by Wojtek Kuznicki
| Translated by Hanna Kuznicka - Published in DN Europe 1986/87 (Note: This file is only partially complete - Check back again for complete text and tables) Edited (a little) by Bob Dill |
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| 1. INTRODUCTION Ice boating needs ice and wind. Ice is the most important factor of course. The complex of ice properties, serviceable for ice boating, is usually called ice conditions. As a matter of fact, they determine not only a speed and trim of the ice boat, but above all, safety while sailing. They are very different, often unique, so it is very important to know mechanics of their formation and alteration, that gives a possibility to recognize situation on ice, even in distant regions, properly enough.
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| 2. ICE CONDITIONS Ice conditions for ice boating purposes can be described as a set of ice + ice covering
They both are produced by weather circumstances sequentially, base ice is created first and then ice covering can appear on existing ice. Types of ice and ice covering are mainly dependent on the following weather factors:
Besides, water regions and their surroundings influence the ice conditions. Both the ice formation and the ice covering progress differentiate in some degree relatively to the type of waters:
and to water's environment, especially:
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| 3. THE ICE FORMING PROCESS Ice boating can make use of two types of ice:
The both types differ a little in the ice forming process from each other. The freezing point of water depends on its salinity. Fresh water starts to freeze at temperature of 0 degrees C. Air temperature drop causes the surface layer of water to cool. The maximal weight gravity of water appears at t = +4 degrees C. While cooling surface layers of water become heavier and drop down being displaced by warmer and lighter layers of water from the deep. After getting cooled, full masses of water to t = 4 C, convection currents disappear. The further cooling of surface layers of water cause them to decrease their weight gravity and the remain up. After getting to the freezing point, water forms ice crystals appearing around crystal nuclei e.g. suspended impurities, snow crystals, old ice remains. In relation to weather conditions, freezing water assumes varied forms i.e. glass ice, slush, snow ice--but eventually ice layer. Sea waters freeze with more difficulty due to their salinity decreasing the freezing point. The ice crystals which form when sea water freezes are free from salt--consequently the remaining water becomes saltier and heavier and its freezing point is further lowered. Circumstances with strong wind, snow fall and not too low temperature can cause specific conditions for the ice forming process. Snow taps into snow islets which freeze earlier than water free from snow. Ice surfaces become rough in this situation and snow islets may initiate snow drifts on them. During warm weather snow islets--so called snow pockets--may originate morass--soft and weak ice areas--being troubles for ice boating. Proper conditions for the freezing process are created by:
The water freezing process can be disturbed by environment:
The above factors cause nearby waters to freeze badly and these ice areas to thaw first of all.
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| 4. THE ICE COVERING GROWTH Ice covering (which covers up ice) is a layer attacked by runners. It is of great importance but rather undesirable for ice boating. Ice covering can occur on existing ice and include all this which can appear on ice due to rain or snow fall and/or water coming to surface through openings. For ice boating purposes there are the following types of ice covering:
During the ice season, ice covering varies according to weather circumstances and can sublimate, melt, evaporate and eventually freeze into ice. Usually ice covering is originated by snow, fluffy at the beginning of winter. Even being in a thick layer, this snow is not a big load and therefore exceptionally only causes water to come to surface through cracks or holes. Later on, as a result of air moisture, sunshine or wind, a fluffy snow settles down and its layer becomes thinner but heavier and harder more and more. Frosty and sunny weather can produce a hard skin layer on snow cover surface, softening daily and hardening nightly. This effect can interfere with sailing on ice. Situations can be a little different if a frosty and sunny weather occurs after a tiny snow fall. A thin powdery snow layer, melted a little during the day and getting frozen gradually during the night, forms frozen snow A wet snow, usually falling in large masses at relatively not too low temperatures, can weigh upon the ice plane considerably. Laying in a heavy mass, a wet snow can cause water to come to the ice surface through cracks, fractures, holes and then to saturate snow layer on ice. Simultaneously water from molten snow at its upper layers, being heavier then snow, drops down on the ice surface. The layer of snow saturated with water contains a lot of air bubbles and this is why it freezes badly. While cooling on, this wet layer can transform into a new carrying layer (base ice) called snow ice or gray ice. The color of snow ice depends on the contents of the internal air bubbles and may differ in tint extending from light gray-white to almost black. Snow drifts are a result of the wind action. Snow, swept away with wind on ice, settles down at bumps in the ice surface and initiates snow drifts. Due to strong wind blowing during and/or after snow fall, snow drifts can lump down and then become very hard and 50 (or more) cm. high. Surroundings of the ice terrain have an effect on the ice covering progress too. Banks, buildings, and trees exert an influence on lay out and depth of snow cover and consequently on configuration and height of snow drifts. This influence can differ in connection with the wind force and direction and the kind of precipitation. Less snow and smaller snow drifts occur in places shielded with high banks, tress or buildings. On the contrary, wind nozzles, as a result of the configuration of the shore and objects on it, can cause the snow depth and the height of snow drifts to increase. Configuration and size of snow drifts are very important for the further base ice growing process. Clear, bare ice grows better than ice covered with snow or snow drifts. Ice areas under snow drifts are often soft and weak. Snow drifts, if they remain till the spring, will originate guags (morass). Water appearing on ice surfaces either through cracks, holes and other openings or as rain or thaw water, is a factor acting on ice destructively and can produce gullies. When temperatures below zero happen, again water on ice can freeze as:
Variable weathers may produce specific ice conditions--just as a layer cake--rather ill repeated in ice boaters' opinion. This type of ice consists of a few layers and one of them e.g. water, snow or ice can appear at least two times. Snow cover is constantly submitted to evaporation (sublimation) especially under sunny and windy weather conditions. The fluffier snow is, the more exposed to sunshine and strong winds - the more intensive is its evaporation process. When weather permitting the evaporation process can be so effective that a relatively thick layer of snow or water can disappear during 1 - 3 days.
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| 5. THE ICE THAWING PROCESS The thawing process causes ice to become not only thinner but weaker as well, especially in the spring time as a result of warm weather and warm water. At first water appears on ice surfaces. It may be originated from molten snow rain or partially molten surfaces of ice. Water on ice produces structural changes and decoloration of ice, which becomes consequently porous, honeycombed, weak and extremely crystalline. Air holes generate water piping inside ice and then thaw holes. Being drained at its skin layer, due to water penetrating ice down, the ice surface can be hard enough, but it is the first phase of ice which grows white, scuffs into granular crystals and finally disappears. Besides, the action of winds, swells, and water level changes usually generate stresses breaking ice and advancing its ruin. Relation between the phases of structural changes and mechanical strength of ice is shown in Table 1, quoted W. Zakrzewski's book "lody na morzach" (Ice on Seas). During warm weather, particularly in the spring time when days are long enough, the strength of ice decreases rapidly and the ice layer, even if very thick, may be broken down under pressure of ice boats or people. VIEW AND SPECIFICATION OF ICE RELATIVE STRENGTH OF ICE
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| 6. STRENGTH AND STABILITY OF ICE 6.1 STRENGTH OF ICE During the ice season ice conditions can be differentiated constantly. Cross section of the base ice can show up either all ice in one layer or a combination of two layers; green ice - below and gray ice as the upper layer. Conditions of low temperatures and lack of snow falls produce green ice which is dark (often called black) due to darkness below, crystal clear, hard and strong. GRAY ICE or snow ice is an effect of often and heavy snow falls while freezing water. It can be an individual layer of snow ice or can appear on the surface of green ice as a result of slush formed by snow partially molten or rained upon and then frozen again. Strength of the ice area is determined by the strength of base ice described above. Ice covering does not increase the strength of ice but it rather is an additional load applied to the base ice. Very useful remarks, interesting for ice boaters, have been published by NEIYA (New England Ice Yacht Association). My own experiences agree with NEIYA opinion. To be safe, ice shall have a proper thickness. For several DN's, ice has to be at least 6,5 cm.(2 1/2") thick- equivalent" layer of the gray ice - no less than 13 cm (5"). green ice is about two times stronger than gray" ice. FIG 1 Cross section of the ice 10 cm of green ice + 15 cm of gray ice is equivalent to 17,5 cm of green ice The green ice layer increases from below and its progress depends on:
There is no need of strong wind to sail on. As a result of the strong wind, directional stability of the ice boat can be difficult and sailing can be dangerous. To sail safely and effectively in this situation, the proper runners shall be used. Directional stability is very important too. Runners shall be very sharp and have the angle of sharpening no more than 90 degrees. When ice is not too smooth, it is proper to use runners as long as possible, e.g. T-runners. Green ice, if thick enough, is safe and lack of ice covering does not hide any unpleasant surprises. GREEN ICE, due to its dark color, absorbs heat energy. It results in changes of ice volume so it produces stresses and then cracking ice. Cracks usually happen at narrowings or near to headlands. These cracks can extend several hundred meters unless confined to shore. They form either during a warm day or on frosty nights. This process is accompanied with terrifying noises. If water level remains constant, these cracks may not be harmless. Sailing is safe, provided that cracks are crossed over perpendicularly to avoid troubles because of a runner wedged in a crack. GRAY ICE, also called snow ice - containing a lot of air bubbles is a heat insulation and limits growth of green ice. Gray ice, because of its roughness, is not as fast as green ice but it can be fine to sail on for the runners get a good grip on it. In frosty weather, gray ice is hard but it softens very easy as a result of warm weather. Some troubles can appear if a day is cold but sunny. Ice, hard after a frosty night, can soften in midday and make sailing impossible. It can happen even during one race. Hard gray ice demands sharp runners; softening ice requests using wider, longer and duller blade to keep from cutting through - at first T-runners with a wide web of T-beam then, if needed, angle runners. Runners shall be changed according to ice condition alteration, in advance. Remember, especially the Regatta Committee, that in light wind, the races shall be held early in the morning to be successful. The later the races start, the less chance to hold them effectively. If gray ice is the only layer of ice without green ice under it, it is very important to take a notice on the ice strength drop during the day. BLACK ICE (Note: This probably would be referred to as spring black ice in North America-Ed), usually appears in the springtime. It is very old crystalline because of acting warm weather and water gathered on its surface. It is dull black, porous, honeycombed and weak. Usually hard on its surface, black ice under load easily scuffs up into needlelike ice crystals. It may be possible to sail on, if at least 20 cm. thick and at temperatures below zero only. Black ice, similar in surface conditions to gray ice, demands runners with wide blades and a large angle of sharpening, i.e. long plate runners or, as optimal, T-runners with a wide web. Angle runners can be used only if ice surfaces soften completely due to absorbed heat Black ice absorbs heat energy in a high degree so sunny Two first factors are the most perceptible and important This relation is shown in Table 2 taken from Korovielski's book, titled "buoiernyi sport" (Ice boat sport). Table 2 states values of twenty-four hours' gain in thickness of the fresh water ice as a function of the average twenty-four hours' temperature of air and the initial value of the ice thickness (d)
TABLE 2
(Note: The conversion to inches is approximate - Ed) Text from here down has not been reviewed or corrected, proceed with caution!!! The lower temperatures and thinner ice - the more progress of the ice thickness Snow covering up ice and water currents reduce the ice progress, but evaluation of these factors, being in practice rather difficult and unprecise, can be qualitative only 6 .2 THE BASE ICE GREEN ICE - here and there called black (Note Called Black Ice in North America-Ed) - appears usually at the beginning or in the middle of the winter It is hard, so runners attack it insensibly and resistance to motion is minimal, especially on a very smooth and clean ice surface weather is harmful to it and makes it unsafe. No further air temperatures drop, even big and of long duration, let black ice regain color, structure and strength characterizing green ice. 6.3 ICE COVERING Ice covering is very important. It may either show us or, more often, hide hazards on ice. The type of ice covering determines how much resistance the runners must push through and it affects the sailablity of the area. So it influences the proper selection of runners. FLUFFY SNOW - on hard ice is fine for sailing and is no obstacle, provided that the thickness of its layer is less than 5 cm. It decorates surroundings and prevents drift of runners. These conditions suggest using plate runners or T-runners with a thin web. Angle of sharpening depends on ice hardness. The deeper snow causes drags to rise so it requests plate runners. Deep fluffy snow hides hazards. Not only debris but cracks and new frozen thin spots become unseen under powdery snow. To avoid hazards on unknown ice areas, it is preferable to get information on ice and its covering history and to inspect the area before sailing. WET SNOW - is heavy and causes drag to go up. It requests T- or plate runners. If its layer is too thick, sailing may be impossible. FROZEN SNOW - produces significant drag. Early morning it is so hard that it can make sailing impossible, during the day, while insolation increases, frozen snow softens as a result of heat penetration. In midday, races can be held, even then the wind force does not intensify. Both wet snow and frozen snow need runners having their cross section in the part immersed in snow minimally i.e. T-runners with a thin web if snow layer is thinner than 3 cm., or plate runners if snow is deeper. The runners blades shall be as sharp as possible within class specification requirements. SNOW DRIFTS - are conspicuous obstacles and make sailing difficult and often hazardous, especially for equipment. As a rule, plate runners shall be used in this situation. Snowdrifts configuration is very important for method and way to sail effectively. First of all, chosen way needn't be the shortest one, but rather efficient to pass by the most of drifts. To beat momentary and local drag rises, due to snow drifts, the ice boat shall be driven fast to get its proper inertia. Snow drifts are placed perpendicularly to the direction of wind producing them. On windward side, they rise softly, but they are sharp wedged and compact on their leeward. It causes more drags while sailing windward, in this situation it is better not to tack very close, but bear off a little to pick up speed. Keeping up the speed is more important than the longer way. Drag, met while tacking off wind, are less, so a proper course can be kept better. If the wind direction is not perpendicular to existing snow drifts, they shall be crosses at the minimal angle. Snow drifts hide hazards. Ice under them grows worse and usually is thinner. Water from molten snow, due to warm weather, causes the areas under snow drifts to be usually soft and weak. SHELL ICE - is formed when water in a low area of ice freezes for 5 - 15 mm. from top and leaves a cavity of water or air beneath. A runner will out through the top and make a frightful noise as it rips a slot in the thin layer. If the steering runner goes through, directional control is lost and the ice boat cannot be steered. Where a side runner is caught in shell ice, and a turn attempted, the runner or chock can easily be bent or the plank split where the chock bolts go through it. It is very important to avoid breaking the top of shell ice, if possible. It can be gotten by minimizing unit pressure and by fast sailing. Practically, long runners shall be used (e.g. T-runners with a wide web) and load per runner shall be as uniform as possible. It may be reacted by getting a good speed before shell ice area and by loosing a sheet while sailing on over the shell. Ice chips produced by steering runner can be very dangerous for face and eyes. WATER ON ICE - reduces durability and strength of ice. If water stays not too long, it is not hazardous but rather unpleasant while sailing. Water on ice increases resistance to motion, so it requests runners having minimal surface contact with water. Plate runners are proper but rather with dull blades, because ice under water is not too hard. If the ice surface softens, angle runners shall be used although a steering runner can cause fountains of water attacking a skipper in a cockpit. The ice boaters must not forget hazards on ice. It is important to know how and where they can happen to recognize and avoid them. Generally, ice boaters can meet: 6.4 HAZARDS
Each of them, if not seen early enough, is really dangerous. Restricted visibility, typical of DN class boat, prevent visual inspection. Distinction between open water and luster, dark ice can be very difficult. New snowfall hides thin ice, morass, cracks, and also all debris. Close to these thin spots the ice usually is thinner weaker and damageable. Pressure ridges are hazardous but they are well recognized. Ice edges close to them are strong, but some times cracked as a result of pressure. Ice, broken or cracked by ice breakers, can drift because of wind or current. On leeward side hummocked and rafted ice can appear and on windward side existing cracks may widen Causing troubles with leaving out the ice plate. In 1986 at the end of winter, I experienced this situation on man-made lake (Zegrze). Strong and hard ice was cracked and cut off a little from the shore in a few places. As a result of the violent wind shift, a crack a few cm. wide and possible to cross over widened to about 30 cm. in 10 minutes and then, after 1 hour to at least 100 m. I was alone with my DN on the floe. to make my way back possible, the boat had to be used. Debris on ice can be a real hazard. All these things like branches, leaves, stones, bottles, sticks, absorb sun's heat and prevent ice from freezing and cause it to melt. They melt down into the ice and then refreeze. They can dull a runner, knock it out of alignment or cause the ice boat to lose control. |
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| 7. SPECIFICATION OF WATER REGIONS Every type of water region has its specific properties important for ice boating. Beyond doubts, the best ice conditions happen on natural lakes, especially with no river mouths, no water intakes, no waste waters. Good conditions also are on large man made lakes, even they have some weaknesses. Due to often and significant changes of water level, ice may crack and water can come into surface. These effects usually cause the ice season to shorten on this type of waters. Sea bays and gulfs freeze later because of water salinity but they are good place for ice boating. If they are shallow, ice can be frozen into the bottom. In this situation, while increasing sea level, water may flood ice surface. Sea is continually in motion as a result of swell, wind, tidal streams and currents, which tend to break ice up into separate masses. The wind blowing on shore will press moving floes against the shore and produce hummocked and rafted ice. If it blows off shore, it will produce or increase a channel between the coast and ice. Both events are dangerous, particularly at the end of winter, when ice is not too strong. Total decay of ice may progress very quickly, even in a few hours. European rivers practically are unusable for ice boating. They freeze rather rarely, ice on them is thin and hazardous due to water in motion. Only places close to shore, between repelling spurs, can be utilized for training, provided that special precautions are taken. |
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| 8. SHORT CHARACTERISTICS OF ICE CONDITIONS IN EUROPE Especially good conditions for ice boating are in North and East Europe- so in Sweden, Poland, Finland and USSR Winters usually are frosty, and heavy snow falls mainly happen in Finland and USSR. The central part of Europe is a region with differentiated ice conditions: Germany - frosty winters, not too much snow Holland - not too frosty winters but very little snow Czechoslovakia, Austria - frosty winters, relatively heavy snowfalls. First of all ice appears in North Finland - Lapland - on VikaJarvi Lake at Rovaniemi, where on the turn of October and November there are races held traditionally beginning European ice season. Ice season in Lapland is short because of heavy snow falls which happen in November and December and, as a result, stop ice boating. In December, ice season moves to Sweden, at first in the North part, then ice appears in the Central part of the country. From the beginning of January ice appears in Poland, USSR, Austria, Czechoslovakia, on mountain lakes in Switzerland and Italy, but South regions of ice boating are covered with snow, often very large, making them impossible to sail. Apogees of ice boating season happens on the turn of January and February. Ice appears also in Holland and Denmark but for a short time and not every year. The second part of February is the completion for ice boating in West and South Europe. Good enough ice conditions endure in Poland, Sweden, Finland and USSR. At the end of March ice season in Poland ends with sailing then a bit later in Sweden and Finland does. last ice disappears in USSR. Generally, ice boating conditions are pretty good in Europe. Almost always can find ice for races between December and April. There are undoubtedly many areas in which ice boats not been introduced. |
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REFERENCE LIST
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