Living with Light Air
by Rod Carr and Rick West
East Coast 12 Meter skipper Rick West of the Delta Model Yacht Club recently took the time to write up his experiences with sailing in very light air in a fleet which was not short of top notch skippers. Rick has taken on a substantial amount of travel to gain experience by sailing in the active Atlantic seaboard EC-12 Fleets. The following is an edited version of the exchange between Rick and I. Rick's comments are shown in bold. Light air can be very frustrating unless one is prepared to trim the sails expressly for low wind speeds and also to be ready to deal with low boat speeds and equally low accelerations. Conservation of momentum, minimizing tacking and anticipation, anticipation, anticipation become the priorities.
I arrived early at the lake to test the PX75 sails in light air. (Note: PX 75 is a 1.2 oz mylar with two separate grids of load bearing threads.) They had worked fine in Jacksonville in air which varied from 2 to 15 mph in the same race. The air at Elon, on this morning was little to nil. I like those conditions. I set the mast at 25-5/8" from the bow and had no reason to change it later. The backstay tension (BST) was set to 1.7lbs with a full jib and a flat main. Twist was outside of parallel to the boom, my 20-degree setting. The main boom was 7 degrees and the jib was at 12. The luff tension on both sails was very, very light. I run a ¼" luff on the main all the time except in heavier air.
I use the clew hooks, rings and adjusters made of nickel-silver (NiAg) wire as shown in the manuals. I have widened the radius of the clew hooks to accommodate the thickness of the grommet area and then closed the shaft slightly to prevent unhooking on the water.
I was pleased with the set and rotating the boat, on land, the sails filled easily in light air. They performed well in the water on a beat. I had difficulty filling the jib on a run and using a twitcher. While the boom set is the same as the other A rigs, the sail would not move out past about 60 degrees in light air. My perception was weight. The jib boom rises quickly after that angle and in the light air it would not push past.
Here at Carr Sails, we've worked a good deal in light air because of our Puget Sound location, and are well aware of the difficulty that light air can present. The major idea that we base our tuning and trimming advice on is that the lower the wind speed at 6' above the water, the thicker the boundary layer and the slower the wind is going to be moving at the water surface. A masthead velocity of 2 mph, rapidly decays to about ¾ mph at the spreaders and is down to about ¼ mph at the foot of the mainsail. The lesson is therefore to search for power from the upper half of the mainsail. Rick may have overflattened his main, but we don't have a photo available that lets us quantify that.
To power up the upper mainsail one works to set maximum camber (10% or so) in the upper half of the mainsail by using minimum twist, then balance that against a fairly flat jib that can be set somewhat outboard to allow an open slot. In our model world, the lessons of big boat trim sometimes don't translate well in the light air regime since we are so close to the water surface where wind speed goes rapidly to zero. If we plot the direction of the apparent wind from the mast head down to the water, it takes on a substantial twist, allowing the head of the main to be set well off the boom angle.
When the air dropped to very soft and drifting the sails would drape in a shaped fashion with the exception of the clew area. Here, they would sit straight up, with the sails breaking at the leech where the reinforcement ended up from the clew. The main body of the sails was shaped but there was not movement at the clew. The grommet was sitting atop the hook and would not slide to the side being shaped by the sail.
In the light air sail suits on the factory boats, we use the nickel silver rings for clew outhaul adjustment, but tie the ring to the clew grommet with a ¾" loop of dacron line. This allows the clew significant freedom of movement in the horizontal plane, but little in the vertical plane where it would seriously impact control of mainsail twist. This modification seems most useful in the very light air regime, i.e., under 2 mph.
During the five hours I worked with this PX75 suit, the sails would perform well at around 2 mph. A full shape on the beat could not be held below around 1 mph. I lowered the BST to 1.5, which is the lowest limit on the topping lift. I changed the offset on the jib to encourage a better response downwind. I moved my notebook settings two above and two below in the course of testing. Nothing changed the swing of the jib or the break above the clew.
The clew problem would likely have been minimized by a switch to the loop approach outlined above, but consider that the wind pressure on the sail at 1 mph is the same as the pull of gravity on the sail if it is held horizontal. No doubt that the weight of the jib club is the culprit in preventing the full outswing of the jib on the "run". This is why the "jib twitcher" is an allowed R/C function in the EC-12 Class. But, it is also why many skippers have built light air jibs, complete with very slender and lightweight jib clubs that are used only in very light air.
By mid afternoon we had 20 boats in mock racing and I would not move above half the fleet. I removed the rig and put up last year's TriSpi 40 suit and quickly moved to the front of the fleet.
This is pretty good confirmation by yet another skipper that if the wind will remain much below 2 mph and the water is flat, that lighter weight materials such as TriSpi 40 (1.0 oz) and even TriSpi 25 (0.6) ounce will provide better performance. The question then becomes one of guessing how much risk you will take by switching to a light-air optimized sail and then see the wind come up. The situation described by Rick seems to indicate that there was little chance of such a turnabout. The PX75 material combines flexibility with a 1.2 oz weight, and seems to do a good job of holding its cambered shape, as would be important when sailing in lumpy water. The PX75 is also strong enough to hold its shape well up into the 14 - 15 mph wind range, so with appropriate mast bend can act as an all purpose A-suit for the EC-12.
On Saturday I rigged with the TriSpi 40 suit and did well in the light rain the first hour. The water beaded on the sails, adding weight and no doubt awful aerodynamics. Then I started to see the same drape of the sails as I had the day before with the PX75. In the last two hours of the day I was murdered on the course in extremely light air and in the rain. I moved from the top fleet to the bubble between the middle and lower fleets. When I could shake shape into the sails with the winch, she would go till the next tack attempt. As a result of these experiences I am concerned about two things: The heaviness of the clew areas and the clew hook. I will abandon the hook and move to a string slide and adjusting line off the clew to a distant adjuster.
Racing on the East Coast has taught me much. Each race is another day in class. There is such a broad span of thought there. There is much experimentation. I am reaching the point where I question the practicality and functionality of some things in the manual. In many ways it has been limiting to me in the thought process. I do not have much time to experiment and while I do not expect to ever to be a contender, I want to feel, in reflection on the plane, that I gave it my 110%. I was distressed about the rain combination to the light air. You did not comment on that. However, so far, in general, I am please with the effort, the acceptance and I am having a wonderful time and started 30 years too late.
I don't think the "manual (s)" (Note: THE MANUAL FOR THE EAST COAST 12 METER, and OPTIMIZING THE EAST COAST 12 METER published by Ragged Symmetry Publications, Mercer Island, Washington) were meant to cover every nut, bolt and consideration that might be pursued. They certainly provide a lot more data relative to the EC-12 than I've seen for any other R/C model yacht class. But even the authors lament that the manuals are getting old, having been available for well over 6 years now.
As far as rain drops on the sails, there is no doubt that surface smoothness is a key component of aerodynamic efficiency for the sails, and the mylar promotes the formation of very bumpy lumps of water on their surfaces. The surface smoothness of the PX 75 is suspected to contribute to its efficiency, but there have been events which I have attended where former Class Secretary Jerry Brower walked away with the silver in rainy, light air races by using a set of 2 oz dacron sails that I built for him in 1985. The cloth seems to wick away the bubbles and it could be seen dripping off the foot of the sails.
Question: If I were to trim the curve between the luff and the clew, on either sail, would it have any major effect on performance? In light air I am concerned with drag across the boom using the NiAg rings.
Trimming the sails will not change performance much, just reducing area a bit on the run. But given our focus on light air, it must be said that likely the airspeed is so slow and burbled by being shoved over the gunwale, that we would be better off working on camber in the upper parts of the main (and jib) and then using aft streaming telltales from the upper two battens to make sure we don't allow them to become stalled.
East Coast 12 Meter skipper Rick West of the Delta Model Yacht Club recently took the time to write up his experiences with sailing in very light air in a fleet which was not short of top notch skippers. Rick has taken on a substantial amount of travel to gain experience by sailing in the active Atlantic seaboard EC-12 Fleets. The following is an edited version of the exchange between Rick and I. Rick's comments are shown in bold. Light air can be very frustrating unless one is prepared to trim the sails expressly for low wind speeds and also to be ready to deal with low boat speeds and equally low accelerations. Conservation of momentum, minimizing tacking and anticipation, anticipation, anticipation become the priorities.
I arrived early at the lake to test the PX75 sails in light air. (Note: PX 75 is a 1.2 oz mylar with two separate grids of load bearing threads.) They had worked fine in Jacksonville in air which varied from 2 to 15 mph in the same race. The air at Elon, on this morning was little to nil. I like those conditions. I set the mast at 25-5/8" from the bow and had no reason to change it later. The backstay tension (BST) was set to 1.7lbs with a full jib and a flat main. Twist was outside of parallel to the boom, my 20-degree setting. The main boom was 7 degrees and the jib was at 12. The luff tension on both sails was very, very light. I run a ¼" luff on the main all the time except in heavier air.
I use the clew hooks, rings and adjusters made of nickel-silver (NiAg) wire as shown in the manuals. I have widened the radius of the clew hooks to accommodate the thickness of the grommet area and then closed the shaft slightly to prevent unhooking on the water.
I was pleased with the set and rotating the boat, on land, the sails filled easily in light air. They performed well in the water on a beat. I had difficulty filling the jib on a run and using a twitcher. While the boom set is the same as the other A rigs, the sail would not move out past about 60 degrees in light air. My perception was weight. The jib boom rises quickly after that angle and in the light air it would not push past.
Here at Carr Sails, we've worked a good deal in light air because of our Puget Sound location, and are well aware of the difficulty that light air can present. The major idea that we base our tuning and trimming advice on is that the lower the wind speed at 6' above the water, the thicker the boundary layer and the slower the wind is going to be moving at the water surface. A masthead velocity of 2 mph, rapidly decays to about ¾ mph at the spreaders and is down to about ¼ mph at the foot of the mainsail. The lesson is therefore to search for power from the upper half of the mainsail. Rick may have overflattened his main, but we don't have a photo available that lets us quantify that.
To power up the upper mainsail one works to set maximum camber (10% or so) in the upper half of the mainsail by using minimum twist, then balance that against a fairly flat jib that can be set somewhat outboard to allow an open slot. In our model world, the lessons of big boat trim sometimes don't translate well in the light air regime since we are so close to the water surface where wind speed goes rapidly to zero. If we plot the direction of the apparent wind from the mast head down to the water, it takes on a substantial twist, allowing the head of the main to be set well off the boom angle.
When the air dropped to very soft and drifting the sails would drape in a shaped fashion with the exception of the clew area. Here, they would sit straight up, with the sails breaking at the leech where the reinforcement ended up from the clew. The main body of the sails was shaped but there was not movement at the clew. The grommet was sitting atop the hook and would not slide to the side being shaped by the sail.
In the light air sail suits on the factory boats, we use the nickel silver rings for clew outhaul adjustment, but tie the ring to the clew grommet with a ¾" loop of dacron line. This allows the clew significant freedom of movement in the horizontal plane, but little in the vertical plane where it would seriously impact control of mainsail twist. This modification seems most useful in the very light air regime, i.e., under 2 mph.
During the five hours I worked with this PX75 suit, the sails would perform well at around 2 mph. A full shape on the beat could not be held below around 1 mph. I lowered the BST to 1.5, which is the lowest limit on the topping lift. I changed the offset on the jib to encourage a better response downwind. I moved my notebook settings two above and two below in the course of testing. Nothing changed the swing of the jib or the break above the clew.
The clew problem would likely have been minimized by a switch to the loop approach outlined above, but consider that the wind pressure on the sail at 1 mph is the same as the pull of gravity on the sail if it is held horizontal. No doubt that the weight of the jib club is the culprit in preventing the full outswing of the jib on the "run". This is why the "jib twitcher" is an allowed R/C function in the EC-12 Class. But, it is also why many skippers have built light air jibs, complete with very slender and lightweight jib clubs that are used only in very light air.
By mid afternoon we had 20 boats in mock racing and I would not move above half the fleet. I removed the rig and put up last year's TriSpi 40 suit and quickly moved to the front of the fleet.
This is pretty good confirmation by yet another skipper that if the wind will remain much below 2 mph and the water is flat, that lighter weight materials such as TriSpi 40 (1.0 oz) and even TriSpi 25 (0.6) ounce will provide better performance. The question then becomes one of guessing how much risk you will take by switching to a light-air optimized sail and then see the wind come up. The situation described by Rick seems to indicate that there was little chance of such a turnabout. The PX75 material combines flexibility with a 1.2 oz weight, and seems to do a good job of holding its cambered shape, as would be important when sailing in lumpy water. The PX75 is also strong enough to hold its shape well up into the 14 - 15 mph wind range, so with appropriate mast bend can act as an all purpose A-suit for the EC-12.
On Saturday I rigged with the TriSpi 40 suit and did well in the light rain the first hour. The water beaded on the sails, adding weight and no doubt awful aerodynamics. Then I started to see the same drape of the sails as I had the day before with the PX75. In the last two hours of the day I was murdered on the course in extremely light air and in the rain. I moved from the top fleet to the bubble between the middle and lower fleets. When I could shake shape into the sails with the winch, she would go till the next tack attempt. As a result of these experiences I am concerned about two things: The heaviness of the clew areas and the clew hook. I will abandon the hook and move to a string slide and adjusting line off the clew to a distant adjuster.
Racing on the East Coast has taught me much. Each race is another day in class. There is such a broad span of thought there. There is much experimentation. I am reaching the point where I question the practicality and functionality of some things in the manual. In many ways it has been limiting to me in the thought process. I do not have much time to experiment and while I do not expect to ever to be a contender, I want to feel, in reflection on the plane, that I gave it my 110%. I was distressed about the rain combination to the light air. You did not comment on that. However, so far, in general, I am please with the effort, the acceptance and I am having a wonderful time and started 30 years too late.
I don't think the "manual (s)" (Note: THE MANUAL FOR THE EAST COAST 12 METER, and OPTIMIZING THE EAST COAST 12 METER published by Ragged Symmetry Publications, Mercer Island, Washington) were meant to cover every nut, bolt and consideration that might be pursued. They certainly provide a lot more data relative to the EC-12 than I've seen for any other R/C model yacht class. But even the authors lament that the manuals are getting old, having been available for well over 6 years now.
As far as rain drops on the sails, there is no doubt that surface smoothness is a key component of aerodynamic efficiency for the sails, and the mylar promotes the formation of very bumpy lumps of water on their surfaces. The surface smoothness of the PX 75 is suspected to contribute to its efficiency, but there have been events which I have attended where former Class Secretary Jerry Brower walked away with the silver in rainy, light air races by using a set of 2 oz dacron sails that I built for him in 1985. The cloth seems to wick away the bubbles and it could be seen dripping off the foot of the sails.
Question: If I were to trim the curve between the luff and the clew, on either sail, would it have any major effect on performance? In light air I am concerned with drag across the boom using the NiAg rings.
Trimming the sails will not change performance much, just reducing area a bit on the run. But given our focus on light air, it must be said that likely the airspeed is so slow and burbled by being shoved over the gunwale, that we would be better off working on camber in the upper parts of the main (and jib) and then using aft streaming telltales from the upper two battens to make sure we don't allow them to become stalled.