In article ,
Tim Watts wrote:

Can you explain why tree surgeons almost always have a tripod ladder?

Tripod ladders are easier to get closer to trees.

They have a very wide area of footing and 3 legs is inherently stable on
unplanar ground.

You're missing the point. For a given leg separation, the distance
from the centre (at ground level) to the closest point outside the
triangle is much less than it is for the quadrilateral. Therefore,
the ladder will fall over for a much lower imbalance in the weight
or sideways force.


Regards,
Nick Maclaren.

Nick Maclaren wrote:

You're missing the point. For a given leg separation, the distance
from the centre (at ground level) to the closest point outside the
triangle is much less than it is for the quadrilateral. Therefore,
the ladder will fall over for a much lower imbalance in the weight
or sideways force.

Isn't the whole point that the design under consideration doesn't
have the same leg separation as a conventional ladder. For
instance, the 3 m ladder is 1.45 m wide at the base.

https://www.niwaki.com/store/niwaki-tripod-ladder/

Chris
--
Chris J Dixon Nottingham UK


Plant amazing Acers.

In article ,
Chris J Dixon wrote:

You're missing the point. For a given leg separation, the distance
from the centre (at ground level) to the closest point outside the
triangle is much less than it is for the quadrilateral. Therefore,
the ladder will fall over for a much lower imbalance in the weight
or sideways force.

Isn't the whole point that the design under consideration doesn't
have the same leg separation as a conventional ladder. For
instance, the 3 m ladder is 1.45 m wide at the base.

https://www.niwaki.com/store/niwaki-tripod-ladder/

Ah. That would be enough, PROVIDED that the single leg is at a shallow
enough angle. Most step ladders have the non-step legs more vertical
than the other ones, which means the CoG is closer to them - and, if
there is a single one, that leads to instability. From the picture,
that looks the case.


Regards,
Nick Maclaren.

On 21/02/17 17:19, Nick Maclaren wrote:
In article ,
Tim Watts wrote:

Can you explain why tree surgeons almost always have a tripod ladder?

Tripod ladders are easier to get closer to trees.

They have a very wide area of footing and 3 legs is inherently stable on
unplanar ground.

You're missing the point. For a given leg separation, the distance
from the centre (at ground level) to the closest point outside the
triangle is much less than it is for the quadrilateral. Therefore,
the ladder will fall over for a much lower imbalance in the weight
or sideways force.


Regards,
Nick Maclaren.


However, the tripod ladder leg spacings are MUCH larger than 4 legged
ladders - and a 4 legged ladder would be very unstable on non planar ground.

So tripods of a suitable size seem like a win to me for that particular
purpose.

On 21/02/2017 17:19, Nick Maclaren wrote:
You're missing the point. For a given leg separation, the distance
from the centre (at ground level) to the closest point outside the
triangle is much less than it is for the quadrilateral. Therefore,
the ladder will fall over for a much lower imbalance in the weight
or sideways force.

You're missing the point. Unlike a floor in a house a garden isn't a
flat plane. Which means that one leg of a 4 legged ladder is always off
the ground.

And that means it is _less_ stable than a properly designed three legged
one, as it rocks between the two stable configurations...

I have a step ladder with bars across the base of each step. It's great
indoors. Outdoors I have to fiddle around for ages so it doesn't rock,
sometime putting bricks under it

Andy

In article ,
Vir Campestris wrote:

On 21/02/2017 17:19, Nick Maclaren wrote:
You're missing the point. For a given leg separation, the distance
from the centre (at ground level) to the closest point outside the
triangle is much less than it is for the quadrilateral. Therefore,
the ladder will fall over for a much lower imbalance in the weight
or sideways force.

You're missing the point. Unlike a floor in a house a garden isn't a
flat plane. Which means that one leg of a 4 legged ladder is always off
the ground.

And that means it is _less_ stable than a properly designed three legged
one, as it rocks between the two stable configurations...

I have a step ladder with bars across the base of each step. It's great
indoors. Outdoors I have to fiddle around for ages so it doesn't rock,
sometime putting bricks under it

I've only ever seen (on't'telly) tripod ladders in use with
trees/hedges. One was Monty Don doing his Product Placement thing [he's
good at that] when cutting his 15' tall beech hedge[1], with the odd
leg shoved through into the bottom of the hedge -- you couldn't do that
with a 4-legger. "Damn good!" I thought, as a regular hedge trimmer
myself.

Another was when a programme visited an orchard, and they were using the
tripod to pick apples -- perfect.

In both cases, the tree/hedge is giving extra stability to the lad/lass
at the top of the ladder.

John

[1] You never, ever, see a sign of the small army of "assistant
gardeners" who must inhabit Monty's VAST garden at lovely old Long
Meadow. He wouldn't remotely have time, let alone the energy, to do
everything that gets done there. Bloody annoying.

In article ,
Vir Campestris wrote:

You're missing the point. For a given leg separation, the distance
from the centre (at ground level) to the closest point outside the
triangle is much less than it is for the quadrilateral. Therefore,
the ladder will fall over for a much lower imbalance in the weight
or sideways force.

You're missing the point. Unlike a floor in a house a garden isn't a
flat plane. Which means that one leg of a 4 legged ladder is always off
the ground.

And that means it is _less_ stable than a properly designed three legged
one, as it rocks between the two stable configurations...

I am sorry. I was assuming that most people knew how to use a step
ladder safely. One of the critical things to do is to put small
sheets of wood, concrete etc. under the feet to stabilise the ladder.
That is as important for a tripod as a tetrapod, because it is
critical that the ladder does not lean significantly towards one of
the sides of the enclosing polygon. Yes, that is slightly easier for
a tripod, but not doing it for either kind is a serious error.


Regards,
Nick Maclaren.

On 22/02/2017 09:39, Nick Maclaren wrote:
I am sorry. I was assuming that most people knew how to use a step
ladder safely. One of the critical things to do is to put small
sheets of wood, concrete etc. under the feet to stabilise the ladder.
That is as important for a tripod as a tetrapod, because it is
critical that the ladder does not lean significantly towards one of
the sides of the enclosing polygon. Yes, that is slightly easier for
a tripod, but not doing it for either kind is a serious error.

If you have a tripod ladder with well spread legs it will be stable on
any piece of firm, near level ground.

This is not the case for one with 4 or more legs.

I have direct experience of using both types. Do you?

Andy

In article ,
Vir Campestris wrote:

If you have a tripod ladder with well spread legs it will be stable on
any piece of firm, near level ground.

Unless the ground is absolutely level, it will lean, and THAT is the
form of instability it is twice as prone to (relative to its base
dimensions) as a tetrapod ladder. Even a slight lean is a worse danger
than most people realise, because it will put extra weight onto the
downhill legs and, if the ground is not absolutely solid, that will
cause the ladder to lean further as the user climbs it. Quite often
suddenly and unexpectedly.

If tripods did not have a serious disadvantage over tetrapods, they
would have replaced the latter millennia ago, because they are simpler
to make, lighter and (as you say) easier to position.


Regards,
Nick Maclaren.

On 24/02/17 09:01, Nick Maclaren wrote:

If tripods did not have a serious disadvantage over tetrapods, they
would have replaced the latter millennia ago, because they are simpler
to make, lighter and (as you say) easier to position.

Not entirely - they are less suitable for building work. With a tree or
a hedge, you can get the 3rd leg around the tree or through the hedge.

With a building, you can't and that puts the top, which is not as wide
as the 2 step bearing legs, well away from where you want to be.

I don't think it is a simple as "one is better". They are made for
different purposes and each suits its purpose better than the other,
mostly (there are always exceptions).

Cheers, Tim

In article ,
Tim Watts wrote:

If tripods did not have a serious disadvantage over tetrapods, they
would have replaced the latter millennia ago, because they are simpler
to make, lighter and (as you say) easier to position.

Not entirely - they are less suitable for building work. With a tree or
a hedge, you can get the 3rd leg around the tree or through the hedge.

With a building, you can't and that puts the top, which is not as wide
as the 2 step bearing legs, well away from where you want to be.

I don't think it is a simple as "one is better". They are made for
different purposes and each suits its purpose better than the other,
mostly (there are always exceptions).

I didn't say they were useless - I said that they are NOT more stable
than tetrapods (as was originally claimed) and, in fact, are less
stable. Yes, you can fix that by increasing the base by about a
factor of two but, as you point out, that means they cannot be used
straight ahead and must be used diagonally sideways (or straight up).
I should be surprised if the tripod ladder in the link was enough
larger in all dimensions to achieve the same stability as the 10'
ladder I have - yes, the width is ample, but what is the length from
the steps to the single leg, and how far is the step from the single
leg (in a horizontal direction)? With those figures, I could easily
calculate the relative stabilities.

Returning to what you responded to - being unsuitable for many (most?)
of the uses that stepladders are used for surely counts as a serious
disadvantage?

Overall, my advice to the non-expert is "watch out, and remember
that it is as important to ensure the ladder is upright as it is for
a tertrapod."


Regards,
Nick Maclaren.