MULTIHULLS PERFORMANCE

Shock loadings can snatch an anchor right out of the sea bed. Here’s how snubbers can help you stay put

2017-09-01 - Corsair Marine, corsairmarine.com Manufacturing Inc., sailstiletto.com Corsair Marine, corsairmarine.com

CORSAIR 760 An evolution of the popular Corsair 24, the new Corsair 760 pocket cruiser offers a combination of wave-piercing bows and some additional volume/buoyancy in the amas to provide that much more speed and stability underway. Like the rest of the Corsair trimaran line, the amas easily fold in for trailering, and the boat offers a surprising amount of accommodation space belowdecks for its size. For those in search of even more speed in 24ft of LOA, a “sport” version is also available, which includes a carbon mast and boom, carbon bowsprit and a special lightweight interior for pegging the speedo no matter what the conditions.

CORSAIR 970 SPORT/CARBON

The popular Corsair 970 Cruze trimaran has received a makeover with more than a little pepper thrown in to create a pair of distinctly new iterations: the Sport and Carbon. The new Sport variant carries a taller 44ft aluminum mast, and the main is trimmed via an aft traveler arrangement that in combination with the taller stick affords about 10 percent more power. A carbon rig is also available. As for the Carbon version of the boat, it features not only the carbon mast, but full carbon construction with an eye toward creating an especially light, stiff and more powerful platform. Both boats include the same folding amas for which Corsair is known, making the boats easily trailerable, either to distant regattas or cruising grounds.

STILETTO X AND XF

Over four decades and 500 hulls after it first splashed in the mid-1970s, the dramatically styled trailerable Stiletto 27 is back in an “X” version that has been redesigned for the the twenty-first century with cutting-edge materials and modern features, such as wave-piercing bows and improved appendages. Better still, there is also an all-carbon Xf version capable of full-foiling in the works. If what we’ve seen so far is any indication, look for the latest iteration of this classic, which is now built in Columbia, North Carolina, to make just as big of an impression as its forebears. Stiletto

A key British naval port since the early 18th century, Antigua has long been a favored destination for sailors. When I first visited the island in 2012, I fell in love with the place. Strolling around historic Nelson’s Dockyard, I was captivated by the history and grandeur of the 18th century sail lofts, officers’ quarters and capstan house used to careen and repair the navy’s old wooden ships.

At that time, I was on a two-week cruise through the Leeward Islands on a 40ft Jeanneau I had chartered from Sunsail in St. Martin. I had just missed Sailing Week, but the aura of this massive yearly gathering of some of the world’s best sailors and yachts still hung in the air.

I was running short on my charter, so I only spent two nights in Antigua. However, I vowed that I would one day return and see Sailing Week and the dockyard in full swing. When I heard that 2017 would mark the 50th edition of this awesome week of sailboat racing, I booked a ticket and packed my sailing gloves.

This year’s event, which ran from April 29 to May 5, brought sailors from all corners of the globe, racing on boats ranging from the massive 115ft Farr mega-yacht Sojana to a 24ft Melges.

One of the more legendary entries was Kialoa III, a 78ft custom yacht built by Palmer Johnson that broke the Sydney to Hobart Yacht Race record in 1975 and retained the title for 21 years.

I had the pleasure of racing against Kialoa III on Sapphire III, a 76ft CNB yacht from 2016 owned by John O’Connor, and while it would have been exciting to race on Kialoa III, the view was just fine from the luxurious decks of O’Connor’s CNB.

I also hopped on Hot Ticket for a day’s racing. This speedy King 40 owned by Jim Hightower is crewed by some very friendly and talented good ol’ boys (and girls) from Texas. My job was trimming and grinding; thanks to the boat’s undersized winches and jib-sheet twing that added a lot of friction, this was a pretty physical race to say the least.

With 145 boats in 16 classes, there are many opportunities to hop on boats and race, and for those in search of a spot, there’s an official crew board you can sign up on, or you can just walk the docks and ask if anyone’s shorthanded. You can also grab your sailing buddies and rent a special race-rigged boat from charter companies like Sunsail and Dream Yacht Charter.

I met a group of Germans who were racing in the bareboat charter class on a boat called Klassenfahrt, which means “school trip.” They were all celebrating their 50th birthdays on a 50ft Jeanneau on the 50th edition of Sailing

choose your priorities wisely. I checked out a number of resorts, and each has its perks.

For those who want to be close to the events at Sailing Week, my favorite resort is The Inn at English Harbour. This classic inn is a collection of colonial-style, whitewashed, simple but elegant wooden structures strewn across a lush green lawn in front of a quiet, protected beach. They offer complimentary water taxi service to Nelson’s Dockyard, and the chef is one of the best on the island.

If you’re looking for more of a classic beach hotel, with lots of water toys and more action, Carlise Bay is also relatively close to Nelson’s Dockyard. While on one of my kayaking adventures at Carlisle, I found an empty little stretch of sand just around the headland on the eastern end of the main beach that became my private little getaway.

One of the spots on the Caribbean coast I especially liked is the Cocos Hotel, whose cozy bungalows are perched on a hillside overlooking Valley Church Bay and Jolly Beach, one of Antigua’s most famous and popular beaches.

Also on the Caribbean side of the island is the rather upscale Hermitage Bay, which is set on a quieter and more picturesque, semiexclusive bay. The elegant beachfront cottages and high-end service make it a favorite among honeymooners and romantics.

If Sailing Week didn’t “sail you out,” Nonsuch Bay Resort also has a full-service sailing school and a huge fleet of allinclusive sailing boats of various lengths and performance ratings. It even has a kite surfing school called 40 Knots. The instructors at the school told me sailors generally make good kite surfers, so I decided to give it a try. In spite of all the encouragement, I encountered a bit of a learning curve during my first lesson. That said, it was a blast, and I plan to take more lessons in the future.

I always try to get in a couple of dives whenever I’m in the Caribbean, and Jolly Dive is one of the oldest operations on An- tigua, with owner Paul Roos a treasure trove of info about diving in the area. As the name suggests, his shop is on Jolly Beach, just down from Cocos Hotel. As such, he takes guests mostly to sights on the Caribbean side of the island where you find more soft corals.

Mamora Bay Divers, on the other hand, is located at St. James’s Club & Villas on the Atlantic side. Here you see more hard corals, as well as some interesting boulders and canyons to dive through. I also encountered more sharks on the Atlantic side. They were mostly harmless reef sharks. However, Mamora Bay Divers manager Linda Swann told me Antigua has a very healthy and diverse shark population.

If you’re looking to really get away from it all and enjoy strolling along endless miles of empty beach, you’ll have to hop over to Barbuda (Antigua’s sister island), which is only a 20-minute plane ride away. (Taking the ferry is also an option.)

The place to stay on Barbuda is Barbuda Belle. Situated on a deserted, seemingly endless stretch of blazing white and pink sand beach on the northern most point of the island, this simple but elegant resort is paradise.

Behind the resort is a mangrove protected area that is home to a huge colony of frigate birds. The biggest spectacle here is during mating season (September through April) when the male birds show off their scarlet red gular pouch on their necks. That being said, it was equally amazing to see these birds offseason, and my guides and I were the only people there.

Sailing Week isn’t the only notable sailing event held annually in Antigua. There’s also the Super Yacht Challenge in February and the Classic Yacht Regatta, which runs mid-April. Now that I know what I’ve been missing, Antigua’s got a spot on my annual calendar. Next up, Super Yacht Challenge! s

A 45ft, 12-ton yacht (26,500lb/12,000kg) moving at 1 knot (0.5m/sec) would develop 6,000 x 0.25 = 1,500 joules.

We do not know how fast a yacht moves at anchor—our equipment is not sensitive enough—but 1 knot seems a reasonable figure; though it might be higher for a smaller yacht with a fin keel or lower for a heavier displacement, longer-keeled yacht.

Energy is based on the assumption that the yacht veers— in our tests on rode ten- sions, we found that the maximum loads occurred as a result of veering, not windage per se. So an anchored boat that does not veer will have a lower maximum tension in the rode than the same boat when it veers. We want to consider the worst- case scenario, hence the focus on veering.

Let’s say the yacht is attached to the anchor with a length of Kryptonite-strength piano wire. Energy would then be “transferred” directly to the anchor in the form of a snatch load, which will modify the shear strength of the sea bed in which the anchor is embedded ( see Ground Rules in the August 2017 issue of SAIL).

Sticking with our example of our anchor attached with a Kryptonite wire, we could transfer that energy to something “elastic” (in the same way that the impact of bumps on the road are transferred to a car’s suspension). If we had this “mixed” rode, the Kryptonite wire would give us abrasion resistance and the elastic component would absorb energy. Think of a bungy jumper—as his bungy cord extends

This graph shows chain’s low finite ability to absorb energy. In contrast, nylon stretches until it fails. At low tensions—low wind speeds—chain has a greater ability to dampen the movement of a boat and absorb snatch loads, but the differences are marginal, and in the grand scheme of things 30ft of nylon and 100ft of chain are very similar. The graphs are for 30ft of ⅜ in nylon and 100ft of ⅜ in chain; lighter chain will have a lower ability to absorb potential energy, but longer lengths (and 100ft is not very generous, nor is a 5:1 scope) will obviously be beneficial.

In shallow water, we measured the tension for a 45ft monohull with 75ft of lighter 5/16in chain and no snubber, a 5:1 scope. In 30 knots of wind the maximum snatch loads were around 900lb. At shorter scope, snatch loads were severe, in the order of 1,500lb. The increased severity and frequency of the snatch loads beyond about 700-800lb means that the all-chain rode has no ability to absorb more tension. More scope is the answer, as has been known for generations; if you have the room to deploy more chain, by all means do so.

While chain is more than adequate for benign conditions, the simple use of 30ft of nylon will greatly increase safety at anchor when winds are above 25 knots and room in the anchorage is limited.

he feels almost no shock load, just a gentle deceleration. Then think of a snubber as a bungy cord for a yacht. The snubber or bungy cord are simply a facility to store the kinetic energy as potential energy.

A ½in x 30ft length of nylon will comfortably absorb 1,500 (1,440) joules, equivalent to about 900lb of tension (or a 900lb snatch load). Based on measuring rode tensions without a snubber, this 900lb of tension is approximately the maximum snatch load developed on a 45ft, 7 ton yacht in 30 knots of wind with a 5:1 scope; 900lb is also 7.5 percent of the ultimate tensile strength (UTS) of ½in nylon.

Consequently, if you are using a Kryptonite wire rode—totally inelastic and with no catenary effect—then a 30ft length of ½in nylon cordage will absorb all of the energy developed from snatch loading in 30 knots of wind of a 45ft yacht, below the recommended limit of the WLL of 30ft of ½in nylon. If you double the length of nylon to 60ft, the energy absorption will be the same—1,500 joules—and you will only be working with 3.75 percent extension (well below the working load limit of 10 percent).

But if you increase the diameter (weight) of your 30ft nylon snubber to ¾in, then at the same 900lb tension you can only absorb approximately 885 joules, and there will still be a snatch load— the difference between the kinetic energy of the moving yacht and the potential energy of the cordage. This simply illustrates that the thicker (heavier) the cordage, the less it stretches at a given load, resulting in a snatch load.

Therefore, there is a compromise to be made between having enough stretch (with a limit to the WLL) and minimal or no snatch loading at all, or too little stretch (with plenty of WLL remaining) with the risk of snatch loading. (Note that ½in nylon has an ultimate strength of around 3 tons and ¾in nylon has an ultimate strength of almost 8.5 tons.)

If we now return to reality and dump our Kryptonite rode and replace it with 100ft of ⅜in steel chain, how will it perform? Our 30ft x ½in nylon snubber will store 1,500 joules at a tension of 900lb with a 7.5 percent stretch. The maximum energy absorption of our 100ft of ⅜in chain at a 5:1 scope is around 1,300 joules, at a totally unrealistic 3.5 tons of tension. Therefore, at 900lb of tension, still at 5:1 scope, the chain’s potential energy is around 950 joules. Basically, beyond 900lb of tension the chain is a virtually straight steel wire. If we increase tension to 1,350lb, then the chain alone has around 1,100 joules of potential energy, while the nylon has 2,700 joules. At low wind speeds chain, and catenary, is better at absorbing energy than nylon—but at low wind speeds there is little concern anyway.

In 30 knots of wind, our 100ft of ¾in chain at a 5:1 scope behaves like Kryptonite wire and offers no beneficial catenary effect. We can obviously deploy more chain if we have swinging room in the anchorage, but suddenly the idea of a mixed rode—some nylon, some chain—looks appealing. We can marry the abrasion resistance of the chain (and keep some of its ability for potential energy at lower wind speeds) to the benefits of nylon’s ability to add potential energy to the rode. The big issue is the need to join the chain and nylon together and deciding what length of each we need.

The alternative is to have an all-chain rode and a nylon snubber that can be attached anywhere using a chain hook or some form of hitch.

SETTING UP SNUBBERS

It is a good idea to have one set of snubbers to use up to 35 knots and another heavy-duty set to

use beyond. Most people will never experience winds over 35 knots in a recognized anchorage, so the need for “storm” snubbers is exceptional, and the occasional use of a “standard” snubber in 40 knots will not be catastrophic. For cruising around your home port, the absence of storm snubbers is not going to be an issue—you will have access to decent forecasts and know the local bolt holes. However, if you are going to cruise in high latitudes storm snubbers and spares are strongly recommended.

Though keeping within nylon’s WLL will maximize their life, snubbers are consumables and will need to be replaced, perhaps every two years depending on how often you anchor. If you do not replace your snubbers, you should fully expect them to eventually fail (which they will do, with the noise of a rifle shot).

You will roughly double the life of your snubber if you install one on each side and join them at a common chain hook (a bridle). We leave the snubbers on our catamaran permanently installed—they are not in the way and the excess is stored as you would sheets. They are best made from three-strand or multiplait nylon. Bridles can also be employed on monohulls.

Another option for monohulls is to have an “everyday” snubber on one side and a storm snubber on the other. Let the two snubbers meet at a common chain hook and only bring the storm snubber into service when needed by simply slacking off the lighter snubber so the storm snubber takes the tension.

We have tried all sorts of methods for attaching the snubber to the chain, and the simplest is a cheap G70 cradle or saddle hook, used in the transport industry. Most “marine” hooks are quite expensive and are seldom tested (and even when tested you have no idea what the specification or test data means). Hooks used in the lifting industry are made for specific chain sizes, and in my experience chain retention is much more secure than the hooks sold for marine application. An alternative is a Prusik knot (our recommendation for a tied attachment), some form of hitch or a Dyneema soft shackle.

Given that snubbers can fail, you must also secure the chain to a strong point on deck so that there is no chance of the snatch loads being transferred to the windlass should the snubber break. The best way to do this is to simply attach a second, short snubber to both the chain and a strong point.

When you rig the snubber you need to let out some slack in the chain, between chain hook and bow roller, to allow the snubber to stretch. If you are really clever you can estimate that slack to be, say, 15 percent of snubber stretch. This then limits the amount of stretch to which your snubber can be exposed. If you have an “everyday” snubber on one side and a storm snubber on the other, you can arrange that your storm snubber comes into play when the everyday snubber reaches 10-15 percent—this then allows both snubbers to work together.

A snubber is not a panacea. It will not make a poor anchor reliable, though it will make it less unreliable. Snubbers are simply part of your ground tackle wardrobe, along with spare anchors, spare rode, rated shackles and so on. If your spare rode is a mix of chain and nylon, it does not need a snubber; the nylon spliced to the chain will offer the required elasticity.

THE CATENARY MYTH

In case it is not yet obvious, your chain catenary has finite benefits. In fact, you should assume that, given the amount of chain you can carry and the limited space in many anchorages (which in turn will limit the amount of chain you can deploy) that any useful catenary will effectively disappear at around 30 knots of wind as the rode straightens out. You can choose nylon snubbers for any and every eventuality, from 20 knots to 70 knots—they will offer elasticity for anything the forecaster can throw at you. You simply need to decide what you think is reasonable.

For everyday anchoring on a 30ft to 40ft yacht with G30 chain, a 30ft ⅜in or ½in nylon snubber will be adequate, upping the thickness to ⅝in for 40-50ft boats. s

Jonathan Neeves has been researching and testing everything to do with anchors and anchoring for many years