by James Dreher (1/29/97)

New Blade Designs: The smooth face blade is being promoted by CII as something that may be better in performance than their current design. I would like to provide some information on a similar design Dreher Scull based on several years of trials with flatter shapes, various types of ridges, etc.

History of the Design - Flatter shape, smooth face, lip or "roof" blade, etc.:
Since 1989 Bob and Mike Dreher have tried just about every conceivable blade shape that can be imagined. The original Dreher blade shape came about because the CII Macon sculling blade had serious deficiencies that we had noticed from 1982 on. The blades were difficult to extract cleanly and were very pitch sensitive with a tendency to dive and then wash out with a characteristic "square root sign" trajectory relative to the best wood oars available at the time. We did not know why this was so at the time but it led Bob Dreher to come up with his own blade shape in 1988-89. After much video analysis and experimentation he produced a blade with a much flatter lengthwise profile but a wider and more rounded or cup shaped width for the blade. Tests of the speed advantage of these sculls were helped because of the technical rowing expertise of the designer and his brother Mike. Because they were technically very good lightweight rowers they could discern subtle differences in performance that might elude others. These Dreher design scull blades were much more stable in the water and released much cleaner than anything available at the time.

In 1989 Bob Dreher and Neil Fitch became the US lightweight double and finished 8th at The World Championships using these sculls. However comments from European coaches and builders were negative, typically saying that the sculls should have more curve, not less at the blade tip. In 1990 Bob and Steve Peterson used these sculls to win the World Championships in the Lightweight Double. U.S. scullers Greg Walker and Doug Burden used the sculls to finish fourth in the Open Double, and the U.S. Lightweight Men’s quad and Open Women’s quad also used the sculls at the World Championships.

With so much acceptance of the new Dreher blade shape in the US among the top scullers CII began trying modifications to their sculling blades by cutting out different outside shapes, without altering the basic contour of the blade, but the same problems inherent to the blade were unchanged - poor tracking and difficult extraction. Meanwhile Bob came up with a changeable length oar used by the 1991 Lightweight Double, Quad and Single. The quad finished 6th and the single sculler-Brian Sweener finished 5th at the World Championships. This acceptance by more and more of the top US scullers might be what helped drive CII to develop the BIG Blade in 1991-1992. Their problem was that their process for making blades while economical from a production standpoint was shape limiting because it consisted of a lamination of a PVC foam board core to composite glass and carbon/epoxy skins. This worked well in 2 dimensions, but anything but limited curves in three dimensions were difficult to produce. Dreher blades are molded to shape and final size using carbon and syntactic foam. This process has it’s own process problems, but it can make more complex 3-D shapes. (CII has recently switched to this process as a cost reduction). In contrast the CII sculling blade and the sweep blade were made from a mold with the same exact contours, only the outside perimeter was cut larger for the sweep. This is what compromised the CII Macon sculling blade. The sculling blade had almost the same length and curve at the tip as the sweep blade, but was much narrower.

The CII Macon sweep blade performed better but was probably a bit too small in surface area. We noticed that at the top levels only the best technical heavyweight crews could avoid white water, or ripping the oar through the water.

In summery: In 1991 the CII Macon sweep oar suffered from being a bit too small in surface area and the shape of the scull suffered by being too narrow relative to its length with too much curve at the end. Both problems were because the sweep and scull shared the same mold surface. Only the cut out shape differed. For CII it seems that the solution to the problem for the sweep oar was to go to the extreme width limit that the mold would allow which gave about a 20% increase in area for the sweep blade. This resulted in the unsymmetrical Big Blade. By proportioning the scull to make it similar it required cutting 6 cm from the tip of the CII Macon blade and widening from 17cm to 19.5cm and later to 21.5cm. This reduced the curve at the tip and increased the cleanness of the finish while the increased width stabilized the blade during the drive. By cutting the length and increasing the width CII made the performance of the CII big blade and the Dreher Macon roughly the same.

In tests conducted by CII with U.S. sculler Brian Sweener alternately using Dreher Macon shape oars and CII Big Blades, the Dreher Macons were showed to be about 3% better, but in tests using CII Macons versus their Big Blade with Peter Haining showed a 10% improvement with the Big Blade! The variables of these tests probably exceeded their accuracy, but it did show that CII big blades were probably as good as the Dreher Macon shape.

With almost complete acceptance of the new Big Blade shape at the top levels 1992-1993 was the last year that Macon shapes were used to any extent at World Championships. Brian Sweener was third and the US lightweight quad was fourth in 1992 World Championships using the Dreher Macon shape. The Italian lightweight quad won with Macon shapes, the other four in the final used Big Blades. In 1993 Cindy Ryder was 6th in The Open Single using the Dreher Macons.

This history has bearing on the new shapes being promoted, because of what was learned changing from the symetrical Macon shape to the big blade shape. I think that two things were learned. 1. Less curve at the tip led to a better release for the sculls. 2. The wider blade was more stable and less pitch sensitive for both sweep and sculling. For Macon shape sculls slippage was not a problem because two scull blades already had considerable more surface area than one sweep blade for the available force, but for sweeps - 20% more blade area led to less slip.

Since it seams clear that by going to a shorter and wider oar the CII blade improved its tracking performance and made for a cleaner extraction at the finish. In 1994 Bob Dreher decided to explore what the change to the curve of the blade in each direction had on the performance. He started with a perfectly flat rectangular Big Blade as a benchmark. Brady Gould was the test driver and the video tapes showed that he suddenly effected an extremely clean, effortless release! The flat blades showed that total elimination of the blade curve made the extraction much cleaner. However the blades went too deep because there was no effective blade shape or volume to provide buoyancy. Also there seemed to be some cavitation at the blade tip.

Final Steps in the evolution of the Dreher flat blade:
In 1995 Mike Dreher refined the flat blade shape a step further to a usable design by designing a blade that in the shaft direction had a slight curve at the tip but much less than current Big Blades. To give buoyancy Mike increased the size and changed the contour of the spline. The most important change had to do with the shape of the "chords" or design lines of curvature. They are not in line with the shaft as in the Macon and Big Blade shape, but are parallel with the flow of the water. This appears to be more important for the back than the front of the blade because the curve being parallel to the water surface does not affect the placement of the oar at the catch but does immediately provide "lift" similar to a wing on a plane. As the blade is submerged the configuration of the front of the blade determines the depth by providing buoyancy and pitch inclination.

The Dreher flat blade accomplishes this with a vertical curve of the blade that is not uniform. The blade face starts almost flat near the tip and then gradually tightens in radius to give the effect of a slight "roof" or lip near to the top. This progressive decrease in radius combined with the thickened spline near to the shaft attachment point limits the immersion depth and sets the pitch. This progressive change in radius and resulting increase in buoyancy assures a constant depth while preserving the clean release characteristic of the flat blade. In effect the blade enters as a flat plate and gradually becomes more positively pitched. The Dreher Flat Blade has been test rowed by Bob and Mike Dreher and other members of the Durham Boat Club at various regattas and trials for the past two years. It is unquestionably easier to extract at the finish. As to speed it is impossible to tell what improvement over the regular Big Blade shape there might be because the variables exceed the accuracy of the test. We are encouraged enough by the performance of this new "Flat" blade that we offer it as an alternative to the Dreher Big blade or Macon Shape. It is available on all Dreher sculls and other private branded oars made under contract by Durham Boat Company.

Others working on blade shape innovation:
Other designers such as Howard Croker, the Australian oar maker has had a flatter blade with very little spline since 1995. It seems to perform well and I think that flotation is probably accomplished by blade thickness. Igor Grinco had a Eastern European oar maker ad a "roof" to the top of his CII big blade sculls in 1995 and Hartmut Bushbacker had Resolute do the same last year to his sweeps. I believe both were trying to accomplish the same thing - to give a constant depth of immersion while reducing pitch to 3 degrees or less while maintaining a clean release. In 1991 Stampfli had a flat shape with no spline and a lip at the top that for one reason or another did not become accepted. Hudson also had a blade with no ridge on the blade face. Alden blades designed by Doug Martin had flatter, no spline shapes well before the event of the Big Blade shape. It is reported that the East German Sports Institute (FES) did investigations of the Martin shapes and found them promising at the time. I suspect that some or all of these designs did not find wide acceptance more for marketing reasons than lack of performance.

I would be interested in any information on discussion of similar shapes or experimentation done with flat type designs.