Great to see a thread on this topic. We've just set up a double for a crew that has two very different stroke lengths: 119cm and 133cm. The rigging has been set so that the oars enter and exit at the same time. To enable this, the oar gearing for the
shorter stroke length needs to be taller than that for the long stroke length.

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On 30/05/2021 03:38, Matt Croker wrote:

Great to see a thread on this topic. We've just set up a double for a crew that has two very different stroke lengths: 119cm and 133cm. The rigging has been set so that the oars enter and exit at the same time. To enable this, the oar gearing for the

shorter stroke length needs to be taller than that for the long stroke length.


It is, inevitably, complex.

We might examine this first on the basis of zero blade-slip, so that we
can forget the influence of blade load on stroke duration. That's not
such a bad idea as, ideally, the blade is so well engaged with the water
that there is no slip. But while zero slip would be good (it would
markedly increase the propulsive efficiency of the stroke), reality
tells us that there is quite a lot of blade slip around mid-stroke,
which is load dependent (& depth dependent) & thus affects stroke duration.

In a zero-slip case, both rowers could use the same rig & the shorter
one try to row longer or the taller one to row shorter. That would seem
to keep the stroke geometry & the flow (fluid dynamics) around the blade
in step, but the reality is that the bigger rower would generate more
blade slip, so finish slightly earlier, while the smaller one would be
tempted to shorten, or to pull harder & overload themselves.

If you try, instead, to match arcs by narrowing span & shortening
inboard for the shorter person, then they have a more severe gearing,
again reducing their blade slip & thus their endurance.

If, to keep the same stroke arcs, you narrow span _&_ oar dimensions in proportion to the smaller rower's range of hand movement, then their
stroke duration will be shorter than that of their partner, so the
bigger rower will be late on their finishes.

So I see no simple rigging solutions. As ever, while fitting a crew
together may be helped by matching statures, most of all it involves
selecting a bunch of disparates who are happy to make effective
compromises for the common good.

Cheers -
Carl

--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Find: tinyurl.com/2tqujf
Email: carl@carldouglasrowing.com Tel: +44(0)1932-570946 Fax: -563682
URLs: carldouglasrowing.com & now on Facebook @ CarlDouglasRacingShells

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Thanks for the comments Carl.

BTW: That's a great web site you have there. Beautiful boats.

I'd been wondering about slip and how it might alter the equation. Based on your comments, I'll do some digging and see what I can find on slip. It will no doubt change the gearing for the taller (stronger) rower more than the shorter one. I think I'll
be making an adjustment based on that - thanks.

So far, we've taken video of the results of the gearing adjustments and we're getting good results with regard to blades entering and exiting at the same time. As you noted, the arcs are vastly different and the ability of the light crew member to put
full load on is compromised.

The question comes down to which parameter gets the priority. We could match arc of travel, optimise gearing for each individual rower or match blade entry and exit. Unfortunately, we can only have one!

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Thanks Henry.

Preliminary feedback from the crew supports your comment. Despite a taller oar gearing (less inboard, longer oar) for the light crew member, the comment is that "compared to the single, it feels about the same".

On Monday, May 31, 2021 at 8:14:30 PM UTC+10, Henry Law wrote:

On Sun, 30 May 2021 21:42:24 -0700, Matt C wrote:

We could match arc of travel, optimise gearing for each individual rower
or match blade entry and exit

As a coach (not a rigging expert) I think I would opt for matching blade entry and exit, because getting those wrong affects balance (without
which nothing else can be optimised) and delays the application of power
for one of the rowers, so that "swing" cannot happen.

--
Henry Law n e w s @ l a w s h o u s e . o r g
Manchester, England

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On Tuesday, 1 June 2021 at 03:45:15 UTC+1, Matt C wrote:

Thanks Henry.

Preliminary feedback from the crew supports your comment. Despite a taller oar gearing (less inboard, longer oar) for the light crew member, the comment is that "compared to the single, it feels about the same".
On Monday, May 31, 2021 at 8:14:30 PM UTC+10, Henry Law wrote:

On Sun, 30 May 2021 21:42:24 -0700, Matt C wrote:

We could match arc of travel, optimise gearing for each individual rower or match blade entry and exit

As a coach (not a rigging expert) I think I would opt for matching blade entry and exit, because getting those wrong affects balance (without
which nothing else can be optimised) and delays the application of power for one of the rowers, so that "swing" cannot happen.

--
Henry Law n e w s @ l a w s h o u s e . o r g
Manchester, England

I started this thread in 2012. It reappears just as we are getting two 2x together for Henley Masters in 2021. This time my (G) 2x is a better physical match but we have a big size disparity in the E 2x.

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