Jack lines

[flyingwelshman]

I just installed anchor-points for jacklines. I put one on either side of my companionway hatch and one on the fore deck (just forward of my foredeck cleat).
I can either run one continuous jackline - clipped on at the hatch, down through the forward anchor point, then back up and clipped on the other side of the hatch. Or I can run two separate lines, one down each side of the boat, with each line clipped on to an anchor point.
Does anyone have any suggestion as to which way is better? and why?
I intend to use nylon webbing as the jackline material.
Thanks in advance.

[PBzeer]

Having two separate one's give you some redundancy.

[pdqaltair]

First, a few posts that might interest you, on jacklines, tethers, and the stresses involved. I have a catamaran, so my priorities are different.

Sail Delmarva: More Climbing Gear for Sailors

Sail Delmarva: Sample Calculations for Jackline Stress and Energy Absorption

Sail Delmarva: Climbing Gear for Sailors--Jacklines and Harnesses for the Unemployed

Pictures would help. I'm assuming the forward anchor point is a padeye that you could simply pass the jackline through. Make sure it is MINIMUM 5,000-pound rated and has 2 X 5/16-inch blots through to a backing plate. I don't understand how you are securing the and tensioning the lines (most people use the bow cleat for that reason--this also makes removing the jacklines easy, since nylon webbing should not be left out on the sun; if it is, the safe life of the jacklines is probably about 12 months, based on UV strength loss studies).

* You will have more stretch since a continuous line is twice as long. Not quite twice as much, as there will be some friction through the bow anchor.
* The load on the bow anchor point is about 175% of the basic jackline tension if the line is simply doubled back (that jackline is pulling and so is the dead end). You would need a very strong anchor to account for this stress doubling (about 8,000 pounds).
* The increased stretch will reduce impact forces but will increase the distance you fall. On a small boat and with nylon webbing, I think the reduced stretch is more important; you don't have the long fall distances a catamaran can have and you do have narrow side decks and bow.
* There will be some increase in chafe, since the line will rub under load through the bow anchor.

I think you might be happier with 2 lines, but if ease of removal is a factor, consider a cow hitch at the bow pad eye to reduce movement and partially reduce bow anchor stress (but I'm not saying how much, as the knot will slip). This knot is very small and will not seize up after being loaded.

[pdqaltair]

Originally Posted by PBzeer

Having two separate one's give you some redundancy.

That seems obvious, but you're only clipped to the windward line.... The second line will be useful when they return to collect you.

[flyingwelshman]

Thanks for the input so far.

The reason I added the forward anchor point (all of the anchor points are 6600 lb padeyes with additional (glastic) over-sized backing plates) was because I have only one cleat on the foredeck. With my bow docking line, spring line and anchor rode attached there's not much room for anything else on there.

I think the concerns regarding stretch and chaffing are very valid. So far it seems that two lines make the most sense. I intended to clip the jacklines to the padeyes. I figured that tensioning would be a challenge.

As I intend to use the lines when single-handing, the only way that two lines would add redundancy would be if I hooked on to both at the same time. This was not my intent. If the jackline gives, whether it's one or two, I'm going over anyway. The benefit of the redundant line would be that whoever finds my boat adrift and unmanned will have a nice, unbroken jackline.