On Sunday, 12 April 2015 at 18:29:13 UTC+1, Carl wrote:

On 12/04/2015 09:00, [email protected] wrote:

And how's about a golf-ball-textured film.

Enough for a Friday!

Another question which has come to mind after watching the Boat Races - in proper headwind conditions, would the reduced diameter of the scull-like C2 skinny sweep shafts compared to more conventional diameter of either normal C2 or Croker sweep

blades have a noticeable effect on a crew?

In short, yes.

For a 5cm diameter cylinder transverse to a 10m/sec air flow, the
Reynolds number is about 450. At that point the drag coefficient for a smooth cylinder will have fallen almost to a plateau of around
1.2<Cd<1.4 & may rise only slightly as diameter, & hence Re, is reduced).

Since reduced diameter reduces frontal area, & since drag is
proportional to the product of frontal area times velocity squared,
slimmer oars should probably reduce wind drag, but not quite in direct proportion to the diameter reduction.

That said, it is within the range 50<Re<800 that you might expect the greatest benefit from fitting boundary layer trips as a means to
re-energise the surface flows & thus to reduce Cd by reattaching an otherwise separating boundary layer.

For the slimmer oar you must be sure that its bending and torsional stiffness remain within acceptable limits, but if the reality is that
you are outside the zone within which these become critical to your use
of the oar, then smaller diameter should be better.
Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
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Hi Carl,

I appreciate I am very late to the thread but I am currently doing some research on the topic and have a couple of enquiries.

If this finds you, please can you explain how you got these values for Reynolds numbers?

Transition from laminar to turbulent for a smooth cylinder happens at Reynolds numbers in the region of 200,000 (see Fundamentals of Fluid Mechanics, p501, http://civilcafe.weebly.com/uploads/2/8/9/8/28985467/fluid_mechanics.pdf). Personally, I
calculated the Reynolds number of the cylinder in conditions you described to be around 32,000, much higher than your value of 450. Some discussion on this would be great :)

Matt

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