Jacklines

full-jacklineJacklines are now available from Westpac. ISAF and US Sailing specify webbing that has a 4500 pound breaking strength. We are using webbing with a 9800 pound breaking strength and the complete jackline has a breaking strength in excess of 5000 pounds.

one-end-under-loadThe above image was taken with over 5000 pounds of pull on the test sample and there was no damage to the stitching or webbing. After considerable research and testing we have found that using a bar-tack stitching pattern with a reinforcing piece inside the joint provided the best strength for this application. We did test the “double W” stitching pattern commonly used on slings (and some off the shelf jacklines) and found it failed below 5000 pounds.

5000-pound-pullAll jacklines are made to order. The standard model has a sewn eye in each end, a large one for the forward attachment point and a smaller one on the aft end so that you can have a lashing to adjust the tension of the jackline. If measuring your vessel is not practical we can also provide jacklines with the forward sewn eye and no eye on the aft end. One can use cleats in the stern of the vessel to attach the webbing which will provide an acceptable connection (although not quite as handy).

They are constructed from 1″ polyester webbing  treated with NanoSphere® technology which provides for longer life due to its dirt repelling properties. While we sell this webbing by the foot it does require a heavy duty industrial sewing machine to properly stitch.

If you need further information or wish to place an order, call Rollie at (253) 627-6000. There is also more information at http://westpacmarine.com

References:
On Rope by Bruce Smith and Allen Padgett
Load Testing by Evans Starzinger
ISO 12401

Testing:
We tested all of our samples between a large tree and a loaded dump truck (fortunately we have both). In line was a 10,000 pound hydraulic ram and a load cell. The hydraulic ram did not provide enough length of pull to get all of the slack out of the system and then pull for the actual test. Using the dump truck allowed us to pre load the setup and then use the ram to bring it up to our desired tension. The 10,000 pound digital load cell provided us with a quick and accurate way to measure the strain from a safe distance. This is why you see pine needles in the photos.

 

 

 

 

Jack line testing

IMG_1183
Jack line is on the left

We are starting to manufacture jack lines for sailboats. They are constructed from 9800 pound polyester webbing with a sewn eye in each end. When we sew the eye we have to calculate how to sew it so it has the required 5000 pound strength. Knowing the thread size tells us the theoretical strength per stitch. Then  it is easy to calculate how many stitches are required to produce the necessary strength. The question is does this really work? The only way to tell is to load test samples.

IMG_1173Most of what we test does not require a tree on one end and dump truck on the other. Even with this set up our first attempt resulted in pulling the dump truck up the driveway with 4000 pounds of load. A bit of weight in the bed and using the real brakes rather than the parking brake fixed that problem.

IMG_11825000 pounds came and went without any damage to the stitching so we know that our design works and we can go in to production.

If you want more information on how to calculate strap strength check out the blog post over at our Westpac Marine site.