Thursday, April 5, 2012

Visual Aids to Navigation: Dispelling aid availability myths—PART 2

Excerpt from U.S. Coast Guard Proceedings of the Marine Safety & Security Council magazine by Mr. Robert Trainor, aids to navigation specialist, U.S. Coast Guard Office of Navigation Systems.

Aids to Navigation Discrepancies
Aid availability is impacted by unplanned outages, or ATON discrepancies, and the Coast Guard’s ability to respond to and correct them.

In 2005, the Coast Guard specified maximum maintenance intervals of 36 months for buoys and lighted beacons and 60 months for unlighted beacons. Specific maintenance intervals for individual aids are determined after considering component reliability and service life, environmental factors, wildlife, vandalism, and other factors.

The USCG uses a discrepancy response factor—a numerical indicator measuring the criticality of the discrepant ATON—to prioritize response. The higher the number, the more critical the aid is to safe navigation, and hence the higher the priority for response and correction.

 An aids to navigation team works on a small buoy. USCG photo.

The annual recurring funding for establishing, maintaining, and operating the U.S. visual aids to navigation system is approximately $300 million. Ninety percent of that goes to personnel, ATON servicing platform operations and maintenance, and indirect support costs.

The remaining $30 million finances everything that either produces or supports an ATON signal (repair, maintenance, and replacement costs of buoys; buoy mooring systems; beacon structure components; optics; power systems; and day signals).

This funding level has been static over the past 10 years, with slight adjustments for consumer price index considerations. During that period, aid availability fluctuated by as much as 1.28% in one year. In the years of low aid availability (2005 and 2006), the ATON mission was allocated supplemental funding to reconstitute the visual aids to navigation system in those waterways disrupted by a series of major hurricanes.

Aid Availability History
The concept of aid availability became a topic of international interest in the mid-1970s when significant numbers of lighthouses were being automated. The Coast Guard implemented aid availability as a performance measure in the 1990s and established an overall strategic aid availability goal of 99.7 percent.
Since waterways have a variety of traffic patterns and risk levels, the Coast Guard assigned each of its aids to navigation to one of three categories based on the critical nature of the aid, the type and volume of marine traffic, the waterway configuration, and environmental considerations.
  • Category 1: Vital navigational significance – aid availability goal = 99.8 percent.
  • Category 2: Important navigational significance – aid availability goal = 99 percent.
  • Category 3: Necessary navigational significance – aid availability goal = 97 percent.
Certain anomalies, such as major weather events, can have a short-term negative impact on aid availability. The International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) recommends tracking aid availability for three continuous years to accurately determine trends.

IALA also recommends that the minimum aid availability for any aid should not fall below 95 percent and that consideration should be given to discontinuing or replacing aids to navigation that consistently fall below that threshold.
Full article is available at