Re: How I decided which new sculls to purchase

Edgar wrote:
"Carl Douglas" <carl@xxxxxxxxxxxxxxxxx> wrote in message news:g23utp$n3h$1$8300dec7@xxxxxxxxxxxxxxxx
...
> You have a limited amount of time in which to apply the finite quantity
of work that you can afford to invest in each stroke & still reach the end of the race precisely spent. Your return on investment is lowest in the mid-stroke phase & highest towards the 2 ends.

As I understand what has been said in respect of this matter, and neglecting what _feels_ comfortable, the stroke can be broken down as follows:-
Beginning of stroke (catch)-most efficient
Middle of stroke-most inefficient
End of stroke (finish)-efficient, but less so than at the catch.

If this analysis is accepted it surely makes no sense to store energy by bending the oar/scull during the most efficient part of the stroke only to release said energy during a less efficient part later.
In other words, the stiffer the better so that you use the available energy immediately during the most efficient phase.
If this is accepted it would seem to follow that by selecting a more flexible oar one is sacrificing efficiency for comfort.


Edgar -
I like your very crisp analysis, & the further contributions from Richard & Kieran. All very much to the point.

The blade is highly elastic, Richard (low hysteresis, doesn't dissipate energy, high coefficient of restitution, whatever) so it is an efficient energy store. No losses there of energy (or work per stroke). Because the process of energy storage requires flexure, that must slightly delay the application of force to the blade during the first part of the stroke, which does seem undesirable. OTOH, that only matters if the rower could accept more abrupt loading without loss of performance. And this slight delay of load increase as work is absorbed by teh shaft really is like a form of gearing. Do we know the answers? Well, very soft shafts would clearly not be a great idea, so for the catch phase, where load increases as blade efficiency falls, maybe flexibility is not greatly needed.

However, at the catch a more flexible blade will undergo a much larger change of AoA between blade & water with increase of load. It's too late tonight to think whether that is a good or a bad thing, but it's well worth considering.

How about the finish phase? In reality (despite what gets said to the contrary) the speed of the hands, & the rate of rotation of the oar about the pin, must & do slow down as the angle of blade to boat axis tightens. In human terms that's because every part of the motion is nearing the end of its range so must slow down. But the body doesn't lose the ability to hold against a load in the process. So the energy return there must be useful. Perhaps there is a large element of swings & roundabouts involved?

Cheers -
Carl

PS I think Richard was restating Sod's Law, but redefined in other terms. But Sod's (or Murphy's) law is perhaps the cornerstone of all engineering.
C



--
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