Mounting & use of Jacklines and tethers and sharks. Oh, my!

[Captain Smollett]

After all, Capn Mullet seems to doubt the G-forces

Uh, are we reduced to name calling now?

I call "foul."  This marks the end of civilized discussion.

He doesn't seem to understand that G-forces don't require great speed...since they don't measure speed but rates of acceleration and deceleration.  For instance, dropping a computer 60 CM onto the floor can generate up to 500 G's of force... since the deceleration cause by the computer hitting the desk and stopping suddenly is very high.

Dan, you are so wrong about this, and I really wish you would stop misleading people.

We are not decelerating the boat in 0.2 seconds like dropping a ball in a plate or in a car crash.  We are talking about TURNING a boat.

If you do not understand the physics of what you are talking about, perhaps it would be better to not comment.

But that's all from me on this subject.  You may once again have the last word.

[AdriftAtSea]

Again, you're missing the important part... the deceleration of the body when it falls across the boat, due to the rotation of the broach.  When it goes from whatever velocity you achieve from the 2.3 G's of acceleration to 0 at the end of the tether is when you get the high G-forces... not when the boat launches you across the deck—which is 2.3 G's according to your calculations.

Free falling after jumping out of an airplane is only going to accelerate you at 1 G... ignoring air friction losses... Hitting the ground because your parachute didn't open isn't going to be a 1 G-force event.  ::)

BTW, Capn Mullet, I'm a bit tired of your pompous and arrogant answers that are usually incorrect.  You're the one making the false assumption that the high G-forces are caused by the acceleration due to the broach, not during the deceleration due to the tether catching you, but you're the one accusing me of being wrong.

[okawbow]

On my bristol 24, I run a single 6000# jackline from the portside of the bow, to the stern. I always move along the starboard side of the boat when possible.

How do you get past the mast?

If i'm using the 6' tether, I can actually reach the headstay to change jibs without unhooking.( only 9' on the Bristol 24) If I want to, I hook my 3' tether in front of the mast, and then unhook the long one. I do whatever possible to avoid the chance of going over.

[AdriftAtSea]

So, you're not bringing the tether, where it attaches to the jackline, forward of the mast, just using the length of the tether and your arms to reach to the headstay, while the tether is partially wrapped around the mast.  That wouldn't work on my boat.

If i'm using the 6' tether, I can actually reach the headstay to change jibs without unhooking.( only 9' on the Bristol 24) If I want to, I hook my 3' tether in front of the mast, and then unhook the long one. I do whatever possible to avoid the chance of going over.

[Auspicious]

Someone here (Auspicious Dave was that you, by chance?) I think posted a link a while back to some MOB rescue 'data' that outlined a BUNCH of at-sea MOB cases.

Yes, that would be these: http://www.ussailing.org/safety/Studies/lifesling_history.htm

There are lots of take-aways from those case studies for any sized boat and crew. I think the most relevant to solo and two-up sailors are:

1. Don't fall off the boat.
2. Complexity is prone to failure in systems and procedures.
3. Being dragged through the water is bad.

The cases are sobering regardless. So often we talk in terms of what we think will happen, or might happen. It is interesting to have a statistically significant number of reports of what did happen.

Directly to the point of staying on the boat, in addition to jacklines--regardless of how they are rigged--I have two very heavily backed padeyes in the cockpit. Clipped to either of those I can't even reach the lifelines much less go over the side.

As in so many areas, there is a lot more opinion than fact. Even technical calculations (certainly including mine above) are just the manipulation of various assumptions. Personally I find case studies (of which there are few aggregations) and racing rules (like the ORC rules) most instructive. The latter may still have a component of opinion in them, but it is the consensus opinion of lots of people with lots of experience. Aside from the electronic equipment and liferafts, the ORC requirements aren't particularly expensive and do provide a baseline from which to scale solutions to smaller boats.

Having laid the foundation for more opinion <grin> I will say that based on direct personal side-by-side comparison that I do *not* like the fancy expensive Wichard double-action hooks on tethers. Under even moderate stress I found them awkward to get off the jackline. I like either a quick-release snap shackle or a carabiner for connection to my harness and a carabiner for connection to padeyes and jacklines. YMMV.

[s/v Faith]

Dave said;

Directly to the point of staying on the boat, in addition to jacklines--regardless of how they are rigged--I have two very heavily backed padeyes in the cockpit. Clipped to either of those I can't even reach the lifelines much less go over the side.....

  Excellent point.  Fixes the problem I was talking about below... I will add this to Faith's cockpit.  Grog for Dave...  ;)

FWIW,

Just a little more 'opinion' with a little experience mixed in.

  If we are talking about jack lines on small boats, I doubt a system can be made that would both allow mobility and keep you from going over the rail.  The distance from the sidedeck to the rail is just too short, your jacklines (even low stretch) will stretch enough if rigged fore/aft for ~20 -25'.  Even if you ran the jacklines through the 'D' ring on your harness you are going to have enough stretch to flip over the rail.

  The distances are simply too short... unless you are talking about multiple attachment points along the jackline.... which would be a real pain when going fwd.

[Sid T]

The OSHA requirements for safety harnesses and safety lanyards are a holding strength of 6000 lbs. This is based on test that show a 200 lb. person free falling for six feet will exert a force of 5500 lbs. It is also true that the breaking strength of a line is measured for a straight line force, if you attach in the center it varies with the force exerted for and aft and with the side pressure of the safety lanyard attached the results can reduce the breaking strength easily by one half. I only have about 30 days of blue water sailing experience but I have 35 years of industrial maintenance experience much of it 20 to 100 feet above the ground. Alway error on the side of safety. On offshore trips we uses a 10000 lb flat jack line each side fore to aft attached to thru bolted and backed attachment points

[Godot]

The OSHA requirements for safety harnesses and safety lanyards are a holding strength of 6000 lbs. This is based on test that show a 200 lb. person free falling for six feet will exert a force of 5500 lbs. It is also true that the breaking strength of a line is measured for a straight line force, if you attach in the center it varies with the force exerted for and aft and with the side pressure of the safety lanyard attached the results can reduce the breaking strength easily by one half. I only have about 30 days of blue water sailing experience but I have 35 years of industrial maintenance experience much of it 20 to 100 feet above the ground. Alway error on the side of safety. On offshore trips we uses a 10000 lb flat jack line each side fore to aft attached to thru bolted and backed attachment points

Sobering thought.  Ok.  I'm convinced. 

[Pappy Jack]

What Sid T is true. BUT the thing won't work unless you are hooked on. I had a guy fall 17 ft. in a power plant in Arkanas. He suffered a broken pelvic bone and a compression fracture of the spine :o. He did have his safety harness on... BUT... he didn't have it hooked to anything ::) ::) ::). He turned out OK and I tell this story to all the new hires I work with. Anything dealing with safety only works if it is used.

Fair winds,

Pappy Jack

[AdriftAtSea]

Very true... that's one reason I switched to integrated harness/pfds earlier this year. They're a lot more comfortable to wear than the separate PFD/Harness combos.

[CharlieJ]

This had been an interesting thread UNTIL the name calling began. I'm sorry but I quickly lose interest when that happens. Disagreement, even vehement disagreement can be managed without that.

[CapnK]

Agreed wholeheartedly, CJ, and this is very disappointing... I am surprised that I am having to post this, at being made to put on this hat.

We here are - or at least SHOULD BE - adult enough to handle disagreements without resorting to that sort of thing. I regard being disrespectful of others in any manner as being disrespectful to all of us. It doesn't make discussion points any better, it doesn't educate our readers any more, and it adds absolutely nothing to the discourse nor to the Community we have.

I do not want to, and I do not like even the idea of having to, exercise dictatorial powers on this site.

But - I will. And without remorse, when the time comes for it.

And for clarity: there will be no 'appeals process' involved, if and when I am forced to act in this manner. Having to do so will not have been my choice; it will have been something forced upon me by someone else. That makes me grumpy, stubborn, and recalcitrant.

I say the above, and absolutely mean it, out of respect and regard for the sailFar Community, for all the other people here who willingly conduct themselves with decorum and propriety, as well as for the shared goals and ideals which we all purport to love and hold among our highest aspirations and dreams.

Keep it civil. Or take it elsewhere.

That's the Rules.

Period.

--------------------

That said, I am both enjoying this discussion and learning from it, and I hope that it will continue.

:)

[CapnK]

I don't have the numbers to back it up, just a basic understanding from things I've read, but from what I do know I'd say that just about everything written here so far is correct to a point. It's obvious that the loads imposed on the tether/jackline system peak much higher than you'd think, even if the initial forces don't seem to be that large. Same thing on your standing rigging; that single 1x19 wire might be able to hold 2 or 3 of your boats weight up in the air, but the shock loading it can get when just 1 of your boats falls off a wave with a loaded rig can pop it like it was a single cotton thread, if everything happens *just so*. That's why a true 'bluewater boat' will have a rig that is much, much stronger than it apparently needs to be (and conversely, a weekender might not have quite that same margin).

Some random info: My brother is a pilot, and he told me that airline seats are rated at 19G's vertical. Wikipedia has some interesting info, including that race car driver Kenny Brack survived a crash that sensors in his car put at 214g's. But a post I read on another site seemed to put it in perspective best:

Instantaneous G's don't mean much.
A flick of your middle finger is all it takes to trigger a 100G shipping shock sensor.

You have to look at the entire acceleration (de-acceleration) curve vs. time to
get a better picture of whats going on.

So I'd say that based on this, and what SidT relates above, instead of arguing over how many/much G's are produced, it would be a lot easier to say "The continuity of my cruising lifestyle is of such importance to me that a 6,000#/10,000#/pick-a-personal-number# breaking strength jackline would be a Good Thing to have, even if it is more than I will probably ever need..."

We can be guilty of over-analyzing things, eh? ;D

[OptiMystic]

Having been married for almost 20 years, I can tell you that having facts on your side in argument means something. What, I am not sure, but something. This post might have a point, but I am not sure what it is... Dear???

[Godot]

Since I started this thread, I want to apologize for any induced enmity and hurt feelings.  I'm afraid that is always a risk when challenging conventional wisdom.  It was certainly not my intention.  What was my intention was to answer...

1. Is a 6000# jackline really necessary and why.  Apparently, it IS necessary because the forces it could be forced to survive can be quite extraordinary.  I still find it hard to accept they can be as high as suggested; but that doesn't mean it is not true.  Prudence will probably win out, here.

2. The best way to string the jacklines across the deck.  No consensus at all here that I can figure.  I think I'm going with my original plan of jacklines in two pieces, the first piece on the left and right sides of the dodger up to a point just forward of the mast, and the second piece a centerline jackline from just forward of the mast to as far forward as necessary to handle all tasks up there.

3. How to get back on board after going swimming (while still attached via harness and jackline).  Some want to run the jacklines bow to stern on the outside of the shrouds (I'm assuming deck mounted shrouds that are well inboard).  Others just shudder and get fatalistic about surviving at all.   I'm kind of falling into the second camp at the moment.  I am getting some ideas, though.  Sadly, to see if they are valid may require actually being dragged via jackline beside a moving sailboat.  I'm not sure I want to try that out (I suspect injuries ranging from bad bruises to cracked ribs to worse are possible, even with a safety crew).

[CapnK]

Adam, one other thing I have seen some cruisers do:

Run a line up well above the stanchions, secured to the shrouds, as an additional thing to grab onto in order to hopefully avoid going off the side.

Using a tether which has 2 'biners (in addition to the one clipped to your harness) would allow you to have multiple short jacklines that would make it impossible for you to go off the side (or very far off). Yes, you have to clip/unclip more often as you move forward on deck, but if the point is for the thing to keep you on the boat, then that necessity would seem to outweigh convenience...

Idea: It might be being done already, but it might be an interesting thing if someone would make a tether which had a 'speed brake' (acceleration brake?) built into it, like a car seatbelt. Moving slow, it would unreel/reel in tether as needed, but if a sudden unreeling were to start, it would simply slam on a stop, and thus perhaps keep one from being thrown off.

Food for thought. :)

[Godot]

I think that with the two shorter jackline lengths that are as near as possible to the centerline the amount of stretch would be significantly reduced and with a 3 foot tether I would be far less likely to end up overboard.  I have to measure; but let's say eight or nine feet from the companionway to forward of the mast, and maybe a seven footer from the mast just close enough to the bow to do what needs to be done.  I would have to change jacklines as I moved to and from the foredeck which is slower and less convenient; although, maybe slowing down would be a good thing.  For extended work, I should be able to clip on to a hardpoint at the bow and at the mast, in addition to being clipped onto the jackline. 

Here is a thought ... if there where multiple places to clip on AT THE RAIL (how about one of those genoa rails where you would hook snatch blocks), say, at every place the swimming sailor would likely get caught up, would it be possible to build a kind of portable boarding ladder with maybe one step that can be carried with the harness?  Something that could be clipped on to a nearby point and used to give the poor drowning rat a booster step up.  Did I explain that well?  I don't know if it would work.  Being dragged along the side of your boat at five or six knots with an inflated vest might make doing work like this difficult; but I figure anything is better than nothing.

[Tim]

This has been quite an informative thread. I probably will continue to use the climbing webbing that I have rated at 17.8 kilonewtons LOL.  

Since I am redoing all my deck fittings right now I will keep in mind attachment points that keep the webbing as close to the centerline as possible, along with adding a closer attachment carabiner on the tether perhaps with a friction braking knot (gonna have to talk with climbing friends about that).

Obviously I am in the camp that has no intention of getting on the out side of the deck.

[Godot]

I just thought of a problem with my jackline scenario ... the forward jackline would go right over the top of my forehatch.  I'm not certain I want that blocked off (in fact, I'm fairly certain I DON'T want that blocked off).  I might need it for ventilation, stuffing things in the cabin in a hurry, or emergency egress.  So, to make things even more complicated, I guess I would need two jacklines running from either side of the forehatch it a single point at the bow.  Or, I would need to extend the aft jacklines up to either side of the hatch, and do a very short line from just forward of the hatch to the bow.  I need to make it to my boat (either this evening or after tomorrows sail with Auspicious) and see how things lay.

[Auspicious]

Just a thought -- most people clip on and go forward on the windward side without thinking about it much. Most of the "I fell overboard" stories including falling off to leeward. Accordingly, if jacklines are outboard you have the width of the boat to fall before going over the side.

Run a line up well above the stanchions, secured to the shrouds, as an additional thing to grab onto in order to hopefully avoid going off the side.

I've seen this also. I don't like it, *particularly* on small boats. If you hit that high lifeline at speed (falling across the deck for example, or even stumbling when the boat falls off a wave) you are putting a significant load (reference the jackline discussion) on the shroud in a direction it wasn't designed to take a load. That is one thing on my rigging (big stuff - 3/8" at least, with fore and aft lowers in addition to principal shrouds) and something else entirely with 1/8" wire.

A risk management approach to one risk (falling overboard) that adds a new risk (adding a failure mode for the rig) is not one I would participate in.

In my personal opinion this is a superficially good idea that doesn't work out in practice.

I would suggest as an alternative standard lifelines, standard jacklines, shorter tethers, and a practice of crawling out on deck. I'm not proud -- sometimes I crawl. In fact, my offshore foul weather gear has pads sewn into the knees to make crawling more comfortable.

sail fast, dave