(1) Chart Datum, Lake Huron.-Depths and vetical clearances under overhead cables and bridges given in this chapter are referred to Low Water Datum, Which for Lkae Huron is on 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, indexed as such, chapter 1.)

Dimensions, etc.
(2) Length, steamer track, De Tour Passage to Fort Gratiot; 223 miles.

(3) Length, steamer track, Straits of Makinac to Fort Gratiot; 247 miles.

(4) Length (right line), Drummond Island, at nearest point to entrance of False Detour, to Blue Point; 206 miles.

(5) Breadth (right line), on about latitude 44 30'N.; 183 miles.

(6) Depth, Maxium recorded by NOS; 750 feet.

(7) Water surface of lake (including St. Marys River below Brush Point, North Channel, and Georgian Bay); 9,100 square miles (U.S.), 13,900 square miles (Canada).

(8) Entire drainage basin (including St. Marys River below Brush Point, North Channel, and Georgian Bay); 25,300 square miles (U.S.), 49,400 square miles (Canada).

(9) General description.-Lake Huron is the second largest of the Great Lakes. Three large bays extend from the main body of the lake, Saginaw on the W. side and the North Channel and Georgian Bay on the NE side. The lake receives the waters of Lake Michigan through the Straits of Mackinac and those of Lake Superior from the St. Marys River. The Lake discharges at its S end into St. Clair River at Fort Gratiot. The lake is a connecting link in the Great Lakes chain. The depth of water in St. Marys River, St. Clair River, and Detroit River governs the draft of vessels navigating Lake Huron to and from Lake Superior and Erie.

(10) Vessel Traffic Services.-The Canadian Coast Guard operates a Vessel Traffic Service in Canadian waters from Long Point in Lake Erie through the Detroit and St. Clair Rivers to De Tour Reef Light in Lake Huron. (See chapter 3 and the Annual Edition of Canadian Notices to Mariners forcomplete information.)

(11) 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.

(12) In addition to the nomal sesonal 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 sloaping inshore bottom which even further reduces the flow of the lower return currents. This condition is very pronounced at the mouth of Saginaw River.

(13) Weather.-Gales are most frequent in autumn. By late summer ther is a noticeable increase, lakewide, in the frequency of gales, and this increase until the end of the navigation season. During November and December, gale are blowing 5 to 10 percent of the time, while windspeeds of 28 knote or more may be encountered up to 23 percent of the time. These winds are mainly generated by winter storms; their frequency falls dramatically in spring. By June and July, gales are expected less than 1 percent of the time, while wind of 28 knots or more blow less than 3 percent of the time. However, squall lines and thunderstorms can produce violent short period wnd from spring through fall. For example, the strongest measured wind on Lake Huron's open waters occurred in August 1965 and was measured at 95 knots from NWN. Shoreline extreams range from 43 to 53 knots. Directions of these extremes are often out of the SW; but W, NW, and NE winds have set some of these records. Most of the records were set from late fall through late winter.

(14) The shape of Lake Huron is such that stong winds from any quater may generate rough seas somewhere on the lake. S through W winds are common in early autumn, while westerlies and sothwesterlies prevail in late autumn. W through NW winds are often the strongest. Winds from the northerly quarant can raise dangerous seas in the S, especially near the S outlet of the lake. In the central waters a long fetch of strong easterlies or northeasterlies can generate high seas along the Michigan shore, which run athwart the N-S traffic through the lake. Southerlies can be dangerous particularly near the converging N shore. If the fetch and duration are sufficient, waves of 10 feet or more can be generated in open waters by winds from any direction once they reach 20 knots or more. This occurs most often during October, November, and December, when waves of 10 feet or more can be expected 2 to 4 percent of the time in the NW and S parts of the lake and 4 to 7 percent in the wide central portion. Extreme waves of 20 to 22 feet have been encountered throughout the lake.

(15) Dense fog plagues the mariner most often in spring and early summer over the open lake waters. From April into July visibilities drop below 0.5 mile upto 11 percent of the time. May and June are the worst times, and the cold, central waters are the most likely place. These fogs are usually the result of warm air moving across the still cold lake. They often come on winds with a southerly component; but NW, NE, and E winds also bring them. Fog is most prevalent and thickest during the morning hours. Rain, blowing snow and low clouds also reduce visibilities, particularly from late fall through early spring.

(16) Thunderstoms are most frequent fom April through October, with peak activity during June, July, and August. Over the open water during this peak season thunderstorms are encountered 2 percent of the time. They are most likely between midnight and sunrise. Onshore thunderstorms can be expected on 4 to 7 days per month in the summer months. They are most likely during the afternoon.

(17) Ice.-The centeral part of Lake Huron is mainly an open water area, but drifting patches of thin ice may be present from early February until mid-March. These patches drift S tward the St. Clair River. An ice bridge forms across the head of the river. Ice accumulates to a depth 12 to 18 inches above the ice bridge; the bridge itself achieves a much greater thickness. The ice bridge is occasionally broken by high winds.

(18) In North Channel, fast ice forms in mid-January and reaches a thickness of 25 to 30 inches by mid-March, then decays rapidly and clears by mid-April. In Georgian Bay, ice begins to form near the end of December, and fast ice is well established by early January. The cover spreads over the entire bay by the end of January, but although concentrations are high the ice is moved around by the wind to form leads and dispersed ice areas. This ice usually reaches the thick category during the first half of March. Decay begins in mid-March; the ice melts within the bay, and the area is clear by mid-April. Rotting fast ice may be present in some areas until the end of April.

(19) The Straits of Mackinac is subject to severe problem ice conditions. The area is very susceptible to wind actions, and the ice cover is unpredictable. Ice forms early in the season in the Straits and attains an average thickness of 17 inches and an average maximum thickness of 25 inches. The solid ice thickness remains about the same throughout the season. The prevailing W winds cause considerable ridging and 4- to 6-foot windrows are common. Some ice ridges as much as 30 feet deep have been reported.

(20) Ice normally begins to form in harbors and shallow-water areas in early December with ice fields and concentrated brash forming in early January. The first ice barrier across the Straits usually forms between Waugoshance Point and St. Helena Island.

(21) As ice forms in South Channel between St. Ignace and Mackinac Island, these waters are closed to navigation to allow the formation of ice bridges. Mariners are notified of the closure by Broadcast Notice to Mariners.

(22) Prevailing W winds cause ice conditions at the Lake Michigan end of the Straits of Mackinac to be more difficult than at the Lake Huron end. From the Mackinac Bridge to Lansing Shoals, the straits are normally frozen over with solid plate ice by mid January. Heavy accumulations and ridging occur in the vicinity of St. Helena Island, White Shoal, and the reefs along the Upper Peninsula of Michigan. To avoid danger to vessels, Grays Reef Passage may be closed to navigation; mariners will be informed of any closure by Broadcast Notice to Mariners.

(23) As deterioration begins in March or April, stable fast ice becomes drift ice moving with winds and currents. Tracks cut by icebreakers become unreliable as the ice field detteriorates and shifts. Thick shore ice may drift into otherwise open channels endanger even ice-reinforced vessels. A vessel which becomes beset in drift ice is vulnerable to grounding because of the many shoals, reefs and shallow-water areas in the Straits of Mackinac.

(24) Wind-driven currents in the western straits run eastward. Vessels beset in ice southeast od St. Helena Island have become endangered by drifting toward McGulpin Pointor the Mackinac Bridge pilings.

(25) The brash and drift ice between Mackinaw City, St. Ignace and Round Island remains east of the Mackinac Bridge, trapped by the ice in South Channel. The NNW winds will flush this ice out into Lake Huron when the ice in South Channel begins to break up.

(26) Coast Guard icebreakers assigned to the Straits of Mackinac are based in St. Ignace and Cheboygan. Their services can be requested through Commander, Coast Guard Group Sault Ste. Marie; VHF-FM channel 16. (See Winter Navigation, chapter 3.)

(27) 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 Huron:

(28) Downbound vessels shall lay a course from De Tour Passage of 137 for 56 miles to pass not less than 15 miles 045 from Middle Island Light, then a course of 161 for 105 miles to not less than 12 miles 067 from Harbor Beach Light; then a course of 180 for 57 miles to the entrance to Lake Huron Cut.

(29) Downbound Vessels from the Straits of Mackinac shall lay a course of 070 for 6 miles from a point S of Poe Reef; then a course of 115 for 61 miles to join the regular downbound course from De Tour Passage at a point not less than 15 miles 045 from Middle Island Light.

(30) Downbound vessels from Calcite from a point abreast of Adams Point (45 24.9'N., 83 43.0'W.) shall lay a course of 100 for 30 miles to intersect the regular downbound course from De Tour Passage at a point 15 miles 045 from Middle Island Light.

(31) Downbound vessels from Stoneport Harbor shall lay a course of 098 for 18 mile sto intersect the regular downbound course from De Tour Passage at a point 14 miles 071 from Middle Island Light.

(32) Downbound Vessels from Alpena shall steer 159 for 58 miles on Harbor Beach Light to a point 12 miles 353 from Pointe aux Barques Light; then a course of 134 for 28 miles to intersect the regular downbound course from De Tour Passage at a point 12 miles 067 from Harbor Beach Light.

(33) Downbound vessels from Detour Point Passage to Cove Island from a postion abreast of De Tour Reef Light shall lay a course of 137 for 12 miles; then 123 for 37 miles to a position 10 miles 213 from Great Duck Island Light, then 103 for 61.25 miles to a position with Cove Island Lighted Bell Buoy T abeam.

(34) Downbound vessels from Cove Island to Lake Huron Cut from a postion abreast of Cove Island Lighted Bell Buoy T shall lay a course of 225 for 7 miles; then 189 for 157 miles to Lake Huron Cut.

(35) Eastbound vessel from the straits to northern ports on the W side of Lake Huron shall take departure from 0.5 mile NNE of Cordwood Point Lighted Buoy 1 and steer not less than 117 for 47 miles to a point 2.5 miles off Presque Isle Light; then steer 138 for 23.4 miles to a point on the upbound recommended course off Nordmeer Wreck Lighted Bell Buoy WR1.

(36) Southbound vessels bound for Alpena from Nordmeer Wreck Lighted Bell Buoy WR1 shall steer 189 for about 7.25 miles to a point 1.5 miles abeam of Thunder Bay Island Light; then steer 227 on Thunder Bay Traffic Buoy for 5.5 miles; then to destination.

(37) Southbound vessels bound for Sagnaw from Nordmeer Wreck Lighted Bell Buoy WR1shall steer 181 for 29.5 miles to a point 6 miles E of Sturgen Point Light; then steer 189 for 27.75 miles to a point 3 miles E of Au Sable Point Lighted Buoy 1; then steer 224 for 19.25 miles to Charity Island Lighted Buoy 5; then to destination.

(38) Upbound vessels shall lay a course of 353 for 54 miles to pass not more than 5 miles 067 from Harbor Beach Light; then steer 341 for 99 miles to pass not over 7 miles from 071 off Middle Ground Island Light; then a course of 325 for 60 miles to De Tour Passage.

(39) Upbound vessels for the Straits of Mackinac shall lay a course of 318 for 16.5 miles from off Middle Island Light to a point 5 miles 050 from Presque Isle Light; then steer a course of 295 for 47 miles to abreast of Cordwood Point Lighted Buoy 1; then steer a course of 270 for 3 miles to a point off Poe Reef Light.

(40) Eastbound vessels from Round Island Passage shall lay a course of 090 for 22 miles to a point 4.75 miles off Martin Reef Light; then steer a course of 061 for 14 miles to a point 0.75 miles 128 from De Tour Reef Light.

(41) Upbound vessels from Lake Huron Cut to Cove Island shall steer a course of 037 for 15 miles; then steer a course of 008 for 143.5 miles to Cove Island Lighted Bell Buoy T.

(42) Caution.-A wreck covered by 29 feet is W of the trackline about 10.5 miles 018 from Fort Gratiot Light in about 43 09.2'N., 82 21.5'W.

(43) Upbound vessels from Cove Island to De Tour Passage from a position abreast of O'Brien Patch Lighted Bell Buoy TC shall lay a course of 284 for 61.5 miles to a position 6 miles 194 from Great Duck Island; then steer 300 for 48 miles to a position 3 miles 137 from De Tour Light; then steer 317 for 3 miles to a point 0.75 mile 128 from De Tour Light.

(44) It is undestood 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 chart 14860, Lake Huron.

(45) It is recommended that the following limit of anchorage be observed in Lake Huron off De Tour Light so that vessels may enter or leave De Tour Passage in time of congestion due to fog or other conditions: No vessel to anchor E of a bearing on De Tour Lights of 340 , or closer than 0.75 mile to the light or N of the De Tour Martin Reef course.

(46) Pilotage.-The waters of Lake Huron in the approach to St. Clair River S of 43 05'30"N. are Great Lakes 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. The remaining waters of Lake Huron are Great Lakes undesignated waters; the above 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 St. Clair River are supplied by Lakes Pilot Association, and for Lake Huron 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 wuth an aluminum cabin, and HURON MAID and HURON LADY each have an international orange hull with a white cabin. (See Pilotage, chapter 3, and 46 CFR 401, chapter 2.)

(47) Principal ports.-The principal ports on Lake Huron are Bay City and Saginaw in the Saginaw River and Cheboygan. Private docks for deep-draft vessels are also at Alabaster, Port Gypsum, Alpena, Rockport, Stoneport, Calcite, and Port Dolomte.

Sections 48 - 633 ommitted

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