Another question - Blade Angle

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GYXU > General > Another question - Blade Angle 9 March 2005 20:54:41

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Another question - Blade Angle
Andy Nield 9 March 2005 19:21:07
	When you set the stern pitch, does the blade stay at that angle through the stroke, or does it find it's own angle? I was on a IA course, and the instructor said it goes in over square (i.e. the stern pitch angle), and then squares itself in the water during the drive... ok, well now I am slightly confused... I'd previously assumed that the back of the blade collar locked onto the swivel face and kept the blade at the same pitch through the drive (ignoring the effects of lateral pitch). The instructor was sure that stern pitch was just the catch angle, and the blade then found it's own angle and squared up regardless of the swivel pitch... Is this correct?
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Phil 9 March 2005 20:07:31 [ permanent link ]
	If you ignore torsion in the blade shaft/head, and the effects of lateral pitch (not negligible unless zero!) - then the pitch of the face of the blade must be the stern pitch with a blade that has zero pitch inbuilt.
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Neil Wallace 9 March 2005 20:26:57 [ permanent link ]
	Phil wrote:> If you ignore torsion in the blade shaft/head, and the effects of> lateral pitch (not negligible unless zero!) - then the pitch of the> face of the blade must be the stern pitch with a blade that has zero> pitch inbuilt. Minor correction. Stern pitch + whatever is built into the gate. But interesting that you mention torsion in the shaft. I would wager that the angular deflection along the long axis of the oar shaft (rotation, if you like) is far from negligable... espescially with the non-symetrical (i.e.non-macon) blades we use. I've often wondered whether measurement of this torsion in a crew boat could indicate who is pulling hardest. I've also often wondered what sort of tolerance the different manufacturers accept for the modulus of their shafts.
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Jon Anderson 9 March 2005 20:34:37 [ permanent link ]
	Neil Wallace wrote:> I've often wondered whether measurement of this torsion in a crew> boat could indicate who is pulling hardest. There must be a few strain gauge systems out there to measure how much your oar bends (as opposed to twists). Some bloke at our club made one about 12 years ago from a material that changed resistivity when stretched. He recorded the data on a BBC Micro of all things... I'm not entirely sure that the blade will "square" itself regardless of stern pitch though. If it did, why do we worry about negative lateral pitch decreasing the stern pitch at the finish of our stroke? Jon -- Durge: jon@durge.org http://users.durge.org/~jon/ OnStream: accounts@rowing.org.uk http://www.rowing.org.uk/ [ All views expressed are personal unless otherwise stated ]
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Neil Wallace 9 March 2005 20:54:28 [ permanent link ]
	Jon Anderson wrote:> Neil Wallace wrote:>> I've often wondered whether measurement of this torsion in a crew>> boat could indicate who is pulling hardest.> There must be a few strain gauge systems out there to measure how> much your oar bends (as opposed to twists). yes, I know they are commonplace. just wondered whether twisting has been done. I reckon the data would be very interesing for a variety of reasons. Some bloke at our club> made one about 12 years ago from a material that changed resistivity> when stretched. He recorded the data on a BBC Micro of all things... oh happy days! 10 mode 7 20 end
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Walter Martindale 9 March 2005 20:54:41 [ permanent link ]
	andy.nield@ps.ge.com wrote:> When you set the stern pitch, does the blade stay at that angle through> the stroke, or does it find it's own angle?> I was on a IA course, and the instructor said it goes in over square> (i.e. the stern pitch angle), and then squares itself in the water> during the drive...> ok, well now I am slightly confused...> I'd previously assumed that the back of the blade collar locked onto> the swivel face and kept the blade at the same pitch through the drive> (ignoring the effects of lateral pitch).> The instructor was sure that stern pitch was just the catch angle, and> the blade then found it's own angle and squared up regardless of the> swivel pitch... Is this correct?> IA? Oh well. If you have confirmed that your blades are zero pitch (acc. to the manufacturer's specs), and if you have your pin vertical, the pitch will/should stay the same through the stroke, and that should/will be the pitch to which your oarlock is set (using the eccentric pitch plugs in C2, for example). If your pins are pitched outwards (i.e., laterally) 1 or more degrees, but vertical relative to fore-aft, the pitch on the blade will change during the stroke; greater pitch at the catch, less pitch at the release. The theoretical aim of this lateral pitch business is to increase the pitch at the start of the drive, reducing the depth to which you enter, and to decrease the pitch at the end of the drive, tending to keep the blades buried in the water a little longer. The practice I've seen in NZ, Ireland and home here in Canuck land over the past decade has been to set the pin to vertical, set the gate to 3 or 4 degrees, use (and confirm) zero pitch blades so that the blade has a chance to stay the same pitch through the stroke. Walter
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Douglas MacFarlane 9 March 2005 21:03:12 [ permanent link ]
	In article <398mdhF5vg52tU1@individual.net>, rowing.golferNOSPAM@virgin.net says...> Phil wrote:>> If you ignore torsion in the blade shaft/head, and the effects of>> lateral pitch (not negligible unless zero!) - then the pitch of the>> face of the blade must be the stern pitch with a blade that has zero>> pitch inbuilt.> Minor correction.>Stern pitch + whatever is built into the gate.> But interesting that you mention torsion in the shaft.> I would wager that the angular deflection along the long axis of the oar >shaft (rotation, if you like) is far from negligable... espescially with the >non-symetrical (i.e.non-macon) blades we use.> I've often wondered whether measurement of this torsion in a crew boat could >indicate who is pulling hardest.> I've also often wondered what sort of tolerance the different manufacturers >accept for the modulus of their shafts.> It will be "Stern pitch + whatever is built into the gate" when the oar is at right angles to the boat. If the pin is not verticlal then the patch may change through the stroke, even with zero degrees of lateral pitch. The pitch is the sum of the pin angle plus the gate pitch plus the oar pitch. You hope that the gate pitch and the oar pitch don't vary through the stroke. The angle of the pin, which may be adjustable, sets the axis around which the gate rotates. Douglas
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Carl Douglas 9 March 2005 23:56:41 [ permanent link ]
	andy.nield@ps.ge.com writes>When you set the stern pitch, does the blade stay at that angle through>the stroke, or does it find it's own angle?> I was on a IA course, and the instructor said it goes in over square>(i.e. the stern pitch angle), and then squares itself in the water>during the drive...> ok, well now I am slightly confused...> I'd previously assumed that the back of the blade collar locked onto>the swivel face and kept the blade at the same pitch through the drive>(ignoring the effects of lateral pitch).> The instructor was sure that stern pitch was just the catch angle, and>the blade then found it's own angle and squared up regardless of the>swivel pitch... Is this correct?> Doesn't say very much for the quality of the instruction given, Andy! I sense someone was wandering slightly out of their depth, which really isn't excusable. This is a dead simple matter, ably explained already by Douglas & Walter. I would only add: 1. The more you bend the blade, the less affected you should be by pitching errors because the blade trails further behind the line from hand through gate and is thus less twitchy (imagine if the shaft had a reversed bend!) 2. Pin pitch really does matter, because you can't correct for errors in pin pitch by altering the inserts in the gate 3. Trying to get your pin vertical if it is not pitch-adjustable is a damaging & crazy exercise, only achievable on soft riggers The proper solution is a simple & rigid rigger, combined with a pitch-adjustable pin. For answers, see below ;^) Cheers - Carl -- Carl Douglas Racing Shells - Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK Email: carl@carldouglas.co.uk Tel: +44(0)1784-456344 Fax: -466550 URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)
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Stan 10 March 2005 00:39:56 [ permanent link ]
	andy.nield@ps.ge.com wrote in message news:<1110381667.174625.112160@l41g2000cwc.googlegroups.com>...> When you set the stern pitch, does the blade stay at that angle through> the stroke, or does it find it's own angle?> I was on a IA course, and the instructor said it goes in over square> (i.e. the stern pitch angle), and then squares itself in the water> during the drive...> ok, well now I am slightly confused...> I'd previously assumed that the back of the blade collar locked onto> the swivel face and kept the blade at the same pitch through the drive> (ignoring the effects of lateral pitch).> The instructor was sure that stern pitch was just the catch angle, and> the blade then found it's own angle and squared up regardless of the> swivel pitch... Is this correct? While there is possibly some wobble in the gate at the catch. I would cite the infamous demon of lateral pitch as the usual reason for pitch variation through the stroke. The effect of 1 degree +ve lateral pitch would definately produce the effects mentioned at your IA's course.
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Guest 10 March 2005 02:03:32 [ permanent link ]
	Vertical pins.....Get ur spirit level out and spend an age getting it right if necessary, but get it right! Forget the 1/2 or 1 degree lateral that people will say stops going deep at the catch, If you need that with a big blade your catch is wrong.
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Phil 10 March 2005 12:47:42 [ permanent link ]
	Minor correction - Stern Pitch being the angle that the back face of the gate (or swivel in ARA - speak) makes with the vertical ... this naturally includes what is built into the gate - I did not say "the angle indicated on the little blue inserts".
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Phil 10 March 2005 12:52:26 [ permanent link ]
	Minor correction - Stern Pitch being the angle that the back face of the gate (or swivel in ARA - speak) makes with the vertical ... this naturally includes what is built into the gate - I did not say "the angle indicated on the little blue inserts".
		Add comment


Andy Nield 10 March 2005 13:50:11 [ permanent link ]
	Thanks for the replies. I'd loosely used the term 'stern pitch' to include total pin/gate/blade pitch and assumed a vertical pin (probably should have been more explicit). But even so plenty of helpful replies. It's just a shame those yellow and blue plastic bits don't come in a choice of colours so you can match the boat/blade colours... Hey Carl, how about some colour options...?
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GYXU > General > Another question - Blade Angle 9 March 2005 20:54:41

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