Every once in a while, some brave soul joins us who bought a DS and is starting without or without much sailing experience. Or it's been a while, or they know more about windsurfing than dinghy sailing. Actually, that seems to be happening with some greater frequency recently.
Anyway, I thought, I'd collect some of the more basic concepts, terms and techniques here. Not trying that in an organized way, but as a loose collection of posts, each centered on an interesting picture, graph or diagram and with a bit of discussion each.
Over time, I'll add additional posts as loosely inspired by the discussions elsewhere on the forum. So, check back occasionally.
Here are some shortcuts to particular topics. This list is not complete.
UPDATE: After some reflection, I would like to suggest that we keep this thread concentrated, so we should discuss any questions elsewhere. There's no better place for a discussion of these topics than the "Everybody is an Expert Sailor?" thread right here. Feel free to comment on my explanations (or lack thereof) and / or ask questions about these and other concepts and techniques for boat handling there. I'll make updates and additions here to reflect those and other discussions on the forum, so hop on over there and discuss!!
In case that wasn't obvious: the stuff I pulled together in this topic is based on my own understanding and often on personal experience, which may not match the conditions you are sailing in. None of it has been verified or approved by anyone. I won't be offended if you treat it as opinion rather than gospel. In fact, if in doubt, go look it up for yourself. If not in doubt, look it up anyway. Always make sure to check local regulations and safety information. Use common sense and caution. Sail safe.
Basic Concepts and Techniques
Moderator: GreenLake
36 posts
• Page 1 of 3 • 1, 2, 3
Points of Sail
by GreenLake » Tue Jun 23, 2020 3:07 pm
I'll start with this diagram showing the points of sail:
The diagram shows the approximate sail positions, boat speed (distance from center) and apparent wind (approximate strength and direction) for sailing in a true wind of a given direction.
When sailing before the wind (running), the sail can be on either side. Main and jib may even be on opposite sides (wing on wing).
As you sail closer upwind, the sails are trimmed in, the strength of the apparent wind increases, and it appears to come from further forward, but, except if you sail directly downwind, it never has the same direction as the true wind.
The boat speed roughly follows the pattern shown by the dotted line. Running (sailing dead downwind) is not fast, because the boat speed is subtracted from the wind speed. Likewise, as you approach the red "no go zone", the speed drops as you begin to stall your sails. Close hauled is the term for the point of sail closest to the wind where you are still making good progress. If you try to sail a little bit closer than that, you are pinching the boat: it will appear to point a bit higher, but you will slow and also drift sideways, so you will actually make less progress.
- Diagram showing the points of sail
- Points-of-Sail-sm.gif (89.81 KiB) Viewed 10838 times
The diagram shows the approximate sail positions, boat speed (distance from center) and apparent wind (approximate strength and direction) for sailing in a true wind of a given direction.
When sailing before the wind (running), the sail can be on either side. Main and jib may even be on opposite sides (wing on wing).
As you sail closer upwind, the sails are trimmed in, the strength of the apparent wind increases, and it appears to come from further forward, but, except if you sail directly downwind, it never has the same direction as the true wind.
The boat speed roughly follows the pattern shown by the dotted line. Running (sailing dead downwind) is not fast, because the boat speed is subtracted from the wind speed. Likewise, as you approach the red "no go zone", the speed drops as you begin to stall your sails. Close hauled is the term for the point of sail closest to the wind where you are still making good progress. If you try to sail a little bit closer than that, you are pinching the boat: it will appear to point a bit higher, but you will slow and also drift sideways, so you will actually make less progress.
~ green ~ lake ~ ~
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A Delicate Balance
by GreenLake » Tue Jun 23, 2020 3:38 pm
When sailing, a number of forces act on your boat:
The wind creates a force on the sail, part of which will act to heel your boat and push it sideways, and part will act to drive it forward.
The hull produces drag that opposes the drive force and lift -- a force from mainly rudder and centerboard that opposes the sideways movement of the boat. (There's a small contribution from the hull as well).
When you are sailing at a steady speed, these forces are always balanced (if they weren't your boat would accelerate or decelerate until they are).
Note that the true wind is assumed to come from the side in this picture, not from the top as in the Points of Sail. Your boat speed (black arrow) causes a head wind, which is added to the true wind to form the apparent wind. The apparent wind is what actually acts on your sails. (Your sails are trimmed to where they form an angle of 20-25 degrees to the apparent wind).
In order to generate the lift needed to balance the sideways force from the sail, your CB needs to go through the water at a small angle: your boat doesn't actually go in the direction the bow points, but it makes a bit of leeway, just a few degrees normally. The rudder is angled a few degrees as well, otherwise the boat would turn into the wind.
- Forces acting on a sailboat
- Boat-Force-Balance.gif (20.89 KiB) Viewed 29354 times
The wind creates a force on the sail, part of which will act to heel your boat and push it sideways, and part will act to drive it forward.
The hull produces drag that opposes the drive force and lift -- a force from mainly rudder and centerboard that opposes the sideways movement of the boat. (There's a small contribution from the hull as well).
When you are sailing at a steady speed, these forces are always balanced (if they weren't your boat would accelerate or decelerate until they are).
Note that the true wind is assumed to come from the side in this picture, not from the top as in the Points of Sail. Your boat speed (black arrow) causes a head wind, which is added to the true wind to form the apparent wind. The apparent wind is what actually acts on your sails. (Your sails are trimmed to where they form an angle of 20-25 degrees to the apparent wind).
In order to generate the lift needed to balance the sideways force from the sail, your CB needs to go through the water at a small angle: your boat doesn't actually go in the direction the bow points, but it makes a bit of leeway, just a few degrees normally. The rudder is angled a few degrees as well, otherwise the boat would turn into the wind.
~ green ~ lake ~ ~
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A Delicate Balance - 2
by GreenLake » Tue Jun 23, 2020 3:58 pm
There is another direction in which the forces on your boat are in balance (or you would capsize):
It is convenient to treat the sail forces as if they acted on a single point in your boat, the so called center of effort. Likewise, it is useful to think of all the forces acting on the hull to be concentrated in a single point, the center of lateral profile. These two forces are balanced whenever your boat doesn't accelerate. Together these forces act to rotate your boat, they make it heel.
What opposes the heeling is the weight of your crew and the boat acting on a combined center of gravity. This is offset from the center of buoyancy, especially if the boat heels a bit already. Unless your boat is sinking, these to forces are equal and opposite, but because they are offset, they want to counter-rotate your boat to oppose the heeling.
If your crew is heavy enough and hiking out far enough for the conditions (moving the center of gravity outboard) then your boat will assume a stable angle of heel as you sail along. Ideally, that angle is close to zero, because other than very light winds, the DS sails fastest when flat.
- Lateral Balance
- Heeling-Balance.gif (13.18 KiB) Viewed 29354 times
It is convenient to treat the sail forces as if they acted on a single point in your boat, the so called center of effort. Likewise, it is useful to think of all the forces acting on the hull to be concentrated in a single point, the center of lateral profile. These two forces are balanced whenever your boat doesn't accelerate. Together these forces act to rotate your boat, they make it heel.
What opposes the heeling is the weight of your crew and the boat acting on a combined center of gravity. This is offset from the center of buoyancy, especially if the boat heels a bit already. Unless your boat is sinking, these to forces are equal and opposite, but because they are offset, they want to counter-rotate your boat to oppose the heeling.
If your crew is heavy enough and hiking out far enough for the conditions (moving the center of gravity outboard) then your boat will assume a stable angle of heel as you sail along. Ideally, that angle is close to zero, because other than very light winds, the DS sails fastest when flat.
~ green ~ lake ~ ~
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Center of Effort and Center of Lateral Plane
by GreenLake » Wed Jun 24, 2020 9:58 pm
If the forces on the sail were uniform, the averaged location of the total sail force would be at the center of each sail surface. The combined Center of Effort (CE) lies along a line connecting the two points on each sail that corresponds to the averaged location of sail force. The theoretical combined CE lies along the dashed line.
In actual conditions, the contribution of the mainsail is not as strong — area for area — as that of the jib, and the forces are stronger towards the front of each sail. This moves the combined CE forward and down.
The actual location of CE changes based on sail trim and the wind speed at different heights along the mast.
Ideally, the averaged location of the actual sideways force from hull, rudder and centerboard, or CLP, lies more or less directly underneath the location of the combined CE; otherwise, if the two forces are offset they would turn the boat.
In actual conditions, it's desirable to rig the boat, rake the mast and trim the sails so that the CE is just slightly behind the CLP: the boat gets a tendency to turn into the wind, and you need to apply a bit of weather helm with the rudder to counter that tendency. A slight angle on the rudder increases the rudder's total contribution to lift, too much angle and the drag increases, slowing down the boat.
If you sail with only the mainsail, your CE moves back, unbalancing the boat. You may be able to partially compensate by raising the CB a bit: as it swings, it first moves back, then up, so initially, the effect is to move the CLP in the same direction as the CE, re-balancing the boat.
In actual conditions, the contribution of the mainsail is not as strong — area for area — as that of the jib, and the forces are stronger towards the front of each sail. This moves the combined CE forward and down.
- Center of Effort and Center of Lateral Plan
- Center-of-Effort.gif (21.21 KiB) Viewed 29338 times
The actual location of CE changes based on sail trim and the wind speed at different heights along the mast.
Ideally, the averaged location of the actual sideways force from hull, rudder and centerboard, or CLP, lies more or less directly underneath the location of the combined CE; otherwise, if the two forces are offset they would turn the boat.
In actual conditions, it's desirable to rig the boat, rake the mast and trim the sails so that the CE is just slightly behind the CLP: the boat gets a tendency to turn into the wind, and you need to apply a bit of weather helm with the rudder to counter that tendency. A slight angle on the rudder increases the rudder's total contribution to lift, too much angle and the drag increases, slowing down the boat.
If you sail with only the mainsail, your CE moves back, unbalancing the boat. You may be able to partially compensate by raising the CB a bit: as it swings, it first moves back, then up, so initially, the effect is to move the CLP in the same direction as the CE, re-balancing the boat.
~ green ~ lake ~ ~
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Laminar and turbulent flow
by GreenLake » Wed Jun 24, 2020 10:12 pm
Below 5 or 6 knots, the wind has laminar flow over the water. At the ground or at the water surface, the air is stopped. Each layer above moves a bit faster, until at the mast top it has reached the maximum speed experienced by your boat. The increase in true wind speed is steady and pretty linear with height. As a result, both apparent wind speed and direction change along the sail, reducing the average force per sail area. The sail should have some twist to accommodate the different directions.
At about 6 knots (breeze), the flow becomes turbulent. The wind speed increases rapidly to its maximum value, which may be reached well below the mast top. Wind speed and direction are more or less constant along the sail, with an increase of the total force acting on the sail. The sail should have little twist because no matter how high above the deck, it should be at the same angle.
For the jib, you control twist by the location of the jib car. With the car forward, the jib sheet pulls downward more; that keeps the leech (back edge) of the sail straight (no twist). With the car aft, the jib sheet pulls more in a horizontal direction, keeping the foot of the sail straight, but putting less tension on the leech (aft edge of the sail): as a result, the sail twists off -- the upper parts blow out.
The stronger the true wind is, the less contribution there is from the head wind: the apparent wind comes more from the side, and therefore the angle of attack of the sail needs to be deeper. A twisted sail approximates this effect for the case of laminar flow, which appears to come more from the side the higher up the mast you go.
In high winds, you may add twist to your jib for a different purpose: to spill some of the excess sail force near the top. That depowers the sail and moves its CE lower, which reduces the heeling moment. Hence the seeming paradox of similar jib car settings for really light and really strong winds and the opposite in between.
- Laminar and turbulent flow
- Laminar-turbulent.gif (19.18 KiB) Viewed 29338 times
At about 6 knots (breeze), the flow becomes turbulent. The wind speed increases rapidly to its maximum value, which may be reached well below the mast top. Wind speed and direction are more or less constant along the sail, with an increase of the total force acting on the sail. The sail should have little twist because no matter how high above the deck, it should be at the same angle.
For the jib, you control twist by the location of the jib car. With the car forward, the jib sheet pulls downward more; that keeps the leech (back edge) of the sail straight (no twist). With the car aft, the jib sheet pulls more in a horizontal direction, keeping the foot of the sail straight, but putting less tension on the leech (aft edge of the sail): as a result, the sail twists off -- the upper parts blow out.
The stronger the true wind is, the less contribution there is from the head wind: the apparent wind comes more from the side, and therefore the angle of attack of the sail needs to be deeper. A twisted sail approximates this effect for the case of laminar flow, which appears to come more from the side the higher up the mast you go.
In high winds, you may add twist to your jib for a different purpose: to spill some of the excess sail force near the top. That depowers the sail and moves its CE lower, which reduces the heeling moment. Hence the seeming paradox of similar jib car settings for really light and really strong winds and the opposite in between.
~ green ~ lake ~ ~
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Tacking
by GreenLake » Fri Jun 26, 2020 6:18 pm
Tacking is turning your boat "head through wind". There's the basic concept, then there are things that can go wrong, and then there's optimal technique.
Let's discuss some of these. This is a very rough diagram showing four stages.
What can go wrong?
Advanced concepts: when working with a tiller extension you need to practice how to best switch hands; also, if you heel the boat to windward initially you can then right the boat forcefully at the end of the tack, which will help accelerate it again (roll-tack). As these are advanced concepts, we'll just introduce, but not develop them quite yet.
Let's discuss some of these. This is a very rough diagram showing four stages.
- Tacking
- Tacking.gif (18.5 KiB) Viewed 28944 times
- Sailing close-hauled before the tack, just before pushing the helm alee to start the turn.
- The turn has started, the jib continues to draw for a bit on the old side, the main is starting to come across
- The turn continues, the main has come across; the jib, if not released, will be backwinded. You can do that deliberately, to help the boat come about, but it will slow the boat
- After the turn, sailing close hauled. Initially, the boat would have slowed down, so you may need to ease the sails a bit and sail slightly deeper than close hauled for a short stretch to accelerate.
What can go wrong?
- The jib can get hung up on something and not come across. Most likely it will force the turn to become much more than 90 degrees until things are sorted out
- You may stop the turn too late, and end up below a close-hauled course. Sailing a bit low after coming out of the tack will help you accelerate, but too much, and you'll be giving away hard-won distance upwind. That said, you may find that your best tacks rarely come to the textbook 90°.
- You may stop the turn too soon and end up above a close-hauled course. The boat will slow down, until you fall off -- the best way to avoid this is by picking out a spot on the horizon that is at 90 degrees (or a bit more) to your current heading; then you know when to stop the turn.
- The extreme case of this is ending up pointing directly into the wind ('in irons") with the boat not responding to the rudder one way or the other. Best way out of that is to push the main out by the boom so the boat starts to sail backwards. Push the rudder over, so it turns. Once it's no longer pointing into the wind, you can trim the sails and sail forward again.
- If you keep the sail trim unchanged as before (or mirror image for the jib) it's not correct for the reduced speed of your boat exiting the tack; you'll want to ease the sails just a bit and steer down just a bit to help the boat accelerate, before trimming back in
Advanced concepts: when working with a tiller extension you need to practice how to best switch hands; also, if you heel the boat to windward initially you can then right the boat forcefully at the end of the tack, which will help accelerate it again (roll-tack). As these are advanced concepts, we'll just introduce, but not develop them quite yet.
~ green ~ lake ~ ~
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Gybing
by GreenLake » Sat Jun 27, 2020 9:16 pm
Gybing is turning your boat with the wind from behind, so that the main goes from one side to the other.
Let's discuss the basic concept based on this rough diagram showing four stages:
What can go wrong?
Let's discuss the basic concept based on this rough diagram showing four stages:
- Gybing
- Gybing.gif (18.95 KiB) Viewed 29302 times
- Sailing downwind (running) before the gybe, just before starting the turn by pushing the tiller to windward.
- Before starting the turn, the main is pulled tight. If the gybe starts not from a course that's close to dead downwind, this happens a bit after the turn has started, but in any case should be done while the jib continues to draw the old side. Unlike this stage of a tack, the main has to be actively sheeted in.
- The turn continues, the main has come across and is being let out quickly but controlled; the jib has been released and comes over. At this point it can be useful to give a bit of counter helm to steady the boat. Note the rudder position.
- After the turn, running on the other gybe. Unlike the case with tacking, there's nothing special you need to do about accelerating the boat.
- If the gybe is a start of a steeper turn, to go back upwind for example, now would be the time you drop the centerboard and pull in the sheets as you continue the turn (not shown).
What can go wrong?
- The main can come over while you are not yet ready. This can be quite violent and may even damage the rigging. Hence the need to pull in the main and be ready to let it out.
- The main is not let out fast enough, the boat broaches and catches the wind full from the side. Capsize?
- The mainsheet is not pulled in; therefore it hangs loose and can get snagged, with the result that the main can't be fully let out on the new side.
- The centerboard could be down (it should have been raised during the run). As a result the boat can "trip" over the centerboard during the gybe (instead of sliding sideways). Capsize?
- A gybe, especially an unintended one can be quite violent in stronger winds. You may not realize how strong the wind really is while sailing downwind (away from the wind). Some people opt to tack through 270 degrees instead ("chicken gybe") when conditions are rough.
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Re: Basic Concepts and Techniques
by BlackPirate » Thu Jul 02, 2020 3:12 am
These are very helpful for a newbie like me. Thanks 
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Telltales
by GreenLake » Thu Jul 02, 2020 5:01 pm
Telltales are small threads of wool or strips of light fabric that indicate the airflow around your sails.
They are a valuable (some would say invaluable) aid in making sure your sails are trimmed correctly to the conditions (or that you are sailing correctly to the chosen sail trim).
The most basic set of telltales is as shown in the picture:
For the main, place one telltale per batten pocket at the leech. The goal is for all of them to stream happily aft, while the top one may flick forward part of the time. Especially on a reach you will notice that it makes a difference whether these are flying correctly or whether you have the main oversheeted or let out too far. If you have a vang, you should be able to see the telltales react as you adjust it. What the telltales indicate is that the airflow over the main has remained attached all the way to the leech. It is this attached airflow that translates the wind force to your sails.
In all but light (except: very light) winds, you may need to tighten your outhaul a bit to make the sail flat enough so the belly doesn't cause the air flow to separate. This should be something that you can observe in the right conditions with the lowest telltale (the outhaul acts mostly on the foot of the sail). In very light winds, you tighten the outhaul so that the flow stays attached. In light winds, you allow a belly to form to get a bit more power. In stronger winds you tighten the outhaul to flatten the sail to reduce power: at some point you already have more power than you need and the goal is to reduce heeling force.
For the jib, place one set of telltales of opposite color about 1/3 up and 18" from the luff on opposite sides of the sail. Usually, the starboard one would be green and it would be placed a bit above the port one. The goal is to see both of them streaming aft, but the windward one (in this picture the starboard one) is allowed to rise or flicker a bit. (That would indicate that the trim is for optimal upwind sailing.)
When sailing close-hauled, the jib is sheeted in as much as possible without pulling the jib too flat. The only possible adjustment would be to let it out (and sail a bit lower). So, instead of changing the sail trim, you would steer in response to wind shifts: if the windward (inside) telltale rises, you would fall off, and the reverse, if the leeward (outside) one does -- you steer away from the rising telltale until both are flying again.
If you are on a reach and want to maintain a fixed course, you would trim the sail instead: if the windward (inward) telltale rises, you sheet in, and the reverse, if the leeward (outside) one rises; you fall off. Both the steering and the sheeting change the angle of attack of the jib in the same direction based on the feedback from the telltales.
It may be challenging to find a seating position where the helm can monitor the jib telltales, but it's worth it.
Some boats have Barber inhauls that can pull in the sheeting angle of the jib without adding to the jib sheet tension. This is an adjustment for moderate air 6-10 knots. For lighter air, leave them out, and also let out some jib sheet for a rounder shape (to generate a bit more power), except for the lightest airs where a flat shape is needed to keep the airflow attached. In that range, the jib car also goes forward to allow more twist (see laminar flow). For stronger winds, let out the inhauls as well and sheet the sail tight for a flat shape (with jib car forward to allow the top to twist off to depower).
Sometimes additional pairs of telltales are placed on the jib at various heights above the first set. These can be used to check that the twist of the sail is correct: moving the jib fairlead fore and aft changes the twist and when set correctly, both sets of telltales should fly simultaneously.
They are a valuable (some would say invaluable) aid in making sure your sails are trimmed correctly to the conditions (or that you are sailing correctly to the chosen sail trim).
The most basic set of telltales is as shown in the picture:
- Telltales
- Telltales.gif (18.04 KiB) Viewed 29227 times
For the main, place one telltale per batten pocket at the leech. The goal is for all of them to stream happily aft, while the top one may flick forward part of the time. Especially on a reach you will notice that it makes a difference whether these are flying correctly or whether you have the main oversheeted or let out too far. If you have a vang, you should be able to see the telltales react as you adjust it. What the telltales indicate is that the airflow over the main has remained attached all the way to the leech. It is this attached airflow that translates the wind force to your sails.
In all but light (except: very light) winds, you may need to tighten your outhaul a bit to make the sail flat enough so the belly doesn't cause the air flow to separate. This should be something that you can observe in the right conditions with the lowest telltale (the outhaul acts mostly on the foot of the sail). In very light winds, you tighten the outhaul so that the flow stays attached. In light winds, you allow a belly to form to get a bit more power. In stronger winds you tighten the outhaul to flatten the sail to reduce power: at some point you already have more power than you need and the goal is to reduce heeling force.
For the jib, place one set of telltales of opposite color about 1/3 up and 18" from the luff on opposite sides of the sail. Usually, the starboard one would be green and it would be placed a bit above the port one. The goal is to see both of them streaming aft, but the windward one (in this picture the starboard one) is allowed to rise or flicker a bit. (That would indicate that the trim is for optimal upwind sailing.)
When sailing close-hauled, the jib is sheeted in as much as possible without pulling the jib too flat. The only possible adjustment would be to let it out (and sail a bit lower). So, instead of changing the sail trim, you would steer in response to wind shifts: if the windward (inside) telltale rises, you would fall off, and the reverse, if the leeward (outside) one does -- you steer away from the rising telltale until both are flying again.
If you are on a reach and want to maintain a fixed course, you would trim the sail instead: if the windward (inward) telltale rises, you sheet in, and the reverse, if the leeward (outside) one rises; you fall off. Both the steering and the sheeting change the angle of attack of the jib in the same direction based on the feedback from the telltales.
It may be challenging to find a seating position where the helm can monitor the jib telltales, but it's worth it.
Some boats have Barber inhauls that can pull in the sheeting angle of the jib without adding to the jib sheet tension. This is an adjustment for moderate air 6-10 knots. For lighter air, leave them out, and also let out some jib sheet for a rounder shape (to generate a bit more power), except for the lightest airs where a flat shape is needed to keep the airflow attached. In that range, the jib car also goes forward to allow more twist (see laminar flow). For stronger winds, let out the inhauls as well and sheet the sail tight for a flat shape (with jib car forward to allow the top to twist off to depower).
Sometimes additional pairs of telltales are placed on the jib at various heights above the first set. These can be used to check that the twist of the sail is correct: moving the jib fairlead fore and aft changes the twist and when set correctly, both sets of telltales should fly simultaneously.
~ green ~ lake ~ ~
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True vs. Apparent Wind
by GreenLake » Sat Jul 04, 2020 11:16 pm
Let's revisit an earlier diagram, but this time, focus on the way the true wind and the boat speed interact to create the apparent wind seen by the sails.
Head wind: Just like when you walk, run, ride a bike or drive a car, your boat generates a head wind when moving. This headwind moves with the same speed, but in the opposite direction from your boat speed (black arrows in the diagram). Because the wind always pushes your boat sideways a bit there's a drift angle or leeway of about 8 degrees when sailing upwind. The headwind will have the same angle, so it does not appear to come from directly forward, except if there's either no wind, or the true wind is coming from behind.
Apparent wind: What your sails feel is the apparent wind. This is a resulting wind from the overlap of true wind and head wind. This is also the wind that you feel when sitting in the boat. As you can see, as long as your boat is moving forward, the apparent wind will be more forward than the true wind.
The goal of sail trim (and of steering to the wind) is to get the apparent wind to have an angle of attack (or angle to the sail) of about 20-25 degrees. As we've seen, you use the telltales to find out when you have reached the correct angle to the apparent wind. (So no need to pull out your protractor or do calculations)
If the true wind changes direction, so will the apparent wind, but the same is true when true the wind speed increases or decreases in a gust or lull.
- True vs. Apparent Wind
- apparentwind.gif (14.1 KiB) Viewed 29185 times
Head wind: Just like when you walk, run, ride a bike or drive a car, your boat generates a head wind when moving. This headwind moves with the same speed, but in the opposite direction from your boat speed (black arrows in the diagram). Because the wind always pushes your boat sideways a bit there's a drift angle or leeway of about 8 degrees when sailing upwind. The headwind will have the same angle, so it does not appear to come from directly forward, except if there's either no wind, or the true wind is coming from behind.
Apparent wind: What your sails feel is the apparent wind. This is a resulting wind from the overlap of true wind and head wind. This is also the wind that you feel when sitting in the boat. As you can see, as long as your boat is moving forward, the apparent wind will be more forward than the true wind.
The goal of sail trim (and of steering to the wind) is to get the apparent wind to have an angle of attack (or angle to the sail) of about 20-25 degrees. As we've seen, you use the telltales to find out when you have reached the correct angle to the apparent wind. (So no need to pull out your protractor or do calculations)
If the true wind changes direction, so will the apparent wind, but the same is true when true the wind speed increases or decreases in a gust or lull.
~ green ~ lake ~ ~
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Gusts and Lulls
by GreenLake » Sun Jul 05, 2020 12:53 am
Let's look at what happens to the apparent wind in a gust and a lull. At first glance, there's a lot of detail in the diagram, but as we walk through these two scenarios, things should fall into place.
Gust: When the wind increases, in a gust, at first, the boat speed remains the same (until the boat has accelerated) and therefore the head wind remains the same. As a result (shown in the top left) the apparent wind both increases and seems to come from a bit further aft (or not as forward). When sailing upwind, we experience that as a lift. We can sail a bit closer to windward without changing sail trim (or sheet in a bit if we aren't close-hauled already). As the boat accelerates because the wind is now stronger, the head wind will increase and the final apparent wind will be stronger, but closer again to the original direction and we need to adjust course and trim accordingly (see top right).
A gust may also come with a simultaneous change in direction of the wind which may then require either require a stronger or lesser trim and course adjustment than required by the increase in speed alone, or more rarely some correction in the opposite direction. Sometimes, a gust is so much stronger that we let out the main a bit to initially depower it, hike out, and then trim again ("ease - hike - trim").
Lull: A lull proceeds in the opposite sense. Initially, the apparent wind moves forward and gets weaker. You are being headed. As the boat decelerates, there's less head wind, and the apparent wind gets ever weaker, but is now closer to the original direction. A header that is due to a sudden decrease in the true wind speed is sometimes called a velocity header. If you feel that the wind is getting weaker, you may not want to change trim and course as much as you would for a real header, because after deceleration, the change in direction is less. In particular, if you expect the lull to be of short duration you may largely maintain trim and course, so as to make best use of the wind when it comes back. For example, if there's a temporary wind shadow from another boat.
If the true wind dies suddenly (in a complete lull) the apparent wind will be mostly from your headwind as your boat continues to cost on momentum. It will appear as if you are sailing against the wind at that moment, but no amount of steering or adjusting your sail trim will be able to get you back a favorable angle: no matter where you direct your boat, as long as there's no true wind, the apparent wind will appear to come from dead ahead.
In very light winds, there may be no continuous wind, only a series of puffs. It can pay to set your sail trim to take advantage of the apparent wind in these puffs and not change it as they die down. Part of the reason is that after making any change in sail trim in (very) light winds, it takes some time to re-establish flow over the sails.
- Gust and Lull
- GustAndLull.gif (15.09 KiB) Viewed 29185 times
Gust: When the wind increases, in a gust, at first, the boat speed remains the same (until the boat has accelerated) and therefore the head wind remains the same. As a result (shown in the top left) the apparent wind both increases and seems to come from a bit further aft (or not as forward). When sailing upwind, we experience that as a lift. We can sail a bit closer to windward without changing sail trim (or sheet in a bit if we aren't close-hauled already). As the boat accelerates because the wind is now stronger, the head wind will increase and the final apparent wind will be stronger, but closer again to the original direction and we need to adjust course and trim accordingly (see top right).
A gust may also come with a simultaneous change in direction of the wind which may then require either require a stronger or lesser trim and course adjustment than required by the increase in speed alone, or more rarely some correction in the opposite direction. Sometimes, a gust is so much stronger that we let out the main a bit to initially depower it, hike out, and then trim again ("ease - hike - trim").
Lull: A lull proceeds in the opposite sense. Initially, the apparent wind moves forward and gets weaker. You are being headed. As the boat decelerates, there's less head wind, and the apparent wind gets ever weaker, but is now closer to the original direction. A header that is due to a sudden decrease in the true wind speed is sometimes called a velocity header. If you feel that the wind is getting weaker, you may not want to change trim and course as much as you would for a real header, because after deceleration, the change in direction is less. In particular, if you expect the lull to be of short duration you may largely maintain trim and course, so as to make best use of the wind when it comes back. For example, if there's a temporary wind shadow from another boat.
If the true wind dies suddenly (in a complete lull) the apparent wind will be mostly from your headwind as your boat continues to cost on momentum. It will appear as if you are sailing against the wind at that moment, but no amount of steering or adjusting your sail trim will be able to get you back a favorable angle: no matter where you direct your boat, as long as there's no true wind, the apparent wind will appear to come from dead ahead.
In very light winds, there may be no continuous wind, only a series of puffs. It can pay to set your sail trim to take advantage of the apparent wind in these puffs and not change it as they die down. Part of the reason is that after making any change in sail trim in (very) light winds, it takes some time to re-establish flow over the sails.
~ green ~ lake ~ ~
- GreenLake
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Rules of the Road
by GreenLake » Sun Jul 05, 2020 3:12 pm
Everybody should download and study the nautical rules of the road, often called "Colregs" but formally known as IRPCAS or "International Rules for the Prevention of Collisions at Sea". The full rules cover many cases a beginner may not encounter right away, so here's an attempt at picking out some concepts and prescriptions to serve as a practical foundation and basis for further study.
The aim of the rules is to prevent collisions; if a collision occurs, quite often both parties are considered at fault for not avoiding it.
You are required to keep a look out at all times - be aware of where other boats are and which might cross paths with you.
Unlike vehicular traffic rules, there is no "right-of-way". Instead there are a stand-on vessel and a give-way vessel.
If you are the give-way vessel, you are to make an early and obvious change to your course (so the stand-on vessel knows you've seen them and to clearly remove the chance of collision). In a crossing situation, the safe thing is to go behind the other vessel.
When you encounter a large ship, barge and the like, they may be constrained by their draft to follow the channel, or they may have some priority based on one of the more specialized rules. They are also unlikely to be able to get out of your way at the last moment, and any collision with such a vessel is extremely dangerous - to you. So, whether it is required or not, it's best to stay out of their way early, well before there is a risk of collision. If you get five blasts of their horn, you know you've done something stupid.
But what about encountering another boat?
In this situation it does not matter who is the motor boat and who is the sailboat. It matters who is overtaking whom.
Overtaking: When you are overtaking any other vessel, you are the give-way vessel. Kayak, row boat, sailboat, motor boat: no difference. If you come from behind, even diagonally, you get to keep clear until you've finished overtaking.
In the diagram, either the boat under motor is just about to finish overtaking the sailboat and, from that point on, is no longer burdened under the rules. Or the sailboat is the one catching up with the motor-driven one and needs to turn promptly to avoid collision.
The aim of the rules is to prevent collisions; if a collision occurs, quite often both parties are considered at fault for not avoiding it.
You are required to keep a look out at all times - be aware of where other boats are and which might cross paths with you.
Unlike vehicular traffic rules, there is no "right-of-way". Instead there are a stand-on vessel and a give-way vessel.
If you are the give-way vessel, you are to make an early and obvious change to your course (so the stand-on vessel knows you've seen them and to clearly remove the chance of collision). In a crossing situation, the safe thing is to go behind the other vessel.
When you encounter a large ship, barge and the like, they may be constrained by their draft to follow the channel, or they may have some priority based on one of the more specialized rules. They are also unlikely to be able to get out of your way at the last moment, and any collision with such a vessel is extremely dangerous - to you. So, whether it is required or not, it's best to stay out of their way early, well before there is a risk of collision. If you get five blasts of their horn, you know you've done something stupid.
But what about encountering another boat?
- Overtaking
- overtaking.gif (15.6 KiB) Viewed 29166 times
In this situation it does not matter who is the motor boat and who is the sailboat. It matters who is overtaking whom.
Overtaking: When you are overtaking any other vessel, you are the give-way vessel. Kayak, row boat, sailboat, motor boat: no difference. If you come from behind, even diagonally, you get to keep clear until you've finished overtaking.
In the diagram, either the boat under motor is just about to finish overtaking the sailboat and, from that point on, is no longer burdened under the rules. Or the sailboat is the one catching up with the motor-driven one and needs to turn promptly to avoid collision.
~ green ~ lake ~ ~
- GreenLake
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Rules of the Road (2)
by GreenLake » Sun Jul 05, 2020 9:11 pm
Crossing: in any crossing situation with a motor boat, kayak, row boat etc. you are the stand-on vessel while under sail alone. That means, you get to maintain course and speed (to remain predictable) up to the point where you can tell the other boat isn't going to keep clear. If it looks like they won't, you should try to get out of their way.
While motoring it's "right before left", as in other traffic: a boat approaching you from your starboard side as you are motoring or padding your boat is a stand-on vessel, as is a sailboat from any direction other than behind.
Crossing another sailboat: Here is where it gets interesting. It depends on which side of the boat your mainsail is on. If it's on the port side, as when the wind is from starboard, you are on the starboard bow, and any sailboat on another tack is a give-way vessel.
The boat on the top right is on starboard (mainsail to port), while the boat on the bottom left is on port. This is a classic crossing situation when two sailboats are sailing upwind and both are tacking, crossing and recrossing each other. There's a useful technique, worth knowing, to tell whether you and another boat are likely to collide or not.
Standing bearing: If you spot another boat in the distance, whether faster or slower, there's a simple test. Line up the boat with something on your boat. The mast or a stay, or some fixed spot on your deck. If the boat continues to line up with that spot, it's called a standing bearing and the two of you will collide (unless one of you speeds up, slows down or turns). If, however, the other boat moves forward compared to that spot, you will safely pass behind it. If it falls behind the spot you chose, you may be able to pass in front of it, but that's a maneuver that requires some good margin, lest you hit a lull and get stuck in their path. It's always best to turn early, aim at their transom, and pass safely behind - close enough to touch them in a race, but with a bit more distance otherwise
While motoring it's "right before left", as in other traffic: a boat approaching you from your starboard side as you are motoring or padding your boat is a stand-on vessel, as is a sailboat from any direction other than behind.
Crossing another sailboat: Here is where it gets interesting. It depends on which side of the boat your mainsail is on. If it's on the port side, as when the wind is from starboard, you are on the starboard bow, and any sailboat on another tack is a give-way vessel.
- Port vs. Starboard
- Port-Starboard.gif (17.81 KiB) Viewed 10839 times
The boat on the top right is on starboard (mainsail to port), while the boat on the bottom left is on port. This is a classic crossing situation when two sailboats are sailing upwind and both are tacking, crossing and recrossing each other. There's a useful technique, worth knowing, to tell whether you and another boat are likely to collide or not.
Standing bearing: If you spot another boat in the distance, whether faster or slower, there's a simple test. Line up the boat with something on your boat. The mast or a stay, or some fixed spot on your deck. If the boat continues to line up with that spot, it's called a standing bearing and the two of you will collide (unless one of you speeds up, slows down or turns). If, however, the other boat moves forward compared to that spot, you will safely pass behind it. If it falls behind the spot you chose, you may be able to pass in front of it, but that's a maneuver that requires some good margin, lest you hit a lull and get stuck in their path. It's always best to turn early, aim at their transom, and pass safely behind - close enough to touch them in a race, but with a bit more distance otherwise
~ green ~ lake ~ ~
- GreenLake
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Rules of the Road (3)
by GreenLake » Sun Jul 05, 2020 10:00 pm
Crossing another sailboat (cont'd): Here is another crossing situation between sailboats. Guess whether you can tell the stand-on vessel.
The boat on the bottom right in the diagram is on starboard, but the boat on the top left is on port. Which one is the stand-on vessel? In this case, it is easy: the starboard boat is the stand-on vessel.
However, the boat on the top left is running dead downwind. If it had its mainsail on the opposite side, both boats would on the same tack. In that case the windward one would be the give-way vessel. Again,the bottom right in the diagram would be the stand-on vessel.
As you can see, if you are on starboard bow, you are the stand-on vessel, except to windward of another starboard bow boat, or when overtaking.
If you are on the port bow (wind from port, main on starboard) then you are the give-way vessel in all situations except another port-bow boat to windward of you.
Head on while motoring: If you meet another motor boat, kayak, row boat, etc. head on while motoring or paddling your boat you are supposed to pass "port-to-port", that is, keep to the right.
Other Rules: Depending where you sail, there may be other rules that can be quite essential to know, for example special vessel traffic separation (VTS) schemes. Also, technically, the international rules are not in force in many inland waters - the Inland Rules are (or possibly some local regulation). However, the two sets of rules don't differ much as far as these basic concepts are concerned. Then there are the Racing Rules, which you need to know if you ever want to race. Most of the basic rules overlap with the ones here, except that there's no such concept as "overtaking keeps clear"; and there are many specific rules about marks of the course, obstructions and other situations that tend to come up in sailboat races, but not in general traffic.
Practice and further study: It's definitely recommended that you study and know the applicable rules. And that you practice: any time you see another boat on the water, determine whether you are on starboard bow and what that means in a possible crossing, head on or overtaking situation. Make sure you crew knows what to watch out for and is keeping a good lookout in your blind spots.
- Which is the stand-on vessel?
- stand-on-vessel.gif (16.82 KiB) Viewed 29166 times
The boat on the bottom right in the diagram is on starboard, but the boat on the top left is on port. Which one is the stand-on vessel? In this case, it is easy: the starboard boat is the stand-on vessel.
However, the boat on the top left is running dead downwind. If it had its mainsail on the opposite side, both boats would on the same tack. In that case the windward one would be the give-way vessel. Again,the bottom right in the diagram would be the stand-on vessel.
- Which is the stand-on vessel?
- stand-on-vessel-2.gif (15.86 KiB) Viewed 29081 times
As you can see, if you are on starboard bow, you are the stand-on vessel, except to windward of another starboard bow boat, or when overtaking.
If you are on the port bow (wind from port, main on starboard) then you are the give-way vessel in all situations except another port-bow boat to windward of you.
Head on while motoring: If you meet another motor boat, kayak, row boat, etc. head on while motoring or paddling your boat you are supposed to pass "port-to-port", that is, keep to the right.
Other Rules: Depending where you sail, there may be other rules that can be quite essential to know, for example special vessel traffic separation (VTS) schemes. Also, technically, the international rules are not in force in many inland waters - the Inland Rules are (or possibly some local regulation). However, the two sets of rules don't differ much as far as these basic concepts are concerned. Then there are the Racing Rules, which you need to know if you ever want to race. Most of the basic rules overlap with the ones here, except that there's no such concept as "overtaking keeps clear"; and there are many specific rules about marks of the course, obstructions and other situations that tend to come up in sailboat races, but not in general traffic.
Practice and further study: It's definitely recommended that you study and know the applicable rules. And that you practice: any time you see another boat on the water, determine whether you are on starboard bow and what that means in a possible crossing, head on or overtaking situation. Make sure you crew knows what to watch out for and is keeping a good lookout in your blind spots.
~ green ~ lake ~ ~
- GreenLake
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