SJ distances table... can someone please explain?

PapaFrita

PapaFrita

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OK, I found this very handy table on a US website but I don't understand... I mean, I thought I understood... but I don't...

Look here

Now, I've assumed (because of the arrow pointing!) that the bars at the top indicate wether 1st fence of a combination is an upright or a spread, and the ones at the side indicate if the 2nd fence is an upright or a spread. BUT following this rationale, it would seem to indicate that the ideal distance between 2 uprights is in fact (a wee bit) longer than 2 spreads....
Surely that can't be right?
Can someone please explain (preferably in short words)
Thank you!!
 
It looks to me as though the distances in the top left are upright to upright, top right is upright to parallel, bottom left parallel to upright and bottom right parallel to parallel. I think it is right that the strides between uprights should be longer than spreads
 
Is it that the parabola over an upright means that the horse lands further away from the back of an upright - meaning a longer distance to get to the next jump than jumping a spread where the natural arc takes the horse back onto the ground relatively closer to the back line of the jump?
 
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I think it is right that the strides between uprights should be longer than spreads

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Surely not? Especially if you're juming into a combination over a spread you'll land closer to the next fence, so need a bit more room?
 
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I think it is right that the strides between uprights should be longer than spreads

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Surely not? Especially if you're juming into a combination over a spread you'll land closer to the next fence, so need a bit more room?

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You see I thought you landed further out over a spread
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I guess I should confess that I'm at the stage of having aclever horse who hates to touch a jump and can always produce another leg from somewhere or disappear a leg if it's going to get in the way!
 
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Is it that the parabola over an upright means that the horse lands further away from the back of an upright - meaning a longer distance to get to the next jump than jumping a spread where the natural arc takes the horse back onto the ground relatively closer to the back line of the jump?

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This is kind of what I thought, but wasnt sure how to word it
 
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You see I thought you landed further out over a spread
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That's what I meant; sooo, if you have a spread 1st, then an upright (or 2 spreads) you need a greater distance between the fences than if you have an upright 1st and then a spread (or 2 uprights)
 
See where your going now - the distance is shorter because you've already gone some of the distance when landing from the spread - i think the table makes sense if you look at it like that... so confusing!!
 
Maniscorse is right, I believe....if the horse jumps a distance of say, 12 foot over each jump then he'll take off 6ft (roughly) in front of an upright. If the 'spread' of a fence is say, 4 foot, then he'll take off about 4ft in front (again, very roughly).
If a canter stride is about 12 ft then the table looks right to me....
But what do I know????
S ;-)
 
I agree with PF, it doesn't make sense but it could just be right - it has to be based on some assumptions as to how you will jump those particular types of fence, and that the heights of the spread and the upright are the equal and teh width of the spread is small.

The first thing to note is the effective height of the spread is greater than the upright because to clear the spread the heighest point in the trajectory will be mid-way between the spread elements and higher than either of them. The further the spread elements are apart, the higher or faster you need to jump to clear them.

There are two ways of increasing the maximum jump height (1) you can take off at a greater angle relative to the ground (2) you can take off travelling faster. As you increase the angle of take-off up until 45 degrees to the horizontal, you travel further horizontally in the air and well as jumping higher. If the angle of take-off is increased above 45 degrees the horizontal distance travelled during the jump decreases (until at 90 degrees you would be jumping vertically upwards and land on the same spot you took off from).

SO here's the potential explanation of the table: First, you would have to gain the extra height to clear the spread rather than the upright by altering take off angle because if you increased speed, the stride length would increase and the hence the distance between fences would be larger for the spread (which is not what the table says). If you increase angle in such a way as to take off and land closer to the fence, the implication is the take-ff angle was around 45 degrees for the upright and is above 45 degrees for the spread. This would only work if the spread wasn't very wide, if the spread had width you would need the horizontal travel to clear the width of the spread. It's possible but unlikely I would have thought.
 
ok..... short answer is; you take off & land closer to an oxer than an upright !
that is why a double of 100cm oxers could be 23' & a double of uprights 24'
 
OK - In english.....
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You need to think about where the middle of each fence is if you are looking at it side on. For an upright this is directly over the pole, for a spread it is halfway between the front and back pole. Think of a perfect semi circle (which is how a horse should jump) and imagine each fence inside it.

A horse should bascule (round) over a fence and the highest point of the jump should be in the middle of the fence. So for an upright this means directly over the pole and a horse should land further away from the pole than if it was jumping a spread as the highest point of the jump would be before the back pole and the horse would already be starting to land when it went over it. It would therefore land closer to the back pole and the distance would need to be shorter.

As the fences get bigger you also need to increase the distance between the fences as the semi circle is increasing in diameter. The distance between 2 fences at British Novice should be less than the distance in a 1.40 class as in the bigger class you jump 'further' into the distance.

I do think they have got the distances wrong a bit as anything that starts with a spread in should be shorter than an upright in.
 
but you've said two contradictory things.... first you said that the highest point of the trajectory over a spread is between the two poles - which means that if we assume the front and back poles of the spread and the upright pole are equal heights then the spread is a bigger fence - you have to jump higher to clear it. BUT you say that you land closer after a spread.

A bit further down you say as fences get bigger the distance between fences increases because the semicircle (it isn't really a semicircle but near enough) increases diameter. Well if the semicircle increases diameter for bigger fences and a spread is bigger than an upright, then you would land further away from the spread fence.

which are you putting your money on ????
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but you've said two contradictory things.... first you said that the highest point of the trajectory over a spread is between the two poles - which means that if we assume the front and back poles of the spread and the upright pole are equal heights then the spread is a bigger fence - you have to jump higher to clear it. BUT you say that you land closer after a spread.

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Think about it - you will land closer to the back bar as a horse *should* jump in a nice even round bascule shape. And yes a spread is a wider fence.



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A bit further down you say as fences get bigger the distance between fences increases because the semicircle (it isn't really a semicircle but near enough) increases diameter. Well if the semicircle increases diameter for bigger fences and a spread is bigger than an upright, then you would land further away from the spread fence.

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Yes but just because a fence has got bigger it doesn't mean that the centre of the fence has suddenly changed position does it?

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which are you putting your money on ????
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My money is on what I wrote above. I haven't contradicted myself anywhere. If you built a BN distance and put the fences upto 1.40 you'd find it too short. A good coursebuilder takes in all these factors when building a course
 
If it helps at all with the discussion the table shown states that it's for a 1.20m course and that if you're using smaller jumps then shorter distances should be used.
 
(Sorry for the delay in replying - went away for the weekend)

Yes, sorry I was wrong, you weren't contradicting yourself, I was being a bit stupid and forgetting that the distance between fences is measured to the back/front of a spread and not the middle.

Also my intuition was wrong in my first post, having checked it out, you would be pretty much constrained to changing angle of take off rather than speed to jump bigger fences in SJ competitions (see below). So PF's table is correct. The thing you said in reply to my first post which I thought was a very nice image is the idea that the horse is already on the way down as it goes over the the back pole in a spread - so it lands nearer to the fence. This isn't necessarily true but in practice it nearly always will be.

"Think about it - you will land closer to the back bar as a horse *should* jump in a nice even round bascule shape. And yes a spread is a wider fence."

I agree with everything you say in practice but I think your reasons are wrong. Whether the horse bascules is pretty much unconnected to it's trajectory, this is one of the hardest things to explain to people but very easy to show with props. What determines how close it lands after the fence is simply it's speed and angle of take-off. There is another bit the horse has to do which is to impart enough rotation on the body to make sure it lands on its front legs (that's the bit to do with bascule) but basically it has to get that fairly right anyway for the jump to be successful. Whether it drops its head and rounds its back has effectively nothing to do with where it lands - again very easy to show, very hard to explain.

OK here are some examples of jumping dynamics that show why PF's table could have been wrong and could be right. The trajectories are the actual trajectories taken by a jumping horse
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The situation DDog has described is shown in A and C. In these graphs the horse has kept the same approach speed but taken off at a slightly higher angle to clear the spread. If you look at the distances you can see the horse takes off and lands closer to the spread than the upright.

The reason this doesn't have to be true is shown in B where the approach speed is increased to take the spread at a lower take off angle. You can see it takes off and lands further away from the fence.

So that is why PF's table could be right or wrong, it depends how you jump the fence. HOWEVER what I got wrong was I forgot the relative sizes of the effects of speed and jumping angle. If you look and A and C you will see that only a 3 degree increase in take off angle is necessary to jump the spread but if you look at A and B you can see a 3m/s increase in speed is needed. Since 4m/s is a fastish trot and 7m/s is a mediumish canter that's a big difference and within the constraints of a SJ course it's not a reasonable strategy.
 
Thank god I don't have to remember all that when i'm jumpng
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I'd be stuffed lol!

For me, if it's 24' upright to upright I know it's a 'normal' stride. If it' oxer to upright I know I need to kick on a bit more. Sorry. It doesn't get more complicated than that for me
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I agree very very much with what you say 99% of the time 99% of people don't need to know how it works. The reason it's useful is there comes a point in elite competition where you can benefit from deconstructing how jumping works and working out what matters most. Amongst sports equestrianism is very slow to adopt this approach but it's getting there.
 
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