JSD ver1.3

[Lars_L]

I do not want to change the size of cones or the number of cones. I want to know how to make a JSD with the new material that exist today.

The main rope is made of dyneema or a similar but cheaper material. But the cone itself, should they be made of polyester?

The straps should be made of polyester, but do it need to be 25 mm wide? The cones have a very limited size, so the force on the straps can’t be that strong. Aint it enough with 10 mm?

How do I attach the straps to the rope? I can let the strap go through the rope and make a figure-eighth knot on the other side? Or I can go in to the centre, out 4 cm down and make a figure-eighth knot at the end? In the back end of the cone, would it be enough with 2 cm? With 10 mm straps the figure-eighth knot will maybe to small and slipper out?

The dyneema-line is very slipper. When I shall retrieve the JSD, it’s not easy to hold the rope. If I have the straps via the centre of the rope, the knots will be in the same place around the line. On that place I can hold the rope temporary with a chain-hook. But what about the first 25 m? Shall I make dummy straps every 2 m?

The opening end of the cone is a sensitive part. I want to make the cone 1.5 cm large (longer) and then fold and stitch the edge. That way I will get down to the origin size, and a much stronger edge. If I have a strong edge, do I need that thick cloth in the cone?

The dyneema-line floats. Is that a problem? If the cones and straps are made of polyester, will that be so heavy that the JSD will sink? If floating is a problem, what about to splice in one 8 mm link of chain every 2 m. That would be a very good place to hold the line when I retrieve the JSD. Or should I splice in two 10 mm link of chain every 5 m?

My boot has a weight of 4500 kg. The rope should then have a breaking limit of 36 kN. A 8 mm dyneema have a breaking limit of 45 kN. Each bridle leg will get a load of 23 kN. According the table I need 100 cones. That will be a load of 360 N per cone. Or 120 N per strap. I believe that a 10 mm strap can take that load. A heavier boot has more cones, so the load per cone will be the same.

The boat is 2 m wide it the transom. The bridle should then be 5 m long.
Shall I let the main rope go all the way to the transom of the boat and 5 m out make a splice with another 8 mm dyneema-line, and that way get a bridle?

The dyneema-line is very easy to splice, but it is also slippery. Do I need to stitch the splicing?

A foldable padeye on the stern can easily take a load of 23 kN. Wichards 8 mm foldable padeye have a breaking limit of 50 kN. But be aware that when mounting a padeye with tree 8 mm bolts, the bolts need to be classified so they can stand the load. An 8 mm stainless bolt class 70 have a stretch limit of 16.4 kN, tree bolts have then a limit of 49 kN. (The break limit is 25.6 kN.) If a bolt aint classified, the manufacturer do not guarantee ANYTHING. The breaking limit can easily be down to the half.
When a bolt has reached the stretch limit, the padeye will not sit tight. The treads will be deformed and therefore it’s not possible to tighten the bolt.