Join Date: Mar 2008
Thanked 0 Times in 0 Posts
Rep Power: 0
FWIW In a previous career I ran a factory manufacturing climbing harnesses and related equipment, I designed (and tested to destruction) all the equipment we made. I tend to shop in outdoor stores for most of my safety equipment (unless I make it myself) as it climbing gear is made to CE & ISO standards which (IMO) exceed any demands that may be made while sailing. I am not sure of the standards for sailing safety gear but have seen some very dodgy teathers for sale in marine shops over here (in Australia). (I have also seen some good stuff so do your research carefully).
Knots vs Stitching
The correct knot is stronger than stitching. The strongest sewn join is a bar tack, followed by a box pattern. The bar tack is made using a programmable sewing machine, the strongest pattern (number of bars, width, size and number of stitches) will vary from webbing to webbing, so it needs to be tested to destruction. Generally a bar tacked join will reduce the strength of the webbing by 10 to 20%. A knot will reduce the strength of the join by less than 10%. And a join sewen with a walking foot machine (as used by your sailmaker) will reduce the strength of the webbing by 15-50%. Keep in mind that if you are sewing a loop on the end of a tether there are two lengths of webbing in the loop vs 1 length for the rest of it. The teather that failed in the 88 sydney to hobart was sewen using a walking foot machine, with a basic box pattern.
As a previous poster pointed out most climbing gear is alloy, this performs badly in a salt water environment, especially if it uses a mix of metals. The advantage of climbing Karabiners is that they have a locking mechanism that is designed to be opened with one hand. Snap locks with no locking mechanism can undo themselves when connected to a solid ring, or another karabiner. This includes pad eyes, so if you want to be safe you should use a locking Karabiner. I generally use alloy biners and accept the fact that I will need to replace them every year or so. Washing after use & proper storage helps them to last. I have noticed a few stainless locking karabiners around the place.
When a line is stretched tight and a load is placed in the middle of it, pulling at 90 degrees the load on the line will be several times greater than if the line was pulled straight. Think how you can haul a sail up by pulling on the halyard between the mast exit and the block on the coach roof. The person pulling the halyard can exert more force than the person grinding a winch with a significant mechanical advantage. For the maths on this you will need to check out a high school trigonometry text. One quick example, if we have a jack line that is 5m from one attachment to another and stretched tight. If someone falls on the mid point of this line and the line deflects by 10 degrees the force exerted on each end point will be 5.7 times the weight of that person.
Nylon has very poor UV resistance, but good strength & stretch (this helps to reduce shock load)
Polyester has reasonable UV resistance and reasonable strength.
Last edited by pyro42; 08-18-2008 at 08:49 PM.