Boatworks

Mechanical Leverage

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This article originally appeared in the December 2009 issue

Your boomvang is a key tool for adjusting the shape of your mainsail. Sailing off the breeze without a vang, the pressure on your sail causes your boom to rise up, degrading sail shape. On small dinghies you sometimes don’t need a boomvang as the mainsail may be small enough that you can control sail shape with mainsheet tension, especially if the boat has an end-boom mainsheet.

Most modern cruisers have mid-boom sheeting, so the vang plays a crucial role in keeping the boom pfrom rising when sailing off the breeze. There are four basic varieties of vangs: tackle systems; rigid vangs with either an internal coil spring or a compressed air/gas cylinder with an external tackle system; flexing fiberglass rods controlled with a tackle; and hydraulic vangs. Typically, hydraulic vangs are found on boats larger than 50 feet, as the loads involved are too great to handle with a tackle; the exception being some high-end raceboats that use a cascading tackle system or that runs cordage from the boom to a hydraulic cylinder belowdeck to reduce weight and windage. Here, we consider boomvang systems for cruising boats up to roughly 50 feet LOA.

If you own a boat in this size range, chances are that it has a boomvang. Typically, the smaller the boat, the better the chances it has a simple tackle (usually either a 4:1 or a 6:1 purchase) to vang the boom. But once you get into larger boats, say 35 feet and above, there are drawbacks to this system.

“With rigid vangs, the idea is to take the weight of the boom off the sail’s leech section and eliminate the topping lift,” says Seldn Masts’s Scott Alexander. “If you’re putting in a reef, you don’t have to worry about tightening up the topping lift, as there’s no way [with a rigid vang] that the boom can drop into the cockpit. Rigid vangs are much safer because of this.”

Hall Spars’s Kristan McClintock agrees. “Vang springs help to ease the vang out more smoothly than a soft vang. Since the spring is extended when at rest and compressed when sheeted on, a rigid vang will help your boom defy gravity. A rigid vang also helps with dropping the main—particularly if you have lazy jacks or a furling boom. The vang holds the boom reasonably horizontal so you get a good roll/flake.”

Besides being safer, a rigid vang also offers a performance edge. According to Alexander, “a rigid vang allows you to lift the boom and twist off the sail in light air. For racing sailors, this is huge.” But cruisers can also benefit from a rigid vang in light air, as the weight of the boom sagging down in the light stuff can negatively impact sail shape. This is why most rigid vangs use a spring or compressed-gas system to support the boom. The tackle outside a rigid vang is used to overcome the lifting force generated by the vang and to pull the boom down.

This then raises the question as to where the tackle should be led. Some raceboats (usually those below roughly 38 feet) will use a rigid vang with a camcleat mounted on either end. This allows a forward hand to quickly adjust the vang when sailing downwind. Most cruisers, however, lead the vang-control line (and likely the reefing lines) back to the cockpit, as this spares the crew a trip forward to make adjustments.

Regardless of where your vang control lines are led, it’s important to consider the amount of load on the vang sheet. “On boats bigger than 38 feet, the loads get high enough that you’ll want to lead the control line through a stopper to a winch,” says Alexander.

If you have an older tackle, or soft-vang system, or an old rigid vang, odds are good your boat would benefit from a new vang. Rigid vangs maintail sail shape in lighter air, and they make it easier to control the boom in stronger breezes. But if your boat doesn’t need a rigid vang, soft vangs also work well. Ronstan’s Scot West says the company’s soft-vang systems use sleeve-bearing blocks, but ball-bearing blocks can also be used, especially if you’re a racer. One consideration for offshore sailors using either soft or rigid vangs is that ball bearings might distort if exposed to prolonged loads (for example on a long downwind passage involving constant vang tension). This is why sleeve-bearing blocks might be the way to go for the primary tackle, especially aboard passagemakers. Consult your rigger when it comes to determining which blocks to use.

While rigid vangs are generally preferable on bigger boats, there are a handful of advantages to using a soft-vang system. For example, you can remove the mast end of the system and shackle it to the toerail (provided you have enough cordage), where it can function as both a vang and a preventer. This is especially useful on longer downwind passages. Or, should you get overpowered, you can quickly detach it from the mast (or, if you have enough cordage, simply uncleat it and let the end run) and “scandalize” the mainsail by pulling in on the boom’s topping lift, thus lifting the boom and quickly depowering the mainsail. Also, because soft vangs easily attach and detach from both the mast and the boom, it’s a snap to remove this system if you’re trying out trysails, or worse, using them in anger.

Rigid-vang systems are built robustly and should perform well for long periods of time. “A rigid vang will last almost forever, with little maintenance required,” says McClintock. Depending on the type of spring or compressed-gas system on your boat, you might occasionally have to change a seal or a spring, but this isn’t a worry until you encounter problems. Vangs are fairly problem free, but as with all boat parts that are exposed to salt water, rinse your vang with fresh water on a regular basis. And, be sure to rinse seals on a rigid vang and hose down the blocks themselves. Salt crystals can wreak havoc on certain types of ball bearings.

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