RIGGING FOR LARGE DIFFERENCE IN CREW SIZE

[Brian Chapman]

We are about to put a masters double together with the aim of going to Duisburg. We have quite different heights, and of course weight. Do we rig bow and stroke for the size of each athlete and have possible different spans and gearing or rig a compromise that suits us both?

[Teaplant]

On Apr 9, 7:44 pm, Brian Chapman <jbc8...@gmail.com> wrote:
> We are about to put a masters double together with the aim of going to Duisburg. We have quite different heights, and of course weight. Do we rig bow and stroke for the size of each athlete and have possible different spans and gearing or rig a compromise that suits us both?

in my humble opinion:

rig differently to achieve similar arc lengths. This will usually
meaning gearing the smaller man more heavily (inboard shorter, bring
the span in) than the big guy. It depends on many factors as well as
size, of course, like rowing style and flexibility. It is tempting
to give the big man more work to do with a stiffer rig, but this will
severely limit how much the small man can achieve. The small man's
heavy rig will be compensated by the fact he has a 7ft gorilla
helping him along - with none of the timing/rhythm issues caused by
different arc lengths. If both men (or women) feel that they connect
and release together, with some resistance to work against in between,
then you have a winning solution.

same goes for swivel heights - rig individually so you can each row
your best arc. Big guy likely to need more height than the small
guy.

Fingers-crossed you both scull left-over-right....

Standing-by for contradiction...
teaplant.

[Carl]

Nothing to contradict there - you're very much on the money.

Keeping it simple, arc lengths (how do you measure these?) matter less
than a rig which, as you say later, results in equal stroke durations
for your disparate crew. Nothing worse than one guy being left in the
water at the finish.

And remember that you can't materially change stroke duration by pulling
harder (unless also on the edge of washing out, which is pointless).

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: http://tinyurl.com/2tqujf
Email: ca...@carldouglas.co.uk Tel: +44(0)1932-570946 Fax: -563682
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)

[Teaplant]

> Keeping it simple, arc lengths (how do you measure these?) matter less
> than a rig which, as you say later, results in equal stroke durations
> for your disparate crew.  Nothing worse than one guy being left in the
> water at the finish.
>
> And remember that you can't materially change stroke duration by pulling
> harder (unless also on the edge of washing out, which is pointless).
>

I would go so far as to say that similar arc lengths would more-or-
less demand similar stroke durations - given that during the stroke
the swivels of both oars remain separated by a constant distance, as
do the spoons of the oars. the parallelogram (if rigged correctly)
made by the outboard sections of the oars connected by the spoon-spoon
and swivel-swivel lines remains a parallelogram throughout the stroke
(without washing out etc). Not sure I agree that the arc length
matters less than stroke duration - I would not distinguish between
the two in terms of importance! It's like saying work done (force x
distance or torque x angle) is no less important that momentum
transfer (force x time).

arc length is probably the wrong phrase - what I mean is that the oars
(on same side of boat obv.) are parallel at both catch and finish -
which would necessitate a shorter inboard and narrower span for an
athlete with less stature/flexibility/reach/layback...

Good luck to Mr Chapman in Duisburg.
teaplant.

[Carl]

It's a bit more complicated than it might seem. Arc length alone
doesn't guarantee equal stroke durations, nor does arc angle. It
depends, inter alia, on outboard length & spread & on where said arc is
centred. The blade moves through its arc much slower at either end of
that arc, particularly at the catch (where the angle is most acute & the
boat is moving slowest). So it might be a better solution to give the
smaller person shorter sticks & a wider arc angle, but as you say it
also depends so much on physique factors affecting length which are not
directly related to stature.

That's why I prefer the frankly empirical approach with the final
objective of catch & finish being in time. It's also quite quick easy
to get there with a few modest observations & adjustments to the usual
parameters of stretcher position, blade inboard & outboard & spread. It
side-steps perhaps unwarranted geometrical assumptions & should give the
crew a good outcome in a shorter time. They need also to work within
the adjustment ranges of the boat & rigging - this may mean adjustments
by both towards each other's capabilities rather than one guy adjusting
towards the other - & the "perfect rig" rule books going straight out of
the window.

We seek the same objective, but these guys need to be wary of placing
trust in supposedly simple geometry when, as in the sculling stroke,
effective gearing varies so rapidly through that stroke. But I'm sure
they'll sort it out between them - unless they are now completely confused!

[magnus....@gmail.com]

I would add too that equal arc-lengths, as apparent from someone standing on a bridge observing from a distance, does not necessarily guarantee that each sculler is having the same experience, especially if they are of very different strength or power.
Even with equal arc-lengths, the stronger sculler's scull will bend more than the weaker one's, which means that the angle the blade-face makes with the water will be different at most points of the stroke. Ensuring the blade entries and exits are simultaneous, as suggested by Carl, will mean that these angular mismatches will more or less compensate for each other through the stroke, but they likely will not be the same angles at the same times.
Another way to mitigate this effect, with the explicit aim of trying to maintain more equal blade-face angles throughout the stroke, would be to give the weaker sculler a more bendy set of sculls.
Cheers, Magnus

[Matt Croker]

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.

[carl]

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: ca...@carldouglasrowing.com Tel: +44(0)1932-570946 Fax: -563682
URLs: carldouglasrowing.com & now on Facebook @ CarlDouglasRacingShells

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[Matt C]

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!

[Henry Law]

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

[Matt C]

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".

[Brian Chapman]

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.