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Sea Anchors on Catamarans

S/C-20 Catamaran, Crowther

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S/C-20

Catamaran, Crowther

49' x 24' x 8 Tons

15-Ft. Dia. Sea Anchor

Force 8-9 Conditions

SW gale vs Agulhas Current

File S/C-20, obtained from Jean Claude Barey, Montreal, Canada - Vessel name Chasse Galerie II, hailing port Montreal, Spindrift catamaran, designed by Lock Crowther, LOA 49' x Beam 23' 6" x Draft 3' x 8 Tons - Sea anchor: 15-ft. Diameter Shewmon on 300' x 3/4" nylon three strand tether and bridle arms of 40' each, with 5/8" galvanized swivel - No trip line - Deployed in a whole gale in 500' of water about five miles SE of Port Elizabeth (South Africa) with winds of 40-45 knots and seas of 17-20 ft. - Vessel's bow yawed less than 10° - Drift was estimated to be 8 n.m. during 42 hours at sea anchor.

Jean Claude Barey took Chasse Galerie II on a circumnavigation in 1991. After transiting the Suez Canal he sailed her down to Durban, East London, Port Elizabeth, and was en route to Cape Town when he ran into a blow on the continental shelf, in close proximity to the Agulhas current. Transcript:

The conditions were not bad, but we could not take long tacks against the wind, because we were too close to the Agulhas current. We then used the sea anchor. Other boats without sea anchors decided to run back [to Port Elizabeth] after a few hours because they were not making progress to windward. Our Shewmon sea anchor worked well in those conditions. The boat was very steady (less than 5° yaw I will say).

The Gulf Stream and the Kuroshio (Japan) notwithstanding, the Agulhas is likely the strongest and most articulated current on earth - with a reputation for breaking ships in two. Because of it, the southeast coast of Africa represents a gauntlet that mariners need to run with great care and prudence. Charts of the region warn: "Abnormal waves of up to 20 meters in height, preceded by a deep trough, may be encountered in the area between the edge of the continental shelf and twenty miles to seaward thereof. These can occur when a strong southwesterly wind is blowing."

The Agulhas runs mainly from northeast to southwest, following the two hundred meter contour of the continental shelf and dissipating over the Agulhas Bank south of Mossel Bay.

SW gale vs Agulhas Current
SW gale vs Agulhas Current

If the Agulhas could be likened to a great river - moving 80 million tons of water per second at speeds of up to six knots - the high-crested waves that form on it during southwesterly storms would be akin to the tidal bores that travel up the Amazon and the Bay of Fundy.

Since the current extends to depths of more than 1000 meters, and since it generally does not intrude onto the shelf regions, but tends to lie just offshore of the shelf edge, evasive procedure for cruisers has always been to stay clear of the area seaward of the edge of the continental shelf. What many sailors do after leaving Durban is to sail offshore just far enough to "kiss and ride" the current south, but not so far that they can't make a hasty retreat out of its axis and duck inshore at the slightest indication that there is a southwesterly gale brewing.

As always, the cardinal rule is never leave according to clock or calender, nor have a deadline at the other end. According to literature forwarded to Victor Shane by Chris Bonnet, Principal of the Ocean Sailing Academy in Durban, the best time of the year to travel south is January to March.

The gauntlet from Durban to East London is 250 miles with absolutely no safe place to duck into in between. Bonnet advises sailors to wait for a favorable window. Leave Durban at the tail-end of a southwesterly blow when the barometer has topped out, preferably at about 1020 milibars. Clear customs and immigration at the advent of a southwesterly, which will normally blow from 36 to 48 hours, then sail on to the two hundred meter line as soon as possible as this is where you can obtain a several-knot boost from the current.

It also means that in the event of not reaching East London before another southwester, you can quickly duck inshore and avoid being caught in the middle of the current - where sixty foot walls of water have been known to break ships in two. You will find that on average the two hundred meter line will give you a distance offshore - between Durban and East London - of approximately ten miles.

The gauntlet from East London to Port Elizabeth is shorter - 120 nautical miles. Kiss and ride the current, move inshore if caught. The Port Elizabeth to Cape Town leg is a little safer as there are decent places to anchor or put into - Knyasna, Cape St. Francis or Krombaai. But watch the charts and proceed with caution as there are rocks and reefs all about.

Sea Anchors on Catamarans

S/C-16 Catamaran, Crowther

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S/C-16

Catamaran, Crowther

40' x 26' x 2.75 Tons

16-Ft. Dia. Sea Anchor

Force 9 Conditions

 

File S/C-16, obtained from Dr. Gavin LeSueur, Mallacoota, Australia - Vessel name Windswept, hailing port Mallacoota, catamaran, designed by Lock Crowther, LOA 40' x Beam 26' x Draft 2' 6" x 2.75 Tons - Sea anchor: 16-ft. Diameter Para-Anchors Australia on 300' x 3/4" nylon braid tether and bridle arms of 28' each, with 5/8" galvanized swivel - No trip line - Deployed in a storm in shallow water (40 fathoms) in the Bass Strait with winds of 45-58 knots and seas of 30 ft. - Vessel's bow yawed 20° - Drift was estimated to be 12 n.m. during 6 hours at sea anchor.

Dr. Gavin LeSueur is an Australian country doctor who lives in Mallacoota, Victoria. He is also among the world's leading multihull safety experts, having weathered storms, used a wide variety of drag devices on different multihulls, and pioneered an adjustable drogue that is now being manufactured by Para-Anchors Australia. The intrepid doctor windsurfed 750 miles from Melbourne to Sydney in 1982. He has written three books - Windswept, The Line, and Multihull Seamanship Illustrated (distributed in the United States by Multihulls Magazine). Transcript:

In January 1988 I raced two-handed from Sydney to Auckland (1000 nm) on my catamaran, D Flawless. This was a 37' x 24' x 4600 lbs. open bridgedeck offshore racing catamaran. My crew was 21 year old Catherine Reed [wife to be]. After rounding the northern tip of New Zealand, the fleet was hammered by cyclone Bola. This tropical cyclone followed an unusual route and was unforeseen by me due to lack of high seas forecasts at the time, because of an industrial dispute at the Australian Meteorological Bureau! By the time we realized what was on the way (we first heard about it on New Zealand commercial radio stations!) we were in 60 knots plus and 25-35 ft. seas - with a lee shore 30 miles away!

I carried a 12-ft. parachute made by Para-Anchors Australia on board without a float or trip line, and with 300 ft. of nylon anchor line. I was unable to set the parachute. The conditions were such that it was not possible to crawl forward on deck due to the sea state and wind. It was like trying to move with your hands full on the roof of a car going along a bumpy road at 80 mph. We had removed all sail (and boom) except a small storm jib, lashed the helm over to drive the boat into the wind, and raised both daggerboards. [Emphasis added.] Thus D Flawless tracked at 70 degrees off the wind for the next 36 hours. We moved at about 2 knots, passing the edge of the eye and were ejected out of the "bad" quadrant. Wind strengths on land reached 96 knots. It was not pleasant huddled in the hull in our survival suits, awaiting the capsize that did not happen. The boat remained remarkably intact and we sailed into Auckland to finish the race.

En route back to Australia two months later we struck a 43 ft. humpback whale at 3:00 am in 25 knots of wind. We were surfing with our centerboards not fully raised. The whale awoke as we embedded our port centerboard in its back. It took off with the centerboard, the case and a good portion of the side of our port hull. The mast came down and speared itself through the remaining "good" hull! Over the next 45 minutes the catamaran wrenched itself to pieces. There were four of us on board at the time and we were 60 miles off the Australian coast. So close, and yet so far.

With no option but to get into our life raft we left the tangled wreckage and joined many of the foam sandwich hull pieces drifting downwind. The life raft was an Australian Yachting Federation approved offshore raft. Sea conditions deteriorated to 45 knots and 20 ft. waves. We were on the edge of the continental shelf and occasional seas were higher and breaking. We were capsized out of the raft four times! The parachute drogue on the water ballasted raft was useless. The only way we could stop capsizing on most waves was to dive to the windward side of the raft on each wave. It worked some of the time. We were rescued nine hours after hitting the whale. Rescue was quick and by helicopter (thus accurate wind and sea condition measurements). We had drifted over 20 miles in that time and rescue was effected due to our initial Mayday, missed radio schedule, EPIRB (which later failed - waterlogged), hand-held VHF radio (helicopter got a directional fix on this) and rocket flares. We were in good condition in survival suits, with extra water and flares over and above what was already in the raft.

Catherine and I now sail three handed with our three year old daughter (and dog - but she doesn't count). We have continued to experiment with drogues and parachutes and have used both many times since. I have no major problems with our parachute system. We use a 16-ft. diameter one made by Para-Anchors Australia, and carry 400 ft. of braided nylon rope. We do not use a swivel, or a trip line. The parachute has a float on 30 ft. of line on it's vent hole. Only once have we added a catenary weight down the line with a snatch block. We used a 25 kg CQR. In the 40-knot conditions it made little difference and it was a trial. We winch the line in while motoring up to the float. The bridle is a separate line and is tied to the tether with a rolling hitch. When the load is taken back on the tether in the cockpit, the rolling hitch is easily undone.

 

NOTE: Dr. LeSueur was a participant in the rough and tragic 1988 Round Australia Race in which he used and destroyed several drogues (see also File D/C-8).

Sea Anchors on Catamarans

S/C-9 Catamaran, Crowther

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S/C-9

Catamaran, Crowther

36' x 17' x 6 Tons

24-Ft. Dia. Parachute Sea Anchor

Force 8-9 Conditions

 

File S/C-9, obtained from Gary Jones, Rockville, MD. - Vessel name Corinthian XIII, hailing port Chester River, MD, "Witness" catamaran, designed by Lock Crowther, LOA 36' x Beam 17' x Draft 2' x 6 Tons - Sea anchor: 24-ft. Diameter military chest reserve parachute on 450' x 3/4" nylon three strand rode and bridle arms of 25' each, with 5/8" galvanized swivel - Full trip line - Deployed in low system in shallow water (12-15 fathoms) about 50 miles SE of Cape Fear, NC, with winds of 35-45 knots and seas of 8-12 ft. - Vessel's bow yawed 10° - Drift was estimated to be 5 n.m. during 10 hours at sea anchor.

Parachute sea anchors are worth their weight in gold in difficult coastal situations with the wind on the rise and the crew sick and exhausted. Their low rate of drift means that they require practically no sea room, making them the only viable means of stopping the boat and calling "time out" in close quarters. Transcript:

Wind and sea started building about 1800 hrs as we came up on Frying Pan Shoals. With the wind on the nose and the sea becoming choppy we weren't making any progress toward Charleston, South Carolina. At midnight the wind had turned the sea white and many waves were coming over the bow. We were heavy with provisions for a long cruise and five people were aboard. One crew member got sick and the rest were exhausted from fighting the weather.

The prospect for weather during the next 8 hours sounded bad and we knew the chances of being set into the shoals were great, so we decided to set the chute. Holding onto the heaving deck with one hand and setting the chute was tough due to water coming over the bow. It took 1.5 hours to deploy the rig, but it worked great and gave us time to go below and get much-needed rest.

Sea Anchors on Catamarans

S/C-6B Catamaran, Crowther

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S/C-6B

Catamaran, Crowther

43' x 25' x 7.5 Tons

18-Ft. Dia. Sea Anchor

Force 10 Conditions

 

File S/C-6B, second file (see S/C-6A) obtained from Josh Tofield of Tucson, AZ. - SAME VESSEL - SAME SEA ANCHOR - SAME BRIDLE & TETHER DIMENSIONS - Deployed in a storm in deep water about 800 miles northeast of Hawaii with winds of 50-55 knots and seas of 25 ft. - Vessel's bow yawed 10° - Drift was 5 n.m. during 72 hours at sea anchor.

This is the second file involving Ariel. In the previous file she successfully rode out Force 8-9 conditions on the same parachute with a 250' tether. In this file we see that the 250' tether was clearly too short when Ariel ran into a much heavier storm on her way back from Hawaii. The 250' x 3/4" tether was not long enough to provide adequate shock absorption, as a result of which the boat took a severe pounding. Ariel's tether should have been at least 400' in this instance (the general rule of thumb being LOA x 10). Transcript:

Ariel departed Hawaii 11/10/91 with delivery skipper aboard. He has documented over 100,000 miles in deliveries for Compass Yacht Services alone. Approx. 800 miles NE of Honolulu a rapidly moving, intense LOW which was squeezing against a massive hi-pressure cell caught Ariel in the exact center of reinforced winds. Barometer dropped from 1018 to 1002 in 3 hours! (Weather Fax attached). Wind started one hour later and built to Force 10 where it stayed, never dropping below Force 9 in 48 hours. Waves were 25' (conservatively measured from the back of wave height and not from the troughs). Bridle (3/4" nylon) chafed completely through & had to be replaced with 5/8" backup bridle. Later one leg of the 5/8" bridle SNAPPED in the center when hit with very large wave, throwing Ariel backward, shearing the foam & fiberglass off of one rudder completely, and leaving only half of the other rudder (which later broke off). Crew eventually added 100-150' of anchor chain to the 250' of 3/4" nylon tether and rode out the rest of the storm.

Recovery, using the "partial trip line" was very difficult. Engines both out because during the storm, while motoring up to relieve pressure on bridle (while changing it) a large wave submerged entire stern, forcing water up exhaust system and drowning the engines (exhausts 2' above waterline under aft bridge deck !!!!!) Jury rigging done after storm passed. Ariel was then sailed 1500 miles to San Diego. Moral of the story: USE LOTS OF PRIMARY TETHER! What is adequate for Force 9 is not adequate for Force 10!

Sea Anchors on Catamarans

S/C-6A Catamaran, Crowther

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S/C-6A

Catamaran, Crowther

43' x 25' x 7.5 Tons

18-Ft. Dia. Sea Anchor

Force 9 Conditions

File S/C-6A, obtained from Josh Tofield, Tucson, AZ. - Vessel name Ariel, hailing port San Diego, catamaran, designed by Lock Crowther, LOA 43' x Beam 25' x Draft 3' 3" x 7.5 Tons - Sea anchor: 18-ft. Diameter Para-Tech on 250' x 3/4" nylon three strand tether and bridle arms of 75' each, with 5/8" galvanized swivel - Full trip line - Deployed in a tropical depression in deep water about 400 miles SE of Cabo San Lucas, Mexico, with winds of 45-60 knots and seas of 18 ft. - Vessel's bow yawed 10° - Drift was 2 n.m. during 20 hours at sea anchor (confirmed by GPS).

Several weeks after Ariel left San Diego for points south she ran into an unforecast loop of ITCZ - Inter Tropical Convergence Zone - at 21° 09' North, 106° 52' West. In his book, Weather For The Mariner, William J. Kotsch has this to say about the phenomena (Naval Institute Press, reproduced by permission):

     "The ITCZ is usually characterized by strong, ascending air currents, a great deal of cloudiness, and frequent heavy showers and thunderstorms. The intensity does, however, vary greatly. Sometimes the ITCZ looks like a tremendous wall of black clouds, with the top extending to 55,000 feet and higher.... The width of the ITCZ varies from about 20 to 150 nautical miles, and as a general rule, the narrower the zone (i.e., the greater the convergence), the more intense is the weather associated with it. When the ITCZ is near the equator, only small and weak cyclonic circulations can develop within it. But when it migrates away from the equator (at least five degrees or more), the influence of the earth's rotation becomes great enough to transfer sufficient "spin" to the converging air currents to permit tropical cyclones, hurricanes, and typhoons to develop."

One really needs a chart of Mexican waters to appreciate the value of a parachute sea anchor in tight quarters. Ariel was about 100 miles off the Mexican coast proper, with the rocky islands known as Tres Marias to her lee. The crew consisted of owner Josh Tofield, his wife, and two small children. Tofield deployed an 18-ft. diameter Para-Tech sea anchor and "anchored" Ariel to the surface of the sea.

Tres Marias is a Mexican prison compound. There is a 20-mile forbidden zone around it and pleasure boats have been known to be rammed by gunboats for intruding into the zone. It being dark, and apprehensive about getting too close to the islands, Josh Tofield kept a close eye on the GPS readings. Incredibly, he found that Ariel drifted no more than 2 nautical miles in the 20 hours that she was tethered to the sea anchor. Transcript:

Only 100 miles from Puerto Vallarta and with the Islas Tres Marias in our lee we got caught in a brief but fierce (unpredicted by WX or WXFAX) loop of ITCZ convection sucked up to our latitude. Winds of 45 knots sustained, gusts to 60 for 6-8 hours, with 30-35 knots sustained for 6-8 hours before and after. As long as the wind was blowing from the SE the seas were highest - but also most comfortable, as our catamaran rocked up and down in 18-ft. maximum seas, with 3-ft. breaking tops, and almost no side to side [yawing] motion. However, as the wind veered, large cross swell came under and slammed bridge & deck viciously - but no damage and no excess heeling.

My alternative would have been to run off to the West - which we could have done - but I didn't want to as we would have been blown all the way to Cabo before the wind subsided.

Only problem was the trip line. Perhaps I tied it on wrong to its small swivel, but it fouled fender severely and pulling in required anchor windlass and much bad language!

ADJUSTING BRIDLE FOR BEST RIDE.
ADJUSTING BRIDLE FOR BEST RIDE.

This is one of numerous files in which boats had problems with fouled up trip lines. Yet another reminder that FULL trip lines should be kept fairly taut at all times (see Fig. 39 and review last paragraph of file S/T-7). Also, the problem relating to cross swells mentioned by Tofield can in most instances be lessened by adjusting the lengths of the bridle arms on multihulls. By shortening one bridle arm and lengthening the other (Fig. 41) it is possible to rotate the bows into a direction more accommodating to changing sea conditions. If the wind and dominant waves have been coming from the north (0°), for example, and a secondary disturbance begins to squeeze in a different set of waves from the northeast (45°), the skipper may wish to adjust the bridle arms so that the bows are pointing somewhere in between the two sets of waves (about 22°).

Drogues on Catamarans

D/C-8 Catamaran, Crowther

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D/C-8

Catamaran, Crowther

40' x 26' x 3 Tons

Sea Squid Drogue

Force 9-10 Conditions

File D/C-8, obtained from Dr. Gavin Le Sueur, Mallacoota, Australia - Vessel name Windswept, hailing port Mallacoota, catamaran, designed by Lock Crowther, LOA 40' x Beam 26' x Draft 2' 6" x 3 Tons - Drogue: Sea Squid on 300' x 3/4" nylon braid tether, with bridle arms of 28' each - Towed in a whole gale in deep water from Perth to Adelaide with winds of 40-50 knots and seas of 20-30 ft. - Vessel's stern yawed 20° - Speed was reduced to about 4 knots.

SEA SQUID (no longer available).
SEA SQUID (no longer available).

Although the Sea Squid is no longer in production we are presenting files that involve its use because they contain invaluable insights relating to the use of speed-limiting drogues in general. Dr. Gavin Le Sueur (see also S/C-16) used Australian Sea Squid drogues in the rough 1988 Two Handed Around Australia Race, the same race in which Peter Blake participated on Steinlager II (File D/T-1). Transcript:

I was offered a 40ft Crowther catamaran to sail in the 1988 Two Handed Around Australia Race. I crossed the starting line with Catherine [wife to be] as my crew. We were given a plastic "Sea Squid" drogue to test during the race. The first night brought a southerly buster that capsized a 35ft trimaran (Escapade), sank a police launch and cost the life of a crewman on a monohull (Boundary Rider). We towed the Sea Squid on 300ft of 1" braided nylon. It porpoised all night [diving in and out] and by dawn we were just dragging rope with a small plug of plastic shackled on the end. At the first stopover we were given a second Sea Squid. This one had a reinforced head (fiberglass resin poured into the bolt attachment). After a gale in the Coral Sea the inlet valves of this Sea Squid had split and folded back. Again this one would leap out of the water on occasions. At Darwin we were given a third Sea Squid to test. This time the inlet valves were smaller and reinforced across the center. We added 6ft of anchor chain right next to the drogue. This stopped the porpoising.

While crossing the Southern Ocean from Perth to Adelaide all competitors went through gale after storm. We could not carry full sail for 3000 miles! We towed drogues and warps for most of the way. The last Sea Squid worked famously. With the chain, reinforcing and altered inlet valves, we had no further structural failure. It was speed limiting to approximately 7 knots. We no longer surfed down waves, and often would add sail before taking in the Squid so that we could maintain a constant 7 knots and not stall in the troughs.

The drogue bridle ran inboard from each hull to two winches so that the arms could be adjusted for steering. The tether itself continued into the cockpit and the bridle arms were spliced together and the combined end bent onto the tether with a rolling hitch with a lock. The tether was then let out until the bridle grabbed. It was secured to another winch as a backup if the bridle arms failed, or the knot came undone. This never happened. We finished the Around Australia Race in second place in the 40ft division, third multihull over the line behind Steinlager (Peter Blake) and Verbatim (Cathy Hawkins and Ian Johnston). On the finish line I asked my crew to marry me and surprisingly she said yes!

Our drogue system has continuously undergone experiment and changes. These changes are entirely experimental and apply only to our catamaran, but may be of use to others. Our first problem was the stowage of the Sea Squid, and rigging it for convenient use. It meant getting out our short length of chain off the breakfast anchor line [lunch hook]. It usually meant digging the Squid out from the recesses of the bow. We read about textile drogues and have tried four systems since 1992. The first was a scaled down parachute. It worked out but slowed the cat to less than 3 knots in 35-knot winds. Too slow to avoid getting pooped. We then tried a "series" drogue, provided as a trial. It slowed the boat, but was a stowage mess and very impractical. We then tried a textile drogue that was fluted. It was like a normal parachute (3ft diameter) but with the middle ten inches removed and the continuous shrouds holding the two pieces of material together [see image below]. This fluted drogue worked as well as the parachute - 3 knots and too slow in 35-knot winds and 12ft seas. We had the drogue re-shaped by Para-Anchors Australia, the outlet hole enlarged and a rope tie put into the ends of the shrouds so that we could adjust the outlet [as with a drawstring bag].

Adjustable pull, "fluted" drogue conceived by Australian Gavin Le Sueur is similar to drogue used by NASA to lower the Pathfinder mission onto the surface of Mars. Note the drawstring arrangement on the smaller ring, allowing the outflow diameter to be adjusted from 14" to 4" to increase or reduce pull. The optimal pull for a particular boat will have to be determined through prior trial and error and in practice runs. The drogue cannot be adjusted while in use.
Adjustable pull, "fluted" drogue conceived by Australian Gavin Le Sueur is similar to drogue used by NASA to lower the Pathfinder mission onto the surface of Mars. Note the drawstring arrangement on the smaller ring, allowing the outflow diameter to be adjusted from 14" to 4" to increase or reduce pull. The optimal pull for a particular boat will have to be determined through prior trial and error and in practice runs. The drogue cannot be adjusted while in use.

With all three drogues and the Sea Squid we put out to sea for a twelve month cruise. We have used the variable outlet - fluted - drogue four times in anger, using it to control our speed, or to stop surfing, or to ease the work of the autopilot. In 37-knot gusty conditions we sailed up to 8 knots with the outlet open. We put up our storm spinnaker (a small, bulletproof racing kite with a low center of gravity) and we were unable to push the boat speed over 8 knots. With 200ft of rode it appeared that the drogue rapidly increased the turbulence as we increased the pulling power [by adding sails]. It was as though we had hit a speed barrier. We winched it in (about ten minutes hard yakka) and then re-launched it with the outlet hole tightened up (from 10 inch diameter to 4 inches). We were then back to three knots boat speed. Again we were unable to exceed this speed. It took a bit longer to haul it in the second time but the exercise seemed fruitful. I thought it justified further development and sent a copy of the reports to Para-Anchors Australia. Why a variable drogue? Vary the outlet hole so that one drogue can work for different boats. On any boat, with practice (essential) you can "dial a speed limit." A simple system that is stowed in the cockpit without hassle. At no time did any of the textile drogues break the surface, although I would add a weight if I was to run downwind in tumbling sea conditions.

Dr. Le Sueur's "fluted" parachute drogue is similar in concept to the ringsail and disk gap-band drogues used by NASA and the Aerospace Industry. Alby McCracken of Para-Anchors Australia has developed Dr. Le Sueur's idea - replete with drawstring drag adjustment - and is now offering models for sale (see Appendix III at the back of this publication).