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Sea Anchors on Trimarans

S/T-2 Trimaran, Kismet

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KISMETS/T-2

Trimaran, Kismet

31' x 18' x 2.5 Tons

20-Ft. Dia. Parachute Sea Anchor

Force 10+ Conditions

 

File S/T-2, condensed from the writings of Randy Thomas - Vessel name Celerity II, hailing port Victoria BC, "Kismet" trimaran designed by Bill Kristofferson, LOA 31' x LWL 29' x Beam 18' 6" x Draft 30" x 2.5 Tons - Sea anchor: 20-ft. Diameter cargo parachute on 300' x 7/16" nylon three strand tether and bridle arms of 100' each, with 1/2" galvanized swivel - No trip line - Deployed in hurricane Freida in deep water in the South Pacific, with winds of 50-60 knots and seas of 30 ft. - Vessel's bow yawed 20°.

 

This file was condensed from articles by Randy Thomas and additional information provided by others, among them Bob Wilson of the British Columbia Multihull Association, to whom the author is indebted.

Celerity II, a Kristofferson-designed, light displacement Kismet 31 was en route to Kosrae from Rabaul (Solomon Islands) when she had an encounter with hurricane Freida in February 1982. As the wind and seas continued to build, Randy Thomas found options narrowing. Running off was out of the question. It would take Celerity II into a screen of low-lying atolls, and toward the eye of the storm. And Randy had once tried lying a-hull in a blow off Point Conception, California. It had been a bad experience.

With her reefed main set as a riding sail and the tiller lashed amidships, Celerity II lay quietly hove-to for a while. But the wind was building in 5-knot increments and soon it became clear to Randy that the mains'l would have to come off altogether - taken off the boom. It was time to set the parachute sea anchor. Randy had never set the chute before. With safety harnesses snapped on, he and his companion Thea carried the 20-ft. diameter parachute on deck. Crests broke over the boat as Randy crawled onto the narrow floats to shackle each end of the bridle to the heavy duty U-bolts which he had installed three feet inboard. "`Next time rig the bow bridle before you leave port,' ran my mental memo." (Writing in the article that appeared in SAIL Magazine). They dunked the chute and watched, as the boat's drift payed out the 400' of tether and bridle. But Celerity II continued to lie-ahull!

Bridle should be attached to the extreme outboard ends of the floats to obtain maximum leverage possible.

Overcome with dismay, Randy wanted to get the knife and cut the whole rig away, but Thea shouted above the noise of the wind that he should try leading the bridles off the extreme outboard tips of the floats before doing so. Randy was skeptical at first, but then decided to give it a try. He would have to unclip the two snatchblocks from the U-bolts (three feet inboard), wriggle out to the ends of the narrow floats and re-attach them to pad-eyes forward. It was a formidable struggle, but it did the trick. Celerity II immediately rounded up and began facing the seas. In his article appearing in the June 1982 issue of SAIL, Randy describes Celerity II's behavior (reproduced by permission of SAIL Magazine):

She bobbed easily over the upwelling crests, first backing swiftly, then popping upward like a suddenly released balloon. I was certain we would be buried under each seemingly perpendicular wall. No water came on deck. The bridle led perfectly, never coming into contact with either the hulls or the deck. There was no jerking at the blocks - only a gradual tension and relaxation as the nylon "springs" dissipated the heavy loads. We were anchored in mid-Pacific. We might have been anchored in a monsoon-torn harbor, except for the longer periods between each extraordinary rise and fall.

With the situation in hand they went down below and prepared a meal. Radio reception faded in and out, but they were able to piece the fragments together: tropical storm Freida had been upgraded to a hurricane, and her eye was 150 miles to the north! Just before dark Randy estimated the wind speed at about 50 knots sustained, with seas of 30 feet from trough to crest. Many of the waves were observed to be breaking heavily along their full lengths, but Celerity II had settled down into predictable cycles and seemed to be doing OK.

The night was a lonely vigil for the two. Randy writes that lying in the dark cabin they were mentally overwhelmed by the noise of the combers, rising in pitch as they approached the boat and then falling in pitch as they receded - like approaching and receding freight cars. The wind was shrieking through the rigging and the radar reflector up on the mast, creating an incessant racket that tore at their nerves. It was impossible to sleep. At dawn they were able to prepare a breakfast, and the radio informed them that the eye of the storm - packing 100 knot winds - had re-curved and was passing to the north for the second time! Thea put her head into the plastic observation bubble in the coach roof and surveyed the white seas around them. Suddenly she exclaimed she could see the parachute in the distance. As the boat climbed the next wave, Randy saw it too, "a shimmering disc, suspended like a huge jellyfish in the face of the bottle-green sea. The shroud lines reached out like tentacles, holding us safely in their grasp. We knew we were safe as long as our chute held." Well, the chute did hold, and, other than some minor damage to the trim-tab on her self-steering rudder, Celerity II emerged from her encounter with the lady Freida intact. In the same article Randy Thomas sums up his opinions:

Cruising safety depends on having options. And the parachute sea anchor can offer you a crucial alternative when the chips are down. Lying a-hull in heavy seas can result in damage, capsize, or worse aboard a light-displacement boat that is easily "tripped" by a fin keel or a submersible float. A parachute will hold such craft safely head-to-the-seas, minimizing drift and the danger of breaking crests.

Sea Anchors on Trimarans

S/T-1 Trimaran, Horstman Tristar Ketch

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HORSTMANS/T-1

Trimaran, Horstman Tristar Ketch

39' x 22' x 8 Tons

28-Ft. Dia. Parachute Sea Anchor

Force 12 Conditions

 

 

File S/T-1, obtained from Joan Casanova, Oregon City, OR. - Vessel name Tortuga Too, hailing port Seattle, Trimaran, Tristar ketch, designed by Ed Horstman, LOA 39' x Beam 22' x Draft 44" x 8 Tons - Sea anchor: 28-ft. Diameter C-9 military class parachute on 400' x 3/4" nylon three strand tether and bridle arms of 60' each, with 1/2" galvanized swivel - Full trip line - Deployed in numerous storms during 18-year cruise from Seattle to African coast, the Southern Ocean and back to Texas - Severest use case was over the Burwood Bank, between Cape Horn and Falkland Islands, with winds of 85-100 knots and seas in excess of 30' - Vessel's bow yawed about 20° - Drift was estimated to be 16 n.m. during three days at sea anchor.

 

By and large this is probably the most important file in the Drag Device Data Base. Other than a handful of known but poorly-documented cases of commercial fishermen and some sailboats using parachutes, our knowledge about the general behavior of boats at sea anchor was sketchy until the Casanovas came alone. We didn't know if a boat would "rise to the seas," or be pulled through green water. We didn't know if the boat would roll with the punches and "yield to the seas," or stand up against them and break up. We didn't know if the boat would get "slingshotted" off the crests as the elastic rode stretched. We didn't know if the boat would "back down" on her rudder, so as to cause it to break off. We didn't know if the hardware and fittings on boats could withstand the forces involved. Well, thanks to the pioneering work of Joan and John Casanova, now we know.

The parachute anchoring system never failed on Tortuga Too, not once in eighteen years and some 200,000 blue water miles. Off the coast of New Zealand where cyclone winds were recorded at 90 mph, in a hurricane off Fiji where several other boats were lost, in 40-ft. seas in the Indian Ocean, and in a truly devastating storm off the Falklands, time and again Tortuga Too survived without damage by the correct use of the parachute sea anchor. While Lady Luck might have played a significant role in some of the other files in this database, it is clear that her role was minimal in this one. Indeed, the number of times that the parachute was used, and the broad range of life-threatening storms and heavy weather situations in which it was deployed, seem to tell us that luck had very little to do with anything here - though it goes without saying that luck always favors the wise and the well-prepared.

Despite her relatively lightweight - plywood - construction, and despite her 22-ft. beam, Tortuga Too was never in any danger of breaking up. Not once did she get slingshotted off the huge storm crests; she never went crashing through green water; the galvanized swivel did not fail; the deck fittings did not pull out. The 28-ft. diameter military parachute held and the system worked, time and time again.

Tortuga Too's worst-case scenario occurred over the shallow Burwood Bank, between Cape Horn and the Falklands. This was a "bomb" type storm development, to use the expression coined by professor Fred Sanders of the Massachusetts Institute of Technology. The term "bomb" is generally used to describe the rapid development of a secondary storm, which overtakes - and reinforces - its predecessor. In particular it describes the pressure gradient amplifications that result from the overtaking of a surface LOW by a faster moving upper altitude TROUGH, resulting in barometric pressure decreases of 24 millibars or more in a 24-hour period, as well as abruptly angled surface wind fields. This type of storm development - usually identified by high-altitude comma-shaped clouds on satellites pictures - was associated with Fastnet '79.

In the book The Parachute Anchoring System Joan Casanova describes Tortuga Too's encounter with a genuine ESW - extreme storm wave. Tortuga Too was tethered to a 28-ft. diameter C-9 parachute when an enormous mountain of curling, roaring water rose before her bows, something akin to the terrifying photographs in Coles's Heavy Weather Sailing. This sobering account should be a source of comfort to multihull sailors in particular. It is reproduced by permission of Chiodi Advertising & Publishing, publisher of Multihulls Magazine:

 

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. While we watched, horrified, this monster welled up for a second time, curling over as if breaking on a beach, then roaring in foamy masses on top of Tortuga Too, covering deck and wheel house before running off into the sea once more. We were so shaken by this experience that it seemed an eternity before we regained our composure to check the boat's condition, but she was all right. In fact, Tortuga Too recovered faster than we. There was no structural damage. She had returned to her original position of facing the storm and was already climbing the next wave....

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... we share this story with you only to prove how this technique can protect a craft in extraordinary circumstances. Although Tortuga Too survived this mammoth wave crashing on her deck, there was no backing down on her rudder, nor any structural damage to the hulls.

 

The experiences of the Casanovas with parachute sea anchors is so broad-based, so extensive that it has entered into the legend and nomenclature of multihull sailing. In the multihull community the name "Casanova" is synonymous with parachute anchoring, to the extent that the names "Voss" and "Pardey" are synonymous with heaving-to in the monohull community. In the course of logging all those blue water miles, Joan and "Cass" tried every conceivable heavy weather tactic known to man, including the use of makeshift drogues off the stern, but they always found themselves coming back to the bow-deployed parachute sea anchor. Multihull sailors owe a debt of deep gratitude to Joan Casanova in particular, for having the vision to see in her valuable storm experiences a responsibility to inform others. (See also her early articles in the Spring 1976, July/August 1979 and August 1980 issues of Multihulls Magazine).