Increasing span and catch angles
Tink
I've been thinking about rigging, particularly the effect of
increasing the span on catch angles.
I have an inboard of 90cm on my sculls and a span of 160cm, I started
assuming a catch angle of 60 deg (line of work -> oar shaft or 30 deg
oar shaft -> saxboard).
I have tried to precede the conclusions with *** so you can read those
sentances if not interested in my workings.
I can draw a right angle triangle, with the hypotenuse of 90cm, and an
angle of oar to boat side of 30 deg. Using trigonometry I calculate
the distance between the pin and a line from the oar handle parallel
to the boat to be 45cm (Sin30 * 90). If I then take the same
hypotenuese of 90cm (i.e. inboard the same), but change the distance I
calculated above from 45cm to 46cm (I.e. moving each pin out by 1cm
from existing position) I can then recalculate the catch angle. So
using trig again, I can calculate the angle as 30.74 deg (sin-1
46/90).
*** So I get that for an existing catch angle of 60deg, increasing the
span by 2cm (moving each pin from existing position by 1cm) loses me
0.74 degrees of catch angle, which doesn't seem an awful lot.
Similar calculations with a starting catch angle of 70 degrees
(further catch) gives a change of 0.68 degrees for moving each pin
1cm, starting catch angle of 50 degrees gives a change of 0.84 degrees
for moving each pin 1cm and an angle of 40 degrees (short catch) gives
a change of 1.00 degrees. So moving the pin out has less of an affect
if you already catch long.
I note that this assumes the handle is the same distance from the
centre of the boat as you change span. Drawing it, this wouldn't
necessarily be the case, as the arm follows an arc around the
shoulder, but it would if we increase the inboard by 1cm. Which is
what I was thinking about doing anyway - increasing span so I can
increase inboard and keep same overlap.
I then started thinking, how would this loss of angle affect my
speed. If I assume a catch angle of 60 degrees, and a finish of 40
degrees (as we have done the calculations for 40 degrees above) we can
approximately calculate the distance between the start and finish
using trig again (sine angle * outboard).
*** For an outboard of 200cm we lose 1.31cm forward of the pin and
2.69cm behind the pin (4.00cm in total). I actually use Concept2
Fat2s, so have an outboard of 190cm, which loses 1.24cm forward of the
pin and 2.56cm behind the pin (3.8cm in total). This shows that we
actually lose more length at the finish rather than the catch when we
increase the span. Which is the opposite of what I thought.
This approximation holds true if we don't move the feet and don't get
a longer finish due to the increased span (which would hold if we
increase the inboard by the same as we moved each pin as I mention
above). I haven't thought about whether the amount of speed generated
during the drive would be the same, I suspect not but have assumed it
is for ease of calculations.
If we lose 3.8cm per stroke then I can work out how much this is in a
race. If I assume 30 strokes per minute. For a 2km race completed in
7minutes 30seconds we take 225 strokes, so losing 3.8cm per stroke
means we lose 855cm (8.55m) over the race - which at that speed is
1.92 seconds. For a 5km race completed in 20minutes we take 600
strokes, losing 2280cm (22.8m) over the race - at that speed it is
5.47s.
I guess the point of increasing the span is that it makes it less
difficult - it reduces the stroke length, and enables you to increase
the inboard whilst maintaining your comfortable overlap (which is an
easier gearing if the outboard is kept constant).
Using the distances for the stroke length I calculated above, from
which I calculated the distance lost per stroke, I can calculate the
increase in stroke rate required to make up for the lost distance per
stroke. I calculated the stroke length (approx distance from catch
point to finish point) as 282.88m (doesn't include distance travelled
on recovery), so it means I need to take one extra stroke every 74.4
strokes (282.88cm / 3.8cm) to cancel out the distance lost. Which is
an increase of stroke rate from 30 to 30.4 (75.4/(74.4/30)).
*** By increasing the span by 2cm (moving each pin by 1cm) and
increasing the inboard by 1cm, I have to increase the rate by 1.33%
(from 30 to 30.4) to maintain the same speed. Hopefully possible by
having an easier gearing.
All this has come about, as I have my oars as short as they will go,
yet it still feels a little heavy and I'm struggling to get the rate
up. So my solution is to increase the span and inboard to make the
gearing easier - and there is no point me doing it if I don't go any
faster.
Tink
Following on from my original post theme...
I was looking at increasing the span as a way to allow me to increase
the inboard and hence have a lighter gearing. I wondered what would
be the case if I was to maintain the gearing - increase the outboard
correspondingly to increasing the inboard.
I previsouly calculated that if I increased the span by 2cm (moving
each pin 1cm) I lost 0.74 degrees of catch angle (with existing angle
of 60 degrees) and 1.00 degrees of finish angle (with an existing
angle of 40 degrees).
I use a 90cm inboard/200cm outboard at 160cm span as the original, and
adjust an oar to 91cm inboard at 162cm span with appropriate
outboard. If I use the definition of gearing as inboard/outboard, the
for the original oar it is 0.45 (90/200). Which means the outboard
for the increase inboard/span oar is 202.22cm (91/(90/200).
For simplicity I'm using stroke length as my previous post, the
distance between catch and finish positions of the oar. The stroke
length I get for the 90/200/160 set-up (using angles 60/40) is
301.76cm. The stroke length I get for the 91/202.22/162 set-up (using
reduced angles 59.26/39) is 301.07cm. A wider span is shorter by
0.69cm.
So increasing the span by 2cm (1cm per pin), inboard by 1cm and
outboard to match the gearing, I get an decrease of distance per
stroke of 0.69cm. Which is 1.55m over 2km (at rate 30) or 0.35s.
Tinus
I didn't check your numbers but generally, a decrease of distance per
stroke of 0.69cm does not equal 1.55m over 2km because the stroke rate
shouldn't be considered constant.
If you change gearing such that the stroke length decreases then you
should be able to increase stroke frequency at a similar rate (first
order) such that both together result in zero effect on boat speed. It
are second order effects which determine whether or not the shorter
distance per stroke is bad or not.
Bad side effects would be: less use of lift force, larger blade slip
due to higher blade forces, and higher ratio of (useless) time spend
performing catch and release. Positive effect would be a
(physiological) better stroke pattern due to higher handle speed.
Without special measurement devices you can only determine these
effects by trial and error.
SwissSculler
flawed as that you assume your arms are gonna get longer or
something... BTW your gearing is heavier than Mahe Drysdale's for
example.
You have to shorten your outboard in order to lighten the load while
not changing your inboard or span.
If you go to roughly 89/288/160 it should be about the same gearing.
The next step is to go towards 88/286 - in that case you also got less
cross-over which will help with the hands for rate.
Carl Douglas
I can't quite see the linkages you are including in your analysis.
Are you including the width between shoulder joints, & then adding on
arms of defined length? If so, what are these dimensions? Only then
can we start to review your deductions.
Does your model adjust your catch angles by moving your work
position/stretcher position? In which case, are you considering how
this may affect finish angles?
Next: stroke length is not of itself a meaningful parameter. The
gearing changes so greatly between catch & midstroke. The result of
this hardening of gearing at the ends of the stroke is that your boat
moves a lot further for the 1st degree of rotation after the catch than
it does for the 1 degree centred about the mid-stroke, & if you lengthen
the catch it moves further still. Note, too, that for that 1st degree
of movement your hands will also move very little towards the bow. And
that, as a direct consequence, the blades actually move forwards through
the water for much of the 1st part of each stroke.
And, since propulsive efficiency of blade in water is much higher at
catch than mid-stroke, yet again these simple models can yield only
preliminary information
None of which gives the slightest reason not to explore these effects,
but these considerations do warn against jumping to too many conclusions
from this kind of modelling.
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)
Tink
>
> - Show quoted text -
I think that in the middle part (and majority) of the race the stroke
rate could be considered constant, and so for a first assumption it
could be fairly useful. So I assumed 30 strokes over 2km, taking
7min30s means 225 strokes – so 0.69cm * 225 gives the 1.55m stated.
The obvious flaw in my estimation I saw was that I assumed that the
distance travelled per stroke during the recovery was the same as the
stroke length was reduced, so only the reduction in stroke length
contributed to the slower boat speed. I’m pretty sure this isn’t the
case, which would mean that the difference would be greater than the
1.55m calculated.
I agree that if we stroke length, we need to compensate this with
increased stroke rate – my back-of-the envelope calculations was a way
to me to gauge by how much. It gave me an increase of 1.33% (rate 30
to 30.4) for a 1cm span increase (160cm to 162cm). I’ve not much of a
feel at the moment if this seems about right.
It seems you can think of more negatives than positives of increasing
the span, which is why I’ve been hesitant to try it (see my problem in
the reply to SwissSculler about why I’m think about this route).
My conclusion from all this was that it would be better to aim for a
good catch angle, adjusting your settings such that you obtain this
(feet, span, inboard), then setting an outboard to give you a good
gearing. Which I think is common sense, and something I already
assumed.
Tink
I agree that there is something missing regarding the inboard – in my
calculations I increased the span by 2cm (1cm on each pin) and then
increased the inboard by 1cm. I started with an angle of 60 deg, and
a inboard of 90cm and calculated the x distance from pin to handle
(which happened to work out as 45cm). Then added 1cm to the x
direction and re-calculated the angle – this was my reduced catch
angle.
Drawing it this doesn’t quite put the handle in the same place on the
plot – same x direction (along line of work), but a y direction of
0.59cm less (0.59cm towards bow). So I don’t think I am massively out
on this point, I used trig rather than curves as we should. The new
handle position might not be on the curve, but could be made with
different body learn, grip in hands, shoulder position… I would
imagine.
Thankyou for talking rig numbers, could we go a little further into my
problem which started all this?
My problem is that I currently have a rig of:
Inboard: 90cm
Outboard: 190cm (280cm overall length)
Span of 160cm.
I am using the big new Fat2 C2 blades, hence the shorter than normal
outboards.
I am struggling to increase the rating.
My thoughts were to ease the gearing to allow me to increase the
rate. Normally I would just decrease the outboard, but my oars are as
short as they will go. So I thought if I increased the span to 162cm,
and increased the inboard to 91cm it would make the gearing easier by
virtue of easer lever and shorter stroke. My hope that I could then
increase the rate to cope with the loss of distance travelled. My
rough calculations were to see if it would be worth it.
I would like to reduce the inboard, but that would mean increasing the
outboard, which would then increase the gearing, and I thought
counterproductive to what I wanted. I should probably do a session
trying different combinations of inboard/span/outboard.
What would you suggest I do? (apart from getting some new oars!)
Tink
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)- Hide quoted text -
>
> - Show quoted text -
I haven’t included anything about the body. I started with my current
rig (90cm inboard, 160cm span) and a first guess was that my catch
angle could be 60 degrees. I made a right angle triangle with hyp
90cm and angle 60 deg, then calculated the x distance from pin to
handle (which happened to work out as 45cm). Then added 1cm to the x
direction and re-calculated the angle – this was my reduced catch
angle.
Drawing it this doesn’t quite put the handle in the same place on the
plot – same x direction (along line of work), but a y direction of
0.59cm less (0.59cm towards bow). So I don’t think I am massively out
on this point, I used trig rather than curves as we should. The new
handle position might not be on the curve, but could be made with
different body learn, grip in hands, shoulder position… I would
imagine.
I assumed keeping the feet position constant, as I thought otherwise I
really do need to consider arm radius etc…
I think the same assumption that stroke length, although easy for me
to calculate with trigonometry, is not the complete picture when it
comes to contributing factors affecting boat speed. It misses so many
other things as you and Tinus have mentioned – ones not so easy to
work out.
I calculated it only for my specific case, my measurements, rather
than a general one, so needs to be read in context. I don’t think I
stated clearly that I know my estimation has many flaws, but I thought
I would continue it through to see where it went. After I had put in
all the effort, thought I might as well share.
Walter Martindale
If you're conventional, and measure inboard to the outside part of
your button/collar, you've actually got 92 cm of lever between you and
the centreline of the pin - remember that most gates are 4 cm wide on
their working face, and you've got to add that to the inboard on your
blade if you're doing the trig.
this, to me, is a very long inboard, leading to 24 cm of cross-over
for the handles. May I suggest that this will a) limit the length of
your catch oar-angle, largely because you have to have your stretchers
positioned to let your handles get to the "finish"; and b) unless you
are very tall, I suspect you may end up bending your lower back a
bunch because of the length of your inboards.
I'm a proponent of "inboard = spread/2+8" (cm) as a starting point,
which gives most people 20 cm of cross-over (8+8+2+2), or near enough
to 20 that it doesn't matter, really. That allows you to move your
feet a little more aft, which allows you to have a longer reach aft
with the handles, and allows you to get a longer catch angle. If you
then move your gates in and keep the same spread:inboard ratio to give
you the same cross over, you'll get significantly greater angles at
the catch where it's important, but you'll need to shorten the OAL of
the blades to give you a reasonable gearing.
My $0.02.
Walter
Zbigniew A.
> Just thought I'd share some workings.
>
> I've been thinking about rigging, particularly the effect of
> increasing the span on catch angles.
Been there, done that.
I mean, i was *exactly* on the same course of thinking a while ago, most
of the 2009 season. And it turned to be wrong.
I started the season with more or less conventional rigging. But it was
sooooooo... heavy, it was so hard to keep a decent cadence. So i wanted
to make it easier.
I started with trigonometric calculations. When i realized that way too
many years have passed since my school years, i took a scissors,
cardboard and pins and started to build a 1:1 model of my rig on the
floor. I wanted to study what really happens when changing a span or how
much i should move a 'workthrough'. When i took into consideration that
we don't hold the handle at the very end and that a pin is not in a
middle of a button, it became bit messy, though.
During the course of the season i have increased the span several times,
ended up with 161,5 if i remember correctly. I have noticed acceleration
during the stroke. I optimised my rig while observing effectiveness of
my strokes during trainings, which was mostly steady state at low
cadence. I counted how many strokes i need to cover certain distance or
clocked the lap times on albano course.
At that time i did not really understand a true effect of these changes,
I only noticed that my performance in some races was disappointing. So i
kept training more and harder, and kept tinkering at the gearing. Only
after the season was finished i realised what really happened.
My performance in races in "normal" conditions -- in terms of wind --
was so-so, in so called "fast" conditions was rather poor. The only
races that turned out good were these against a strong head wind.
Anybody remember last two days of World Masters 2009 in Vienna? This is
what i mean by "strong headwind". :-))
Shortly speaking, that kind of gearing would work OK for me only in the
races when a speed of the boat relative to the water was pretty slow. In
all other conditions it turned out to be ineffective/inefficient.
> *** By increasing the span by 2cm (moving each pin by 1cm) and
> increasing the inboard by 1cm, I have to increase the rate by 1.33%
> (from 30 to 30.4) to maintain the same speed. Hopefully possible by
> having an easier gearing.
>
> All this has come about, as I have my oars as short as they will go,
> yet it still feels a little heavy and I'm struggling to get the rate
> up. So my solution is to increase the span and inboard to make the
> gearing easier - and there is no point me doing it if I don't go any
> faster.
You want easier gearing? May i ask what is your "target time"?
Anyhow, i am afraid that shorter oars is the way to go. If your oars do
not allow adjustment, change them.
I know, i know, to say that something is wrong is not enough.
I wish i could give you a more specific advice, but at the moment i can
not. I need a couple of weeks. The Oslo Fjord is still frozen.
For a time being i would advise you to stay with more conventional
cockpit measurements and adjusting the outboard.
And ask Walter Martindale about a link to his paper on "Some advantages
of a long catch", i can not find it... It will explain why shallow
angles are no good. Especially, if you want to go fast. :-)
--
Yours Virtually, Zibi
Zbigniew A.
[snip]
Oh, Walter,
I was busy typing my reply to Tinus while you posted this. :-)
Would you comment on my post in this thread? Please...
--
Zibi
Walter Martindale
Ok
http://www.rowingnz.com/Article.aspx?ID=633
Cheers,
(with 10 cm of fresh white snow on the ground)
W
Charles Carroll
If Walter can't find his paper, email me. I have a pdf file of it.
Cordially,
Charles
Zbigniew A.
I meant *comment*, not only the link... :-)))
--
Zibi
Walter Martindale
Well, OK, but I'm at work...
Through several consults over a few weeks, Zibi tried a few
modifications to the rig on his boat. In the end, new sleeves were
purchased, the pins were moved as far in as possible, and the blades
were shortened to an OAL in the 270s. This required cutting about 10
cm off the shaft at the handle end, drilling new holes to attach the
handle/clamp thingy, and glueing the new sleeves on to give 1/2spread
+8cm overlap with a range of oar lengths - I think the spread on
Zibi's boat settled somewhere around 157 but I'd have to look through
a bunch of files to find it.
The results - essentially, for pretty well the same boat speed over
1000 m or series of 500s, Zibi was able to rate in the low 30s the
whole way, get an acceleration through the drive, and have about the
same boat speed as when more conventionally rigged, but the two main
differences were that his rate was lower with the conventional rig,
and the load on his back was such that it made him miss training for a
while after the "conventional" row, whereas with the unconventional
row (long angle catch, short sticks) he was able to train and race
without the big loading on the back.
The rig ended up letting him row a front-loaded catch with a long
catch angle (I have yet to measure this angle because we live several
thousand km apart and I've been doing this virtually - the overhead
video I have of him isn't that well suited to siliconCoach, so we'll
see what happens when Oslo and the lake open up...
A lot of the numbers we played with came from Kleshnev's "innovative
rigging" pages.
HTH - back to work...
Walter
Zbigniew A.
>
> Well, OK, but I'm at work...
> Through several consults over a few weeks, Zibi tried a few
> modifications to the rig on his boat. In the end, new sleeves were
> purchased, the pins were moved as far in as possible, and the blades
Oh, Walter, thank you for replying even though you are so busy.
But above -- shortening the oars and decreasing the span -- we have done
in 2010 season and in my previous post i wrote about my /wasted/ 2009
year, before i started to listen to you... :-)
--
Zibi
Zbigniew A.
>
> Through several consults over a few weeks, Zibi tried a few
> modifications to the rig on his boat. In the end, new sleeves were
> purchased, the pins were moved as far in as possible, and the blades
Tink
> But above -- shortening the oars and decreasing the span -- we have done
> in 2010 season and in my previous post i wrote about my /wasted/ 2009
> year, before i started to listen to you... :-)
>
> --
> Zibi
I think the Kleshnev's Biorow rigging calculator came out just before
I bought my oars. Being an admirer of his work I checked it out, but
as it suggested oars shorter than were available at the time, I
hesitated and my courage failed me. I went with a more 'tradiitional'
rig.
The early parts of Zibi's story resonates very much with mine
(thankyou Zibi for sharing your experience, I feel you may shape my
rowing for the better, and thankyou Walter for adding detail).
Finding the work hard and the rating low I tried to come up with ways
to reduce the gearing - this started with shortening the outboard, and
got to the point of increasing span (to allow a larger inboard, and
shorter arc).
After reading Zibi's experience, and from Walters advice, I have found
the courage to do something that I didn't have the courage to do
before - get my oars shortened.
I have revisited Kleshnev's rigging calculator, plugged in my numbers
and it gives an inboard/span based on height. I tried the suggestions
in my boat this weekend, and the inboard/span settings (although
feeling a little odd and wobbly to begin with) feel more comfortable
and allow a larger catch angle - I think they will eventually be
settings for faster rowing. With the outboard as short as my oars
allow, at high rating I find the gearing way too tough, and the rating
very difficult to increase substantially (although oddly I find the
low rate rowing not really much harder). I tried a piece, and my
ratings tied in with Kleshnev's predictions well.
I realised my stubbonness/stupidity - given we spend so much money on
boats, oars, equipment, training kit, race entry fees, transport...
and spend so much time on training why would I not spend a little more
money/time to get the right size oars - why should I sacrifice my
enjoyment and health with rowing because I didn't want to admit I was
wrong and my oars were too long. Looking at it objectively it seemed
stupid.
I'm wondering if it means that standard oars are generally too long...