Sail Theory

Grade III

Wind

• True Wind is the actual wind force and direction. If you are sitting still this is what you feel • Relative Wind is the wind force you are creating with your motion. On a perfectly calm day, you will feel your relative wind as being exactly contrary to your motion. (If you head north at 10 kt, your relative wind will be a southerly 10 knot breeze) • Apparent Wind is the combination of both. This is the wind you are actually experiencing

(Apparent means readily seen or open to view) Apparent Wind

• Some points to remember: – If you are going upwind the apparent wind will be greater than the true wind – If you are going downwind the apparent wind will be less than the true wind – Wind direction will also be affected, becoming somewhere in between true and relative wind. – The amount of change in either speed or direction will depend on the relative strengths of the wind, particularly the strength of the true wind • 25 knots of true wind will not change very much for vessels of our speed, 7 knots will be readily affected.

Calculating True Wind

• You can use vector diagrams to calculate true wind. • One leg will be the vessel’s vector (relative wind), one leg will be the apparent wind as measured, the resultant is the true wind. • For a rough idea you can just look at the waves for wind direction and strength.

Sail Theory

• When sailing off the wind or downwind then sails just catch wind and get pulled along. • If you are sailing upwind then the sail is acting as an airfoil. This is essentially a wing, and if viewed from above you will see how a sail resembles a wing in cross section. Wing Sail

Sail Theory

• A neat thing about studying sail theory is that it is still largely a theory. There are good ideas on why and how sails work, but none have been proven to be entirely true. • For our purposes though, there are two principles that have been proven to work on a sail, regardless of what may or may not be going on at a more theoretical level.

Sail Theory

• Bernoulli's Theorem: States that in the case of a fluid in motion, the ratio of speed and pressure will, to a certain degree, remain constant. – This means that as the velocity increases, the pressure will decrease.

Sail Theory

• The Venturi Effect: Is an applied instance of Bernoulli's theorem, in which a fluid is run through a tube of decreasing diameter. – Using a tube of decreasing diameter, a Venturi tube shows the decrease in pressure that accompanies an increase in flow rate.

Lower Pressure High Pressure Quick Flow

Slow Flow Bernoulli's Theorem and the Venturi Effect, as Applied to Sails • Although this is an oversimplification of the phenomenon, the air travelling over a wing or a sail acts in a similar way to that fluid travelling through the tube. – Because of the curve of a sail and a wing, the air travelling over the forward/upper edge is compressed, increasing the flow rate and decreasing the pressure, while the air over the aft/lower edge is unchanged.

Diagram of a Wing

Fast Air

Low Pressure

Slow Air

High Pressure

Forces at work

• The wind acts upon the sail • This force is transferred through the rigging to the hull (This is an important point. Next time you have a chance take a look at the attachment points for the running and standing rigging as well as the masts, all force is being transferred through these relatively small points of contact) • The force is then transferred into motion, and the keel works to translate as much as possible into forward motion.

Leeway

• Leeway is the sideways movement of the vessel. – The boat makes more leeway when going upwind than downwind – Leeway also increases with stronger winds and particularly with large waves – It is important to calculate for it when navigating, and you can get an idea of the amount of leeway by taking a bearing down your wake to see what the difference between course steered and CMG is.

CE vs. CLR

• CE is centre of effort. This is the theoretical centre of the forces acting up on the ship (sails each have their own CE, the sum of them all will create an overall CE) • CLR is the centre of lateral resistance. This is the theoretical centre of the underwater surface of the ships hull, it is the pivot point. – The CLR will move slightly depending on angle of heel, fore’n’aft trim and speed but is essentially stationary for our purposes. – The CLR is located slightly forward of midships

CE vs. CLR

• When setting and dousing sails you move the CE. Depending on where the CE is you can have a lot of effect on the behaviour of the vessel. – Knowledge of how to manipulate this will allow you to get the most out of the vessel when sailing and when maneuvring • Easing a sheet or sheeting it in will also affect CE, so minor adjustments can be made without changing sail.

CE vs. CLR

• The CE can also raise and lower (discussed later) or move athwartships. • When going downwind you will want to keep CE close to the centreline, or if it must be offset keep it as forward as you can. – Sometimes we reef the main for steering purposes, or even take it all together when running – A stuns’l can help balance this out

Steering and Balance

• Remember that to steer the ship you need water flow past the rudder. The faster you go the more responsive it will be. • While sailing you can also use the balance of the sail plan to assist in steering – If your sail plan makes the bow want to point into the wind you have Weather Helm – If your sail plan makes the bow want to point downwind you have Lee Helm • You usually want to have the forces almost in balance, otherwise you will need to use a lot of rudder which is inefficient as it creates unnecessary drag – Well balanced sail press will allow the boat to stay on course with almost no input

Points of Sail

Points of Sail: A: In Stays B: Close Hauled C: Close Reach D: Beam Reach E: Broad Reach F: Run

Wind

In Stays

• This is when the wind is dead ahead. • Generally we avoid this point of sail, but when we tack we go through it. • It is also a good way to stop the ship down in a real hurry: Square the yards, sheet in the main and head up.

Close Hauled

• Apparent wind will be stronger than true wind. • All sails are acting as airfoils • On modern high-performance boats this is the fastest point of sail. – The design allows the boats to get to very high speeds, and they can often sail faster than the true wind speed. • For the brigantines this can be a very good point of sail as every sail is drawing well, but it is not our fastest. • Generally speaking we will keep CE aft of CLR, so as to create a slight amount of weather helm, which helps in pointing and making it to windward.

Close Reach

• Apparent wind is still stronger than true wind, but less so. • All sails are acting as airfoils • Sail trim is more or less the same as for close-hauled. • CE should be about balanced, or slightly aft

Beam Reach

• Apparent and true wind will be roughly equal • Sails are still acting as airfoils • CE and CLR should be roughly balanced

Broad Reach

• Apparent wind will be less than true wind.

• Squares are being pushed now, fore’n’afters might be getting pushed, might still be acting as airfoils

• This is the fastest point of sail for our boats. – The large sail area can be fully utilized, and as the brigantines are not modern lightweight craft they get pushed more efficiently than they are pulled. • Keep the CE forward, otherwise the boat will try to round up and broach.

Running

• Apparent wind will be less than true wind

• All sails are being pushed

• Not as fast as broad reaching as the forward sails are somewhat blanketed by after sails

• Keep CE forward

Sailing by the Lee

• This is when you are going downwind and the wind is coming over the same side as your fore’n’afters are out on. – This is to be avoided for a few reasons: • Inefficient, you are blocking the forward sails • Major danger of an accidental Gybe

Evolutions

• An evolution is the term given to the actions taken whenever any major alteration is done to the sail press – This includes Tacking, Gybing, Wearing Ship and Bracing – It can also include setting/striking sail and heaving to

Tacking

• When beating to weather it is very important to keep good, tight sail trim and to make sure your helmsman is steering full-and-by (not just full!) • Hold each tack as long as possible, every time you tack you lose speed and are momentarily stopped. – If two boats sail the same distance, one taking 2 long tacks, one taking 4 short tacks, who will get there first?

Tacking

• Surging is an important aspect of tacking. – This is when you put the wheel over slowly enough that you use the momentum of the ship to ‘surge’ to windward before you pass through the eye of the wind and lose your headway. – If done properly you can gain a boat length or so directly to windward from each tack, this adds up to a lot of ground over time. – Watch you don’t tack too slowly though, you can lose the momentum and blow the tack – The only time you shouldn’t surge is when you need to tack very quickly to avoid something, otherwise it should be a regular habit.

Tacking

• Make sure you do not call for the yards to come over too early, they will push the bow back and you will lose the tack. – If you find this happening you can call for a brace back to the original side and hopefully push the bow through. • If you are unsure then wait until the fore-n- afters are properly filling on the new leeward side

Gybing

• The main boom needs a lot of attention when gybing in anything but light wind. – Get another officer on deck to help out with the sheet unless you are absolutely sure your PO can handle it.

Bracing

• You can call either ‘slowly’ or ‘hard’ when bracing. – Hard is when you want the yards hard over to one side or the other – Slowly is when doing small adjustments

• When bracing ‘slowly’ make sure your PO has the trainees keep a turn on the leeward pins so as to maintain control.

Wearing Ship

• Brace - Gybe - Brace

Sail Trim

• When going upwind Squares behave just like fore’n’afters. – Keep the luff tight! • If you are on a run just square the yards • But, if you are between a run and a beam reach you will want to trim the yards like this: – Looking from above imagine a line running along the middle of the ship from fore to aft. – Next, imagine the wind crossing this as a single line, and see the angle it creates – The angle of the yards should be double this angle, or to look at it another way, the angle of the wind hitting the ship should be half the angle of the yards.

Sail Trim

• The wind ‘slotting’ between sails will increase the velocity of the wind, in a funnel like effect. • Because of this each successive sail should be trimmed in a little tighter. – Start at the forward-most sail and work aft. – As an example, the main will be sheeted in more if a Big Fish is set than otherwise, this is due to the funnelling effect the fish has on the wind.

Sail Trim

• Trimming fore’n’afters is pretty simple: – “Let it out ‘til it luffs, pull it in ‘til its trim”

• Remember to account for slotting when trimming fore’n’afters

The Sails a) Mainsail i) Jibtop or Foretopmast b) Main Staysail j) Fore Staysail c) Course k) Studdingsails or Stunsails d) Topsail l) Rafee e) Jib m) Watercatcher f) Gaff Topsail n) Ringtail g) Little Fisherman Staysail o) Jack Yard Gaff Topsail (or h) Big Fisherman Staysail Sparred Gaff Tops’l)

Course Sail

• The Course is the second largest sail in the standard press, beat out only with the main. – The course is an excellent sail, especially downwind. – In a sailing with the wind aft of the beam, it is often better to leave up the course and douse the tops'l if sail reduction must be made – Of the two squares the course cannot point as high

Tops'l

• The tops'l is a good sail, as we can still point quite high with it up. – But it is one to watch as wind begins to pick up, because its CE is very high up, and it will have more effect on the heel of the boat than many of the other sails. – Often very useful in sail ons, as its effect can be changed a lot through adjustment of the halyard and its bunts and clues.

Headsails

• The Jib and Jibtop are relatively similar sails; dousing the Jibtop can be thought of as reefing the headsails. – These sails will do well to move the CE forward on the boat, but as the wind moves aft of the beam, the effect of these sails is diminished as the squares blanket. – Can be useful to get your bow off the wall with a complimentary wind – A storm jib can also be very useful to add stability + avoid broaching in heavy weather Main Stays'l

• While this sail is relatively small, and doesn't have much effect on the CE (Its CE is very close to the boat's CLR), it is a very good stability sail, and should be brought down only in the heaviest of wind (or when the big fish is set). – Keep it sheeted all the way in on a run, as it is a good indicator as to weather you are close to an accidental gybe.

Main Sail

• The main sail is the largest of our standard press sails, and is probably reefed the most of any sails. – This is mainly as a result of the fact that it affects the steering so greatly. In a strong wind, the main can cause a strong enough weather helm that the rudder cannot counteract it. – Its effect on the CE is so great that it is possible to steer the boat sheeting only the main in and out. Luffing

• When setting a sail it is very important to get the luff as tight as you can. – A loose luff means you will not have proper sail shape – You will also not be able to have the sail as close to the wind as you otherwise could • If a sail is luffing it is not generating any lift, and it is also bad for the sail (takes life off of it very quickly) and very bad for the rig (the jib-top or fisherman can bring down a topmast if they luff too badly)

Luffing

• Despite the issues related to bad luffing, you can use slight luffing to your advantage in some situations. – If you want to slow down then you can head up a bit too far, or alternately just ease the sheets on some of the sails to let them luff slightly. – If you have a bit of luffing you are fine, but if the sail starts to shake badly, especially if you can feel it, then you have luffed too much.

Altering Course

• When altering course, think out what you will need to do with each sail prior to the manuevre. – You should brace and/or sheet in sails prior to heading up – You should brace and/or ease sheets after bearing off – This will help to avoid any unwanted luffing, and remember that the crew will always respond a little slower than you want, so give them advance warning. – This is of particular importance if you may Gybe, you need to be ready on running backstays and the mainsheets as well as other lines.

Sailing Stability

• Just as CE moves fore and aft with different sail combinations, it also moves up and down, which affect angle of heel and stability • As you heel the hull creates more drag, which is overcome by setting more sail, to a certain point • There is a line between pushing the vessel and overdoing it, at which point you are actually no longer helping the ship, but slowing her down. – If you have the deck edge in the water you are dragging a lot of excess stuff.

Deck Edge Immersion

• This is an important threshold to be aware of while sailing. • When the edge of the weather deck is immersed it is the point of diminishing stability – This doesn’t mean that the vessel is about to capsize, but the righting arm is starting to decrease in length

Tuning the Rig

• All components of the rig are connected! • For the best performance under sail spars must be sitting in the best position, and stays and shrouds must be at the appropriate tension. – Without this the rig will not give you the best performance, and chances of breakage are much higher. • Rigging officer should monitor the tune of the rig daily while under sail and adjust when necessary, and major rig tuning should be done a few times a summer – When tuning remember that forward leading rigging has more leverage and therefore requires less turns on the bottlescrew for the same tension (roughly a 1:3 ratio)

Sailing on to an anchorage

• The best technique for sailing on to an anchorage is to beat upwind to the desired location. When you drop the anchor, you want to be as close to head to wind as possible. – Remember that to set an anchor, reverse motion is needed, so generally the yards are squared with sail still set after the anchor is dropped, to allow the anchor to bite.

Sailing off of an anchorage

-When sailing off an anchorage the ship will be in stays -To fall off as quickly as possible you want to bring the CE as far forward as possible -You can set your jib, or a square that is backed will have the same effect -The benefit of using your squares is that they allow you to choose the side that you wish to fall off on -Remember to wait until the anchor is away to begin setting sail

Sailing On and Off a Wall

-Sailing on and off a wall is fun and rewarding, but can cause damage to the ship or injury to a crew member if the crew is not paying attention -It is important that every officer on deck is aware of the plan prior to execution -this does not mean that the plan will always be executed perfectly, but it helps -There is no one way to execute a sail on or off properly -so try and think of all possible outcomes when coming up with a plan

Sail Ons

-when sailing on to a wall your stern line is almost always the most important line -there should always be an officer handling this line and it should be surged to slow down -The topsail is a better sail to use than the course -it is easier to handle on deck, it does not get in the way of line handling, and it's smaller -Make sure that you do not approach the wall too fast

Sail Offs

-The primary objective of a sail off is to get off the dock -this is easier said than done in a following wind -If the boat is going to scrape up against the wall make sure there are lots of roaming fenders -Make sure that when you are off the wall that there is sufficient water to manoeuvre