Sunday, January 18, 2009

Small Boats Crossing Coastal Bars

Coastal Bar Conditions
Tides (changes in water level) are caused mainly by the gravitational pull of the sun and moon. A flood tide is the tidal movement of water towards shore, and an ebb tide is the movement away from shore or downstream. Slack water is when there is no tidal movement. Tidal current is the flow of water. Tidal currents can have considerable velocities, especially during an ebb tide.

Coastal Bars
The most dangerous condition occurs when a swift ebb current meets heavy seas rolling in at a shallow river entrance (called a bar). At these coastal bars the water "piles up" and then "breaks". Even on calm days a swift ebb tide may create a bar condition that is to rough for small craft (any vessel under 65 feet). It is safest to transit from harbor to ocean only on slack water, flood tides, or then the sea state is calm. If you are inside the bar when rough conditions exist, stay inside. If you are trapped outside a rough bar on an ebb current, wait a few hours until the tide floods. Waves can build up around sand spits and shallow areas. These areas are dangerous and shoud be avoided. In a bar area, sea conditions can change fast and without warning.

Bar Restrictions
Federal statutes authorize the Coast Guard to terminate the use of recreational boats on coastal bars when unsafe boating conditions exits. Bar restrictions are activated when, in the judgment of the Coast Guard, conditions of wave height and surface current make boating unsafe. The Regulated Boating Area Warning Sign is a diamond-shaped white daymark with a orange reflective border and the words "Rough Bar" in black letters. Generally, two alternating quick flashing yellow lights are displayed when seas exceed 4 feet in height. Lights are usually extinguished when the sea conditions lay down, but this is no guarantee that the bar is safe. In general, jetties continue seaward for several yards past the visible end. By all means AVOID CROSSING OVER A SUBMERGED JETTY. Navigate with caution near jetties when wind and sea are setting you toward the jetty.

Range Markers
Front and rear range markers are rectangular-shaped dayboards either red, green, black, or white, with a contrasting colored center strip. (most range markers are KRB, red with a black center stripe.) For nighttime use most range markers are lighted. By steering a course which keeps the two range markers or their lights in line with one another, the you will remain within the approximate channel. Because entrance channels are constantly shifting, the range markers do not always mark best water. You should remain in the approximate channel by steering a course that keeps these range markers in line.

Seasonal Aids to Navigation
Due to severe weather conditions and reduced vessel traffic during the winter, numerous aids to navigation (lights, buoys, fog signals) are seasonally discontinued, withdrawn, or replaced by smaller aids. These changes occur at regular intervals each year. The approximate dates are contained in the most recent edition of the Light List. The actual dates may change due to adverse weather conditions. You can look at the Coast Guard's Local Notice to Mariners and listen to a Broadcast Notice to Mariners on the VHF radio.

Weather Warning Displays
1. Small Craft Advisory: Alerts mariners to sustained (more than two hours) weather or sea conditions, either present or forecast, that might be hazardous to small boats. If you should here of a Small Craft Advisory you can determine the reason by tuning your radios to the latest marine broadcasts. The decision as to the degree of hazard is left up to the you, based on his / her experience, and size and type of boat. The conditions for the Small Craft Advisory are usually 18 knots of wind (less than 18 knots in some dangerous waters) or hazardous wave conditions.

2. Gale Warning: To indicate winds within the range of 34 to 47 knots are forecast for the area.

3. Storm Warning: To indicate winds 48 knots and above are forecast for the area. If the winds are associated with a tropical cyclone (hurricane) the Storm warning display indicates that winds 64 knots and above are forecast for the area.

4. Hurricane Warning: Issued only in connection with a tropical cyclone (hurricane) to indicate that winds 64 knots and above are forecast for the area.

NOTE: A "HURRICANE WATCH" is an announcement issued by the National Weather Service via press, and radio and television broadcasts whenever a tropical storm or hurricane becomes a threat to a coastal area. The "Hurricane Watch" announcement is not a warning, it indicates that the hurricane is near enough that everyone in the area covered by the "Watch" should listen to their radios for advisories and be ready to take precautionary action in case “Hurricane Warnings” are issued. A SPECIAL MARINE WARNING BULLETIN is issued whenever a severe local storm or strong wind of brief duration is imminent and is not covered by existing warnings or advisories. Boaters will be able to receive these special warnings by keeping tuned to a NOAA or Coast Guard VHF-FM radio frequency and commercial radio stations that transmit marine weather information.