11. Lake Michigan

(1) Chart Datum, Lake Michigan.-- Depths and vertical clearances under overhead cables and bridges given in this chapter are referred to Low Water Datum, which for Lake Michigan is an elevation 577.5 feet (176.0 meters) above mean water level at Rimouski, Quebec, on International Great Lakes Datum 1985 (IGLD 1985). (See Chart Datum, Great Lakes System, indexed as such, chapter 1.)

Dimensions, etc.

(2) Length, steamer track, Chicago to Straits of Mackinac; 321 miles.
(3) Length (right line), from about longitude 87 30'W. at the S end to 85 45'W.
at the N end; 307 miles.
(4) Breadth (right line), on about latitude 45 25'N.; 118 miles.
(5) Depth, maximum recorded by NOS; 923 feet.
(6) Water surface of lake (including Green Bay); 22,300 square miles.
(7) Entire drainage basin (including Green Bay); 67,900 square miles.

(8) General description.-- Lake Michigan is the third largest of the Great Lakes and is the only one entirely within the United States. The only natural outlet of the lake is at the N end through the Straits of Mackinac. At the S end of the lake, the Illinois Waterway provides a connection to the Mississippi River and the Gulf of Mexico. The N part of the lake has many islands and is indented by several bays; Green Bay and Grand Traverse Bay are the largest. The shores in the S part of the lake are regular, and it has been necessary to construct artificial harbors. The forested shores in the N part of the lake are sparsely populated, while those in the S part are near the heart of the great urban industrial area of the U.S. Midwest.

(9) Fluctuations of water level.-- The normal elevation of the lake surface varies irregularly from year to year. During the course of each year, the surface is subject to a consistent seasonal rise and fall, the lowest stages prevailing during the winter and the highest during the summer.

(10) In addition to the normal seasonal fluctuations, oscillations of irregular amount and duration are also produced by storms. Winds and barometric pressure changes that accompany squalls can produce fluctuations that last from a few minutes to a few hours. At other times, strong winds of sustained speed and direction can produce fluctuations that last a few hours or a day. These winds drive forward a greater volume of surface water than can be carried off by the lower 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 lake, 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. This condition is very pronounced at Green Bay Harbor.

(11) Weather.-- Rough water is created when strong winds blow over a long fetch of water. Northerly winds cause this on the S part of the lake and southerly winds have the same effect on the N part of the lake. They raise dangerous seas and generate hazardous currents at harbor entrances. Winds with southerly components are prevalent during the entire navigation season. Northerlies are a little less frequent, but are common, particularly in spring. The sea conditions are worst in October and November, when, lakewide, wave heights of 5 to 10 feet are encountered about 35 percent of the time. In October, S through SW winds are most often responsible, while by November W through N winds often generate rough seas. Seas of 10 feet or more are encountered 3 to 5 percent of the time from November through March. Extreme waves of 20 to 22 feet have been encountered. During the spring, high seas are infrequent, but 5- to 10-foot seas develop 15 to 30 percent of the time in the S and 20 to 40 percent in the N. Summer seas climb above 10 feet less than 1 percent of the time, while those in the 5- to 10-foot category drop to less than 20 percent in June and July. By August, the fall buildup begins.

(12) Gales are most likely from September through April, particularly in the fall. During this season gales blow 3 to 7 percent of the time; speeds of 28 knots or more occur from 12 to 20 percent of the time. Strong winds often blow out of the W and NW, making E shore harbor entrances dangerous. The strongest measured over-the-lake wind was out of the WSW at 58 knots. However, since Green Bay recorded a 95-knot southwesterly one May, it is not unrealistic to expect a wind extreme of 100 knots or more over open waters. Spring winds can still blow strong, with winds of 28 knots or more encountered about 4 to 8 percent of the time. They do slacken from their winter fierceness, with southerlies and southwesterlies becoming more frequent and northerlies less so as summer approaches. Strong winds are infrequent in summer and mostly associated with thunderstorms. S and SW winds prevail particularly in the N; southeasterlies are also common in the S. Northerlies are a secondary wind.

(13) Coastal winds are more localized and variable. Along the Michigan shore, spring winds are variable, particularly in the morning, when northerlies, easterlies, and southerlies are among the most common. By afternoon, aided by a lake-breeze effect, there are a preponderance of winds out of the S, particularly with the approach of summer. Summer also brings a slackening of windspeeds. The likelihood of encountering winds of 28 knots or more falls from a 4- to 10-percent chance in March to less than 3 percent by May. The most likely cause of strong winds in spring and summer are thunderstorm gusts. By summer, windspeeds of 28 knots or more occur less than 4 percent of the time and less than 2 percent most of the time. Summer winds along the shore are usually out of the E through S during the morning hours, swinging to the S and NW by afternoon, with an increase in speed. By October, there is a noticeable increase in windspeeds. Speeds of 28 knots or more increase to 4 to 6 percent. By December, these speeds can be encountered up to 11 percent of the time. Morning directions are variable, with E, S, and W winds among the most common. Afternoon winds are most often out of the S through W. The strong winds continue throughout the winter and are associated with winter storms, which bring a variety of winds from SW through NE.

(14) Along the W shore of the lake, spring winds are variable, but the influence of the land-lake breeze is already noticeable, Morning winds often have a westerly component, while an easterly influence is evident during the afternoon. Wind strength gradually abates during spring; by May, winds of 28 knots or more are encountered less than 1 percent of the time. Except for occasion; thunderstorm gusts, summer winds rarely exceed 28 knots through September. Morning breezes are generally out of the S through W. During the day, they strengthen slightly and blow out of the NE through SE; SW and W winds are also common during the afternoon, when the prevailing circulation interferes with the lake breeze effect. With autumn comes an increase in strength and less diurnal variability. By November, winds of 28 knots or more are encountered about 1 percent of the time. Fall winds blow mainly out of the S through NW, with SW and W winds the most frequent. During winter, westerlies and northwesterlies are common. but unseemingly, winds of 28 knots or more are no more frequent than in fall.

(15) While thunderstorms can occur at any time, they are most likely from May through September. During this period, thunder is heard on an average of 4 to 8 days per month at locations along the shore and 1 to 3 percent of the time over open water. Activity is a little more numerous in the S than the N. Over open water, July and August are the peak months, while June and July are more active along the shore. During the summer, a cool dome of air, the result of the lake breeze, often blocks thunderstorms and squall lines during the day. This results in a nighttime peak in activity. However, a severe squall line may break through this block, or due to a strong prevailing circulation, the block may not exist.

(16) In spring, when there is often a clash between cold and warm air, thunderstorms and squall lines can be violent. On occasion they may trigger tornadoes or even waterspouts. This area lies at the NE edge of the nation's maximum frequency belt for tornadoes. Although rare, tornadoes are most likely from April through June.

(17) Poor visibilities, caused by fog, rain, snow, and pollution, may occur in any season. Fog is the principal cause of visibilities less than 0.5 mile. It is most likely in the spring and early summer over open water (advection fog) and from late fall through spring along the shore (radiation fog).

(18) In open waters, from March in the S and April in the N through June, warm moist air riding winds with a southerly component blowing at 5 to 20 knots reduces visibilities to less than 0.5 mile from 5 to 10 percent of the time. These fogs are most likely during the morning and early afternoon and when the air is 5 to l5 F warmer than the water. May and June are the most likely months.

(19) The shores of Lake Michigan are subject to varying amounts of fog. Upwelling along the NW shores increases the possibility of advection fog in spring and summer; in fact, the W shore waters in general are 5 to 10§F cooler than the E shore waters. N of Chicago, visibilities drop to less than 0.5 mile on about 25 to 35 days annually. In the Chicago area, smoke and haze frequently reduce visibility to the 3- to 6-mile range, but dense fog is less common than it is to the N. It is most likely from fall through late spring with a minimum in July. Along the Michigan shore, the indication from the few locations with fog observations is that frequencies are similar to those along the Wisconsin shore. In comparing Muskegon to Milwaukee, both exhibit a morning maximum from April through October, early morning in the sum- mer and around sunrise in other seasons. The most fog-free times occur during the afternoon in spring and late morning through evening in summer. Milwaukee is more fog prone in spring, but less in summer and fall. Overall, Muskegon averages 5 fewer days annually with visibilities less than 0.5 mile.

(20) Ice.-- The first waters to form an extensive ice cover are Green Bay and the Bays de Noc. The Straits of Mackinac and the shallow areas N of Beaver Island usually follow. The Straits are usually closed by mid-December. (See the discussion of ice in the Straits of Mackinac in chapter 10.) These buildups are aided by windrows resulting from prevailing winds and currents. In a normal winter, an early ice cover is established by the end of January and includes the above-mentioned waters plus the extreme S part of the lake. In general, ice accumulates in a southerly direction with a rapid buildup in the shallows E of Manitou and Fox Islands. In this area, the prevailing NW wind traps ice between the land masses and, with the exception of Grand and Little Traverse Bays which are solid, vessels can expect to encounter drifting ice. The surface features and location of the ice fields change as a direct function of the wind. Shores exposed to the full force of the wind often have large ice fields of very heavy brash extending 1 to 2 miles offshore. In addition, a circular current pattern in the S part of the lake distributes drifting floes along the shore. Even during a mild winter, these floes can build out 10 to 15 miles into the lake. A mild winter on Lake Michigan means about 10-percent coverage compared to an average 40-percent coverage and an 80-percent coverage during a severe winter. Maximum ice coverage occurs by mid-March, on the average, while decay begins a week or two later. By mid-April, ships are once again transiting the Straits of Mackinac.

(21) Routes.-- The Lake Carriers' Association and the Canadian Shipowners Association have recommended, for vessels enrolled in the associations, the following separation of routes for upbound and downbound traffic in Lake Michigan:

(22) Southbound vessels, bound for Milwaukee and W shore points N thereof shall run out on a course of 241 for 30 miles from a point of departure abreast of Lansing Shoals on course to Rock Island Passage then steer 205 for 202.5 miles to Milwaukee, or other courses to destination.

(23) Southbound vessels, bound for W shore points S of Milwaukee shall run out on a course of 241 for 30 miles from a point of departure abreast of Lansing Shoals on course to Rock Island Passage; then steer 196 for 208 miles to a point E of Wind Point to intersect the regular southbound track; vessels bound for Calumet or Indiana Harbor steer 188 for 69.5 miles; vessels bound for Buffington or Gary steer 183 for 73.6 miles; vessels bound for Burns Harbor change course 19.7 miles prior to reaching the point E of Wind Point and steer 180 for 96.75 miles.

(24) Southbound vessels from Sturgeon Bay bound for ports near the S end of Lake Michigan shall lay a course of 172 for 47.5 miles to a point 19 miles 114.75 from Rawley Point Light.

(25) Southbound vessels from Porte Des Morts Passage bound for the S end of Lake Michigan shall lay a course of 189 for 79.5 miles to a point 19 miles 114.75 from Rawley Point Light.

(26) From the point 19 miles E of Rawley Point Light vessels shall steer 183 for 165.25 miles to Buffington or Gary, or when 090 from Wind Point Light vessels can change course to 188 for 69.5 miles to Calumet or Indiana Harbor.

(27) Southbound vessels from the Straits of Mackinac bound or E shore points may use the Grays Reef Passage or the northbound course by Lansing Shoals. If they choose to use the Grays Reef Passage they shall lay a course from the Mackinac Bridge, s teering 275 until abeam of New Shoal Lighted Buoy 1 when change is made to 260 . Steer 260 until turning to the 186 course through Grays Reef with White Shoal bearing 006 .

(28) From Grays Reef, take departure from Grays Reef Passage steering 237 and haul to 217 when abeam Ile Aux Galets Light. Then when abeam Leland Light, change course to 197 until abeam North Manitou Shoals Light when haul is made to 242 for about 13.25 miles for Sleeping Bear.

(29) When abeam Sleeping Bear Lighted Bell Buoy 7, steer 205 for 17.5 miles to a point 3.75 miles W of Point Betsie Light; then steer 195 for 45.25 miles to a point 3 miles W of Big Sable Light; then steer 183 for 28 miles to a point 3 miles W of Little Sable Light; thence to destination.

(30) Northbound vessels for the Straits of Mackinac will navigate via Manitou Passage. This rule does not apply to vessels coming out of Green Bay. Vessels from Southern Lake Michigan set a course for a point 4.75 miles abreast of Big Sable. These courses and distances are: from Burns Harbor 009 for 169.5 miles; from Gary and Buffington 012 for 168 miles; from Calumet and Indiana Harbor 015 for 163.75 miles, and from Chicago 017 for 158 miles; then, from abreast Big Sable, steer 015 for 44 miles until 5.75 miles from Point Betsie Light; then steer 029 for 17.5 miles until abreast of Sleeping Bear Lighted Bell Buoy 7 then steer 062 for 14.5 miles until abreast of North Manitou Shoal Light; then 037 for 64.75 miles to Grays Reef.

(31) Vessels eastbound out of St. Martin and Rock Island Passages shall set a course to pass not more than 6 miles off Seul Choix Point. Taking departure from Rock Island Passage Lighted Gong Buoy RI the course is 056 for 58 miles.

(32) Vessels northbound from ports near the S end of Lake Michigan to Escanaba shall set course for not more than 8 miles off Wind Point. Vessels from Gary and Buffington steer 350 for 75.75 miles; vessels from Calumet and Indiana Harbor steer 354 for 69 miles. Then steer 006 for 98.75 miles to a point not more than 5 miles off Rawley Point; then steer 020 for 75.25 miles to Porte Des Morts entrance Lighted Bell Buoy. Northbound vessels to Port Inland from near the S end of Lake Michigan shall follow the northbound Manitou course to a point 5.75 miles abreast Point Betsie; then steer 013 for 63.5 miles to a point 4 miles W of Boulder Reef; then steer 022 for 23.75 miles to Port Inland Lighted Bell Buoy 2; then steer 000 4 miles to destination.

(33) It is understood that masters may exercise discretion in departing from these courses when ice and weather conditions are such as to warrant it. The recommended courses are shown on charts No. 14900 and 14901, Lake Michigan.

(34) Pilotage.-- The waters of Lake Michigan are Great Lakes 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. Registered pilots for Lake Michigan are supplied by Western Great Lakes Pilots Association (See appendix for addresses.) Pilot exchange points are off Port Huron at the head of St. Clair River in about 43 05'30"N., 82 24'42"W. and at De Tour, Mich., at the entrance to St. Marys River. Three pilot boats are at Port Huron; HURON BELLE has an international orange hull with an aluminum cabin, and HURON MAID and HURON LADY each have an international orange hull with a white cabin. The pilot boat at De Tour, LINDA JEAN, has a green hull and a white cabin. (See Pilotage, chapter 3, and 46 CFR 401, chapter 2.)

(35) Principal ports.-- Most of the harbors on the E side of Lake Michigan are within the mouths of small rivers or in small lakes connected to Lake Michigan by an entrance channel. Parallel piers have been constructed at the mouths of these harbors to aid in carrying the bar into deeper water and to lessen the need for dredging in the harbor entrance. In addition, several harbors along this shore have been provided with stilling basins formed by breakwaters that converge to an entrance opening in deep water beyond the parallel piers. These basins dissipate the force of storm generated waves to prevent them from being conducted through the confined channels between the piers and into the harbors.

(36) The harbors on the W side of the lake are generally at the mouths of small rivers, the only large streams being the Fox and Menominee Rivers which empty into Green Bay. The entrances to the harbors are generally protected by parallel piers, and some have been provided with stilling basins. Some harbor entrances are protected by detached breakwaters. Outer harbors enclosed by breakwaters have been constructed at Calumet Harbor and Milwaukee. Entirely artificial harbors, with basins enclosed by piers and breakwaters, are at Burns International Harbor, Gary, Buffington, Indiana Harbor, Great Lakes, Waukegan, Port Washington, and Port Inland.

(37) The most important harbors in Lake Michigan are Muskegon, Calumet, Chicago, Milwaukee, Kenosha, and Green Bay. Drydocking facilities for deep-draft vessels are at Sturgeon Bay.

Sections 38 - 1154 have been ommitted

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