Review of sinking shows danger of microburstsJan 1, 2003
To the editor: Microbursts are among the most feared and least understood weather systems that plague the offshore sailor. There are countless stories of ships being knocked down in an instant, caught unaware by the powerful blasts of wind that are the result of these systems. One such vessel - along with four of its crew - lost as a result of a microburst was the original square-topsail schooner Pride of Baltimore. It was knocked down in 80 knots of wind in May 1986 off Puerto Rico, immediately down-flooded and sank to the bottom.
I teach a course at the Maritime Institute of Technology (MITAGS) in Baltimore in which students are taught the skills necessary to attain a captain's license (six-pack to 200-ton). In spring 2001, I asked one of the captains of the second Pride, Jan Miles, to describe the microburst incident to my students. I asked him to explain what he does to prepare his vessel and crew for microbursts at sea.
Miles was not aboard that day, but he was dispatched to San Juan to investigate, comfort and escort home the survivors. The eight survivors described to him how Pride was knocked over that afternoon by a sudden "wall of mist." Some sails had been reefed, most others were furled, due to a weather pattern of slowly increasing ENE winds of 20 to 25 knots, backing towards the northeast. The sky was completely overcast with a ceiling of about 2,000 feet. Miles asked the eyewitnesses if they observed any dark gray cloud bottoms and any heavy rain, but they described only sporadic, light rain. The sky was a monochromatic gray. Just prior to the incident, Pride of Baltimore was carrying a double-reefed mainsail and a full fore-staysail. All other sails were furled.
Survivors reported that the deadly wind came from the same direction as the prevailing wind. There had been no time to turn the vessel into the maelstrom. The manually activated EPIRBs, mounted in the vessel's hatchways, had not been grabbed as the vessel rolled over. Survivors scrambled into a small, leaky liferaft where they spent the next four days before being rescued by the passing Norwegian tanker Toro.
Miles described several other aspects of the sinking. Crew on deck had been wearing single-clip harnesses. They had been clipped to various points about the deck, but as the wind and waves struck the vessel and she went over, the second mate - on a deck that was rapidly becoming vertical and awash - had to reach down under the advancing wall of rushing water and cut the tethers. That second mate saved the lives of several crewmembers. Today, harnesses aboard Pride II are double-clipped so that one can unclip oneself at the chest.
The radar was not in use at the time the microburst struck. The scanner was not mounted permanently to the mast but had been stowed below, ready to be mounted on a collapsible post whenever desired. Miles explained that preservation of Pride's authentic appearance as a replica vessel was the deciding factor against permanent installation. The original Pride was not a certified vessel and was not required to have a radar set. Miles has since concluded that without radar in use that day, Pride was without an imperative means to interpret the conditions around the vessel that afternoon. Today, Pride of Baltimore II is certified and inspected, and the crew uses the X-band radar for collision avoidance and to track squall lines routinely.
The original Pride was well equipped for ocean crossing and had a sharp crew. But according to Miles, she had been designed to survive lists of up to 80°. Pride II is load-line certified and has undergone an inclining experiment. However, Miles has said that probably very few vessels caught broadside the way in which the original Pride was could have stood up.
According to eyewitnesses that day, when the wind and waves struck, Pride went over on its beam ends with alarming speed. Once over, the vessel spent more than a minute flooding through the only hatch open, located aft, before it sank.
Lee Chesneau, an Ocean Navigator weather seminar instructor and senior forecaster at the Marine Prediction Center, in Camp Springs, Md., explained what microbursts are: "A microburst is considered a small-scale event, lasting as little as two minutes and as long as 30. Microbursts are associated with what we call a triple point, whereby, several weather fronts of various temperature gradients converge. We then expect to see massive cumulonimbi and thunderstorms. The microburst is created when the sudden cooling of uprising warm air falls with alarming speed. The speeding vertical downdrafts strike the surface of the water, fanning out up to five miles in all directions. Downbursts hit so rapidly that few signs are available, but look for blowing spray under or slightly ahead of a thunderstorm. The mechanics of microbursts are still not fully understood."
Shoreside, since the 1970s, airports and television news programs have made use of large Doppler radar systems that graphically display wind speed and direction, as opposed to simple marine pulse-modulated radar sets aboard typical yachts. The sailor remains on his own, relying on his manipulation of available weather data to forecast potential microburst activity. But there is no substitute for constant vigilance.
The continuous National Weather Service broadcasts are still a reliable source of current weather data. Seven frequencies between 162.400 and 162.550 MHz are dedicated to weather broadcasts. In the event of severe weather, taped broadcasts may be interrupted by live broadcasts. The U.S. Coast Guard broadcasts marine weather on VHF 22.
In the classroom that day a hand went up, and a student, a retired businessman planning to sail his 44-foot ketch from Annapolis to the Azores, asked Miles what he does aboard Pride II when he sees a line of squalls off to windward.
Miles explained that his standing orders require a call to the master when they see and hear lightning, squall lines that are to windward or any darkly painted targets on the radar.
Generally speaking, with canvas up, squalls are to be avoided. Miles will first use his eyes to examine the bottoms of the squall clouds. If he can see the horizon beneath squall lines, he will not be as concerned as when he sees rain and darkening color at the surface level.
Once alerted, he will tune his radar and examine the intensity of the painted targets on the screen. The sharply defined targets often indicate intense precipitation. Next, he will manipulate the electronic bearing line (EBL) on his radar to determine the relative motion and speed of the squalls to windward.
On a relative motion radar, when a squall is seen headed to the center of the screen, right down the EBL, the storm cell and the vessel will meet. Miles will also calculate the storm's closest point of approach (CPA) and time of CPA (TCPA). His aim is to alter course by 20° or 30° and simply avoid the oncoming squalls. At all costs, cautioned Miles, he does not allow the wind from a squall to cross amidships. It is best to give a five-mile CPA to what appears to be violent thunderhead activity.
Armed with radar information and visual observation, but unable to outrun or avoid what appear to be dangerous squalls, Miles will prepare to shorten sail. If necessary, he will position Pride II so that it meets wind and waves either on the bow or stern, thus making full use of the vessel's longitudinal stability. Crew will secure all loose objects about the deck and close all hatches. SOLAS lifesaving appliances are checked for readiness, espe(ially the liferafts and EPIRB. Aboard Pride II, Miles has made arrangements with a certified liferaft inspection vendor to stow CAT II EPIRBs and VHF survival craft radios in each of two liferafts, thus ensuring they will be available.
By regularly following forecasted weather and remaining in tune with the vessel and changing weather conditions, Miles prepares his crew and Pride II for potential microbursts.
John Carlisle is a MITAGS instructor who divides his time between teaching and sailing as second mate aboard containerships.