Secondary menu

Designing an Open 50

My reflections on designing the Open 50, Everest Horizontal.

When I first met Bob Gay, he had already accomplished what is probably the most difficult challenge facing any solo sailor intent on a round the globe race - that of obtaining sponsorship. Corporate America has been slow to recognize the potential marketing value of high profile sailboat race campaigns. Bob had presented his goals to Ascend Communications in a language they can understand - a business plan. Not long after construction contracts were signed, Ascend merged with Lucent Technologies, a communications giant who immediately recognized the fit - a solo adventurer facing brutal challenges in the most remote part of the planet, all the while immediately connected by phone, fax, and email with sound and video to the population at large, at home in their civilized world - an aquanaut on an electronic umbilical cord. They named the yacht “Convergence”, reflecting the merging of technologies and communications at the turn of the millennium.

Bob’s goal has been as steadfast as it is simple: he intends to be the first American to complete a Vendee Globe race. The Vendee Globe is the most difficult sailboat race ever conceived - one man, alone, non stop, around the world. The middle third of the race is sailed in the high winds and awesome seas of the Southern Ocean. It has been jokingly (and not inaccurately) called “the Round Antarctica Race”.

The Vendee Globe is open to boats between 50 and 60 feet with one class and no rating - first to finish wins the race. On first thought, it would seem unwise to enter the race with the smallest boat in the class. However, this choice makes sense when evaluated against Bob’s goal. The Open 50’s are tremendously fast and powerful. An Open 60 is all the more so, to the point where you have to ask whether the boat or the skipper is in charge. Only one 60 managed to complete the last Around Alone race without major catastrophe. The Vendee Globe, being a non stop race, is even more a war of attrition than the Around Alone. A 50 is simply more likely to finish than a 60.

We are not so arrogant as to expect to beat the 60 footers to the finish line. After all, the French have long dominated these races with excellent sailors and fast boats. However, we do expect to be nipping at their heels. Our design challenge has been to create a boat that increases the safety margin and is extremely rugged while still advancing the performance envelope beyond the current crop of Open 50s.

For downwind speed, weight savings is the number one concern. Contrarily, in a war of attrition, redundancy and reliability become the key words. The “reliability first” concept made the choice of water ballast over swinging keel an easy one. Evidence of this philosophy is evident throughout the boat, especially in the systems - multiple systems for electrical generation, multiple autopilots, watermakers, GPS systems, communication systems.

Reliability means minimizing the risk of damage. Following this line of thinking, we carried the keel right through to the deck. This strong and structurally efficient geometry, in combination with Kevlar grounding straps similar to those used in my multihull daggerboard trunks should make the keel to hull attachment stronger than the steel fin itself.

Open class rules now require five watertight bulkheads and positive flotation even with all watertight compartments violated. Let’s hope the proclivity for abandoning boats in the Southern Ocean is a thing of the past, or contestants will soon have more than icebergs to worry about. Round the world races could become a trip down memory lane.

James Betts Enterprises was completing construction of America True as our design was being finalized. I was pleased that Jim Betts was interested in using prepregs for the Lucent project. Hull, deck, and all interior bulkheads and structure were built of YLA supplied prepreg carbon skins over Baltec’s new SuperLite Balsa core. Outer skin of the hull/deck shell included two layers of S-glass/Kevlar hybrid for impact resistance and crack arrest.

Betts and his versatile team also built the prepreg rudder posts, the rudder blades, the keel fin weldment. They vacuum formed the windows, and installed the engine, generator, and water ballast system.

With the new positive flotation requirement, we decided to increase the core thickness of the hull/deck sandwich. A thicker sandwich is stronger and stiffer, in this case well in excess of ABS guidelines.

On the engineering fun side, we developed a bowling ball impact test models to represent a collision at 25 knots. Our plywood baseline panel was demolished, while the prepreg/balsa panel received only a scuff mark. Continuing the evaluation, the composite panel survived a sledgehammer test, finally failing under splitting wedge impact. We’ve instructed Bob to avoid splitting wedges.

The essence of the Open Class Monohull rule is a limit of 10 degrees heel with all moveable ballast shifted. This simple restriction defines the entire character of the boats. A wide hull is extremely stable at small heel angles. More stable hull means more ballast can be shifted, means even more stability, means more sail can be carried, means astronomical sail area to displacement ratios. Unfortunately, wide boats are also stable upside down. Upside down is slow and unpleasant - so difficult to stir your stew or to find your toothbrush.

In the early design phase, considerable effort was put into beam optimization and capsize recovery. Essentially the goal was to make the boat powerful in the sailing heel range, yet unstable when inverted. We accomplished this by a “convergence” of several features-

Cambered decks and a large coachroof - These features have been employed by the European designers recently. We pushed them a little further.

Large radius to the hull deck edge - This very effectively reduces the waterplane area when inverted and should help a bit with tripping in a high speed broach. Further benefits are reduced windage, reduced weight, rapid dumping of foredeck water, and increased strength and rigidity of the hull/deck shell.

Wide cockpit - Again our goal was to eliminate inverted waterplane. The cockpit sole extends all the way out to the face of the water ballast tanks. This feature very significantly improves recovery from inversion. In fact, if ballast tanks are full on one side the boat is completely unstable in the inverted position and will complete a barrel roll and return to upright.

Ability to fill ballast tanks when inverted. In the unlikely event the boat capsizes with tanks empty and stays there, ballast tanks are plumbed to allow them to be filled with the boat inverted, which will cause her to self right.

Watertight mast - A watertight mast greatly enhances the ability of the boat to right from an extreme broach. To do this, of course, it has to survive the roll. We applied extra carbon laminate in the hoop direction to withstand the tremendous water pressure the mast would see if immersed. This extra off axis laminate will make the mast significantly more rugged under normal use as well. With a watertight mast, the choice of all external halyards was obvious; and I believe this makes sense in any case for a single-handed ocean race. Easy check for chafe, easy replacement. Sometimes low tech is the best choice.

Higher ballast ratio - Convergence has a heavier bulb than most of the current fleet of Open 50s. Probably this is the most significant feature on the list; because the lower center of gravity is most effective when the boat is knocked to 90 degrees. Bigger bulb and a buoyant mast will make it highly unlikely that the boat will invert in the first place. Ignoring the watertight mast, limit of positive stability is about 130 degrees. Including watertight mast, it is about 155 degrees. With water ballast on one side, it is 180 degrees.

The Vendee Globe is primarily a downwind race, and buoyancy forward will allow the boat to be pushed hard in big seas. In addition to rather high forward freeboard, bow sections are full near the sheerline. A retracting and articulating bowsprit is mounted in a raised pivot ball at the stem, which serves a second function as a wave break. Ancient Polynesian canoes had a similar feature - a raised stem piece which serves to relieve downward pressure when the foredeck is driven under water. Water which does make it onto the foredeck will be deflected outward by the wide flaring house.

Open class designs are not at their best upwind. Ultra light displacement and wide beam do not make for a pleasant ride against the seas. We’ve attempted to improve on this scenario somewhat by keeping the bow relatively fine at waterline and below. Furthermore, our studies indicated that a slight increase in keel fin area would enhance upwind speeds. Larger fin area made a steel weldment an obvious choice over a milled steel fin; and with that decision it was logical to use the fin as a diesel tank.

These races are won by boats which sail fast in the Atlantic legs and survive the Southern Ocean leg. By not pushing transom beam as hard as most existing designs, we sacrifice some power but reduce wetted surface in light air. Further, the more balanced hull shape has a gentler edge of control and can often be pushed at a higher performance percentage.

Remarkably, non-dimensional performance ratios for sail area, displacement, wetted surface, and stability are quite similar to those on the Antrim 27, a boat of approximately half the waterline length. In effect, water ballast replaces crew weight on the rail. High stability allows for a big sail plan, which drives the ultra light hull at exhilarating speeds.

A comfortable crew will push the boat harder than one who is cold, tired, and miserable. Obviously comfort is a relative term here. We extended the lines of the house aft to form a rigid dodger, which will be a welcome feature both in cold weather and under the hot tropical sun. A small diesel heater will help in the cold climates, and seemed a justifiable addition to the tight fuel budget.

Designing a boat for the Vendee Globe is a privilege, a challenge, a thrill, and a responsibility. We thank Lucent for their support and Bob for his confidence; and look forward to greeting him at the finish line.

Contact Us

phone

4018 Archery Way
El Sobrante, CA 94803

(510) 223-9680

contact@antrimdesign.com