of the boat during a gybe in a controlled fashion. 

A simple preventer run back to the cockpit for easier tensioning.

Preventers 
Preventers range from simple and nearly free to more complicated and up to $500 USD. Regardless, a preventer only works if it’s used.

The simplest preventer is a line that runs from the end of the boom to a point on deck forward of the mast. A loop is tied to the boom end of the line and the other end is secured to a strong point on the deck (pad eye, toe rail, anchor roller, etc.). The disadvantage of this system is that it requires being set every time the point of sail changes, forcing a crewmember to go forward to tension the line. When it comes time to gybe, the mainsail must be trimmed as close as possible to facilitate placing the loop over the end of the boom, making the boat less stable in the wind.

An extension of the simple preventer allows the line to run through a block, port and starboard, forward of the mast and back to the cockpit where it can be secured. This saves a crewmember from having to go forward to tension the preventer line. However, whenever a gybe is made, the line has to be changed from the previous leeward side to the new leeward side, which requires a crewmember to go forward and rerun the preventer line. To avoid this, many sailors run two lines to the boom on each side of the boat. Leave the windward line lazy when the leeward line is tensioned; when a gybe is made, simply reverse the tension.

Two lines (or a single with a bight) run from midpoint on the boom to turning blocks and back to the cockpit.

There are many variations on the simple preventer to improve rope management, deck access or ease of rigging. Some attach midpoint to the boom and some use pendants that are permanently installed along the boom. It is important to design a system that works for your boat and sailing style. One important detail when locating the forward attachment location is that the preventer will be strongest when the brake line runs perpendicular to the boom.

Boom brakes
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The advantage of a boom brake over a static preventer is that in the case of an accidental gybe, the brake will slow down the movement of the boom and allow it to cross over to the other side. This prevents the main from being held in a backwinded position, which can lead to excessive heel and a potential broach. There are three main types of boom brake.

Friction path brakes are the most simple of the boom brakes. The brake line runs port to starboard and through the brake, which is attached to the midpoint of the boom. There are usually a number of ways to run the brake line through the brake depending on the friction desired. 

Three types of boom brakes: top, drum; middle, friction path; bottom, adjustable sheave.

Drum brakes are similarly designed in that they have no moving parts and use friction to slow the boom’s travel. The brake line is run from port to starboard and wraps around a smooth fixed cylinder or drum. The more wraps, the more tension.

An adjustable sheave brake makes use of two static sheaves and one adjustable sheave to create tension on the brake line. The main advantage of an adjustable sheave brake is that the brake line does not need to be rerun to increase or decrease friction in the system. 

Setting the headsail
Sailing dead downwind with a headsail can be an exercise in frustration. If flying wing-on-wing, ocean swell and wind waves can cause the headsail to collapse and fill repeatedly. Unfortunately, the mainsail will blanket the headsail in apparent wind angles of 140 to 220 degrees, which means you have to head up more than 40 degrees from your intended destination. As a result, many short-handed crews take down the headsail and turn on the motor. Another option is to use a pole.

Poling out the headsail requires a support pole that is strong enough to handle the compression loads of the sail when it is backwinded and it is important to check a reputable source to determine the strength required for your boat. Appropriately sized spinnaker poles or whisker poles are most often used. A spinnaker pole is often too short for a 120 to 150 percent genoa and so a telescopic whisker pole is used to allow the full use of the sail.

Rigging a pole for the headsail is the same as rigging a pole for the spinnaker; it requires a topping lift and a downhaul or foreguy. The foreguy should run from the downhaul attachment point or from the outboard end of the pole’s jaws to a turning block well forward of the mast and back to the cockpit. The foreguy is necessary to prevent the pole from putting pressure on the shrouds while under sail.

There are eight steps for rigging the pole. The first step (1) is attaching the topping lift to the pole before lifting it from the deck. A crewmember in the cockpit can take up slack as the pole is lifted so that the weight is not borne solely by the person rigging the pole. Connect the foreguy (2) and leave a few feet of slack in the line to allow for movement of the pole. Next, connect the outboard end of the pole to the jib sheet (3) and the other end of the pole to the mast (4). Level the pole with the expected clew of the headsail using the topping lift, foreguy and mast track (5). Adjust the length of the pole to fit your sail if it is a whisker pole, or move the inboard end up and down the mast track to fit the sail if it is a spinnaker pole (6). Keep the pole as level as possible to push the sail out to its maximum extent. Tension the foreguy to ensure that the pole will not make contact with the shrouds when the sail is unfurled (7). Unfurl and trim the headsail (8).

The view downwind with a preventer set up for use on both sides and with a pole for the jib.

Gybing the headsail
The easiest way to gybe the headsail is to furl it in, unclip the pole from the jib sheet and rotate it over before clipping to the opposite jib sheet and unfurling again. If using a spinnaker pole, you will most likely have to unclip it from the mast as well and swing it through before clipping to the opposite jib sheet and mast in the same way you would gybe the spinnaker. It is not recommended to remove the pole and attempt a gybe with the headsail up. There are too many lines on deck that can get caught and having a heavy pole swinging around is a recipe for disaster.

Sailing dead downwind is a scenario that every sailor will encounter. By setting up a preventer and rigging a pole for the headsail, sailing dead downwind can be comfortable, efficient and fun, lending credence to the old saying, “May the wind always be at your back.”

Robin Urquhart and his partner, Fiona, set sail in September 2015 on a multi-year trip to Australia, aboard their Dufour 35, Monark. Robin holds a master’s in building science engineering. For more on DIY projects, misadventures and tips for life aboard, visit their blog at www.happymonarch.com.

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