The paper describes innovations in blade design by Durham Boat Company, Inc. since January of 1999. We have just completed two blade design changes.

The Next Generation of blade shapes – The APEX since “New Blade Shapes – Part II” was issued in January of 1999, which are as follows:

 

• The APEX Sweep Blade design was completed in the October with production release date in November of 1999;

 

• The APEX Sculling Blade design was completed in November 1999 with a production release date of December 1999.

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Following are a discussion of the APEX blade designs.:

The Dreher APEX blade shape is a result of attempts over the past three years to improve excellently performing blade shapes – the Dreher BB2198 scull blade shape and the BB5597 sweep blade shape. Customers had frequently asked us if we would offer a smooth faced blade comparable to the “Smoothie” by CII. Our answer was that if we could show any performance advantage over what we currently offer we would. However, all our speed tests showed that our existing blades performed better than the our competition’s blades. Our observation that the CII Smoothie became even a greater liability as the water conditions became more challenging and that very few top level sweep rowers were using the blades in any important competitions. We thought CII had come up with a great name for their product, but the product’s design did not exactly match the theory.

The theory of a smooth faced blade being less disturbing to the flow of water over the concave face of the blade seemed to us to be in direct contradiction to basic hydrodynamic theory. Potential gains in hydrodynamic lift could be achieved if the convex back, is freed of impediments to the smooth flow of water in the direction of flow. It is not the front, but the back of the blade with its longer curved surface that accelerates the water flow and should provide a lifting force as the blade traverses out to the 90 degree stall position and back again during each stroke. By making the back surface “smooth” with the spine, or shaft attaching ridge parallel to the water flow, the blade should be more efficient and easier handling.

The APEX shape is very similar to our current blade shapes with all the chord lines parallel to the flow of the water. What we have done is to move the attachment spine to the top (i.e., the APEX) of the blade on both the front and back parallel to the direction of water flow as the blade traverses out and back from the boat. The spine was changed to a smooth contour and the volume determined to effect a displacement just enough to give the correct buoyancy. The comparison tests on successive generations of test prototypes using the current production blades as the control as well as CII’s oars. As a result of favorable prelimanary testing results and observations of the testers relative to the ease of the blade handling relative to previous designs, we went ahead with the expense of making permanent tooling.

Since the new APEX oars have begun to be shipped to customers in mid-December, we are pleased to announce that we have already received repeat orders from people still able to row.

The APEX Sculling blade shape will be offered as an option to the popular BB2198 (Big Blade) and LS1999 (Large Symmetrical) sculling blades. The APEX blades exhibit no unusual tendencies. You can replace existing sculls and sweeps with APEX oars without changing pitch and adjust to the new oars quickly. They are very stable and stay at a constant height during the drive. The release is the best we have seen. The ease with which these sculls can be rowed “oars squared” with full pressure really shows the benefit of eliminating all obstructions to flow on the backside of the blade.

by James Dreher (01/01/00)