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Brad Stephens


August 8th, 2007

Interview with Brad Stephens

Australian Brad Stephens was one of the principal developers of the D4 membrane system. He has worked in the area of sail design since 1975. We spoke with him on the subject of D4.

Question: It’s understandable that you are often the first to hear about the success of sails made with D4 membranes from DIMENSION-POLYANT. What’s the latest news?

Brad: Both as manufacturers and sailors we like to follow the use of our products closely. I have just returned from the Dubois and Superyacht Cup‘s held in Palma de Mallorca. Sailing on the Dubois 37m „Midnight“ we had a convincing win in the Dubois Cup using a set of sails manufactured with Taffeta/Taffeta Carbon/Vectran D4 membranes. Superyacht pursuit racing has it’s own unique relaxed style but we race and trim hard putting the sails to the test.

Question: It’s quite evident that more and more Open 60 teams are using D4 membranes in their sails. What’s caused this to occur?

Brad: I’d say that there are a number of reasons. Incidences Sailmakers have had a long and close relationship with the D4 product and have a very good understanding of it’s potential and are always very keen to push the boundaries at the Grand Prix level. They are putting a lot of effort into sail development in the class and we are responding with D4  development as our contribution to the success of all.

Consequently , the Open 60 clients of other sailmakers are requesting D4 membranes to be used as the basis for their sails. It’s very gratifying - really.

Question: What exactly makes D4 fast?

Brad: Above all else I think that the subtle change of yarn directions , both vertically and horizontally is a defining factor in D4. Angle changes between yarns are in the order of a fraction of a degree compared to sails made of conventional rolled goods or membrane products where the yarns are not laid in curves. This is a very important factor in how a sail loads, how the load is distributed and ultimately how the shape changes in use, even when the sail is new.

And with the D4 process we are able to carry those yarns directly into the corner as an integrated structure for superior load carrying. With a D4 membrane the external corner patching is simply protective unlike some of our competitors who must apply extensive external patching to adequately address corner loads.

In fact, at the Grand Prix level a number of our sailmaker clients do not even use the standard D4 external patching only applying the necessary minimal polyester patching to attach corner webbing. It’s not something that we would recommend for every sail but it show’s what is possible with the D4 system from DIMENSION-POLYANT.

Question: What was the critical sail design step in the development of D4 and what advancements can we look forward to?

Brad: One of the critical design steps happened well before we started the development process for D4. Using modern warp orientated laminates it’s very important to re-orientate the material to the direction of the loads in the sail. This essentially means that there will be a number of horizontal sail sections within which this warp orientated material is aligned to the local loads.

Beyond that we where very comfortable with and had a preference for horizontal shaping of sails rather than shaped radials in working sails.

We did studies investigating exactly how many seams were required to provide the final 3 dimensional shape beyond which additional joins presented the possibility of reduced accuracy and additional labour in sail assembley!

When it came time to consider the alternative production methods for the D4 process we already knew that the required 3 dimensional shape could be achieved with a relatively small number of seams and effectively replaced the orientated conventional laminates in each section with custom load orientated yarns.

Looking forward I believe that one of the most important area’s of D4 design we are working on is the optimisation of the yarn structure. Consider the America’s Cup where we supplied membranes to the sailmakers for the China Team and all the rest where from a single source. Those other teams all used very different yarn layouts to each other even though they where all using the same design tools!

So, we have started down this long road and currently have both mechanical engineers and material scientists working within DIMENSION-POLYANT to develop the tools and determine complex material properties necessary to feed into this optimisation process.

Question: D4 seems a very important product for the racing market but what’s happened in the cruising scene?

Brad: Actually , when we developed D4 we always considered the cruising market as a very important sector that we believed would be well served by the possibilities of the D4 system.

Reef yarn arrays that make a reefed D4 mainsail essentially a smaller version of the full size sail and double taffeta constructions are two area’s that provide superior longevity for cruising sails.

Question: Ok, so which cruisers should use D4?

Brad: For a start , the bigger the cruising boat the more significant the advantages of the D4 system become and any large cruiser that’s going to spend significant time reefed should consider D4.

Question: How well do sails made with D4 membranes last?

Brad: I think that it’s well understood by sailors now that a well made sail using the appropriate woven polyester will outlast anything else structurally. But , it will be heavier , change shape faster and ultimately is a poor choice ( class rules aside ) if you want to win a race.

Structurally a well made sail using either DIMENSION-POLYANT’s rolled goods laminates or D4 membranes should have a similar life expectancy with similar use. I do believe and my experience is that a sail produced from a D4 membrane will hold it’s shape better and longer then a sail made from conventional rolled goods laminates.

Question: How has D4 changed the work of a sail designer? Previously they designed panel layouts and now they have to consider yarn maps.

Brad: Well, in many respects it’s the same job. Modern paneled sails make use of orientated materials that to be used effectively must be orientated to address the loads in a sail. But that only involves the issue of a relativley limited number of panels in a sail.

However, with a D4 membrane there are typically kilometer’s of yarn that can be individually orientated by the mm to address the loads in a sail.

This is where the expertise of DIMENSION-POLYANT’s design staff come to the fore taking the sail designers panel geometry and applying a uniques set of tools and experience to provide a custom yarn layout for every membrane.

However, sail designers like to be creative and as it’s our goal to be the industries prefered supplier of membrane product we work closely with the sailmakers to incorporate their special individual requirements and additionally a limited number of pre-qualified sailmakers supply their own yarn maps.

Question: The D4 membrane sails of DIMENSION-POLYANT are custom made to order from the start. As such , why do they not replace conventional laminated sailcloth’s faster?

Brad: As you say, D4 is a custom made product. That means we cannot commence production before the sailmaker has taken the order and designed the sail and demand means that there is generally a production queue even if we work constantly on minimizing this!

Consequently, if a sailor decides that he must have a new laminate sail in a time less then our production queue then DIMENSION-POLYANT has a substantial range of superior laminate sailcloth that’s ideal for a sailmaker to turn into that sail.

Finally, there is a price issue. As a custom product in which we manufacture a membrane for a specific sail on a specific yacht it is more expensive compared to making conventional rolled goods laminate for inventory.

Question: Well then , please tell us something about the prices of D4 in comparison to sails made from conventional sailcloth. For example, how much more can an owner of a 40ft/12m Cruiser-Racer expect to pay for D4?

Brad: Good question ! If we take DIMENSION-POLYANT’s GPL product line as a comparison then a sailmaker should be able to produce a film/film carbon sail using D4 at a 10~20% premium above the GPL sail.

The D4 membrane is more expensive for the sailmaker to buy but there is a lot less work for him to turn it into a complete sail.

Question: You have been working on D4 for more then 10 years now. How did this all start?

Brad: In 1994 our sail loft had the sails on all three Australian team members in that year’s Kenwood Cup ( International Ocean Racing Series ) held in Hawaii. The USA team won and for various reasons our team did not perform that well.

What stood out at the end of that regatta was that North Sails , with their 3DL sails had managed to produce a product that differentiated themselves from every other sailmaker.

The following year at the Admiral’s Cup we observed the dominant effect of that previous observation and it was quite clear that we needed to respond.

Whilst some suggested that we “give up“ we took this as a challenge and thus started the development process that became D4.

Question: DIMENSION-POLYANT, the largest manufacturer of sailcloth purchased the know how of D4. Has this resulted in a faster development of D4?

Brad: Prior to DIMENSION-POLYANT purchasing this know how we had already recognized that the future development of D4 needed the resources of a company such as DIMENSION-POLYANT.

Since the acquisition to address the increased demand and improve efficiency we have upgraded the production faciltiy in Australia. Further more we have set up a second production facility at DIMENSION-POLYANT’s headquaters in Germany.

At the product level there are a number of innovations we are working on in the area’s of adhesives and fibres that are in final testing. These product innovations are in use on the water undergoing evaluation from sailors and sailmakers alike.

So, yes , the acquisition has provided the resources absolutely necessary for and is resulting in faster (but proven) development of D4.

Thank you for the news Brad.