Windage is the resistance a boat presents to the wind through everything above the waterline that is not usefully driving her: the hull topsides, mast, boom, standing rigging, furled sails, dodger, bimini, radar, dinghy, fenders and so on. For a beginner, windage is why a boat drifts sideways in a marina and why the bow blows off when you stop. The experienced sailor knows two further things: that windage is a permanent drag term working against you every mile you sail to windward, and that it matters most precisely when the sails are not up – at anchor, under bare poles in a gale, or motoring into a headwind.
What Creates Windage
Anything that stands in the airflow creates drag, but some items are far worse than their size suggests. Round sections like masts and wires are poor aerodynamic shapes; a wire shroud can produce drag comparable to a streamlined section many times its width. Add spreaders, halyards, lazy jacks, a furled headsail on the forestay and a stack pack on the boom, and a modern cruising rig presents a great deal of frontal area before a single sail is set. High freeboard, a large coachroof and a full cockpit enclosure add more. A dinghy on davits is a sail you cannot trim.
Windage and Sailing Performance
Upwind, the total aerodynamic force on a boat is the sum of the sails’ lift and drag plus the parasitic drag of everything else. On a typical cruising boat the rig and hull windage can account for a substantial share of total aerodynamic drag, and unlike sail drag it produces no lift in return. It reduces the effective angle you can sail to the wind and slows you down for nothing. This is why racing rigs have small-diameter rod or fibre rigging, swept spreaders with minimal hardware, and why serious offshore racers strip anything that does not have to be there. For the sailmaker, windage is a reminder that a furled headsail is not a neutral object: a big genoa rolled on a furler in thirty knots is a fat cylinder on the leading edge of the rig, which is one argument for a smaller working headsail or a dedicated staysail on boats that sail a lot in a breeze.
Windage at Anchor and in Harbour
At anchor, windage is the load on your ground tackle. A boat with high freeboard, a big dodger and a dinghy on deck sails around her anchor, yawing from side to side and snatching at the chain. Catamarans, with two hulls and a tall bridgedeck, are notorious for it. The cures are a longer scope, a good snubber, a riding sail set on the backstay to hold the stern downwind, and stowing the dinghy on the stern or in the water. In a marina, windage decides which way the bow goes when you lose steerage way: a boat with a lot of forward windage will always blow bow-downwind, and a skipper who knows that plans the approach accordingly.
Windage in Heavy Weather
In a storm the rig alone can drive a boat at several knots under bare poles, and the windage of a furled headsail adds to it. This is one reason to get a headsail off the forestay altogether before the worst weather, rather than leaving it rolled, and why a boat lying to a drogue or sea anchor should be as clean as possible on deck.
Cruising Versus Racing
The cruiser accepts windage as the price of comfort. A dodger, a bimini, solar panels, a wind generator and a dinghy on davits all make life aboard better, and a well-found cruising boat sails a little slower to windward as a result. The sensible approach is to be aware of it, plan anchoring and berthing around it, and avoid the truly gratuitous items. The racer treats windage as free speed: low freeboard, a clean deck, a bare rig, and nothing on the stern.
Frequently Asked Questions about Windage
Does windage really slow a sailing boat much?
Upwind, yes. Parasitic drag from the rig and hull can be a large fraction of the total aerodynamic drag, all of it without producing lift. Downwind it matters far less, and a little extra area can even help.
Why does my boat sail around her anchor?
Windage forward of the boat’s pivot point pushes the bow off, the boat falls away until the chain checks her, then the sequence repeats on the other side. A riding sail aft, more scope and a good snubber all help, as does stowing anything bulky on the foredeck.
Is a furled headsail a windage problem?
It is. A rolled genoa is a large cylinder on the leading edge of the rig, and the bigger the sail the fatter it gets. In heavy weather it is better to drop it altogether; day to day, it is one reason to pick a headsail size suited to how you actually sail.
Windage is the drag you cannot trim away. Understand where it comes from, plan your anchoring and boat handling around it, and strip out what you do not need, and the sails you do carry will get to do their job with a little less fighting the rest of the boat.