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Drogues on Monohulls

D/M-10 Monohull, Charter Vessel

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D/M-10

Monohull, Charter Vessel

35' x 15 Tons, Long Keel

36" x 12" Cylindrical Device

Force 12 Conditions

Seabrake Mk I
Seabrake Mk I

 

File D/M-10, obtained from John Abernethy, Woollahra, Australia - Vessel name Papeo, hailing port Port Fairy, monohull, charter vessel, LOA 35' x Beam 10' x Draft 6' x 15 Tons - Long keel - Drogue: 36" x 12" Diameter stainless steel calf bucket on 100' x 1" nylon three strand rode - Deployed in a "Southerly Buster" storm in shallow water (15 fathoms) near Lady Julia Percy Island (Bass Strait) with winds of 100 m.p.h. and seas of 50 ft. - This event led to the genesis and development of the Australian Seabrake drogues.

 

Seabrake was born in the Australia's notorious Bass Strait, as treacherous a body of water as one could wish for. The Bass Strait is a 170 mile wide gauntlet that divides the Australian mainland from Tasmania. It has claimed thousands of lives. The roaring forties and mature Southern Ocean waves roll in unabated all the way from Africa, and run headlong into this gauntlet. As they try to squeeze into the narrow Bass Strait they jump over the shallow Continental Shelf and undergo a metamorphosis that can only be described as a sailor's nightmare. Sudden storms can come up without warning, producing life-threatening conditions within hours.

roaring forties
The Roaring Forties aim straight for the Bass Strait

 

Running before such steep and unstable seas is a little like barreling down muddy hills on a dirt bike without brakes. Imagine flying over bumps, skidding and careening sideways, somehow trying to keep the bike from falling out from under you, dirt and mud flying all over the place. If you can imagine all this, you will understand the logic and thinking behind the invention of the Australian Seabrake.

As a yacht is running down the face of such seas there will be times when the rudder will be ineffective. Because of orbital rotation and the movement of water on waves that are breaking, helm control will decrease on the crests, where it is needed most (see Figs. 7-10 and Fig. 49). As the boat is picked up and accelerated by a crest, the flow of water past the rudder is suddenly diminished and the helm goes limp. Small craft rudders are all but useless on the crests of breaking seas. If the boat is "captured" by such a crest and cannot disengage from it, the wave-induced yawing moment will be greater than the restoring moment available from the rudder and the result may be a broach, a capsize or even a 360° roll. This is where the directional restraint of a drogue (situated elsewhere on the wave train) is needed to help keep the vessel aligned, as well as to provide the drag needed to disengage the boat from the fast moving crest.

The incident that sparked the creation of Seabrake took place in 1979 - the year of the Fastnet tragedy.  Abernethy's boat, Papeo, was on a charter, looking for great white sharks. She was anchored in the lee of Lady Julia Percy Island, some twenty miles from the Australian mainland, when a "Southerly Buster" came up. The wind quickly built up to hurricane force and in no time Papeo had lost all three of her ground anchors. With her engine started she began to make a desperate run for safe harbor on the mainland. However no sooner out of the lee of Lady Julia Percy Island than she was pummeled by mountains of fast moving white water. A cone-shaped sea anchor, several feet in diameter, was deployed off the stern as an emergency measure, but it slowed the boat down too much. She was squarely hammered by a breaking wave. This wave wiped her entire deck clean, breaking a number of items as well as ripping off the focs'le hatch and taking it out to sea. A miracle of sorts then occurred when three dolphins that had been seen in the vicinity of the boat swam to the floating hatch and pushed it back close enough so that Captain Abernethy could gaff it and bring it back on deck. With the hatch hastily reinstalled, Abernethy took the knife and cut away the rode to the sea anchor. Papeo was then picked up by another huge wave and sent hurtling down into the abyss-like trough. Instinctively, Abernethy reached for the only remaining item that could function as a drogue - a stainless steel cylindrical calf bucket. These calf buckets are commonly found on Australian farms and often used as bait buckets on Australian fishing boats. Abernethy attached some line, grabbed an axe and sliced open a few holes in the bottom of the bucket and threw it over the transom. This calf bucket, since dubbed "the most famous milk bucket in Australian maritime history," then took hold of the situation and produced the desired effect, both in terms of limiting Papeo's speed, and also in terms of keeping her attitude safely aligned with the seaway.

The ride was exhilarating, to say the least. Abernethy described it to Victor Shane as "a lazy elevator." The boat would be picked up, half rolled and carried along, but never thrown or overwhelmed or broached by the mountains of confused water. By sheer luck the restraint of the makeshift drogue was just enough to keep Papeo on an even keel throughout the ordeal. She was able to keep plenty of water beneath at all times and never even came close to falling off a wave, or burying her bow into the bottom of a trough. It was a defining moment. It left an indelible mark on Abernethy's mind and several years later he came up with the first prototype of the Seabrake drogue. Subsequent models underwent extensive tank tests in the Australian Maritime College, and Seabrake came to be. Abernethy's firm has since produced a wide variety of drogues for sailboats, powered vessels and even large ships and submarines. When Abernethy was in the United States Shane had the privilege of interviewing him in Los Angeles. A synopsis of that interview follows (by permission):

The development of Seabrake was preceded by ten years of commercial operation in Australia's Bass Strait. As a commercial fisherman and charter boat owner based in the most dangerous stretch of Bass Strait, I was routinely operating in heavy seas and often towing large game fish in them. I was frequently involved in Search and Rescue operations as well, towing various types of distressed vessels to safety. Typically, conditions involved combined seas in excess of 20 feet and sustained winds of 30 knots or more. On many outings I have encountered 50 ft. seas and 50 knots winds. The incident that occasioned the birth of Seabrake involved 80 ft. combined seas and winds peaking at 100 m.p.h. There were other factors that contributed to the development of Seabrake. Contact with many who have lost vessels in the Bass Strait in the past 40 years, for one thing. My own experience showing that "speed kills," and that conventional cone-shaped drag devices don't assist and in fact can be dangerous, for another. Moreover I have found that towing items such as large game fish, bundles of rope, etc. on a short warp can create too much drag and cause a "stall" at the wrong moment - the bottom of a trough. And towing them on a long warp does not always produce the desired effect either. Drag and restraint can vary from too much to too little, depending on the direction of pull and how much rope remains in the water.

From the above I endeavored to devise a drogue that could maintain a consistent ratio between speed and drag. Never is the statement "speed kills" more relevant than when applied to vessels running before strong following seas. Finding a happy medium is the key to success. Seabrake is designed to kick in at around 7-8 knots and then continue to increase its effectiveness as the load increases beyond this speed. The ultimate goal is to maintain helm and choice of direction while keeping the ship's speed below 6 knots. In survival conditions the trick is to prevent taking on board any water and keeping the vessel as buoyant as possible, which means avoiding breaking crests or becoming bogged down in troughs. This is only achievable if the vessel has headway and helm. In my experience, even in the worst conditions it is far easier to obtain "safe water" running with a sea than jogging into it [with the engine]. And this is where Seabrake comes in.

The development of Seabrake evolved from a need to travel in harmony with the sea, with room to maneuver, much the same as rolling along at speed in heavy traffic - as opposed to being out of control and all over the road. Seabrake, in simple terms, is a remote control two-stage speed regulator, activated by a compression spring that opens and closes the drogue's baffle gates. With the baffles closed the flow of water around Seabrake is laminar, exerting just enough drag to improve steering control below hull speed or safe maximum speed. Any sudden acceleration or surfing brought on by a wave crest will cause Seabrake's nose cone to extend, which triggers the compression spring and opens the baffles inward. With the baffles open the flow of water around Seabrake becomes turbulent, instantly increasing its drag by about 70%. Conversely, a sudden deceleration in boat speed (in a wave trough) will release the spring, which will close the baffles, instantly reducing drag and preventing a "stall."

By running before the seas under restraint of a two-stage system of speed suppression and compensation, a vessel may be steered through the worst conditions in relative safety. Reading the immediate wave astern and maneuvering to expose the least amount of stern - quartering the seas rather than taking them on square - is all that needs to be done in order to avoid both the PUSH and the FALL as a dangerous wave passes under the boat. The Seabrake principle has now been in effect for some 15 years and has been tested and evaluated both academically and in the field. It has saved many lives and vessels under horrific conditions, doing so without any technical knowledge or formal training on the part of the users - the "set it and forget it" principle truly applies here.

As a final comment I need only repeat my earlier statement, "speed kills." While running before heavy seas it is important to try to keep the speed range below 6-7 knots, but above 3 knots. Slowing down below 3 knots will result in loss of steerage and allow a vessel to wallow, which is equally unsafe. I base the above on personal experience, but note that individual applications may be subject to a great many variations. Following these guidelines, however, will assist in measuring the general situation.

 

NOTE: A rival Australian company, Broachbrake International Pty., Ltd., was manufacturing a similar plastic drogue called the Sea Squid for a while. John Abernethy brought suit against the company for infringement of certain legal rights. Broachbrake was subsequently issued a court order to cease and desist and has since stopped making the device. Abernethy told Shane that Sea Squid was an altogether inferior imitation of his product. There is an illustration of the now outlawed Sea Squid in file D/M-12 of this publication.

Drogues on Monohulls

D/M-3 Monohull, Custom Ketch

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D/M-3

Monohull, Custom Ketch

50 x 22 Tons, Full Keel & Centerboard

36" Dia. Galerider

Force 10 Conditions

 

File D/M-3, obtained from Frank Snyder, Vice Commodore, New York Yacht Club - Vessel name Southerly, hailing port New York, monohull, center-cockpit aluminum ketch designed by Sparkman & Stephens, LOA 50' x LWL 45' x Beam 14' x Draft 5.5' x 22 Tons - Full keel & centerboard - Drogue: Galerider on 200' x 1¼" nylon three strand rode, with 1/2" stainless steel swivel - Deployed in low system in deep water in the Gulf Stream, with winds of 50 knots and seas of 10 ft. - Vessel's stern yawed 20° with helmsman steering - Speed was reduced to 3-4 knots.

Galerider drogue produced by Hathaway, Reiser and Raymond
Galerider drogue produced by Hathaway, Reiser and Raymond

Frank V. Snyder, Vice Commodore of the New York Yacht Club, ran across an article in a British magazine summarizing the results of experiments conducted by the National Maritime Institute on life rafts in heavy weather, in the North Sea. The article emphasized the importance of sea anchors - small, synthetic cones - when it came to keeping life rafts from capsizing, but revealed that the same cones were often among the first parts of the raft to fail. The article went on to say that the Institute had then designed and built new sea anchors from a close mesh netting material which, unlike their predecessors, did not fail in a second set of sea trials. One raft even lost its ballast bags but still did not flip: its sea anchor held it down.

When preparing his 55-ft. ketch Southerly for a late fall passage from New York to Antigua in 1984, Commodore Snyder decided to equip her with a flow-through drogue of his own design. He approached Skip Raymond of the sailmaking firm of Hathaway, Reiser & Raymond, Inc., with his ideas. Raymond then went to work, building a small model at first, and then the full scale prototype of the first Galerider drogue. It was three feet in diameter and four feet long, shaped a little like a basket made from two-inch nylon webbing. On Saturday, November 17, Southerly departed New York Harbor and broad-reached all Saturday and Sunday morning, making better than eight knots in seas that were building. On Sunday afternoon the barometer began dropping rapidly and, by the time she entered the Gulf Stream at dusk, the wind had piped up to southwest, Force 9-10. Soon she was in very confused conditions, with two big seas crossing at an angle of 90°.

In a related article appearing in the September 1986 issue of Yachting Magazine entitled Galerider Handles a Gale, Frank Snyder wrote that despite being a big, strong, stiff and seakindly boat, Southerly couldn't handle the turmoil. He directed the crew to douse the trysail and they began running before it under bare poles, trying to keep the new seas slightly on the starboard quarter. But as the confused seas continued to build Southerly became unmanageable, now and then her speed racing up to 12 knots or more on the face of a bigger wave. To have her surging at these speeds under bare poles was alarming. The vicious cross seas would catch her on the downslide and roll her rail down under. Her hull form would then cause her to broach in the trough - dangerous if the waves got any bigger. It was time to deploy the Galerider. The rode, 200 feet of 1¼" nylon three strand, was attached to the drogue and the bitter end given four turns around the coffee grinder on the after deck (Southerly is a center-cockpit boat). In went the drogue. When it took hold there was no shock at all; in fact the crew couldn't tell for sure the precise moment when the drogue did take hold, but were soon aware that the boat was slowing down. Commodore Snyder writes that the effect of slowing the boat in that big, confused seaway was magical:

At one moment the boat had been charging like a mad bull, with the helmsman struggling at the wheel; in the next, she was docile and under full control. The helmsman found that Southerly would still answer her helm - though slowly - and that she could steer through about 90°. Everyone relaxed, and the off-watch turned in, even though the motion wasn't all that comfortable, with the cross sea still rolling us 20° either side of vertical. But the boat was safe.

The seas continued to build for the next three hours and several big ones came aboard over the stern, though no green water reached the cockpit. Had the cockpit been aft, it would probably have filled a couple of times. At 0200, the wind veered to north and began dropping. By 0400 it was down to Force 7, and the storm was over - another of those six-hour Gulf Stream "local lows." (Yachting Magazine, September 1986, by permission).

Commodore Snyder's creation has caught on and many offshore yachts now carry a Galerider on board. The "flow-through" concept is rugged, simple, stable, and does not get turned inside out. The stainless steel wire hoop that keeps the Galerider's mouth open can be folded on itself, allowing for compact storage.

Drogues on Monohulls

D/M-2 Monohull, Bermuda Ketch

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JOSHUAD/M-2

Monohull, Bermuda Ketch

39' 6" x 13.4 Tons, Full Keel

Warps, Net and Pig Iron Drags

Force 10 Conditions


File D/M-2, derived from the writings of Bernard Moitessier - Vessel name Joshua, monohull, canoe-stern, center cockpit Bermuda Ketch build of steel, LOA 39' 6" x LWL 33' 9" x Beam 12' x Draft 5' 3' x 13.4 Tons - Full keel - Drogue: assorted drags used in concert, including 22 fathoms 4.5" hemp rope weighed down by 3 pigs of iron 40 lbs. each; 16 fathoms 3" hemp rope weighed down by two pigs of iron 40 lbs. each; 32 fathoms of 1.5" nylon rope trailing freely - Deployed while running before a mature storm in the high latitudes of the Southern Ocean with sustained winds of 50 knots and seas of 30 ft. - Joshua came near to pitchpoling several times and Moitessier elected to cut away all the drags.

 

Bernard Moitessier is undoubtedly one of the most extraordinary seamen that has ever lived. Fortunately he is an extraordinary writer as well. The critic Jonathan Raban once said, "I'd sooner read Moitessier than any other nautical writer alive." Indeed one never tires of reading Moitessier. He holds the imagination captive, from the first page to the last. Born in French Indo-China, Bernard's first odyssey was aboard his dilapidated junk, Marie Therese, which ran aground after a fifteen round - eighty five day - battle with a monsoon in the Indian Ocean. He then spent three years on the island of Mauritius, building Marie Therese II, which ran aground in the Antilles, after a long lonely Atlantic crossing. A few years later the resilient Moitessier had finished his book, Vagabond des Mers du Sud, and was in Chauffailles, France, getting married to "a little slip of a woman called Francoise" and overseeing the building of his new 39-ft. steel boat Joshua. In October 1963 he took Francoise "for a sail" on Joshua - across the Atlantic, through the Panama Canal, to the Galapagos and the South Pacific. The couple spent two happy, carefree years in Polynesia. In the winter of 1965 they "went sailing" again - Tahiti to Spain non-stop, via Cape Horn, 14,216 miles in 126 days.

It was on 13 December 1965 that Joshua ran into a heavy storm in the high latitudes of the Southern Ocean, mid-way between Tahiti and Cape Horn. Mindful of the experiences of Smeeton and Robinson, Moitessier deployed an array of drags to slow Joshua down - all told some 900 feet of heavy ropes weighed down by five 40-lb. iron pigs and a large heavy net used to load ships. Despite all the drag devices in tow Joshua came very close to sharing the fate of Tzu Hang - going end over end. As he struggled with the helm, Moitessier began to take stock of his situation and compare it with the experiences of other "Cape Horners," among them the renowned Argentinean singlehander Vito Dumas.

In the famous episode that followed we find Moitessier engaging the ghost of the Dumas in a debate, as it were. "But what was your secret, Vito Dumas.... You did it... and Legh II was a small boat... you carried sail, I believe you... but you couldn't have carried any sail in this kind of seas, don't spin me that yarn, for if you had carried any sail in these seas you would have been pitchpoled like Tzu Hang... and like Joshua, almost.... And yet, you covered the three oceans...." (Cape Horn, The Logical Route, Grafton Books, London 1987, by permission).

Moitessier then writes that he doesn't believe in ghosts, but could have sworn that he heard a voice - that of Dumas - telling him the answer. Once he had the answer he was aft, cutting away all drags and warps, allowing Joshua to run unimpeded on bare poles. He noticed an enormous change in her: "She had no longer anything in common with the wretched boat of the night before which had made me think of the little hunter trying to parry the blows of a gorilla, with his feet caught in the undergrowth." (Ibid.) Thereafter Moitessier adopted the technique of "putting down the helm," and Joshua began taking the seas more safely on the quarter. Later on in the storm, as they are sitting in the inside steering station, he explains the technique to his wife Francoise:

 

I'm running dead before the wind to keep the maximum speed on the boat and make sure that she answers on the helm when she has to. Now watch carefully, you see that wave coming up [behind]... I am still dead before... and just before the stern lifts I turn the wheel right down... You see... she heels over and veers to the right as she ought to... she is pushed forward and a little sideways... the moment the stern settles down again, just after the wave has passed I turn the wheel right over in the opposite direction to bring her back again stern on; this is the best moment because the rudder is deep in the water and very effective... you see... we are back dead before the wind, and the business starts all over again. (Ibid.)

Remarkably, Moitessier seems to be using his instincts to avoid pitchpole (see image in previous file). It must have been instinct because the phenomenon of orbital rotation was not well known at the time - nowhere in his writings does Moitessier refer to the orbital rotation of waves. Indeed, one can only infer that Moitessier must have been directed by some rare and spontaneous instinct peculiar to extraordinary seamen. By that, or by the ghost of Vito Dumas.

To fly dead straight down a wave face would have placed Joshua in the same head-over-heels predicament as Tzu Hang - the bow impaling itself in the approaching "current" in the trough as the stern was being hurled downwind by the motion at the crest. So, in maneuvering across the face of a wave (like a skier zig-zagging down a slope), Moitessier is in effect trying to cheat the pitchpole demon - trying to keep the bow from burying itself in the adjacent trough. To some extent the same principle is used by a surfer when he puts down his heel to "spin out" and disengage from the wave. Needless to say in order to execute this maneuver with precision over and over again in a storm, the helmsman of a sailboat would require the reflexes, the skill and the stamina of a Grand Prix driver, attributes that Moitessier no doubt possessed at that time, but hardly common to all sailors. Bear in mind also that Joshua was made of steel, had a canoe stern, a center cockpit, and an inside steering station where the helmsmen could concentrate on what he was doing, unaffected by the cold and the wet. It is interesting to note what the late Miles Smeeton had to say about this technique:

When Bernard Moitessier, that fine seaman, offers an opinion, it should be well considered, because he has twice sailed Joshua round Cape Horn... but his answer is not necessarily the right one for all yachts, any more than mine is, and it requires a superman to steer accurately like this through a dark night.... Even if his theory is correct for other yachts, tired men and irregular waves are apt to defy it. (Because The Horn Is There, Granada Publishing, London, 1984 & 1985, Appendix, by permission).

In 1982 Joshua was anchored in Cabo San Lucas, Mexico, when a tropical storm swept over the crowded anchorage. A large motorboat dragged down on Joshua, forcing her up on the beach, where numerous other yachts ended their careers as well. When the fiasco was over nothing remained of the famous boat other than her bare steel hull. Two brothers from Port Townsend, Washington bought the hull for $20 and spent two years rebuilding her, later selling her to a Seattle woman. The woman's dream of sailing Joshua around the world was rudely shattered by the indiscretion of her sailing partner - he turned out to be married. The French newspaper Voiles & Voliers heard about the affair and sent a photographer to Seattle. After the article - showing magnificent photographs of Joshua under sail - was published, a number of famous sailors banded together to form the Joshua Foundation. The French Maritime Museum then purchased the dear old boat, put it on a ship and took it to La Rochelle France, where she is on display today.

Drogues on Monohulls

D/M-1 Monohull, Bermuda Ketch

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HANGD/M-1

Monohull, Bermuda Ketch

46' x 12 Tons, Full Keel

Warp, 60 Fathoms 3" Hawser

Force 10 Conditions

 

File D/M-1, derived from the writings of Miles Smeeton - Vessel name Tzu Hang, hailing port Victoria, B.C., monohull, Bermuda Ketch, built in Hong Kong in 1938, LOA 46' x LWL 36' x Beam 11' 6" x Draft 7' x 12 Tons - Full keel - Drogue: Warp consisting of 360' x 3-inch manila hawser - Deployed while running before a storm in the high latitudes of the Southern Ocean with winds of 50 knots and seas of 30-40 ft. - The warp had little effect in preventing the pitchpole of Tzu Hang about 1000 miles from Cape Horn on 14 February 1957 - The yacht was sailed under jury rig to Chile, reaching Arauco Bay 36 days later.

 

This is probably the classic pitchpole in all of yachting history. All the major works on the subject of heavy weather tactics make mention of it. Adlard Coles refers to the 1957 pitchpole of Tzu Hang six times in Heavy Weather Sailing. In her two celebrated attempts to round Cape Horn, Tzu Hang was pitchpoled the first time and rolled the second. On the first attempt she was manned by a crew of three, owner Miles Smeeton, his wife Beryl, and the renowned singlehander John Guzzwell of Trekka fame, (Trekka Around The World, John Guzzwell, 1963).

Tzu Hang had been running before mature seas in the high latitudes (50° South) of the Southern Ocean, trailing 60 fathoms of 3-inch manila hawser. Unlike nylon, manila has the sponge-like quality of soaking up water and was at one time considered to be ideal for use as warps. In this case it was not very effective, for Miles Smeeton writes, "I watched the sixty fathoms of 3-inch hawser streaming behind. It didn't seem to be making a damn of difference, although I suppose that it was helping to keep her stern on to the seas. Sometimes I could see the end being carried forward in a big bight on the top of a wave." (Once Is Enough, Granada Publishing, London, 1984, by permission).

As the boat continued to run before the storm, one breaking wave did come aboard, but Tzu Hang showed little tendency to broach. She seemed to be doing quite well in fact. "It was a dangerous sea I knew, but I had no doubt that she would carry us safely through, and as one great wave after another rushed past us, I grew more and more confident." (Ibid.) At the time of the incident Beryl had just relieved Miles at the helm, and was steering the boat when a great wall of water approached from the stern, so wide that she couldn't see its flanks, so high and so steep that she knew Tzu Hang could not ride over it. Water was cascading down its face, like a waterfall. Miles was down below, reading a book: "As I read, there was a sudden, sickening sense of disaster. I felt a great lurch and heel, and a thunder of sound filled my ears. I was conscious, in a terrified moment, of being driven into the front and side of my bunk with tremendous force. At the same time there was a tearing cracking sound, as if Tzu Hang was being ripped apart, and water burst solidly, raging into the cabin. There was darkness, black darkness, and pressure, and a feeling of being buried in a debris of boards, and I fought wildly to get out, thinking Tzu Hang had already gone down. Then suddenly I was standing again, waist deep in water, and floorboards and cushions, mattresses and books, were sloshing in wild confusion around me." (Ibid.)

Beryl had been catapulted out of the cockpit and into the sea, landing some 30 yards to leeward. Miraculously she was able to swim toward the trailing wreckage of the mizzen mast. Her shoulder was badly injured and it took the combined strength of the two dazed men to pull her back on board. But the situation was now critical. Tzu Hang had received a near death blow. Both masts were gone and there was a gaping - six foot square - hole where the doghouse had been. The weather was not getting any better and she was taking on great amounts of water. She would no doubt have gone down, had it not been for the tenacity and sheer will power of her crew.

From the onset Beryl, although in great pain, did her best to provoke, spur and cheer the two men on into life-saving action. She was the driving force that kept resignation and despair at bay. And John "Hurricane" Guzzwell would soon put his resolve, his backbone and his skills as a carpenter to keep Tzu Hang afloat. He patched the hole in the deck. He sawed and hammered, laminated and improvised, putting back together the pieces that would - thirty six days later - bring Tzu Hang safely into Arauco Bay, Chile. What transpired in those thirty six days on the wastes of the Southern Ocean should serve as an important lesson to all sailors regarding the mindset that is so often crucial to survival itself, the lesson being this: Never give up.

What exactly happened? There is much speculation about the exact movement of the boat during the mishap. Miles Smeeton is certain that it was a somersault: "When she pitchpoled a very high and exceptionally steep wave hit her, considerably higher than she was long. It must have broken as she assumed an almost vertical position on its face. The movement was extremely violent and quick. There was no sensation of being in a dangerous position with disaster threatening. Disaster was suddenly there. Whether she had been 20° to it or her stern directly presented to it, or whether she had been running at 2 or 7 knots could, in this case, have made no difference. Her stern came up and just went on going with no hesitation at all right over the bow." (Because The Horn Is There, Granada Publishing, London 1986, by permission).

The reader may wish to compare Smeeton's observations with the statement of Joan Casanova (File S/T-1), who survived a similar wave in the Southern Ocean: "It was the type of a wave which pitchpoles yachts in these oceans, the type which every voyager sailing in the high latitudes of the Southern Ocean fears.... We want to stress here that no vessel, multihull, monohull or freighter, could have survived such a sea unless tethered with a long line from a sea anchor...."

Formula for Disaster
Formula for Disaster

 

Whereas a rising tide will lift a boat vertically by a force equal to her displacement (usually many tons), a steep wave will "lift" the same boat horizontally with equal displacement force (DF) at wave speed. Speed of molecular rotation is already about 7 knots on the crest of a 40-ft. wave (A). The decaying crest hurls tons of water at a wave speed of 20 knots at her transom (B). Force of gravity (C) drives the bow down into the adjacent trough where it is briefly met with 7 knots of reciprocal rotation coming from the opposite direction (D). Result: The stern goes flying right over the bow without any hesitation at all.

Miles Smeeton later wrote a short Postscript which may be the key to our understanding of the dynamics of pitchpole. This Postscript can be found on the last pages of Once Is Enough and includes the following remarks:

Since I wrote this book I have had a number of letters - mostly from well informed sources - on the reasons for Tzu Hang's two mishaps... the major cause was probably due to the orbital velocity of a big wave. I had never heard of this theory which is that, although the mass of water in a seaway, seen as a whole, is static, each particle of water moves in an orbit around the place which it would occupy at rest. If we were to throw some rubbish overboard so that it represents a particle of water on the surface, we would see it drawn back towards the approaching swell, lifted up, carried forward, and dumped in approximately its original position again; seen from the side it would trace an orbit against the background of sea and sky.

The important thing is the speed at which the water moves in this orbit, and for a forty-foot wave with a ten second period the speed is approximately seven knots. With seven knots on the top of the wave with the wind, and seven knots against the wind at the bottom, a forty-foot ship on the point of a forty-foot wave is subjected roughly to a seven knot push one way at her stern and a seven knot push the other way at her bow, a formidable overturning couple. A longer ship is already overcoming the push at her bow by the time her stern is subjected to the maximum thrust. The answer seems to be to keep forty-foot ships out of forty-foot seas, but if forced to run before them to tow long enough lines so that there is an effective drag in spite of the forward movement of the water on the crest.... (Ibid.)