Big Fresh Water Ice


by Ken Smith Jr. - December 1987

Big fresh water ice is ice on bodies of fresh water which are large enough that thermal expansion of the ice sheet will cause fractures of the sheet. Green Bay freezes the full 20 mile width and most of its hundred mile length. It counts. Lake Nocquebay, and our other local sailing site, is about three by six miles. It doesn't. Lake Mendota in Madison seems to develop only one or two active cracks. At about 8 miles in diameter, it counts sometimes .

The sun heats the ice during the day, the "thousandths per inch per degree" (ice grows 0.000052 inches per inch per degree F) of thermal expansion accumulate across long enough stretches that the ice fractures. As the edges of the sheet press against the shore, the internal stresses in the ice builds until a failure point splits the sheet in two. These 'active cracks' are where the ice fails by buckling. The two sheets push together to form a pressure ridges where the ice breaks and tilts. Sometimes one sheet will ride under the other. The forces of wind blowing over the surface of the ice can cause movement of one of the sheets laterally. Since the active cracks are not straight. a lateral movement of one of the sheets will somewhere cause a 'bump' to pile ice on top of another bump. Two 'hollows' coming together may cause open water.

The conditions at an active crack can change dramatically during a twenty four hour period. Early morning and later afternoon present the times of greatest hazard at cracks. The ridges often grow in height during the day. Overriding sheets can push further over their neighbor, for the ice grows as it warms. Wind generated movement may close open water or cause open areas to grow. Safe crossing from the morning may be impossible at noon. Evening can present hazards as conditions, often secretly, change. Areas safe to cross at lunch time may open later as the temperature falls. At night, the ice sheets shrink as the temperatures fall. In the morning, not only might open water have appeared where yesterday was safe, but skim ice may hide newly opened water. On especially cold nights, parts of previously active cracks may seal. It they seal early in the night, edges of either sheet may fail in tension as the sheet continues to shrink with the cold, a new active area may appear, or the shape of the active crack may change.

At the site of a crack, some broken chunks of ice are usually piled on the edges. From an Iceboat, even a few inches of broken chunks look like an impenetrable wall. Though they look big from far away, they are often passable. Even crossing under sail is usually possible somewhere (but not recommended, ED.) . Sometimes the cracks are no longer active and can be crossed most anywhere, and sometimes walking, pushing the boat, or using the fuselage as a bridge is the only way to cross. Race committees with experience set the course so active cracks, even benign ones, are not crossed in the course of the race. Conditions sometimes occur where the size of the sheet may place a crack on the race course, or close enough that one is tempted to cross at one of the corners of the course. Pick a spot that you've scouted in advance, that you are certain has no open water, where ice chunks will not hit your hull and where there is no step up. Your runners MUST be able to climb over any steps up unless you REALLY enjoy rebuilding boats. Do not count on the ice chunks marking cracks-their presence means only that the ice came together before it went apart. SCOUT THE ICE BEFORE YOU SAIL IT.

Active cracks can form anywhere. One always seems to appear more or less parallel to the shore line, hoping from point to point. Coves are often clear of active cracks, but one must be crossed when sailing over from a cove to the wider ice beyond. Ice by the shore is locked in. Newer, better and bigger ice is usually outside the first crack. (The grass IS always greener...)

On big water, an excellent area to sail can often be on the newest Ice--free of snow, black, hard and bound by open water on one side. Growing new ice in this way keeps our sailing active though the early parts of the winter, despite frequent snow storms. Though often under consideration for local races, such a site bears watching. An off shore (off sheet?) wind threatens to break the new sheet free and send it into the waves. Waves are great destroyers of big water ice.

Racing in a building southerly breeze, the local club, a very few years ago, had a sheet break loose with a race aboard and in progress. Movement began at an active crack. Fortunately the only loss was a course mark. Boats raced to and pushed across the sliding edge of the moving sheet where it touched a point of land and the bound-in ice by shore. Selection of local race sites became more conservative and will continue to be so for many years. The several mile square sheet was gone within five miles (35 minutes) of when and where it departed the bound-in ice. It was broken into chunks too small to be seen from shore .

When the whole bay is frozen, snow ends our first season. Spring always brings a second season to big water ice. In this part of the world, ice sheet do not melt thinner and thinner until they are gone. Snow cover is melted from the top. The water on top of the ice which results makes thousands of tiny pores through which it rejoins the lake. On warm days, the white sheet of snow, slush and ice suddenly become black again. This starts the second season. On cold days, the ice is much bumpier than black ice. A standard runner will cover two to five bumps. Dull edges hold and any runner is very fast in all but light air. On warm days (above 28 deg F) conditions will be excellent until the sun, warm air and passing runners convert the surface into slush. Mike'O'Brien's description of sailing salt ice in the OCTOBER (1987) NEWSLETTER, except the worry over corrosion, matches my experiences with fresh water and warm spring ice. Sailing in slush is dangerous as the boat's runners will not skid when overloaded in an aggressive turn or gust of wind. Unable to slip sideways, the boat wilt break things and bend masts.

The ice is 'honeycombing' during this time of the year. The drain pores are growing beneath the surface of the ice so the once solid sheet is becoming weaker, thought not much thinner. The ice daily is forming itself into grains, each is fist size at the surface. As melting from the top continues to weaken the grain boundaries, the ice is becoming ripe for a shove. It is appearing more and more white as air and water pores grow in size. Sunshine on the shallow bottom is warming the water and speeding melting from the bottom at the shore and over bars. The sheet is now in danger of disappearing most any night as more and more open water appears in the active cracks. Boats are taken off the ice at night. Sailing is restricted to the bound-in ice between points and inside bars. The first crack is the outer sailing boundary.

If calm weather prevails the ice rots in place as holes appear and grow. If it blows, however, wholes sections of the big water will be clear as the sheet may have gone visiting only to return a day or two later. Or wind may have moved the sheet into waves and turned it into millions of fist sized cubes. If the edge of a sheet blows over a shallow spot or a beach, spectacular piles of these ice crystals grow into a shove. My wife witnessed a three foot high shove walking over our beach. With a sound like a thousand chandeliers in a windy hallway, in minutes it walked fifteen feet onto our lawn. Our ice season was over--and barely in time for Easter.

The conditions at an active crack can change dramatically during a twenty four hour period. Early morning and later afternoon present the times of greatest hazard at cracks. The ridges often grow in height during the day. Overriding sheets can push further over their neighbor, for the ice grows as it warms. Wind generated movement may close open water or cause open areas to grow. Safe crossing from the morning may be impossible at noon. Evening can present hazards as conditions, often secretly, change. Areas safe to cross at lunch time may open later as the temperature falls. At night, the ice sheets shrink as the temperatures fall. In the morning, not only might open water have appeared where yesterday was safe, but skim ice may hide newly opened water. On especially cold nights, parts of previously active cracks may seal. It they seal early in the night, edges of either sheet may fail in tension as the sheet continues to shrink with the cold, a new active area may appear, or the shape of the active crack may change.

At the site of a crack, some broken chunks of ice are usually piled on the edges. From an Iceboat, even a few inches of broken chunks look like an impenetrable wall. Though they look big from far away, they are often passable. Even crossing under sail is usually possible somewhere (but not recommended, ED.) . Sometimes the cracks are no longer active and can be crossed most anywhere, and sometimes walking, pushing the boat, or using the fuselage as a bridge is the only way to cross. Race committees with experience set the course so active cracks, even benign ones, are not crossed in the course of the race. Conditions sometimes occur where the size of the sheet may place a crack on the race course, or close enough that one is tempted to cross at one of the corners of the course. Pick a spot that you've scouted in advance, that you are certain has no open water, where ice chunks will not hit your hull and where there is no step up. Your runners MUST be able to climb over any steps up unless you REALLY enjoy rebuilding boats. Do not count on the ice chunks marking cracks-their presence means only that the ice came together before it went apart. SCOUT THE ICE BEFORE YOU SAIL IT.

Active cracks can form anywhere. One always seems to appear more or less parallel to the shore line, hoping from point to point. Coves are often clear of active cracks, but one must be crossed when sailing over from a cove to the wider ice beyond. Ice by the shore is locked in. Newer, better and bigger ice is usually outside the first crack. (The grass IS always greener...)

On big water, an excellent area to sail can often be on the newest Ice--free of snow, black, hard and bound by open water on one side. Growing new ice in this way keeps our sailing active though the early parts of the winter, despite frequent snow storms. Though often under consideration for local races, such a site bears watching. An off shore (off sheet?) wind threatens to break the new sheet free and send it into the waves. Waves are great destroyers of big water ice.

Racing in a building southerly breeze, the local club, a very few years ago, had a sheet break loose with a race aboard and in progress. Movement began at an active crack. Fortunately the only loss was a course mark. Boats raced to and pushed across the sliding edge of the moving sheet where it touched a point of land and the bound-in ice by shore. Selection of local race sites became more conservative and will continue to be so for many years. The several mile square sheet was gone within five miles (35 minutes) of when and where it departed the bound-in ice. It was broken into chunks too small to be seen from shore .

When the whole bay is frozen, snow ends our first season. Spring always brings a second season to big water ice. In this part of the world, ice sheet do not melt thinner and thinner until they are gone. Snow cover is melted from the top. The water on top of the ice which results makes thousands of tiny pores through which it rejoins the lake. On warm days, the white sheet of snow, slush and ice suddenly become black again. This starts the second season. On cold days, the ice is much bumpier than black ice. A standard runner will cover two to five bumps. Dull edges hold and any runner is very fast in all but light air. On warm days (above 28 deg F) conditions will be excellent until the sun, warm air and passing runners convert the surface into slush. Mike'O'Brien's description of sailing salt ice in the OCTOBER (1987) NEWSLETTER, except the worry over corrosion, matches my experiences with fresh water and warm spring ice. Sailing in slush is dangerous as the boat's runners will not skid when overloaded in an aggressive turn or gust of wind. Unable to slip sideways, the boat wilt break things and bend masts.

The ice is 'honeycombing' during this time of the year. The drain pores are growing beneath the surface of the ice so the once solid sheet is becoming weaker, thought not much thinner. The ice daily is forming itself into grains, each is fist size at the surface. As melting from the top continues to weaken the grain boundaries, the ice is becoming ripe for a shove. It is appearing more and more white as air and water pores grow in size. Sunshine on the shallow bottom is warming the water and speeding melting from the bottom at the shore and over bars. The sheet is now in danger of disappearing most any night as more and more open water appears in the active cracks. Boats are taken off the ice at night. Sailing is restricted to the bound-in ice between points and inside bars. The first crack is the outer sailing boundary.

If calm weather prevails the ice rots in place as holes appear and grow. If it blows, however, wholes sections of the big water will be clear as the sheet may have gone visiting only to return a day or two later. Or wind may have moved the sheet into waves and turned it into millions of fist sized cubes. If the edge of a sheet blows over a shallow spot or a beach, spectacular piles of these ice crystals grow into a shove. My wife witnessed a three foot high shove walking over our beach. With a sound like a thousand chandeliers in a windy hallway, in minutes it walked fifteen feet onto our lawn. Our ice season was over--and barely in time for Easter.

The conditions at an active crack can change dramatically during a twenty four hour period. Early morning and later afternoon present the times of greatest hazard at cracks. The ridges often grow in height during the day. Overriding sheets can push further over their neighbor, for the ice grows as it warms. Wind generated movement may close open water or cause open areas to grow. Safe crossing from the morning may be impossible at noon. Evening can present hazards as conditions, often secretly, change. Areas safe to cross at lunch time may open later as the temperature falls. At night, the ice sheets shrink as the temperatures fall. In the morning, not only might open water have appeared where yesterday was safe, but skim ice may hide newly opened water. On especially cold nights, parts of previously active cracks may seal. It they seal early in the night, edges of either sheet may fail in tension as the sheet continues to shrink with the cold, a new active area may appear, or the shape of the active crack may change.

At the site of a crack, some broken chunks of ice are usually piled on the edges. From an Iceboat, even a few inches of broken chunks look like an impenetrable wall. Though they look big from far away, they are often passable. Even crossing under sail is usually possible somewhere (but not recommended, ED.) . Sometimes the cracks are no longer active and can be crossed most anywhere, and sometimes walking, pushing the boat, or using the fuselage as a bridge is the only way to cross. Race committees with experience set the course so active cracks, even benign ones, are not crossed in the course of the race. Conditions sometimes occur where the size of the sheet may place a crack on the race course, or close enough that one is tempted to cross at one of the corners of the course. Pick a spot that you've scouted in advance, that you are certain has no open water, where ice chunks will not hit your hull and where there is no step up. Your runners MUST be able to climb over any steps up unless you REALLY enjoy rebuilding boats. Do not count on the ice chunks marking cracks-their presence means only that the ice came together before it went apart. SCOUT THE ICE BEFORE YOU SAIL IT.

Active cracks can form anywhere. One always seems to appear more or less parallel to the shore line, hoping from point to point. Coves are often clear of active cracks, but one must be crossed when sailing over from a cove to the wider ice beyond. Ice by the shore is locked in. Newer, better and bigger ice is usually outside the first crack. (The grass IS always greener...)

On big water, an excellent area to sail can often be on the newest Ice--free of snow, black, hard and bound by open water on one side. Growing new ice in this way keeps our sailing active though the early parts of the winter, despite frequent snow storms. Though often under consideration for local races, such a site bears watching. An off shore (off sheet?) wind threatens to break the new sheet free and send it into the waves. Waves are great destroyers of big water ice.

Racing in a building southerly breeze, the local club, a very few years ago, had a sheet break loose with a race aboard and in progress. Movement began at an active crack. Fortunately the only loss was a course mark. Boats raced to and pushed across the sliding edge of the moving sheet where it touched a point of land and the bound-in ice by shore. Selection of local race sites became more conservative and will continue to be so for many years. The several mile square sheet was gone within five miles (35 minutes) of when and where it departed the bound-in ice. It was broken into chunks too small to be seen from shore .

When the whole bay is frozen, snow ends our first season. Spring always brings a second season to big water ice. In this part of the world, ice sheet do not melt thinner and thinner until they are gone. Snow cover is melted from the top. The water on top of the ice which results makes thousands of tiny pores through which it rejoins the lake. On warm days, the white sheet of snow, slush and ice suddenly become black again. This starts the second season. On cold days, the ice is much bumpier than black ice. A standard runner will cover two to five bumps. Dull edges hold and any runner is very fast in all but light air. On warm days (above 28 deg F) conditions will be excellent until the sun, warm air and passing runners convert the surface into slush. Mike'O'Brien's description of sailing salt ice in the OCTOBER (1987) NEWSLETTER, except the worry over corrosion, matches my experiences with fresh water and warm spring ice. Sailing in slush is dangerous as the boat's runners will not skid when overloaded in an aggressive turn or gust of wind. Unable to slip sideways, the boat wilt break things and bend masts.

The ice is 'honeycombing' during this time of the year. The drain pores are growing beneath the surface of the ice so the once solid sheet is becoming weaker, thought not much thinner. The ice daily is forming itself into grains, each is fist size at the surface. As melting from the top continues to weaken the grain boundaries, the ice is becoming ripe for a shove. It is appearing more and more white as air and water pores grow in size. Sunshine on the shallow bottom is warming the water and speeding melting from the bottom at the shore and over bars. The sheet is now in danger of disappearing most any night as more and more open water appears in the active cracks. Boats are taken off the ice at night. Sailing is restricted to the bound-in ice between points and inside bars. The first crack is the outer sailing boundary.

If calm weather prevails the ice rots in place as holes appear and grow. If it blows, however, wholes sections of the big water will be clear as the sheet may have gone visiting only to return a day or two later. Or wind may have moved the sheet into waves and turned it into millions of fist sized cubes. If the edge of a sheet blows over a shallow spot or a beach, spectacular piles of these ice crystals grow into a shove. My wife witnessed a three foot high shove walking over our beach. With a sound like a thousand chandeliers in a windy hallway, in minutes it walked fifteen feet onto our lawn. Our ice season was over--and barely in time for Easter.

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