Jackstay strength

[Kyle2]

I have just bought new jackstays, as the old webbing was badly weathered. The new jackstays are of polyester 25mm webbing. I'm told that the breaking strength of these is 1 tonne, and the stitching (also polyester) is stronger than that. Does anyone know of any authoritative document or boat construction standards advising what the strength of jackstays should be?

 

[poter]

There was a discussion on this some time ago... try a search!

I think you will find that the webbing will only be as strong as the boat part its attached to. The real test is the snatch breaking strain & that is quite difficult to determine. 1 tonne seems a bit low?

Best thing is to have your jackstays inboard or down the centre & keep your harness reasonably short, don't go overboard in the first place. As most of your on deck work will be around the mast or the bow I would have seperate attachments in those critical areas if you want to be really safe. /forums/images/graemlins/smile.gif


poter.

 

[Salty John]

The Offshore Racing Council specifies a minimum of 4,500 lbs (2 imperial tons) for jackstays. This is normally 25mm webbing, but it must be the right type. Some webbing you find on rolls at chandlers may not be right - in the USA the chandlers label this stuff "not suitable for jacklines", I don't know if they do here. It should be UV proof. Mine had loops sewn in each end. Serious racers use tubular section webbing, sometimes with spectra running through the centre. That material is well over 3 tons breaking strain.

 

[William_H]

I would think that more important than the specified breaking strain is the strength after a few summers in the sun. The years can slip by very quickly.
After much discussion and even tests of harness in the water I would agree the system should keep you on board at all times. You are very helpless being dragged along behind a boat unless someone can stop the boat for you. A pull from behind would be far better than from the upper chest but this would make the system more difficult to fit and connect to. So short leads and restrained on the d3eck is the way to go. I would imagine this means loads would be lower maybe. olewill

 

[scarlett]

The problem of not going over the side is compounded by the oft given advice that they should not be taunt but slack.

 

[pvb]

There\'s a very good reason for this...

If the jackstay is taut, the tension induced by a given pull is much greater than if the jackstay is slack. It's all to do with the angles between the pull and the jackstay. Try doing a bit of simple maths using the weight of an oily-clad crewman and you'll be surprised just how high the tension in the jackstay can be!

 

[FullCircle]

As an ex-aviation furnishings designer, I used to design cargo nets among other things. 25mm webbing is available in as much as 4 tonnes SWL, and the double cross stitch box pattern is good for at least that in the correct thread.
Don't let anyone talk you into Kevlar thread, as it is brittle when folded over tightly (put in shear) as in stitching patttern. It is great in tension up the length of a sail.
For UV (ultra violet) sun loadings, max these out at 5 years if you leave them permanently attached. Suggest they are brought in and stowed at the end of each weekend. I only rig mine when it looks like piping up, and I am thinking of thinking about reefing. Takes 2 mins, and is the signal to get the jackets out too.
Review them each year, or take them to a local lifting strop certifying company every 2 or 3 years.
Consider that a 16 stone (100kg) guy in full oilies jumpers and boots will weigh about 140kg, and then sweep him overboard with another 150kg (ish) of accelerating weight of water, then a jerk load when you reach the end of the line, and you are looking at about 16g dynamic load . Then add a second and possibly third person to the same jackstay, and you have a potential for 2 tonnes at least and possibly up to 4 tonnes.

Only last week a 20 stone guy on a bungee jump broke the safety stays, with tragic consequence. 1 tonne is not enough.

Boy, I seem to be getting into this doomsaying lark. I must pack it in.


Jim