3. THE GREAT LAKES
(1) The Great Lakes system includes Lakes Ontario, Erie, Huron, Michigan, and Superior, their connecting waters, and the St. Lawrence River. It is one of the largest concentrations of fresh water on the earth. The system, including the St. Lawrence River above Iroquois Dam, has a total shore of about 11,000 statute miles (9,559 nm), a total watersurface area of about 95,000 square statute miles (24,600,000hectares). With the opening of the St. Lawrence Seaway, the system provides access by oceangoing deep-draft vessels to the great industrial and agricultural heartland of the North American continent. From the Strait of Belle Isle at the mouth of the Gulf of St. Lawrence, the distance via the St. Lawrence River to Duluth,MN, at the head of Lake Superior is about 2,340 statute miles (2,03nm) and to Chicago, IL, near the S end of Lake Michigan is about 2,250 statute miles (1,955nm). About 1,000 statute miles (870 nm) of each of these distances is below Montreal, the head of a deep-draft ocean navigation on the St. Lawrence River.
(2) Small craft and barge traffic may also reach the Great Lakes via two shallow-draft routes ; from the Gulf of Mexico via the Mississippi River and the Illinois Waterway to Lake Michigan at Chicago, IL, a distance of about 1,530 statute miles (1,329.5 nm) and from New York Harbor via the Hudson River and New York State Barge Canal System to Lake Ontario at Oswego, NY, a distance of 340 statute miles (295.5 nm), or to the Niagara River at Tonawanda, NY a distance of 496 statute miles (431 nm).
(3) The following table shows the controlling dimensions for these three routes and for other canals within the Great Lakes System.
(4) The following limiting dimensions in feet (meters) are for each of the three routes described above an for canal navigation in the Great Lakes system:
(5) *St. Lawrence River-
(6) depth, 26 feet (7.9 meters);
(7) width, 76 feet (23.16 meters);
(8) Length, 730 feet (222.5 meters)
when certain conditions are met;
(9) vertical, 117 feet (35.6 meters).
(10) Mississippi River-Illinois Waterway-
(11) depth, 9 feet (2.7);
(12) width, 80 feet (24.38 meters);
(13) length, 600 feet (182.88 meters);
(14) vertical clearance 17 feet (5.18 meters);
(15) N.Y. State Canals-Hudson River to Oswego-
(16) depth, 13 feet (4 meters);
(17) width, 43.5 (13.2 meters);
(18) length, 300 feet (91.4 meters);
(19) Vertical clearance, 20 feet (6.1 Meters);
(20) Hudson River to White hall, and from Three Rivers to Ithaca, Montour Falls, and Tonawanda-
(21) Depth, 12 feet (3.66 meters);
(22) width, 43.5 feet (13.2 meters);
(23) length, 300 feet (91.4 meters);
(24) vertical, clearance, 20 feet (6.1 meters).
(25) Riviere, Richelieu-Lake Champlain to St. Lawrece River-
(26) depth, 6 feet (1.8 meters)
(27) width, 23.2 feet (7.07 meters);
(28) length, 111.4 feet (33.8 meters);
(29) vertical clearance, 29 feet (8.8 meters);
(30) * Welland Canal-
(31) depth, 26 feet (7.9 meters);
(32) width, 76 feet (23.16 meters);
(33) length, 730 feet (222.5 meters), 740 feet (225.5 meters) when certain conditions are met;
(34) vertical clearance, 117 feet (35.66 meters).
(35) St Marys Falls Canal (Soo Locks)- (see limiting dimensions of through channel , chapter 12, St. Marys River.)
(36) * Minimum limiting measurements for transit of the entire Seaway by pleasure craft are a deadweight of 1 short ton or 20 feet in overall length. These control factors are based on requirements for passage through the South Shore Canal, Beauharnois Canal, and the Welland Canal.
(37) The St. Lawrence Seaway includes the waters of the St. Lawrence River above Montreal, Lake Ontario, the Welland Canal, and Lake Erie as far W as Long Point. The canals and locks of the Seaway overcome the rapids and water level differences in the St. Lawrence River between the ocean and Lake Ontario and between Lake Ontario and Lake Erie and enable deep-draft ocean-going vessels to proceed from the Atlantic Ocean to Lake Superior, the farthest inland major lake. The development, operation, and maintenance of the Seaway are under joint control of the Saint Lawrence Seaway Development Corporation, a corporate agency of the United States, and the St. Lawrence Seaway Authority of Canada. The corporation headquarters is in Washington, DC, and the operational field headquarters is in Massena, NY The Authority headquarters is in Ottawa, Ont., with field offices in Cornwall, St. Lambert, and St. Catharines. (See appendix for addresses.)
(38) The Corporation and the Authority jointly publish the Seaway Handbook, which contains regulations issued by the respective governments and other information relating to operational requirements of vessels transiting the Seaway. The Handbook also contains a schedule of Seaway tolls. The regulations contained in the Handbook are also codified in 33 CFR 401. A copy of the regulations is required to be kept on board every vessel transiting the Seaway. (see 33 CFR 401, chapter 2.)
(39) The Corporation and the Authority each issue Seaway Notices, which contain information o f changes in aids to navigation and other information relating to safety of navigation in the Seaway. The information contained in the notices i also broadcast by the Seaway radio stations. The Seaway Notices are available at appropriate locks and canals and at the offices of the Seaway entities.
(40) Aids to navigation in US waters of the Seaway between St. Regis and the head of the St. Lawrence River are operated and maintained by The Saint Lawrence Seaway Development Corporation and are described in the US Coast Guard Light List. Buoys off station, lights extinguished or malfunctioning, and other defective conditions should be reported promptly , by radio or other means, to the nearest Coast Guard unit or to Massena traffic control center via "Seaway Eisenhower" or "Seaway Clayton."
(41) Vessel Traffic Services.- A vessel Traffic Service (VTS) has been established in St. Marys River. The Service has been established to prevent collisions and grounding, to protect improvements to the waterway, and to protect the navigable waters from environmental harm.
(42) The Vessel Traffic Service provides for a Vessel Traffic Center (VTC), voice call, "Soo Control," that may regulate the routing and movement of vessels by movement reports of vessels, specific reporting points, and VHF-FM radio communications. The Service includes one-and two-way traffic areas, areas of allowed and prohibited anchorage, and speed limits.
(43) Participation in the Vessel Traffic Service (St. Marys River) is mandatory. (See 33 CFR 161.801 through 161.894, chapter 2, for regulations affecting vessel operations in the Vessel Traffic Service, and chapter 12 fro details.)
(44) The Canadian Coast Guard operates a Vessel Traffic Service (VTS) in Canadian waters from Long Point in Lake Erie through the Detroit ad St. Clair Rivers to De Tour Reef Light in Lake Huron. The service is mandatory from Detroit River East Outer Channel Lighted Buoy 1 and West Outer Channel Lighted Bell Buoy 1 and West Outer Channel lighted Bell Buoy 1 to a point 30 minutes N of Lake Huron Cut Lighted Horn Buoy 11. The service is voluntary in the remaining waters. The service is designed to enhance the safe and expeditious movement of marine traffic by encouraging the monitoring of a common radio frequency by vessels within each sector of the service. The service provides users with information of traffic situations pertaining to no meeting zones, as well as information to pilots, the St. Lawrence Seaway Authority, the public, vessel owners, and shipping agents.
(45) The service is divided into two traffic sectors, each with a specific operating frequency: Sector 1, VHF-FM channel 11, the Canadian waters from De Tour Reef Light to Lake St. Clair Light in Lake St. Clair; and Sector 2, VHF-FM channel 12, the Canadian waters from Lake St. Clair light to Long Point Light in Lake Erie.
(46) The VTS is administered by the VTS Center at Sarnia, Ont., at the head of the St. Clair River. The center is equipped with VHF transmitting and receiving facilities both locally and from remote sites. Participating vessels should report their name and ETA at the next callin-in-point to the VTS Center and, on request, will receive all reported information on vessel traffic in their area. In the voluntary participation areas of the VTS, calling-in points are located in Lake Erie abeam Long Point Light and abeam Southeast Shoal Light and in Lake Huron abeam Haror Beach Light or Point Clark Light, abeam Cove Island Light, abeam Great Duck Island Light, and abeam De Tour Reef Light. A voluntary calling-in-point is within the mandatory area of the VTS at Lake Huron Cut Lighted Buoy 11. Calling-in points in the mandatory participation areas of the VTS are identical to those of the US Coast Guard vessel traffic reporting system described in 33 CFR 162.130 through 162.140 (see chapter 2). (For complete information on the VTS, including calling--in points and message content, refer to the Annual Edition of Canadian Notices to Mariners.)
(47) Mariners are cautioned that not all vessels navigating in the voluntary areas of the service may be participation. The service is in no way an attempt by the Canadian Coast Guard to regulate the navigation or maneuvering of vessels from a shore station. The VTS does not override the responsibility of the master for the safe navigation of his vessel in accordance with the Navigation Rules.
(48) Navigation regulations.-The US Coast Guard has established avessel traffic reporting systemand related navigation regulations for the connecting waters from Lake Erie to Lake Huron. The reporting system is operated through the Canadian Vessel Traffic Service Center at Sarnia, Ont. (See 33 CFR 162.130 through 162.140, chapter 2, for complete information.)
(49) Vessel Traffic Management.-A Vessel Traffic Management Contingency Plan (VTM) for the Detroit and St. Clair Rivers has been agreed upon by the United States Coast Guard and the Canadian Department of Transport. The purpose of the system is to enhance the safety of navigation in the rivers during periods of exceptionally hazardous navigation conditions and to protect the navigable waters of the rivers from environmental harm. These objectives are accomplished by establishing criteria for allowing vessels to transit the system, by managing vessel entries and transits of the system, and by establishing no passing zones as required. The system is implements only in cases of emergency, upon agreement of the Commander, US Coast Guard Ninth District, and the Director, Central Region, Canadian Department of Transport. The implementation will be promulgated through Broadcast Notice to Mariners.
(50) This VTM system applies to all vessels 65 feed (19.8 meters) or over in length, all commercial vessels 26 feet (7.9 meters) or over in length when engaged in towing another vessel astern, alongside, or by pushing ahead, and each dredge or floating plant operating in the VTM area. Vessels in Sector 1 of the system, the Detroit River and Lake St. Clair S of Lake St. Clair Light, shall communicate with Detroit Vessel Traffic Center on VHF-FM channel 12. Vessels in Sector 2, Lake St. Clair N of Lake ST. Clair Light and St. Clair River, shall communicate with Sarnia Vessel Traffic Center on VHF-FM channel 11. The secondary communications frequency for both sectors is VHF-FM channel 16. Complete information on the system, including callin-in points and message content, is contained in the pamphlet Agreement on Vessel Traffic Management Contingency Plan for the Detroit and St. Clair Rivers, available from the US Coast Guard marine Safety Office in Detroit, Mich.(See appendix for address.)
(51) Ports and Waterways Safety.-(See 33 CFR 160, chapter 2, for regulations governing vessel operations and requirements for notifications of arrivals, departures, hazardous conditions, and certain dangerous cargoes to the Captain of the Port.)
(52) Disposal Sites and Dumping Grounds-These areas are rarely mentioned in the Coast Pilot, but are shown on the nautical charts.(See Dump Sites and Dumping Grounds, chapter 1, and charts for limits.)
(53) Ballast Water Management.-Vessels are required to carry out an exchange of ballast water on the waters beyond the EEZ prior to entry into Snell Lock, at Massena, NY. (See 33 CFR 151.1502 through 151.1516, chapter 2, for regulations.)
(54) Potable Water Intakes.-Vessels operation on freshwater lakes or rivers including the Great Lakes and connecting waters shall no discharge sewage, ballast, or bilge water, within the restricted areas adjacent to potable water intakes as are designated by the Surgeon General of the Untied States. (See 21 CFR 1250.93, chapter 2.)
(55) Note-This regulation, originally published under Title 42, Public Health, by the US Public Health Service, is published in Title 21, Food and Drugs; cognizant agency, Food and Drug Administration.
(56) The current list of restricted vessel waste discharge areas adjacent to potable (domestic) water intakes is contained in the Federal Register of September 16, 1960 (25 F.R. 8925). The areas were described and located by both geographical coordinates and by NOS Chart Numbers.
(57) Except as otherwise specifically indicated in the above list, in each case the restricted area includes the water within a circle having a radius of 3 miles with the domestic water intake as its center, in no event, however, extending beyond the International boundary line with Canada.
(58) This restriction supplies to all vessels which are underway, moored, or anchored within the restricted areas subject to following provisions:
(59) 1. Vessels moored at docks shall not discharge sewage, ballast or bilge water overboard if dock facilities for the disposal of such waste are available.
(60) 2. Vessels required to anchor within a restricted area under emergency condition for the safety of the vessel are exempted.
(61) 3. Vessels which provide sewage or waste treatment approved by the...(Commissioner of Food and Drugs), are exempted from that portion of the restriction applicable to sewage.
(62) 4. The list of intakes and the extent of the restricted areas may be revised from time to time.
(63) Danger Zones have been established within the area of this Coast Pilot. (See 33 CFR 334, chapter , for limits and regulations.)
(64) Drawbridges.- The general regulations that apply to all drawbridges are given in 117.1 through 117.49, chapter 2, and the specific regulations that apply only to certain drawbridges are given in Part 117, subpart B, chapter 2. Where these regulations apply, references to them are made in the Coast Pilot under the name of the bridge or the waterway over which the bridge crosses.
(65) The drawbridge opening signals (see 117.15, chapter 2) have been standardized for most drawbridges within the United States. The opening signals for those few bridges that are nonstandard are given in the specific drawbridge regulations. The specific regulations also address matters such as restricted operating hours and required advance notice of openings.
(66) The mariner should be acquainted with the general and specific regulations for drawbridges over waterways to be transited.
(67) Fluctuations of water level.-The water levels of the Great Lakes are subject to three types of fluctuation: seasonal, long range, and short period. Seasonal and annual fluctuations cover a period of about 1 year, long range fluctuations a few or many years, and short period fluctuations from several minutes to a few days. Seasonal and long range fluctuations generally affect an entire lake, while short period fluctuations are local in scope.
(68) The seasonal fluctuations are the most regular, with the highest levels usually occurring in summer and the lowest in winter. These fluctuations are caused by a number of factors that affect lake levels, including rain and snowfall, evaporation, ground water levels, and runoff from the land. From year to year, the magnitude of the fluctuation between the high and low and the months in which these occur may vary considerable in an individual lake. Lake Superior is generally last to reach its seasonal low and high, in March and September, respectively. Lake Michigan and Huron usually reach their low in February and its high in June. Lake Ontario usually reaches its low in January and its high in June. The amount of fluctuation between the seasonal high and low is generally least in Lake Superior and most in Lake Ontario.
(69) Long range fluctuations of the lake levels are caused by long term variations of the same factors which affect seasonal fluctuations. Precipitation is the most important of these factors. Long periods of above or below normal rain and snowfall are usually followed by higher or lower lake levels, but this effect may be increased or decreased by combination with the other factors that affect lake level. Another cause of long range fluctuations in the uplifting of the earth's crust in the Great Lakes region. When the outlet of the lake is rising in relation to the lake shores, the water level rises with respect to the land. This effect is occurring in all the lakes, except for parts of the NE shores of Lake Superior and Lake Huron.
(70) Short period fluctuations occur in amounts varying from a few inches to several feet and for periods varying from a few minutes to a day, depending on the locality where they occur. These changes, and by oscillations called seiches, which may be caused by one or both of the other two. Sustained winds drive forward a greater volume of surface water than can be carried off by the subsurface return currents, thus raising the water level on the lee shore and lowering it on the windward shore. This effect is more pronounced in bays and at the extremities of the lakes, where the impelled water is concentrated in a small space by converging shores, especially if coupled with a gradually sloping inshore bottom which even further reduces the flow of the lower return currents. Closely spaced high and low barometric pressure centers moving across a lake cause a temporary tilting of the water surface. The amount of this tilting is dependent of the pressure gradient and the speed of the moving centers. Seiche (pronounced saych) is an oscillation that occurs when winds and/or barometric pressure differences causing a fluctuation have diminished. The lake surface is in a tilted condition, and a surge of water takes place from the high area to the low. An imbalance in the opposite direction occurs and causes a return surge. This effect continues, with each successive surge diminished by friction until the seiching action cease.
(71) Lunar tides are know to exist on the Great Lakes, particularly on those lakes with an E and W axis. However, the effects of these tides are so small as to be inconsequential when compared to the effects of other short period fluctuations. (See appendix for a list of water level publications published by NOS and the Corps of Engineers.)
(72) Weather.-Climatoligical tables for coastal localities covered in this volume follow the appendix. Listed in the appendix are National Weather Service offices and radio stations which transmit weather information. The Marine Weather Services Charts, which contain additional important information, are available from Distribution Branch (N/CG33), National Ocean Service. (See appendix for address.)
(73) This section presents an overall, seasonal picture of the weather that can be expected on the Great Lakes. Detailed local weather is discussed in the appropriate chapters.
(74) Weather can make navigation the Great Lakes a pleasure, a challenge, or a terror. Each season has its own weather problems, each waterway its own peculiarities.
(75) Winter navigation is severely restricted by ice and storms. Ice coverage and thickness vary from lake to lake and season to season. Seaway shipping is usually at a stand still from mid-December through early April. Great Lakes shipping extends into the winter but depends upon local conditions. The ice threat is compounded by fierce winter storms which bring a variety of wind, wave, and weather problems on an average of every 4 days. A combination of strong winds, rough seas, and cold temperatures can result in superstructure icing, in which sea spray and sometimes precipitation can freeze to a ship's superstructure. This adds tremendous weight and creates dangerous instability.
(76) Spring storms can generate gales and rough seas, but with the approach of summer they become less frequent and severe. fog is the principal navigation headache. Relatively warm air pumped over still cold lake waters creates an advection fog that plagues the mariner into the summer. In late spring, thunderstorms become an occasional problem.
(77) While fog can hinder navigation and an occasional low pressure system can bring a spell of bad weather, this is usually the most trouble free time. The principal threat is the thunderstorm. While they can occur in any month, they are most likely from May through October. They can spring up quickly and generate strong winds and rough seas.
(78) Autumn is dangerous. Clear, crisp days are often interrupted by rapidly intensifying low-pressure systems whose galeforce winds can whip tumultuous seas. Energy is supplied by the still warm waters, and contrasting air masses can spawn storms right over the Great Lakes Basin. Occasionally, an errant tropical cyclone makes its way to the region. Fog can be a local, generally nearshore, problem on calm, clear nights. It usually lifts shortly after sunrise.
(79) Extratropical Cyclones.-The Great Lakes lie in the midst of a climatological battlefield, where northern polar air often struggles for control with air from the Tropics. During spring and autumn, the zone separating these two armies lies over the Lakes region. The contrast between the two triggers the formation of a number of low-pressure systems, often intense, often fast moving. The Lakes provide moisture and, in the fall, heat to fuel these winter-type storms. They also aid storms that migrate from other regions.
(80) The more destructive storms usually come from the SW or W. Lows spawned in the Pacific southwest, Arizona-New Mexico, and the central Rocky Mountain and Great Plains States account for nearly half of the storms that enter the Great Lakes Basin from October through May. Another source is western Canada, which spawns the "Alberta Lows." At a peak in October, these storms arrive from the W and NW. They are relatively weak and rarely generate gales; however, occasionally one has been known to kick up 60-knot winds after intensifying over friendly waters.
(81) When a ship is S of an eastward-moving storm center, the approach of the low is heralded by a falling barometer, a SE to S wind, lowering clouds, and drizzle, rain, or snow. Precipitation diminishes and the wind veers as the warm front nears. In the warm sector, temperatures rise, skies brighten, and the air is humid with haze or fog. The passage of the cold front is marked by a bank of convective clouds to the W, a sharp veering of the wind to the W or NW, and sometimes sudden squalls with showers or thunderstorms. Behind the cold front, pressure rises, temperatures fall, visibility increases, and cloud cover decreases.
(82) When a ship is N of the storm center, changes in the weather are less rapid and less distinctive than when sailing S of the center. Winds ahead of the low gradually back from the E through N to NW. The weather conditions also vary, gradually shifting from those found in advance of the warm front to those behind the cold front.
(83) Thunderstorms.-While they can develop in any month, thunderstorms are most likely from May through October. They can occur in squall lines or single cell. They can stir a breeze or kick up gusts of 100 knots. They can spring up rapidly or be tracked for several days. They can bring a gentle shower or harbor tornado or waterspout. They can create serious problems for the Great Lakes mariner. The number of days with thunderstorms can vary from year to year, but on the average they can be expected on 5 to 10 days per month during the summer. The Lakes themselves can influence this frequency. Cool water and a strong lake breeze both inhibit summertime convective activity over water. For example, Lake Michigan suppresses thunderstorm activity during the summer, but increases it slightly in autumn. Along the shore, activity is most likely in the afternoon and evening, while over open waters it is more likely at night.
(84) Fog.-Fog can form in any season, but is it most likely in spring and early summer, particularly over open waters. Along the shore, fog is also common in autumn. Occasionally, steam fog will develop during the winter. The densest and most widespread form is the advection type, where relatively warm air flows over cooler water. These conditions exist in spring and summer. Fog is particularly tenacious over the NW portions of the lakes, where the cold water is continually brought to the surface by upwelling. This fog is often persistent. It may lift somewhat during the day, but unless broken up by a good wind, will lower again during the night. Radiation fog is formed by the air in contact with a rapidly cooling land surface, such as occurs on clear, calm autumn nights. This fog forms onshore and may drift out over the lakes during the early morning. It is usually not as dense nor persistent as advection fog and should lift by noon. Steam fog or arctic sea smoke occurs when frigid arctic air moves across the lakes and picks up enough moisture to become saturated. This fog may vary from 5 to 5,000 feet ( to 1,500 meters) in depth, although it is seldom very dense.
(85) Ice.-Ice begins to form slowly, usually in early November, in the shallows, coves, and inlets. Gradually it spreads and thickens, building out from the shore and breaking off. Since during most winters the period of freezing temperatures is not long enough to cause a lakewide solid ice sheet to form, most lakes are besieged by "pack ice," which, in its broadest sense, is any ice that is not fast ice. This pack ice is then susceptible to the whims of winds, waves, currents. This can cause rapid changes in a real coverage, which make prediction of thickness, extent, and distribution difficult.
(86) The ice that builds out from the shore ranges from a few inches to several feet in thickness. Much of it breaks off to form floes and fields. Strong persistent winds cause windrows and pressure ridges to form. Some of these may extend 10 to 20 feet (3 to 6 meters) above the water and 30 to 35 feet (9 to 11 meters) below, anchoring themselves to the lake bottom. Pack slush ice, which is pack ice that is well broken up, is particularly hazardous to shipping. It is difficult to combat as it quickly closes in around a vessel, preventing movement in any direction. It can damage propellers and steering gear, clog condenser intakes, and exert tremendous pressure on the hull.
(87) Ice is often strong enough to halt navigation through the St. Lawrence Seaway by mid-December. The Seaway usually reopens by mid-April. Inter- and intra-lake shipping usually continues well into January with the help of icebreakers. A few channels remain open all season. Ice cover peaks in late February or early March. Soon the decay begins. By April, shipping is in full swing; however, some drift ice remains into May.
(88) Cargo Care.-High humidities and temperature extremes that can be encountered when navigating the Great Lakes may cause sweat damage to cargo. This problem is most likely when cargoes are loaded in warm summer air or can occur anytime temperatures fluctuate rapidly.
(89) When free air has a higher dewpoint than the temperature of the surface with which it comes in contact, the air is often cooled sufficiently below its dewpoint to release moisture. When this happens, condensation will occur aboard ship either on relatively cool cargo or on the ship's structure within the hold, where it drips onto the cargo. If cargo is stowed in a cool climate and the vessel sails into warmer water, ventilation of the hold with outside air can lead to sweat damage of ay moisture-sensitive cargo. Unless the cargo generates internal heat, then, as a rule, external ventilation should be shut off. When a vessel is loaded in a warm weather region and moves into a cooler region, vulnerable cargo should be ventilated.
(90) In general, whenever accurate reading show the outside air has a dewpoint below the dewpoint of the air surrounding the vulnerable cargo, such outside air is capable of removing moisture and ventilation may be started. However, if the outside dewpoint is higher than the dewpoint around the cargo, ventilation will increase moisture and result in sweating. This generally does not take into account the possibility of necessary venting for gases or fumes.
(91) Optical Phenomena-.The two basics types of optical phenomena are those associated with electromagnetic displays and those associated with the refraction or diffraction of light. The aurora and Saint Elmo's fire are electromagnetic displays. Halos, coronas, parhelia, sun pillars, and related effects are optical phenomena associated with the refraction and diffraction of light through suspended cloud particles; mirages, looming, and twilight phenomena such as the "green flash" are optical phenomena associated with the refraction of light through air of varying density. Occasionally, sunlight is refracted simultaneously by cloud suspensions and by dense layers of air producing complex symmetric patterns of light around the sun.
(92) A mirage is caused by refraction of light rays in a layer of air having rapidly increasing or decreasing density near the surface. A marked decrease in the density of the air with increasing altitude is the causes of such phenomena known as looming, towering, and superior mirages. Looming is said to occur when objects appear to rise above their true elevations. Objects below the horizon may actually be brought into view. Towering has the effect of elongation visible objects in the vertical direction. A superior mirage is so named because of the appearance of image above the actual object. Ships have been seen with an inverted image above and an upright image floating above that.
(93) Such mirages, especially with looming towering, are fairly common in the area, with frequency increasing toward the higher latitudes. They are most common in summer when the necessary temperature conditions are most likely. Another type, the inferior mirage, occurs principally over heated land surfaces such as deserts, but may be observed occasionally in shallow coastal waters, where objects are sometimes distorted beyond recognition. In contrast to the superior mirage, the condition necessary for the inferior mirage is an increasing air density with height. Atmospheric zones of varying densities and thickness may combine the effects of the various types of mariges to form a complicated mirage system known as Fata Morgana.
(94) The green flash is caused by refractive separation of the sun's rays into its spectral components. This may occur at sunrise or sunset when only a small rim of the sun is visible. When refractive conditions are suitable, red, orange, and yellow waves of sunlight are not refracted sufficiently to reach the eye, whereas green waves are. The visual result is a green flash in the surrounding sky.
(95) The refraction of light by ice crystals may result in many varieties of hales and arcs. Because red light is refracted the least, the inner ring o f the halo is always red with the other colors of the spectrum following outward. Halos with radii of 22 degrees and 46 degrees have been observed with the refraction angle within the ice spicules determining which type may occur.
(96) Solar and lunar coronas consist of a series of rainbow-colored rings around the sun or moon. Such coronas resemble halos but differ in having a reverse sequence of the spectrum colors, red being the color of the outer ring, and in having smaller and variable radii. This reversed sequence of the spectrum occurs because coronas result from diffraction of light whereas the halo is a refraction phenomenon. The radius varies inversely as the size of the water droplets. Another type of diffraction phenomenon is the Brocken Bow (also known as glory), which consists of colored rings around shadows projected against fog or cloud droplets.
(97) Ice blink, land blink, and water and land skies are reflection phenomena observed on the underside of cloud surfaces. Ice blink is a white or yellowish-white glare on the clouds above accumulations of ice. Land blink is a yellowish glare on the clouds above accumulations of ice. Land blink is a yellowish glare observed on the underside of clouds over snow-covered land. Over open water and bare land, the underside of the cloud cover when observed to be relatively dark is known as water sky and land sky. The pattern formed by these reflections on the lower side of the cloud surfaces is known as "sky map."
(98) Auroral displays are prevalent throughout the year, but are observed most frequently in the winter. Records show that the periods of maximum auroral activity coincide in general with the periods of maximum sunspot activity.
(99) The cloud like, luminous glow is the most common of the auroral forms. The arc generally has a faint, nebulous, whitish appearance and is the most persistent of the auroras. Bay auroras are more spectacular but less pristine phenomena. They are usually characterized by colored streaks of light that vary in color and intensity, depending on altitude. Green is the most commonly observed hue, although red and violet may occur in the same display. The aurora borealis (northern lights) may be observed on occasion.
(100) Saint Elmo's fire is observed more rarely than the aurora and may occur anywhere in the troposhepere. It occurs when static electricity collects in sufficiently large charges around the tips of pointed objects to ionize the air in its vicinity and leak off in faintly luminescent discharges. Saint Elmo's fire is observed occasionally on ship masts and on airplane wings in the vicinity of severe storms. It is described either as a weird, greenish glow or as thousands of tiny electrical sparks flickering along the sharp edges of discharging surfaces.
(101) Winter Navigation.- Ice normally begins to form in various parts of the Great Lakes during December and forms a hazard to navigation by the end of the month. Before the St. Lawrence Seaway closes in late December, most lake vessels lay up for the winter and oceangoing vessels transit the Seaway to the Atlantic. Historically, weather and ice conditions have necessitated the suspension of shipping in the lakes from mid-December until early April.
(102) During the ice season, US Coast Guard icebreakers, sometimes working in conjunction with Canadian Coast Guard icebreakers, conduct operations to maintain a broken track along the main vessel routes through the lakes, St. Marys River, and the Detroit-St. Clair river system and to assist vessels in transit as necessary. Floating aids to navigation, except those designated in the Coast Guard Light List as winter markers, are withdrawn from service immediately prior to the formation of ice on the lakes.
(103) The Coast Guard operates a VHF-FM radiotelephone vessel traffic reporting system on Lakes, Superior, Michigan, Huron, Erie, and the St. Marys River. The system is designed to provide vessel traffic information, aid in the efficient deployment of icebreaking services, and to obtain ice information from transiting vessels. Vessels are requested to contact the appropriate Coast Guard Task Group prior to or upon departure from port, upon arrival at their destination, and at specified calling-in points between.
(104) The Canadian Coast Guard also operates a vessel traffic reporting system designed to provide traffic information to meet the requirements of the St. Lawrence Seaway Authority and the Vessel Traffic Center at Sarnia, Ont. Traffic information so obtained during the ice season is forwarded to Ice Toronto, the Canadian Coast Guard ice operations office in Toronto, Ont. This office provides current ice information, routing advice information on aids to navigation, icebreaking support when available and considered necessary, and coordinates the formation of convoys when conditions dictate. Complete information on Ice Toronto and its services are contained in the Guide to Great Lakes Ice Navigation.
(105) Routes.- The Lake Carriers' Association and the Canadian Shipowners Association have recommended, for vessels enrolled in the associations, separation routes for upbound and downbound vessels on the Great Lakes and connecting waterways. These routes are shown on the Great Lakes charts published by the National Ocean Service and are described in this Coast Pilot at the beginning of each affected chapter.
(106) Pilotage.- By International agreement between the United States and Canada, the waters of the Great Lakes and the St. Lawrence River have been divided into designated and undesignated waters for pilotage purposes. In designated waters, registered vessels of the United States and foreign vessels are required to have in their service a United States or Canadian registered pilot. In undesignated waters, registered vessels of the United States and foreign vessels are required to have in their service a United States or Canadian registered pilot or other officer qualified for Great Lakes undesignated waters.
(107) The designated waters of the Great Lakes are divided into three districts as follows:
(sec. 108-129 omitted)
(130) Towage.- Tugs are available at most major ports; they can usually be obtained for the smaller ports an advance notice if none are available locally. Arrangements for tugs should be made in advance through ships' agents or the pilots. See the text for the ports concerned as to the availability of tugs.
(sec. 131-148 ommited)
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