On 13 Mar 2007 09:50:11 -0700, snipped-for-privacy@hotmail.com mused:
Depends on where you're storing them, if you have soe space about 3.5m long then you'd have no trouble getting some 3.5m triples in. If your space for ladder storage is 3m long then you'd struggle.
I've found Midland Ladders pretty good in the past, some 3.5m triples there at a decent price. I've got some 3.2m triples that I can easily manage on my own and can extend out to the full length in most scenarios, but being 6'5" helps there. ;)
I'm not one for advocating overdoing things on a ladder however it sounds to me like the 7.44m will be 'plenty' big enough....
The standoff would be your contact point (just below the gutter line) and you'd obviously want the ladders to top out slightly above the guttering so a 7.44m max length ladder would still several rungs overlap (and I would hope the 7.44m is the maxium safe length so you'd be well within this).
Unless it is me that's got it wrong?
Mathew
P.S. When climbing on to a roof you obviously need the ladder to be a person height above to enable a side-step off whilst still holding the ladder so if this is your intent then 7.44m might admittedly be pushing it. For me however, the fact my ladders don't safely allow a roof run is a good enough excuse to justify me turning down any invites to get up there! ;-)
To illustrate my point, take a look at the following pic of my ladders:
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're the 2.91m-7.44m triple ladders I mentioned earlier and as you can see they are far from being fully extended and just about reach my gutters which are 6m up. One or two rungs higher and you'll be well placed for them...
What are those black things under the ladder? Reason I ask, is that I was assisting our son, last week, while he was up my ladder and we had a lot of difficulty getting the ladders level on the ground.
it was my first time up ladders at height I bought one when I got the ladders as I felt more comfortable using a purpose-designed product rather than wedging a piece of wood etc. I wanted to feel as if I was at least doing something 'proper' rather than what I might consider in hindsight in a hospital bed to have been an accident waiting to happen.
The nobbled construction mean they can be safely stacked whereas whilst one piece of wood might be okay two would certainly be pushing it (coefficient of friction and all that).
I must say it's a bit pricey at ~=A315 given what they are but at the very least it gave me some reassurance whilst stood at the top.
My understanding (based on something I'd read on the net in the last day or 2) is that a ladder should lean at a ratio of 1:4 (ie ground to height). So to get 6.1 metres up you need to add roughly 25% to allow for leaning, hence 7.6m
It's over 20 yrs since I did any geometry / trigonometry & I've got a feeling that the paragraph above probably demonstrates that clearly...
Your calculations are (wrongly) assuming that the ladder length is the sum of the 'ground length' and 'wall height'. That is, 6.1/4 + 6.1 =
7.6m.
However this is not so, the relationship is actually ladder length ^2 (squared) = ground length ^2 + wall height ^2 (Pythagoras rule for right-angle triangles). However that doesn't really help us directly...
A more useful function for this case is the trigonometry rule tan angle = wall height / ground length. For our 4:1 ratio we have tan angle = 4 / 1 hence Inv tan 4 = 76 degrees. This is the optimium angle for the ladder.
Also, we know that sin angle = wall height / ladder length. Hence swapping everything around gives us ladder length = wall height / sin angle. Using our figures we get 6.1 / sin76 = 6.3m. That is, the ladder length is actually not all that much more than the height.
Of course these calculations don't take into account the fact that you want the top of the ladder to extend beyond the working height, and some spare rung overlap would be also be nice (if only to allow you to remind yourself 'I could be higher and still be safe'!).
A 7.44m ladder would therefore, in your case, be fine.
Off this end topic, but briefly returning to doubles/triples. If you want to go very high then doubles are difficult unless they have a rope lift as you may need to extend on the ground and then lift up as it can be difficult to extend in-situ as your reach is limited. I have
2 sets of 8m doubles (bought off e-bay for =A340 each - my tip for a good deal) and they are a real pain to get up. Triples are easier as you extend the top section first and then the middle one, and can usually do this whilst 'sliding' them up the wall. Trust me trying to take a ladder extended to 7.5m from flat on the ground to resting on the wall is tricky (though not impossible).
Thanks for the link Matt, just what I've been looking for. I often find myself on my own with nobody to foot a ladder and I often find uneven surfaces.
Just ordered one, but it cost me £20 with delivery.
That's splendid stuff - unfortunately I can't understand the maths well enough to work out whether it makes sense, but it has prompted me to have a play with a bit of paper & a pencil and it certainly seems like I'd got it wrong.
The message from "Mathew Newton" contains these words:
I presume the optimum angle is based on consideration on lateral stability as well as vertical stability but if the ladder is steeper than optimum you are only really at risk of toppling over backwards near the bottom of the ladder as that event will only occur if your centre of gravity is further away from the vertical wall than the foot of the ladder. However, particularly low down there is precious little frictional force at the top to prevent the ladder slipping sideways should the footing not be exactly level or you twist sideways as you climb. A stand-off in this respect will usually help lateral stability but if space is limited increasing the angle of the ladder to give room for the stand-off may be counter productive.
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