The words

1x7

Also one by seven, 1 x 7

Wire made as a single strand of seven wires, one core with six laid round it. It is stiff and stretches little, which is what a mast wants, and it is what a 49er's standing rigging is made of.

More wires mean more flexibility and more stretch. A 7x7 or 7x19 wire of the same diameter bends round a sheave better and holds a rig worse.

Abeam

Also on the beam

At right angles to the boat's centreline. The line drawn abeam from the aftermost point of a boat's hull and equipment is the line that decides whether another boat is overlapped with her.

Forward of abeam and abaft of abeam say where something lies on that line, not how far off it is.

Apparent wind

Also AW, apparent-wind angle, AWA

The wind the boat actually meets, the vector sum of the true wind and the wind the boat makes by moving. On a 49er it is always forward of the true wind and usually stronger, and the faster the boat goes the more so.

Telltales, sheets and the gennaker luff all answer to apparent wind. Shifts, laylines and VMG are worked in true wind, so the two have to be kept apart in a debrief.

Astern

Also aft of, behind

Behind the boat. A wind shadow on a skiff falls almost straight astern and a little to leeward, because the apparent wind is so far forward.

Astern is a direction. Clear astern is a rules status, and the two are not the same claim.

Backing

Also backs, backed

The wind shifting anticlockwise. Veering is the opposite, clockwise. Surface wind is backed from the wind aloft because friction turns it.

Backing and veering say which way the wind rotates, not whether it helps. The same backing shift is a header on one tack and a lift on the other. South of the equator the surface turning goes the other way.

Backstay

Also aft stay

On most boats, a standing wire running aft from the mast to resist forward bend. A 49er has none: every one of its four wires runs forward or sideways.

The word still appears in the older Ovington tuning table, whose four labels, forestay, side stays, intermediates and backstays, are used nowhere else in that document and are mapped onto the four actual wires by no source. Anyone arriving from keelboats will expect an adjustable backstay and there is not one.

Backwind

Also backwinding, backwinded

The air leaving one sail's leeward side and striking another sail, or another boat's sails, at the wrong angle. Inside the boat a jib sheeted too hard backwinds the mainsail; between boats it is what holds a windward boat down.

Backwind is not the same as a wind shadow. Shadow is slowed air behind a boat; backwind is bent air off a sail, and it reaches further forward.

Bail

Also strap, U-bolt

A metal loop fitted to a spar or the hull to take a block or a line. The class rules allow one beneath the jib blocks with a single block added, to raise jib sheet purchase.

Nothing to do with bailing water, and nothing to do with a bail-out from a bad start. Three unrelated words spelled alike.

Bail-out

Also escape, get out

The escape from a start that has gone wrong, usually tacking onto port and crossing behind the fleet to find clean air.

It is priced before the gun, not invented after it. The committee-boat end has a thin bad tail because the bail-out onto port is cheap there; the pin end does not.

Band

Also wind band, wind range

A range of true wind speed, with a sea state attached, inside which one set of settings and one mode apply. The 49er's bands are defined by which term in the force balance binds, not by fixed wind speeds.

Band edges are the crew's own logged crossovers. A band taken from another boat, another venue or a published study is not a band for this crew.

Batten

Also battens

A stiffening strip in a pocket across the sail that holds the leech's shape. The top batten lies near the chord at its height, so its angle to the boom reads the exit direction at the head.

A batten sets the shape the leech can hold. It does not set how far the leech is twisted open, which is the sheet and the vang.

Bear away

Also bear off, head down, bear-away

To steer away from the wind. The apparent wind moves aft and weakens, and the sails are eased to match.

On a 49er the vang comes off well before the bear-away, not during it, because a loaded leech turns into rudder load at exactly the moment the boat is turning.

Bear-away set

Also bearaway hoist

Hoisting the gennaker while bearing away round the windward mark onto the same gybe. A gybe set bears away and gybes in one move so the run starts on the other gybe.

Which one is used is a tactical choice made before the zone. Deciding it in the rounding costs the hoist.

Beat

Also windward leg, upwind leg

The leg sailed toward the windward mark, made of two close-hauled tacks because the boat cannot sail at the wind.

Beat names the leg and also the act of sailing it. Neither sense means to go fast.

Black flag

Also rule 30.4

The hardest starting penalty. A boat inside the triangle formed by the ends of the line and the first mark during the last minute before her signal is disqualified without a hearing.

It is the only starting penalty a general recall and a restart do not wipe, so line position under it is priced against the whole race rather than against a length at the gun.

Block

Also pulley, ratchet block

A sheave in a housing that turns a line or multiplies force. A ratchet block grips the line in one direction so the hand holds less than the load.

The class rules count sheaves, so a replacement block must have the same number of them and a sheave of similar or greater diameter.

Bolt rope

Also luff tape, luff rope

The rope or flat tape sewn into a sail's luff or foot that slides in the spar's groove and holds the sail to it.

It wears where the batten ends bear on it, which is why the mast track gets the lubricant and not the sail.

Boom

The spar along the foot of the mainsail. It carries the outhaul, the sheet loads and the vang loads.

Bowsprit

Also pole, prod, sprit, launcher

The retractable spar that pushes the gennaker's tack forward of the bow. On a 49er it is pulled out through a sheave on the deck.

An extended bowsprit counts as part of the boat for an overlap downwind, so a boat with the pole out reaches an overlap sooner than her bow suggests.

Breaking load

Also breaking strength, minimum breaking load, MBL

The tension at which a new wire or rope fails, quoted by the maker. Rigging is worked at a fraction of it, because fatigue and shock loads rather than a steady pull are what break a rig.

A quoted breaking load assumes new, undamaged wire in a correct terminal. One broken strand at a swage mouth, a kink or a pin worn oval makes the number meaningless.

Camber

Also depth, fullness, draft depth

The greatest distance between a sail's cloth and its chord at a given height, divided by the chord length, so it is quoted as a percentage. More camber gives more power and more drag.

Camber is how deep the sail is. Draft position is where along the chord the deepest point sits. They move independently, and a control that changes one usually changes the other as a side effect.

Cap shroud

Also upper shroud, upper, cap, V2, D3

The outermost shroud, running from the masthead over both spreader tips to the hull. Because the swept spreaders carry it aft of the mast, its tension is what holds the forestay straight, and so it sets headstay sag and jib depth.

It is not the primary or main shroud, which is the middle shroud landing just under the top spreader. The two share a deck fitting on a 49er, which is what makes them easy to confuse. Tightening the caps flattens the jib and the mainsail at once, and it is a wind-band decision taken ashore.

Chainplate

Also chain plate, shroud plate

The fitting bolted to the hull that a shroud or a stay pins to. On a 49er these are among the highest-loaded points on the boat and are a named inspection item.

The class documents use chain plate and shroud plate for different fittings on the same boat, so a check list has to name the one it means.

Chine

Also hard chine, knuckle

The hard edge where the bottom of the hull meets the topsides. The 49er's forward chine turns water down for dryness and lift, and the chine is taken away amidships so the boat can be rolled through a tack without a large drag increase.

A chine is an edge in the hull shape, not a strip bolted on. A boat trimmed bow-down puts the wrong part of it in the water.

Chop

Also wind waves, slop

Short steep waves raised by the wind blowing where you are, as distinct from swell that has travelled in from elsewhere.

Current against the wind steepens chop and current with the wind flattens it, so a tide turn changes the sea state with no change in the wind at all.

Chord

Also cord (a common misspelling)

The straight line from the luff to the leech of a sail at a given height. Everything about the sail's shape at that height is measured against it: camber is the maximum gap between cloth and chord divided by the chord's length, and draft position is where along the chord that gap is greatest.

Not the same as the length of the cloth, which is always longer than the line it spans. Pacing along a sail measures cloth and gives a wrong chord.

Clear astern

Also clear ahead

A boat is clear astern of another when her hull and equipment are behind the line drawn abeam from the aftermost point of the other's hull and equipment. The other boat is then clear ahead.

The instant either stops being true the boats are overlapped and different rules apply. Downwind an extended bowsprit is part of the boat, so the overlap begins earlier than the bow suggests.

Cleat

Also cam cleat, clam cleat

A fitting that holds a line under load until it is flicked out. Wedges or risers under a wing-mounted cleat correct the angle the line enters it at.

A cleat that holds well can still fail the test that matters, which is whether the crew can release it from the wire at speed with one hand.

Clew

The aft lower corner of a sail, where the foot meets the leech. The sheet pulls on it.

Clew, tack, head and foot all name corners and edges of the same sail. Tack is the one that also means something else entirely.

Clewboard

Also clew plate

A plate at the jib's clew with several sheet holes. The hole chosen fixes how the sheet load divides between the leech and the foot, so a lower hole sends load along the foot and lets the top of the jib twist open.

It is not the sheeting-angle control. The angle across the boat is set by the track pin position, and the two are logged separately.

Close-hauled

Also on the wind, hard on the wind

Sailing as close to the wind as the boat usefully goes, with the sails sheeted near the centreline. It is how a beat is sailed.

Close-hauled is a band of angles, not one angle. The VMG angle sits inside it, the pointing mode above it and the fast mode below it.

COG

Also course over ground

The direction the boat is actually moving over the sea bed, in degrees, taken from successive satellite fixes.

It is not heading. COG differs from heading by leeway plus whatever the current sets, so the gap between the two is a measurement worth having rather than an error to remove.

Committee boat

Also boat end, starboard end

The race committee's boat, which forms one end of the start line. The pin buoy forms the other.

The two ends differ in more than bias. The committee-boat end has a lower mean outcome and a thin bad tail because the escape onto port is cheap; the pin end has a fatter tail.

Compacted strand

Also compacted wire, compressed strand

Wire whose strands are squeezed after laying so the individual wires deform and fill the gaps between them. For a given diameter it carries a higher breaking load and stretches less than ordinary wire of the same construction.

The outside of the wire is a different shape, so it needs terminals and cone wedges made for it. Pushing it into a fitting sized for standard wire is a failure waiting for a gust.

Consolidate

Also consolidating, banking a gain

To bank a gain by crossing ahead of the boats you have gained on, taking the leverage out of the position rather than leaving it to be given back.

An unconsolidated gain is a position, not points. Every crossing costs distance, so the decision is whether the gain is worth more than the engagement.

Constructional stretch

Also bedding in, settling, initial stretch

The permanent lengthening a new wire shows over its first few loadings, as the wires shuffle into the gaps left by manufacture. It is not elastic and it does not come back.

It looks like the rig going slack and invites a retension every session. A new wire is retensioned once, after it has settled. A wire that keeps stretching after that is failing, not bedding in.

Corrector

Also corrector weight

Lead fixed at rule-named positions to bring a light hull up to the 94.0 kg minimum. Not more than 3.0 kg may be added this way.

A hull that absorbs water loses its correctors to stay at the minimum, and loses with them the only say the crew had over where the weight sits.

Cover

Also loose cover, tight cover, covering

Sailing between a rival and the next mark so that whatever the wind does to you it does to her. A loose cover holds that position while leaving her clear air; a tight cover puts her in your wind shadow.

A cover that has drifted off the strategic route costs more than it defends. Breaking off is part of covering, not a failure of it.

Cross

Also crossing

Passing ahead of a boat on the opposite tack. A closing margin that is growing is a cross and one that is shrinking is a duck.

The expensive part is deciding late. A gain is consolidated by crossing ahead of the boats you have gained on, which is a reason to cross even when you could carry on.

Crossover

Also crossover point, band edge

The wind speed or sea state at which one setting or one mode stops being best and the next takes over.

Crossovers are the crew's own logged numbers. In crossover conditions downwind the low road is the safer option, because a low boat is not exposed to boats gybing onto starboard across her bow.

Cunningham

Also luff downhaul, cunningham hole

The control that pulls down on the mainsail's lower luff against a head held at the masthead, so what it sets is luff tension. Tension draws the draft forward, flattens the cloth behind it and opens the exit.

On this boat the same pull also bends the mast, because tack and head are forced toward each other. Bend on its own drags the draft aft, so the two have to be set against each other rather than one at a time.

Curl

Also luff curl, break, shy

The small continuous fold at the gennaker's luff that shows the sail is at the edge of its angle of attack. Easing the sheet lets it curl and steering lower re-attaches it.

A gennaker showing no curl is reporting nothing. Trimming until the curl goes trades the only feedback the sail gives for a shape that looks tidy.

Daggerboard

Also board, centreboard, plate, foil

The foil that drops vertically through the hull to resist the sail's side force. It makes that force only when the water meets it at an angle, which is leeway, and the force grows with speed.

A centreboard pivots in a case and a daggerboard lifts straight out. The book uses centreboard for the 49er's board in places, so a note about board rake means this part.

Displacement

Also displacement mode

The weight of water a hull pushes aside, which equals the weight of the boat. Displacement mode is the state in which buoyancy carries that weight and the boat is not planing.

The word does duty as a weight and as a speed regime in the same chapter. Buoyancy carries the hull below a Froude number of about 0.4 and hydrodynamic lift carries it above 1.0 to 1.2, and a 49er races on both sides of that.

Distance to line

Also DTL

The perpendicular distance from the bow to the start line at a given instant, in metres.

It is perpendicular, not along the course being sailed. A boat reaching along the line has almost no distance to line and a long way still to run.

Downhaul

Also jib downhaul, tack downhaul

Any control that pulls a sail's tack or lower luff down. On a 49er the mainsail's is the cunningham, and the class rules allow a jib downhaul led aft.

Downhaul names a job, not one fitting. On other boats the word means the pole control or the mast-lowering line, so it needs a sail name in front of it.

Draft

Also draught, draft position

In a sail, the deepest point of the curve, quoted as a percentage of the chord measured from the luff. In a hull, the depth of the boat below the waterline.

Two unrelated meanings, and this book uses the sail one almost everywhere. Draught is the usual British spelling of the hull sense, which separates them in writing but not in speech. Draft position is also measured along the chord, not along the cloth.

Drift

Also rate

The speed of a current, in knots. A tide table gives set and drift together.

Drift also means a boat's slow sideways movement with no way on. The current sense is the one a tidal diamond means.

Duck

Also ducking, dipping

Passing astern of a boat on the opposite tack by bearing away behind her.

A duck taken early and sailed fast and low costs less than the metres suggest, because the boat gains speed doing it. A duck taken at two lengths costs the speed and the lane as well.

Dyform

Also compacted strand wire

A trade name for compacted-strand stainless wire. At the same diameter it gives a higher breaking load and less stretch than ordinary wire of the same construction.

The name gets used loosely for any compacted wire. It is not a straight swap into fittings sized for standard wire, because the terminals and wedges are different.

Entry

Also leading edge, nose

The forward part of a sail, and how sharply it turns the flow that first meets it. A rounded entry accepts a range of angles; a fine entry serves one angle well and breaks down either side of it.

Forestay sag rounds the jib's entry, so rig tension is an entry control as well as a depth control. Entry is a shape; exit angle is a bearing.

Exit angle

Also exit, leech angle

The direction the flow leaves the leech in. It is a bearing rather than a shape, and the top batten's angle to the boom reads it at the head.

Exit angle is not the same as leech depth. A flat sail sheeted hard can have a closed exit and a full sail eased can have an open one.

Fetch

The distance of open water the wind has blown across to raise the waves that arrive. Waves grow with wind speed, duration and fetch until the sea is fully developed.

Fetch also means a course that reaches a mark without another tack. The wave sense is the one in a sea-state briefing and the course sense is the one on a beat.

Flyer

Also banger, corner

A large bet on one side of the course, taken alone and away from the fleet.

A first-beat flyer is priced as a lottery ticket against the series and not against the race. It is most tempting after a large loss, which is when the percentage principle rules it out.

Foil

Also foils, blade

A shaped surface that makes force at right angles to the flow over it. The 49er's foils are the daggerboard and the rudder blade.

Sails are foils too, working in air. The word on its own in this book usually means the underwater pair.

Foot

The bottom edge of a sail, from tack to clew. Outhaul tension sets the mainsail foot's depth and the shape of the lower leech.

Foot is also a verb meaning to sail low and fast. The noun is an edge of the sail.

Footing

Also footing off, free off, fast mode

Sailing a few degrees below the best pointing angle to carry more speed. It buys speed and gives away height.

Footing and pinching are the two departures from the VMG angle and both cost VMG. Each is used for a stated tactical reason with an exit condition, not as a habit.

Forestay

Also headstay, jib stay

The wire from the hounds to the stem head that the jib's luff is set on. On a 49er it is fitted to the centre hole of the stem head fitting and may not be adjusted after the start.

The book uses forestay for the wire and headstay mostly in the phrase headstay sag. They are the same wire.

Forestay sag

Also headstay sag, sag

The bow the forestay takes to leeward under the load of the jib, measured at its middle. Sag rounds the jib entry, makes the sail fuller and moves its draft forward, which widens the steering groove in light air and chop at the cost of pointing.

This book and its sources use forestay sag and headstay sag for the same thing. It is not set by a control of its own: it is what is left over once cap tension, mast bend and mainsheet load have had their say.

Furler

Also roller furler, furling gear

A drum at a headsail's tack that rolls the sail round its own luff to stow it or cut its area.

A 49er has none. The gennaker goes into a sock through a mouth in the foredeck, and the jib stays up for the race.

Gantry

Also rudder gantry, transom gantry

The frame at the transom that carries the rudder fittings. It is a named high-load inspection point.

Gate

Also leeward gate

A pair of marks at the bottom of the course that may be rounded on either side. The boat picks one and leaves the leg on the gybe that follows from it.

The gate is chosen for the next beat, not for the rounding. The pinwheel at the right-hand mark can pin a boat there indefinitely.

Gennaker

Also asymmetric, asymmetric spinnaker, kite, A-sail, chute

The 38 square metre asymmetric downwind sail, tacked to the end of the bowsprit and trimmed with a single sheet.

It is not a symmetric spinnaker. Its tack is fixed and its luff and leech never swap, so it is gybed round the front of the forestay rather than swung across on a pole.

Geostrophic wind

The wind that results when the pressure gradient and the Coriolis effect balance along straight isobars, with no friction. It is the reference the surface wind is compared against.

It is calculated, not felt. Boundary-layer wind is backed and slower than it, so a geostrophic figure is a starting point for a forecast and never a target on the water.

GNSS

Also GPS, satellite positioning

The satellite positioning a logger uses to fix position, and from successive positions to derive speed and course over ground. Dual-band receivers cut the position error that makes a speed trace noisy.

GPS is one constellation inside GNSS. A dual-band GNSS receiver is not the same instrument as an old GPS and the difference shows up in the speed trace, not in the track.

Gooseneck

The fitting joining the boom to the mast. It takes the boom's vertical and sideways loads and is a named high-load inspection point.

A 49er's gooseneck is fixed in height, so mainsail luff tension comes from the cunningham rather than from lowering the boom onto it.

Gradient wind

Also wind aloft, free wind, upper wind

The wind above the friction layer, where the surface has no grip on it. Surface wind is backed from it and slower, turning about 30 degrees over land and generally less over water.

Gradient wind and geostrophic wind are not the same thing. Geostrophic assumes straight isobars, gradient wind allows for their curvature, and forecasts use the words loosely.

Groove

Also the groove, luff groove, sail track, slot (in a spar)

Two things. The slot in a spar or a foil-shaped stay that the sail's bolt rope feeds into, and the span of headings over which the sails keep working, as in sailing in the groove.

A narrow groove in the second sense comes from a fine entry, which points high and punishes small steering errors. Forestay sag rounds the entry and widens it, which is why rig tension is a groove control.

Gunwale

Also gunnel, rail

The top edge of the hull side where the deck meets the topsides. On a 49er the load from the harness passes through the trunk to the feet on it.

Pronounced gunnel. On a skiff most of the time the working edge is the wing, not the gunwale.

Gust

Also puff, pressure, lull (its opposite)

A short rise in wind speed above the mean, and a lull is the matching fall below it. Measurements quoted in this book put gusts at 30 to 40 per cent above the mean, on a cycle of roughly 7 per cent every 6 to 12 seconds, with about half the time spent in each.

A gust arrives twice, first as a force before the boat has accelerated and then as a change of apparent wind once it has. The crew has to move for the first arrival, not the second.

Gybe

Also jibe, gybing

Turning the stern through the wind so the sails cross to the other side. The boat is then on the other gybe.

Jibe is the American spelling. Gybe also names which side the wind is on downwind, so being on port gybe is a state and gybing is a manoeuvre.

Halyard

The line that hoists a sail. The 49er's halyards lock at the top, so the luff can be tensioned from below without the halyard being pulled back down.

A halyard hoisted to its marked full-hoist point is what makes luff tension repeatable. Hoisting by feel changes every control that works against it.

Hank

Also piston hank, snap hook

A clip on a headsail's luff that fastens the sail to the forestay, so the sail can be dropped and still stay on the stay.

A 49er's jib has no hanks. Its luff is carried on the forestay itself, which is one reason the jib stays up and the gennaker does the work of changing gear.

Harness

Also trapeze harness

The webbing the sailor wears to take the trapeze load. The load runs from the harness through the trunk to the feet on the gunwale or the wing.

Harness load is the evidence that the lever is actually deployed. A bent body on a high hook feels secure and is carrying part of its own weight on the boat.

Head

The top corner of a sail. Head to wind means pointing straight into the wind with the sails on the centreline.

Head names a corner of the sail, a state of the boat and a verb, as in head up. The corner sense is the one that goes with tack, clew and foot.

Head up

Also luff up, harden up, come up

To steer toward the wind. The apparent wind moves forward and strengthens, and the sails are trimmed in to match.

Heading up and luffing are the same movement of the boat. Luffing in the rules sense is heading up in order to affect another boat.

Head-to-wind

Also head to wind, in irons

Pointing straight into the wind, sails flapping on the centreline. A tack passes through it.

The book takes its true wind direction from head-to-wind compass bearings logged on the water, so head to wind is a measurement as well as a position.

Header

Also knock, heading shift

A wind shift toward the bow, so the boat must bear away or lose height on the tack it is on.

A header is only a header on the tack you are on. The same shift is a lift on the other tack, which is why the usual answer is to tack rather than to sail on.

Heel

Also heeling, angle of heel

The boat's lean sideways, measured as an angle from upright. The 49er standard is flat, with plus or minus 5 degrees acceptable and plus or minus 10 only just tolerable.

Heel is sideways and pitch is fore and aft. Heel tilts the sail force away from vertical and makes weather helm on its own, so a boat loading up in a gust is usually heeled rather than out of balance.

Helm

Also the helm, tiller load

Two meanings. The person steering, and the force the boat puts into the tiller when the rudder has to be held off centre to hold a straight course.

Weather helm and lee helm use the second sense. The helm calls the shift uses the first. Nothing but context separates them.

High road

Also high mode, heating up

Sailing downwind above the VMG angle to build apparent wind and speed.

Speed comes before depth. The high road fails when it means sailing extra distance for not much extra speed, and the test is whether the boat is actually gaining VMG, not whether it feels fast.

Hole

Also gap, lane gap

A gap in the line of boats that can be accelerated into or tacked into. On the start line the hole to leeward, not which tack you are on, decides the first lane.

Hole also names the positions on the jib clewboard and the jib track, as in the middle hole. A tuning note and a start note use the same word for unrelated things.

Hook

Also trapeze hook, hooked leech

The fitting on the harness that takes the trapeze ring. Also what a mainsail leech does when it is over-tensioned and the top batten turns to windward.

Two unrelated meanings that both appear in a debrief. A hooked leech stalls the upper sail and loads the helm; hook height on a harness decides how much of the body's mass actually hangs on the wire.

Hounds

The height on the mast where the forestay and the upper shrouds attach. Bending the mast brings the hounds closer to the deck and lets the headstay go soft.

The hounds are a place, not a fitting. The fittings there are the key plate and the wire terminals, and the upper spreaders sit at the reinforcing around them.

Hull length

Also boat length, lengths

The boat's length, 4.99 m on a 49er, and the unit several rules and most tactical distances are quoted in.

The zone is three hull lengths, so on a 49er it is about 15 metres, and it is measured from the mark rather than between boats.

Hz

Also hertz, log rate, sample rate

Samples per second. A logger set to 10 Hz records ten fixes a second.

Distance sailed and manoeuvre loss both change with log rate, so two traces are comparable only at the same rate. The rate belongs in the file header.

I flag

Also rule 30.1, round-an-end rule

A starting penalty flag. In the last minute before the start, a boat on the course side of the line must return to the pre-start side round one of the ends before she starts.

Round an end, not straight back through the line, which is what a plain individual recall allows.

Intermediate

Also intermediate shroud

On a keelboat, a shroud landing part way up the mast between the cap and the lower. On a 49er the word comes from the older Ovington tuning table, where it is one of four labels.

The class rules do not use it. They say upper, middle and lower shroud, and the middle shroud is the wire most people mean by intermediate. A rig log should say which wire a reading belongs to rather than trust either vocabulary.

Intermediate shroud

Also intermediate, middle shroud

The middle pair of standing wires, between the caps and the lowers. With the lowers they set how far the middle of the mast may move.

The gauge list and the class rules name these wires differently, so a logged reading has to say which wire on this boat it belongs to.

Jib

Also headsail

The forward sail, 5.1 square metres on a 49er, set on the forestay and sheeted through a clewboard onto a curved track with limit pins.

Three separate things set its shape: forestay sag and luff tension fix the entry, the clewboard hole fixes how load divides between leech and foot, and the track pin fixes the sheeting angle. A jib fault is diagnosed by deciding which of the three moved.

Kinetics

Also body movement, pumping and rocking

Body and sail movement used to move the boat. Rule 42 divides it into handling, which is allowed, and propulsion, which is not.

Fast legal technique and marginal technique look alike from a coach boat and different to a judge with a yellow flag. Breaches in this class concentrate in the 4 to 8 knot range.

Knot

Also kt, kts

One nautical mile per hour, 1.852 kilometres per hour. Wind speed and boat speed are both quoted in knots.

Knots per hour is wrong. And knots of wind and knots of boat speed do not add up, because apparent wind is a vector sum and not a total.

Ladder rung

Also rung, rungs

A line drawn across the course at right angles to the true wind. Upwind the boat on the higher rung is ahead, however far apart the two boats are sideways.

The rungs rotate when the wind shifts, so boats level on the old rungs are not level on the new ones. Downwind the boat on the lower rung is ahead.

Lane

Also clear lane, trapped lane

The strip of clean air a boat has ahead and to leeward of her on a beat. Holding a lane is what lets a boat sail her own mode instead of the mode her neighbours force on her.

A trapped lane is one the boat can neither hold, because the air ahead is dirty, nor leave, because a tack puts her under somebody's bow. Clean air comes first in the first-beat priority order for this reason.

Layline

Also lay line

The course on which the boat can reach the mark without another tack or gybe. There is one for each tack.

There are three of them and they coincide only in a steady wind with no current: the wind-only layline, the one corrected for current, and the tactical one that arrives on starboard with rights. The crew has to name which it is sailing to.

Lee helm

The boat's tendency to turn away from the wind, held off with the tiller to leeward. It is slower than weather helm, because the rudder's lift then works against the daggerboard's.

Lee-bow

Also lee bowing

Tacking just ahead and to leeward of a boat on the other tack so your backwind falls on her.

There is no lee-bow effect from current, and a boat cannot gain by pinching to put the current on her lee bow. Where the move works it is a wind effect.

Leech

The aft edge of a sail, from head to clew. The sheet and the vang set its tension and its twist.

Leech load turns into rudder load. A leech held closed through a gust drives the boat to windward and the helm pays for it in drag.

Leeward

Also lee, downwind side, to loo'ard

The side away from the wind, and the direction the wind is going. Of two boats on the same tack, the leeward one is the one on that side.

Leeward is a relative position and it changes when the boat tacks. The leeward mark is downwind; a leeward boat is the one the windward boat must keep clear of.

Leeway

The angle between where the boat is pointing and where it is actually moving through the water. It is what loads the daggerboard, and racing boats sail upwind in medium breeze with 3 to 5 degrees of it.

Leeway is bought deliberately and is not a leak. The angle needed falls as the boat speeds up, and a boat with no way on has no grip at any angle.

Leverage

Also lateral separation, split

The distance between two boats measured across the wind, along a ladder rung. It prices a shift: 5 degrees changes their relative position by 12 per cent of it.

Leverage works both ways by the same amount. Two boats on the same ladder rung have no leverage between them however far apart they are along the course.

Lift

Also lifted tack, freeing shift

A wind shift toward the stern, so the boat can head up on the tack it is on. Also the force a sail or a foil makes at right angles to the flow over it.

Two senses in the same book. A lift on the beat is a change in the wind; lift on a sail is a force. The shift sense pairs with header and the force sense pairs with drag.

Line bias

Also bias, favoured end

The angle by which the start line sits off square to the wind, and the distance that angle is worth. The favoured end is the one further upwind.

Bias is worth a distance, not an angle. It is the line length times the sine of the bias angle, divided by the cosine of the close-hauled angle, and it is overridden when one side of the course is strongly favoured.

Loos gauge

Also rig tension gauge, tension gauge, PT-1

A spring instrument that pushes a wire sideways between two fixed points and reads how far it moves on a numbered scale. The number is a deflection, and each wire diameter has its own printed column for turning it into kilograms.

The number is not a tension and the columns are printed for 1x19 wire, which is not what this boat carries, so the kilogram conversion does not apply here at all. No metric model has a 3.5 mm column. What the gauge gives reliably is repeatability on the same gauge, the same wire and the same height, which is the only thing a rig log needs from it.

Low road

Also low mode, soaking, going low

Sailing downwind below the VMG angle, trading speed for depth. Soaking is the same move used to pass under a boat ahead while matching her speed.

It is available only once the boat has the speed to hold it. A boat that goes low before it is up to speed sees its apparent wind fall aft and has to heat up again to recover.

Lower shroud

Also lower, D1

The wire from the bottom mast section to the inner chainplate, with its own hull fixing and its own permitted turnbuckle. It controls the bottom panel of the mast, which is to say it controls prebend. The class rules allow it in 1x7 stainless between 3.0 and 3.5 mm.

It is set to a prebend rather than to a tension, so the gauge number on it is a consequence and not a target. It is also not in the forestay's load path: it ends below the hounds, so it reaches forestay sag only through the shape it gives the spar.

Luff

The forward edge of a sail. Luff tension is what the halyard and the cunningham set.

Luff is also a verb and also what a sail does when it flaps at that edge. The noun is the edge itself.

Luffing

Also luffing up, shooting

Steering toward the wind. In the rules, a leeward boat luffing a windward one heads up to force her away, limited where the overlap came from clear astern.

A sail luffing means it is flapping because its angle of attack has gone to nothing. A boat luffing means it is turning. Same word, unrelated events, often in the same sentence.

Mainsheet

Also main sheet, sheet

The line that trims the mainsail. It sets the boom position for the mode and moves first when the wind changes.

Sheet and vang both change twist. The sheet moves first and the vang holds what the sheet has set, so easing the sheet without the vang set moves the boom and not the leech.

Mark

Also buoy, turning mark

A buoy the sailing instructions require the boat to leave on a stated side. Windward mark, offset, gate and finish marks are all marks.

Touching one costs a one-turn penalty. The zone is three hull lengths measured from the mark itself.

Mark-room

Also room at the mark

Room for an inside overlapped boat to sail to the mark and then to round or pass it as required, given from the moment the first of the boats reaches the zone.

It is room to sail to the mark and round it, not room to go wide and come in fast. Overlap status is judged at the moment the first boat reaches the zone, and the entitlement survives the overlap being broken afterwards. In reasonable doubt an overlap is presumed not obtained and not broken.

Medal race

The final race of an Olympic series, sailed by the leading boats. At Paris 2024 its points were doubled and could not be discarded.

Doubled and non-discardable points change the risk calculation completely, so a lead defended in the opening series is defended differently here.

Middle shroud

Also primary shroud, main shroud, V1, D2

The shroud landing on the mast just beneath the top spreader and running to the deck through the lower spreader tip. The class rules allow it in 1x7 stainless between 3.0 and 3.5 mm, the same band as the forestay and the lower.

Ovington sells it as the main shroud and some dealers as the primary shroud, and the class rules call it the middle shroud; all three are the same wire. Its geometry at the hounds is deliberate, holding the middle of the mast forward so the forestay stays taut as the spar bends.

Mode

Also target mode, fast mode, pointing mode

A bounded departure from the target angle that buys a tactical result. Fast mode, pointing mode, high road and low road are all modes.

A mode is not a setting. It is temporary, it is called by name, and it has an exit condition stated when it is called, such as low until clear of the shadow.

Modulus

Also Young's modulus, elastic modulus, stiffness

The stiffness of a material: the load per unit of cross-section divided by the stretch it causes. A higher modulus means less stretch for the same load and the same section.

A wire rope's effective modulus is lower than that of the steel it is made from, because the wires lie in a helix and partly straighten under load. Compacting the strand raises it by taking out the gaps.

Offset mark

Also offset

A short mark set near the windward mark that the boat rounds before bearing away, so hoists happen clear of the boats still beating.

Ooching

Also ooch

A sudden forward lunge of the body checked abruptly. Rule 42 treats it as propulsion.

Oscillation

Also oscillating shift, shift pattern, phasing wind

A wind that swings either side of a mean and comes back, so the tacks alternate between lifted and headed.

The test that separates it from a persistent shift is a trend in the extremes. In an oscillation the highest heading on each tack is reached again; in a persistent shift it is not. A building breeze shortens the period and a dying one lengthens it.

Outhaul

The control that pulls the mainsail's clew out along the boom, setting the depth of the foot and the shape of the lower leech.

On a 49er it is a mode setting changed at the ends of the wind range, not a control worked up the beat.

Overlap

Also overlapped

Two boats overlap when neither is clear astern of the other, or when a boat between them overlaps both. Downwind an extended bowsprit counts as part of the boat.

The rules that turn on overlap are judged at a moment, not continuously: one at the moment the overlap began, another at the moment the first boat reached the zone.

Oversheeting

Also over-trimming

Trimming a sail in past its best angle. Upwind it stalls the sail and loads the helm; downwind on a 49er it is used deliberately to slow the boat against the risk of pitchpoling into a wave.

A stalled mainsail feels heavy on the sheet and gives no acceleration. Load in the hand is not drive in the boat.

Overstand

Also overstanding, overlaying

To sail past the layline, so the last part of the leg is sailed further from the wind than it needed to be.

In current, a layline that looks right is usually short. When the current sets toward the windward mark the true layline lies inside the wind-only one, so a boat that trusts the wind-only call overstands.

Persistent shift

Also trend, geographic shift

A wind change that goes one way and stays there rather than swinging back. The boat wants to be on the side the wind is shifting toward, which means giving up the lifted tack for a while.

It is diagnosed from the extremes, not from the current heading. The highest heading on a tack stops being reached again, and the mean drifts.

Phase

Also in phase, out of phase

Being on the lifted tack of an oscillating wind. A boat in phase gains on each swing and a boat out of phase loses on each swing.

Phase comes third in the first-beat priority order in this book, behind clean air and pressure, because a lane lost is worth more than a swing missed.

Pin

Also pin end, track pin, clevis pin

The buoy end of the start line, the end away from the committee boat. Also a metal pin, as in a jib track pin or a rig pin.

Pin end and pin position turn up in the same regatta. One is a place on the water and one is a hole in a track.

Pinching

Also squeezing, pointing too high

Sailing above the best pointing angle so the sail's angle of attack falls and the boat loses speed. It buys a few degrees of height at a heavy cost in VMG.

Pinching also loses foil grip, because leeway rises as speed falls, so the height it appears to buy is partly given straight back sideways.

Pinwheel

Also pinwheeled, stack

A queue of overlapped boats turning round a mark together, each one outside held wide by the one inside her.

At the right-hand gate mark a pinwheel can pin a boat indefinitely, so arriving on the outside of a pack at the zone buys one place and loses several.

Pitchpole

Also nosedive, digging in, somersault

Burying the bow so deep that the boat trips over it and capsizes forward. It is the downwind failure mode a 49er keeps a margin against.

A nosedive that is recovered is not a pitchpole, but the cure is the same and it has to be applied before the bow goes down: weight aft and the sheet eased, not after the water is over the foredeck.

Planing

Also up on the plane

Sailing fast enough that hydrodynamic lift rather than buoyancy carries most of the boat's weight. The hull rises, wetted area falls and resistance stops climbing the way it did.

The change is not a moment. Buoyancy carries the hull below a Froude number of about 0.4 and lift carries it above 1.0 to 1.2, and a 49er races through that whole span.

Polar

Also polar diagram, polar curve

A plot of boat speed against wind angle at each wind speed, from which the best upwind and downwind angles are read. No published 49er polar exists, so the crew builds its own from logged runs.

A polar is the upper envelope of what the boat has sustained, not the average of what it did. A polar built from means gives targets nobody can sail to and that nobody can fail to beat.

Port

The left side of the boat looking forward, and the tack you are on when the wind comes over that side. A port-tack boat keeps clear of a starboard-tack boat.

Port names a side and a tack, and the two are not the same statement. On port tack the boom is out to starboard.

Prebend

Also pre-bend

The fore-and-aft bow in the mast with the rig tensioned and no sail load, produced by spreader sweep and stay tension. The guidance quoted in this book is somewhere between an inch and a few inches, matched to the mainsail's cut.

Too little leaves the sail deeper than its design; too much removes depth the light-air mode needs and cannot be recovered on the water. It is measured against a taut halyard, not judged by eye.

Pressure

Also breeze, wind strength

Wind strength, as in more pressure on the left. It is read at the limit of vision, at least 200 to 500 metres out, from the darker bands on the water.

The book also uses pressure in its physical sense, force per unit area in the flow over a sail. On the racecourse it means wind strength and nothing else.

Proper course

The course a boat would sail to finish as quickly as possible if the other boats named in the rule were not there. A boat has no proper course before her starting signal.

There is no single proper course. Two boats in the same place can have different ones, and no boat is ever obliged to sail hers.

Protest

A formal allegation that another boat broke a rule, hailed at the first reasonable opportunity and filed inside the time limit.

The hail is part of the requirement and not a threat. A protest not hailed at once usually fails on validity before anybody hears the facts.

Pumping

Repeated fanning of a sail to drive the boat. Rule 42 treats it as propulsion.

A single pull to initiate surfing or planing where the rules allow it is not pumping. Repetition is what makes it propulsion.

Purchase

Also mechanical advantage, gearing

The ratio of line pulled to load moved in a block system. Purchase divides the load and friction taxes it, and friction costs more on the ease than on the pull.

A high purchase makes a control heavy to ease and slow to run out under its own load. A system that will not run out cannot be trimmed from the wire, which is where it has to be trimmed.

Rake

Also mast rake

How far the mast leans aft, measured from a fixed reference on the hull. Raking aft moves the sail plan's centre of effort aft and adds weather helm.

Rake is a lean of the whole spar, bend is a curve in it, and both change helm balance. A change in helm balance at unchanged rake points at a forestay length or a spreader that has moved.

Reach

Also reaching

Any course between a beat and a run, with the wind on or abaft the beam. A 49er sails its downwind legs as a pair of reaches with gybes between them rather than square before the wind.

Reach is also a verb meaning to arrive, as in reaching the layline. A windward-leeward course has no reaching legs and yet every downwind leg on it is sailed as a reach.

Recall

Also individual recall, general recall

The signal that boats were over the line at the start. An individual recall names them; a general recall abandons the start and restarts the fleet.

Under the U flag and the black flag there is no individual recall to sail back against, so a boat can sail an entire race that will not be scored.

Retrieval line

Also takedown line, douse line, drop line

The line that drags the gennaker back into the sock. Its lead and the sock mouth are chafe points, because a drop that jams costs a leg.

Rhumb line

Also direct line

The straight line between two marks. Cross-track error is measured sideways from it.

Rig tension

The tension in the standing rigging, set with a gauge and logged. Cap shroud tension sets forestay tension, and so how far the headstay sags and how full the jib is.

Standing rigging may not be adjusted after the start, so every rig tension is a bet placed before the race on the wind the race will have.

Righting moment

Also RM

The turning moment the crew's weight makes about the boat, opposing the heeling moment from the sails. It is weight multiplied by the lever from the boat's centre.

It is a moment, not a weight. Two crews of equal mass have different righting moments if one is further out, which is why trapeze height and body extension are settings and not style.

Rocker

The fore-and-aft curve of the hull's bottom. A 49er trimmed bow-down meets the flow with the curved forward bottom at a negative angle and ploughs.

Rocker is a shape the builder gave the boat. What the crew changes is where the weight sits, which decides how much of the rocker is in the water.

Rocking

Repeated rolling of the boat by body movement. Rule 42 treats it as propulsion.

Roll tack

Also roll tacking

A tack in which the boat is deliberately heeled to windward through the turn and flattened as it exits, so the rig does some of the steering and the rudder does less.

The 49er's chine is taken away amidships so the hull can be rolled without a large drag increase. Rule 42 still bounds it, and breaches in this class concentrate in the 4 to 8 knot range where the technique pays most.

Room

The space a boat needs in the conditions of the moment to manoeuvre promptly in a seamanlike way, including space to comply with the rules.

Room is not a fixed distance. The same boat needs more of it in waves and at speed, so a gap that was room on a flat day is not room in chop.

Rudder

The steering foil at the transom. It is a lifting foil as well as a steering one, so the angle it is held at measures the boat's balance.

Rudder angle is drag. Corrective steering to hold a course is pure drag, so a busy rudder trace is a trim problem being paid for with the tiller.

Rudder stock

Also rudder head

The part that carries the rudder blade and pivots in the gantry, with the tiller attached to it.

The stock and the blade are treated differently by the weighing rule: the stock counts with the hull and the blade does not.

Rule 42

Also propulsion rule

The rule against propelling the boat by body or sail movement. Repeated rocking, repeated pumping, ooching and sculling that drives the boat are propulsion; steering to follow waves is handling.

The 49er class rules relax it in one respect only, allowing sculling that does not propel the boat in any direction. A judge penalises on the water with a sound signal, a yellow flag and a hail of the sail number.

Run

Also running

The leg sailed away from the wind.

Run names the leg. Running square is slower on this boat than reaching high and gybing more, so a 49er's run is not sailed as a run.

Safe leeward

Also safe-leeward position, lee bow position

The position bow-forward and to leeward of a boat on the same tack, where the wind bending round the front of your sail plan gives you a lift and more pressure while your backwind reaches her.

It holds only while your bow stays forward of hers. Slip back and the same position becomes the one where her backwind reaches you.

Sag

Also headstay sag, forestay sag

How far the forestay bows to leeward and aft under load. Sag makes the jib fuller, rounds its entry and moves its draft forward, which widens the groove.

Sag is a consequence rather than a control. It follows cap shroud tension and mast bend, because bending the mast brings the hounds closer to the deck and the headstay goes soft.

Sail plan

Also sailplan, rig

The mainsail and jib taken together as one force-producing surface with one centre of effort.

The two sails are not trimmed independently. A jib sheeted for its own shape can be wrong for the slot, and the result is a sail plan out of balance with the foils rather than a bad jib.

Sculling

Swinging the rudder back and forth to drive the boat. Rule 42 prohibits it, and the 49er class rules allow it only where it does not propel the boat in any direction.

Set

Also current set

The direction a current is flowing toward. A current setting north runs toward the north.

Wind is named for where it comes from and current for where it goes to. A north wind and a north-setting current run in opposite directions, and mixing the two conventions puts a layline correction the wrong way round.

Sheave

The grooved wheel inside a block that the line runs over. Its diameter decides how hard the line is to pull, and the class rules limit it on some systems.

A block is the whole fitting and a sheave is the wheel inside it. A replacement block must carry the same number of sheaves of similar or greater diameter.

Sheet

Also sheets

The line that trims a sail in and out by pulling on its clew. A 49er has a mainsheet, two jib sheets and two gennaker sheets.

A sheet pulls a clew and a halyard pulls a head. A sheet never hoists anything, whatever it is doing to the sail's shape.

Shroud

Also side stay, stay

A standing wire from the mast to the hull that stops the mast falling sideways. A 49er has three pairs, which the class rules call upper, middle and lower.

Shrouds hold the mast sideways and stays hold it fore and aft, but swept spreaders make a 49er's shrouds do both jobs at once.

Significant wave height

Also Hs, sig height

The mean height of the highest third of the waves, which is roughly what a trained eye reports. The largest individual wave is about twice it.

It is neither the average wave nor the biggest. A briefing quoting one metre means individual waves of about two metres will arrive during the race.

Slot

Also the slot, gap

The gap between the jib's leech and the leeward side of the mainsail, and the shape of the flow through it.

The slot is a gap between two sails, not a device. Sheeting the jib harder to narrow it does not speed the air up; it backwinds the mainsail.

Sock

Also chute, snuffer, launcher bag

The tube under the foredeck that the gennaker is pulled out of and dragged back into. It counts with the hull for weighing.

SOG

Also speed over ground

The boat's speed relative to the sea bed, taken from successive satellite fixes. It includes whatever the current is doing.

SOG is not speed through the water, and speed through the water is not logged directly. In a tide two boats with equal SOG are not sailing equally well, which is why every logged bin records the current.

Spinnaker

Also symmetric spinnaker, kite

A downwind sail set forward of the forestay. A symmetric spinnaker flies from a pole that swings across on each gybe and has two clews that swap roles.

A 49er has no spinnaker in that sense. The class manual and the tuning notes quoted in this book nevertheless call the gennaker the spinnaker, so the two words name the same sail on this boat.

Spreader

Also crosstree

The strut that holds a shroud out from the mast, so the shroud can stop the middle of the mast falling to leeward. A 49er has two pairs, the upper set at the hounds.

Length and sweep do different jobs. Length sets the sideways lever; sweep gives the load a forward component and makes prebend. A spreader that has crept or rotated shows on the water as a mast that bends differently on each tack.

Standing rigging

The wires that hold the mast up and are not adjusted while sailing: forestay and shrouds. On a 49er the class rules require 1x7 stainless wire rope, with the forestay, middle and lower shrouds between 3.0 and 3.5 mm and the upper shrouds between 2.3 and 2.6 mm.

Those are two separate bands, so nothing between 2.6 and 3.0 mm is legal on any wire. The wire may come from any supplier, but only one set may be used through an event. Running rigging is everything that moves, and it is the only thing available as a control during a race.

Starboard

The right side of the boat looking forward, and the tack you are on when the wind comes over that side. A starboard-tack boat has right of way over a port-tack boat on a beat.

The hail states a fact; it does not create the right. Starboard names a side and a tack, and on starboard tack the boom is out to port.

Stem head fitting

Also bow fitting, stemhead

The fitting at the bow that the forestay pins to. On a 49er the forestay goes in its centre hole.

The rule fixes which hole, so rake is set at the mast step and the turnbuckles and not by moving the forestay forward at the bow.

Strop

Also soft link

A short loop of wire or rope used as an anchor point for a fitting. The 49er's vang take-off block attaches to a mast strop.

Swage

Also swaged terminal, swage fitting

A wire terminal made by squeezing a metal fitting onto the wire under pressure until the two are one piece. It cannot be undone and cannot be inspected inside.

All the evidence is outside: broken strands at the swage mouth, a kink, discolouration and a pin worn oval. A wire showing any of these is replaced, not retensioned.

Sweep

Also spreader sweep, swept-back spreaders, spreader angle

How far aft the spreaders angle from square to the mast. Sweep gives the compressive load at the spreader root a forward component, and that is the source of prebend.

Sweep and spreader length are separate settings with separate effects, and unequal adjustment cords give a mast that bends differently on each tack. Sighting up the mast on each tack is the check.

Swell

Wave energy that has travelled out of the area that made it, so its direction need not match the wind on the day.

Where swell and wind waves cross, the two directions are noted separately, because each leg meets them at a different angle and each gybe meets them differently again.

T-terminal

Also T-ball, T-bar, stud terminal

A wire end fitting with a T-shaped or ball head that drops through a slot in a plate on the mast and locks when the wire comes under load. The 49er's upper wires use one at the key plate at the hounds.

It holds because the wire is loaded. Letting the rig right off with the mast up can let a terminal move in its plate, so it is a fitting to check whenever tension has been taken out.

Tack

Also tacking, on port tack, to tack

Three things. The forward lower corner of a sail, which side the wind is coming over, and the manoeuvre of turning the bow through the wind to change which side that is.

The cunningham pulls the tack down, the boat is on port tack, and the helm calls a tack. Only context separates them, and a 49er's tack line holds the gennaker's tack corner rather than having anything to do with the manoeuvre.

Tack line

Also tackline

The line that holds the gennaker's tack down to the end of the bowsprit. It cleats for the hoist and releases for the drop.

Tacking duel

Also tacking dual, tacking battle

A sequence of tacks between two boats, each covering the other.

It takes both boats off the lifted tack and away from pressure, so the third boat gains on both of them. Refusing the duel is usually the stronger move for the boat behind.

Target

Also target speed, targets

The speed, heading, VMG and heel the crew has logged as achievable in a given band, together with the settings that produced them.

A target is the upper edge of what the boat has sustained, not an average. It is the crew's own number by wind band, because no published 49er table exists to replace it.

Telltale

Also tell-tale, woolies, leech ribbon

A light thread or ribbon on a sail that shows which way the air over it is going. Jib luff telltales read the angle of attack at the entry; leech ribbons read whether the exit is still attached.

The leeward telltales are the ones that warn. The aft leeward one lifts and stirs first and the forward ones stall afterwards, so a lifting aft telltale is a warning and a stalled forward one is a verdict.

Tide

Also tidal stream, current

Strictly the vertical rise and fall of the water. The horizontal flow it drives is the tidal stream, which is what moves the boat.

The book uses tide loosely for the flow, as in every bin records the tide. What is meant is the current vector, which is what separates speed over ground from speed through the water.

Tiller

Also tiller extension, stick

The lever that turns the rudder stock. The extension is what lets the helm steer from the wire, and the class rules allow it to be replaced without restriction.

Play anywhere between the tiller and the blade creates a dead band in which the tiller moves and the blade does not, so the correction arrives late and is then too large.

Time to burn

Also time-to-burn

The time left to the gun minus the time it will take to reach the line. It is the slack the boat has to spend before it must accelerate.

Time to burn goes negative before the boat feels late. The boat arrives on time only where the time to burn is at least as long as the acceleration takes.

Transit

Also range, back bearing

A line found by lining up two fixed objects ashore. A transit through both ends of the start line to a fixed object locates the line, and transits taken one on the line, one over and one behind give a bias measurement.

A transit only works while both objects stay visible and the boat is on the line between them. A transit read from an object that moves, such as another boat, is not a transit.

Transom

The flat surface across the stern. On a 49er it carries the rudder gantry.

An immersed transom drags like a brake. At displacement speeds the stern should come clear, and crew fore-and-aft position is what decides whether it does.

Trapeze

Also wire, trapezing

The wire from the mast to a ring the harness hooks to, which lets a sailor carry weight outboard. A 49er has two, and its mast is rated for a combined crew weight of up to 165 kg on them.

Being out is not the whole of it. Righting moment is weight multiplied by lever, so how straight the body is and how low the hook sits decide how much of the mass is actually on the wire.

Traveller

Also mainsheet traveller, track

A car on a transverse track carrying the mainsheet's lower block, so the boom can be moved across the boat without changing sheet tension.

A 49er has none. Its mainsheet leads from blocks on the boom, so sheet tension and boom position are one control here, and the vang is what separates leech tension from boom height.

Trim

Two meanings. Setting a sail's angle with its sheet, and the boat's fore-and-aft attitude, bow-up or bow-down.

Sail trim and hull trim appear in the same paragraph in this book. Hull trim is a crew-weight decision and sail trim is a sheet decision, and confusing them sends the wrong crew member moving.

True wind

Also TW, true-wind angle, TWA

The wind relative to the water, which is what shifts, laylines, ladder rungs and VMG are worked in. On a 49er it is always weaker and further aft than the wind the boat feels.

True wind relative to the ground differs from true wind relative to the water by the current. A tracker's true wind is a derived number built from its own assumptions, not a measurement, so it is checked against the crew's own head-to-wind bearings before it is used.

Turnbuckle

Also rigging screw, bottlescrew

A threaded barrel between a wire and its hull fitting that lengthens or shortens the stay when it is turned.

Turnbuckle, rigging screw and bottlescrew are the same fitting. Turns are the unit that makes a change repeatable and transferable, because a gauge number only means anything with that gauge.

Turns penalty

Also two-turns penalty, one-turn penalty, spins, circles

The penalty a boat takes for herself: two turns in the same direction including two tacks and two gybes for a Part 2 breach, one turn for touching a mark, taken promptly and clear of other boats.

At Paris 2024 and the 2025 World Championship the 49er's two-turns penalty was replaced by a one-turn penalty, so the event documents rather than habit decide what a breach costs.

Twist

How much the sail's chord angle changes from foot to head. Twist matches the sail to a wind that is stronger and further aft aloft than at deck level.

Twist is not slack. A twisted leech is depowered at the head and can still be hard-sheeted at the foot, and a sail with no twist is wrong at one end of the span or the other.

U flag

Also rule 30.3

A starting penalty flag. A boat inside the triangle formed by the ends of the line and the first mark during the last minute before her signal is disqualified without a hearing.

Same triangle as the black flag. The difference is that a restart or a resail wipes the U flag penalty and does not wipe the black flag one.

Upper shroud

Also cap shroud, upper, V2, D3

The class rules' name for the outermost shroud, from the masthead to the deck. It is the thinnest wire on the boat: the rules allow it in 1x7 stainless between 2.3 and 2.6 mm, against 3.0 to 3.5 mm for everything else.

Upper shroud and cap shroud are the same wire. The thinner band is the reason a single spare reel does not cover a whole rig.

Vang

Also kicker, kicking strap, boom vang

The control that pulls the boom down against the mast. It holds leech tension and lower mast bend when the sheet is eased, so it separates twist from boom position.

The vang pulls down only; easing it adds twist. On a 49er it is released considerably before a bear-away, because leech load becomes rudder load in the turn.

VMG

Also velocity made good

The part of the boat's speed that runs along the true wind direction, toward the wind upwind and away from it downwind. It is what the leg pays for.

VMG toward a mark and VMG along the wind are different numbers, and this book means the second. Upwind and downwind values are never compared with each other.

Wake

The disturbed water the hull leaves behind it. Its windward edge leaves the hull at a wider angle than its leeward edge, which is leeway made visible.

Weather helm

The boat's tendency to turn toward the wind, held off with the tiller to windward. A small amount is wanted, because the rudder is then a lifting foil working alongside the daggerboard.

The target is a blade angle, not a leeway angle, and the book quotes a similar figure for each. Heel produces weather helm on its own, so a boat that loads up in a gust is usually heeled rather than out of balance.

Wetted area

Also wetted surface

The area of hull in contact with the water. It is the main source of resistance at low speed, so light-air crew position is chosen to make it small.

Least wetted area and least wave-making want different trims. Below planing speed wetted area dominates; once the boat is up on the plane it does not.

Wind shadow

Also dirty air, bad air, blanketed, disturbed air

The band of slowed and bent air behind a boat. Upwind a 49er throws it over boats within 6 to 10 lengths, reaching 8 to 10 lengths to leeward in light air.

On a skiff the apparent wind is so far forward that the shadow falls almost straight astern and a little to leeward, not abeam. The safe positions are not the ones a keelboat sailor expects.

Windward

Also weather, upwind side

The side the wind is coming from, and the direction it comes from. Of two boats on the same tack, the windward one is the one on that side.

Windward and weather mean the same thing, so the weather mark and the windward mark are one buoy. A windward boat must keep clear of a leeward boat on the same tack.

Wings

Also wing bars, racks, wing

The tubular frames that extend the 49er's deck outboard. They count as part of the hull for weighing, carry the trapeze loads and must be fully extended when racing.

Z flag

Also rule 30.2

A starting penalty flag. A boat inside the triangle formed by the ends of the line and the first mark during the last minute before her signal takes a 20 per cent scoring penalty.

It is a price rather than a bar, and it can be incurred again if the race is restarted, so two attempts at the same start can cost two penalties.

Zone

Also three-length zone

The circle of three hull lengths round a mark, about 15 metres on a 49er. The rules that give mark-room turn on whether boats were overlapped at the moment the first of them reached it.

The zone is measured from the mark, not between boats, and the moment of entry fixes everything that follows. Calling the zone edge as a distance is a crew job done before the boat commits.