CONSTRUCTION OF LAID (with twisted strands) CORDAGES
Here is a summary from the fibres to the cable:
Just so as to 'anchor' ideas in memory here is another summary.
Different way to do the laying.
HOW TO PROTECT CORDAGES : WORMING, PARCELLING, SERVING.
This simple illustration shows how to and with what you worm a cordage to make it
smoother before parcelling it (note the way each layer recover the other as the tiles on a
roof) and finishing by serving it and then tarring it.
Taken straight from The Seaman’s Friend : A Treatise on Practical Seamanship by Richard
Henry DANA Jr First published in 1879.
[Begin quote p 44]
WORMING a rope , is filling up the divisions between the strands, by passing spunyarn
along them, to render the surface smooth for parcelling and serving.
PARCELLING a rope is wrapping narrow strips of canvas about it, well tarred, in order to
secure it from being injured by rain-water lodging between theparts of the service when worn.
The parcelling is put on with the lay of the rope.
SERVICE is the laying on of spunyarn, or other small stuff in tourns round the rope, close
together, and hove taut by the use of a serving-board for small rope, and serving-mallet for
large rope.
Small ropes are sometimes served without being wormed, as the crevices between the
strands are not large enough to make the surface very uneven ; but a large rope is always
wormed and parcelled before being served.
The service is put on against the lay of the rope.
[End quote]
HOW TO FIND THE ANGLE OF THE LAY
Here again a simple illustration should be enough to show how to find the angle between the
axis of the whole cordage and the axis of a part of a strand.
This angle of lay is determined by the amount of twist applied to the strands when laying the
rope.
The smaller the angle the softer the laying.
More twist, that is harder laying, open the angle.
Which leads to : the harder the lay the shorter the ‘step’ in the helical course followed by
the yarns of a the strand and by the the strands of the rope.
For a given hardness of lay the greater the diameter of the rope the greater the step of helices.
Same thing in a strand with the twist applied to the spun yarns.
Note that in each strand a given amount of twist will result in an angle that is more acute for
the inner fibres than for the outer fibres.
Identical remark for fibres in a yarn.
This is what makes that the angle of the lay of the whole rope a not really sure indication of
the physical properties of the rope considered as a whole.
In fact the hardness and stiffness of the rope is the compounded effect of twist of fibres and
yarns, twist of yarns and strands and twist use for laying the strands into a rope.
Were you to input maximal twist to the strands when laying the rope this rope will not be
hard laid if there is not already enough twist in the strands themselves to maintain the laying
of the rope.
The twist in a strand is what make the the resistance of the rope to elongation under load.
When under load the yarn tend to untwist.
Extraits
de
Traité de la fabrique des manoeuvres pour les vaisseaux
L'ART de la CORDERIE PERFECTIONNÉ
de Mon Sieur Duhamel du Monceau paru en M. DCC. LXIX ( 1769 - seconde édition ) à Paris chez Desaint, Libraire, rue du Foin.
Traité de la fabrique des manoeuvres pour les vaisseaux
L'ART de la CORDERIE PERFECTIONNÉ
de Mon Sieur Duhamel du Monceau paru en M. DCC. LXIX ( 1769 - seconde édition ) à Paris chez Desaint, Libraire, rue du Foin.
At the cost of a tremendous - a handful of weeks - work here is the transcript of the essential points
(alas in French and 18th French at that even if I did some 'cosmetics' about that, most
French cannot even read it fluently !) of nearly 600 pages of this monumental work the best
ever done on the subject, present days included! even the Encyclopaedists Diderot et
D'Alembert, took from it and the only clear part in this Encyclopaedia is a direct repro of
Duhamel's work.
This I will not translate or not without many, really many, asking (in number not in repetition)
Even this summary is really much work .
I will never cease to marvel at the very modern approach of Duhamel du Monceau in
auditing the Royal Roperies.
Only tool that is missing there is modern Statistics that were still to be found.
It is not yet finished but you are in for many hours of study just with what is already done.
Fortunately images are international.
Mon dessin montrant un quarré et un chantier
Pas de corderie - Rope walk
Pas de corderie en raccourci - Roprwalk shortened
Toupin et clavette - Top or topper
Planche 1 de l'art de la Corderie en petit format - Engraving from Art de la corderie
Planche 2 de l'art de la Corderie en petit format - Engraving from Art de la corderie
Diaporama grand format des planches de l'Art de la Corderie ( big format , huge even )
Le même diaporama mais en 800 pixels de large pour une ouverture plus rapide.
Diderot & d'Alembert Encyclopaedia engravings : une - deux - trois
FORCES , CORDAGES & KNOTS
These simplistic drawings should be enough to give an idea of the forces inside a cordage in
service ( load )
- in a bending curve, knot or pulley.
- in a strand of a load bearing cordage
ADDED 2008 June 27th : recent documents from Brittany ( Ploumanach )
If those two drawings seem a bit obscure and abstract to you then here is a modelization of
what is 'really' happening.
I used special threads found in a garden centre ( a thin wire with rubber foam around it ) and
plasticine clay to make some modelization.
There is no hidden sleight of hand.
- with these pictures you can see forces N°1 et N°2 in their results :
under loading there is an elongation and the helix "step" become longer and the cylinder it has
been put around see its diameter lessening. The wire cut into the cylinder, just as yarn
situated at the periphery of the strand compact this same strand when said strand is
lengthening and becoming thinner under a pulling force.
- Here is another illustration of the constriction coming from the periphery and leading to a
breakage.
-This makes clear the fact that when a tension is imposed following an helix , there is a
lengthening of the "step" and the cylinder of revolution round which it is inscribed see its
diameter lessens.
- Here you should see the 'cutting' , shearing effect imposed by a tension following an helix.
- This is an illustration of three strands under tension : they lengthen, become thinner, and
the "step" of the helix followed by each strand elongate.
- Strands don't keep a perfectly circular cross section, but they are compacting each other
and friction zones appear.
- Helical distribution of tension can be readily seen here.
-Here is a modelization of how 3 strands are pushing against each other under tension.
I hope that these visuals will have make the phenomena clearer for you.
This photography of springs illustrate the compression zones and elongation zones in a
cordage.
Analyse carefully these zones and where they are.
This slideshow should show what tensions can happen during the building of knots.
There exist friction forces :
- between fibres
- between yarns
- between strands
Illustration done with springs which will give you some sort of approach of the right idea.
This slideshow is about how tensions are born in a knot
HOW TO COIL A CORDAGE SO AS TO GET A SNARL FREE UNCOILING
(MARINE NATIONALE de FRANCE )
Just coil it as shown by this digital drawing created after a photography by Marine Nationale .
HOW A LAID CORDAGE BEHAVE UNDER A LOAD
This photography will not show it while it is in rotation on its axis. The end result of this
rotation is that it somewhat 'un-twist' itself. Photo show the result : the 'step' of the helix
course of the strands lengthen, the angle of the lay lessen and the cordage becomes thinner.
Experience is easy to do with 20" of 3S nylon 3 mm and a 400g weight.
Just take care to leave both extremity to rotate following the vertical axis.
The fibres breaking sequence
ROCHEFORT : THE ROYAL ROPE WALK ( SUN KING LOUIS THE 14th )
LA CORDERIE ROYALE
This covered rope walk was but a small part of a huge naval dockyard.
It was the longest rope walk of the known world in its century : 374 metres ( 390 meters
outside size )
Twisting "to the third" it could give 374m * 0.66 = 246 metres long cordage was the
maximum obtainable.
That is over a French cable length.
[a cable -French- was 1 encablure = 120 brasses = 100 toises = 195 metres
it was 1/10 of 'un mille marin' -- 1 toise = 6 pieds = 1.95 metre - 1 brasse = 10/12 toise =
1/120 encablure = 1.62 metre.]
Some pictures there :
- an oil painting by VERNET, a famous French painter.
- a second one by some other artist.
- yet another one
-This is an aerial photography of La Corderie Royale taken from a kite :
Corderie Royale - ROCHEFORT (17) Juin 1995. (photo André LE BESCONTE)
Copyright © 2001-2006 [BDC HENRI]. Tous droits réservés.
by kind authorization given by Dominique HENRI whose personal pages are really worth to
be seen. ( http://perso.orange.fr/bdc.henri/ )
- my own slideshow of the outside aspect
- what can be seen inside, in Le Centre de la Mer ( The Sea Centre )
This huge building was built on swamp ground.
Thousands of oak were used to stabilize the ground.
" un radier " / a raft was built ; Centuries later it is still there despite huge destruction by
German Army Vandals in WW 2 !