What is the fastest path for a rowing boat through a sharp bend? A car or motorcycle going trough a bend maximises the radius of the bend by going from outside to inside of the bend back to the outside again. This path is longer that the inside curveand shorter than the outside curve. The speed difference for a car between a straight and a sharp bend is large - this ratio is much smaller for a rowing boat – so maybe the shortest path is (in practical terms) the fastest. This is usually complicated
-- CAssuming no current I can't really see that it would be different for a boat, the fastest corner is the 'racing line' which maximises the radius of the curve and avoids sharp rudder movement. The main difference to a car is, unless turning around a buoy,
Leeway drag is a significant cause of speed loss when steering into &[..]
around bends, because it is the only way in which a shell can resist
sideways movement under the centripetal force generated by the changing direction, & then there's the energy absorbed in rotating the long shell
with its high moment of rotational inertia.
Proper control foils (e.g. our HyperSteer system) considerably reduce
turning & cross-wind leeway losses, & enhance directional control at all times.
In principle, one should take the broadest arc around a bend when rowing upstream, going from the outside, crossing to close to the inner bank &[..]
then back to the outside, which imposes the slowest rate of rotation of
the boat itself about its own vertical axis and the smallest amount of centripetal force, but that course passes twice through the swiftest
flow. However, going into shallows on the inside of the bend (rivers
tend to be deepest towards the outsides of bends) may incur additional drag.
I hope that's spread enough confusion?
On Tuesday, February 9, 2021 at 12:30:39 PM UTC, Andy McKenzie wrote:buoy, you aren't de-accelerating into the curve and accelerating out so the path should be more symmetrical. If you watch crews on windy courses like the Charles that's the line they take if they can.
On Monday, 8 February 2021 at 10:20:39 UTC, lin...@gmail.com wrote:
What is the fastest path for a rowing boat through a sharp bend? A car or motorcycle going trough a bend maximises the radius of the bend by going from outside to inside of the bend back to the outside again.Assuming no current I can't really see that it would be different for a boat, the fastest corner is the 'racing line' which maximises the radius of the curve and avoids sharp rudder movement. The main difference to a car is, unless turning around a
I think it's not so clear cut. If you are walking, the shortest line would be the fastest because you almost don't have to slow down into a tight bend. A boat does slow down in a tight bend because of sideway drift which creates drag and because ofcentrifugal forces. So the fastest line depends on this slowdown. I still suspect that you are correct but it's only a hunch.
On Tuesday, February 9, 2021 at 3:58:35 PM UTC, carl wrote:
[..]Leeway drag is a significant cause of speed loss when steering into &
around bends, because it is the only way in which a shell can resist
sideways movement under the centripetal force generated by the changing
direction, & then there's the energy absorbed in rotating the long shell
with its high moment of rotational inertia.
Proper control foils (e.g. our HyperSteer system) considerably reduce
turning & cross-wind leeway losses, & enhance directional control at all
times.
In principle, one should take the broadest arc around a bend when rowing[..]
upstream, going from the outside, crossing to close to the inner bank &
then back to the outside, which imposes the slowest rate of rotation of
the boat itself about its own vertical axis and the smallest amount of
centripetal force, but that course passes twice through the swiftest
flow. However, going into shallows on the inside of the bend (rivers
tend to be deepest towards the outsides of bends) may incur additional drag.
I hope that's spread enough confusion?
I was hoping for your reply - so thank you! The racing line (maximising radius by going
outside, inside, outside) is longer than the shortest line on the inside. You seem to be confident that
the loss of speed (from increased drag) by taking the inside line is enough such that the longer
but faster racing line is beneficial in the typical case.
-- C
On Monday, 8 February 2021 at 10:20:39 UTC, lin...@gmail.com wrote:buoy, you aren't de-accelerating into the curve and accelerating out so the path should be more symmetrical. If you watch crews on windy courses like the Charles that's the line they take if they can.
What is the fastest path for a rowing boat through a sharp bend? A car or motorcycle going trough a bend maximises the radius of the bend by going from outside to inside of the bend back to the outside again.Assuming no current I can't really see that it would be different for a boat, the fastest corner is the 'racing line' which maximises the radius of the curve and avoids sharp rudder movement. The main difference to a car is, unless turning around a
watch the University Boat Race and wonder why coxes love to engage in "handbags at dawn", with close contacts necessitating sudden corrections
& obvious costs in speed, as well as being highly disruptive.
Local knowledge is a great help. And having some grasp of the
principles I've tried to set out may not be a bad thing.
One point I missed: never make sudden steering inputs. Steer as if
driving on ice, so plan your course well before you get there. I often
watch the University Boat Race and wonder why coxes love to engage in "handbags at dawn", with close contacts necessitating sudden corrections
& obvious costs in speed, as well as being highly disruptive.
On 02/03/2021 08:54, lin...@gmail.com wrote:or curvature) of a bend. This would make it possible predict the length/speed tradeoff at various speeds. This would still ignore any stream component. (For cars racing on a track the fastest line is regularly computed but the physical model is much
On Tuesday, February 9, 2021 at 8:10:05 PM UTC, carl wrote:
Local knowledge is a great help. And having some grasp of the
principles I've tried to set out may not be a bad thing.
One point I missed: never make sudden steering inputs. Steer as if
driving on ice, so plan your course well before you get there. I often
watch the University Boat Race and wonder why coxes love to engage in
"handbags at dawn", with close contacts necessitating sudden corrections >> & obvious costs in speed, as well as being highly disruptive.
Boat speed and power per rower are connected by a drag constant: P = D*v^3 and constant D is well known for various boat classes: about D=2.1 (8+) to D=3.6 (1x). For a theoretical model it would be interesting to know how D changes given the radius (
-- C
It would be very interesting indeed, but so much depends on the amount
of leeway made by the boat during the turn, the extent to which that
leeway component increases hull drag & the energy required to start the boat's rotation on entering the turn & to stop it on leaving. While in
ideal circumstances that should all be calculable, it might be a
challenge to get cox to do that during a race in variable conditions &
with other crews around (a moving boat's drag is influenced by the
motion of other nearby boats, even when you're not having to find your
way past them!
But it's certainly an exercise worth pursuing.
It's also why we supply our twin-foil HyperSteer system, which greatly reduces leeway & consequent drag losses during any manoeuvre, & in crosswinds, & when bow take a rest or puts in a harder catch, etc.
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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On Tuesday, February 9, 2021 at 8:10:05 PM UTC, carl wrote:curvature) of a bend. This would make it possible predict the length/speed tradeoff at various speeds. This would still ignore any stream component. (For cars racing on a track the fastest line is regularly computed but the physical model is much better
Local knowledge is a great help. And having some grasp of the
principles I've tried to set out may not be a bad thing.
One point I missed: never make sudden steering inputs. Steer as if
driving on ice, so plan your course well before you get there. I often
watch the University Boat Race and wonder why coxes love to engage in
"handbags at dawn", with close contacts necessitating sudden corrections
& obvious costs in speed, as well as being highly disruptive.
Boat speed and power per rower are connected by a drag constant: P = D*v^3 and constant D is well known for various boat classes: about D=2.1 (8+) to D=3.6 (1x). For a theoretical model it would be interesting to know how D changes given the radius (or
-- C
On Wednesday, 3 March 2021 at 13:29:57 UTC, carl wrote:or curvature) of a bend. This would make it possible predict the length/speed tradeoff at various speeds. This would still ignore any stream component. (For cars racing on a track the fastest line is regularly computed but the physical model is much
On 02/03/2021 08:54, lin...@gmail.com wrote:
On Tuesday, February 9, 2021 at 8:10:05 PM UTC, carl wrote:
Local knowledge is a great help. And having some grasp of the
principles I've tried to set out may not be a bad thing.
One point I missed: never make sudden steering inputs. Steer as if
driving on ice, so plan your course well before you get there. I often >>>> watch the University Boat Race and wonder why coxes love to engage in
"handbags at dawn", with close contacts necessitating sudden corrections >>>> & obvious costs in speed, as well as being highly disruptive.
Boat speed and power per rower are connected by a drag constant: P = D*v^3 and constant D is well known for various boat classes: about D=2.1 (8+) to D=3.6 (1x). For a theoretical model it would be interesting to know how D changes given the radius (
It would be very interesting indeed, but so much depends on the amount
-- C
of leeway made by the boat during the turn, the extent to which that
leeway component increases hull drag & the energy required to start the
boat's rotation on entering the turn & to stop it on leaving. While in
ideal circumstances that should all be calculable, it might be a
challenge to get cox to do that during a race in variable conditions &
with other crews around (a moving boat's drag is influenced by the
motion of other nearby boats, even when you're not having to find your
way past them!
But it's certainly an exercise worth pursuing.
It's also why we supply our twin-foil HyperSteer system, which greatly
reduces leeway & consequent drag losses during any manoeuvre, & in
crosswinds, & when bow take a rest or puts in a harder catch, etc.
Cheers -
Carl
--
It strikes me that this is data that might be available from GPS and a bit of experiment. Putting aside the effect of a stream (by rowing on a lake), if we record velocity continuously while making turns of different radii, we can see exactly how muchspeed is lost. I would expect a fair few rowers actually have the data already recorded and on Strava. I would offer up my own data - but all it would show was 'slows a lot because stopped halfway round the bend to watch kingfishers'
It strikes me that this is data that might be available from GPS and a bit of experiment. Putting aside the effect of a stream (by rowing on a lake), if we record velocity continuously while making turns of different radii, we can see exactly how muchspeed is lost. I would expect a fair few rowers actually have the data already recorded and on Strava. I would offer up my own data - but all it would show was 'slows a lot because stopped halfway round the bend to watch kingfishers'
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