>>> Maybe now is a good time to jump into the conversation. Regarding
>>> modelling the rowing stroke - specifically the hydrodynamic character
>>> of the blade in the water - I have done quite a bit of work, and
>>> recently put together a website to display (most of) it.
>>> https://sites.google.com/site/surgingforwardrowing/ Without getting
>>> into too many specific details of the flow, or directly answering any
>>> of the above posed questions, I'm confident that this research can
>>> effectively be coupled with higher-level boat modelling and rower
>>> biomechanic modelling to design a comprehensive rower-oar-boat
>>> system. So if there is a desire to collaborate on such a model, or if
>>> anyone has any questions related to the topic, don't be a stranger.
>>> I'll apologize in advance if the response is delayed... the lack of
>>> funds available to work on rowing research full time means I'm
>>> generally busy with other work commitments Andrew
>> An interesting site, thanks for creating and sharing it! At the risk
>> of thread jacking however there are some parts I am unsure about and
>> would like clarifying, mostly on the pages talking about blade shape
>> and blade efficency on this page
>> Now although I agree with the fact that it is possible to design a
>> blade that is more efficient that another (using the amount of slip of
>> the blade as a measure of its efficiency) like concept have done with
>> the big blade, I struggle with the connection between the more
>> efficient blade being the faster blade, especially an absolute value
>> of 1% or 2 seconds
>> The issue I have is that I see boat speed being a combination on the
>> force the rower is able to apply, and the way that the rower applies
>> that force (and how the boat/blades accelerate in response to this
>> force). If you run the assumption that the rower has a finite amount
>> of force they can apply, then to me it seems the more efficient the
>> blade the slower the rower would be able to accelerate the boat past
>> the blades connection with the water (as a rower would say it "feels"
>> heavier), which means a reduced acceleration of the boat which means a
>> slower overall boat.
>> Yes you can correct the "heavy" feeling by making the blade outboard
>> shorter but then if that is the solution then why cant you just make
>> the standard smoothie blade shaft longer in response to its reduced
>> efficncy compared to the fat smoothie
>> Unfortunatly ive not really seen a discussion which has clarified this
>> for me which makes me think more that focusing on boat shape is a more
>> effective focus that on blade shape, especially if a rower has a
>> "favourite" shape or type of blade already and the fastest gearing for
>> them is found from testing
> Let me add a few thoughts here:
> 1. Force does is not the only consideration since force alone does not
> move the boat. What does move the boat is Work, which is Force x
> Distance (through which that force application travels.
> 2. The force on the blade is the force that _you_ apply (mediated by
> the leverage of the system). The water around the blade only reacts by
> delivering an equivalent opposing force.
> 3. The work done is the maximum work available to move the boat. Sadly,
> a fair chunk of the work you do gets wasted/dissipated. When this
> happens it is lost from the propulsive process and diverted into moving
> & stirring up water, plus entraining air into the water. This wasted
> energy in part creates the puddle. The puddle is a monument to the work
> which did _not_ move the boat.
> 4. You can like the puddle, the moving of chunks of water & the
> sternwards slip of the blade to wheel-spin & tyre smoke in a car making
> a hasty getaway - it's a dead loss.
> 5. When we discuss blade or propulsive efficiency we are not talking
> about Force; we are discussing how much of the Work (= Force x Distance)
> that we put into the stroke ends up actually moving the boat - what's
> left after the wasted work (puddle, etc) has been taken away. We
> express that as a percentage: 70% propulsive efficiency means that 30%
> of the work we put in simply went to waste.
> 6. Better propulsive efficiency is one big area, largely ignored, where
> rowers have the greatest potential to go faster - did they but know how
> to achieve it.
> Which brings me to a point which I believe Andrew has looked into at the
> suggestion of others, and on which he had some interesting preliminary
> results a while back (so I believe?):
> What he seems not to address in that link, while looking closely at
> blade shapes (which might be a rather secondary element in the overall
> business of blade efficiency) is the Z-axis of the stroke - the vertical
> My own experiments, rational engineering argument, feedback from
> thoughtful scullers, observation of champion scullers' techniques &, I
> believe, some work done by Andrew (but I'm open to correction) confirm
> the how deep you row your blade makes a really significant difference to
> overall propulsive efficiency. Put simply (& I have done this here a
> few times!) somewhat deeper than is generally promoted is somewhat more
> propulsively efficient.
> In short, the rowing stroke is not 7 should not be treated as a
> pre-ordained 2-D process with the 3rd dimension conveniently eliminated
> from what we do & discuss by application of a widespread & dogmatic "no
> deeper than this" rule.
> Why is deeper better?
> 1. Because a deeper blade is entirely surrounded by water.
> 2. So you do not therefore entrain air behind the blade to disrupt the
> essential tensile connection between blade & water & increase wasteful
> slip & puddle-making.
> 3. It feels "heavier" - the obvious consequence of reduced slip causing
> it to take longer to complete the stroke, & your impatience encouraging
> you to pull harder, thus _making_ it harder, instead of pulling normally
> & allowing the stroke to finish naturally in a slightly longer time period.
> 4. Unless you go _very_ deep (I wouldn't want to quantify that here,
> please), you don't incur relevant countervailing losses due to looming -
> the loom is thin, has a relatively low drag coefficient, is at worst not
> moving fast through the water & at times any immersed portion may well
> be moving astern.
> Let's see what that brings :)
> Cheers -
5. If you properly bury the top of the blade you add considerably to the
length of blade edge now subject to shear forces, thus improving
"connection" & reducing slip
6. Standard experiments going back many years confirm that fluid drag on
partially to wholly immersed plates increases with depth as they go
further below the surface.
None of this should be in the least bit surprising. But still those who
row deep get told "it's wrong".