Knots

[Steve Robinson]

Ok, here’s the scenario…

You are laying line in a system with the intention of meeting up with an existing line to form a T Junction. When you intercept this line, what knot do you use to tie on with?

Using a bowline or other loop type knot would not be tight enough, allowing the junction to move along the existing line. My best guess would be to thread a clove hitch and back it up with a couple of half hitches but this may be problematic in poor viz.

Has anyone got a better idea?

Ta, Steve

 

[wormster]

Alpine butterfly??

can be tied one handed:

http://www.animatedknots.com/alpinebutterfly/index.php?LogoImage=LogoGrog.jpg&Website=www.animatedknots.com

 

[francis]

I'm not a diver so I don't know, but would the original line have enough slack to make an alpine butterfly in it? Then you could interlock the new line into the loop.

An alternative might be a knot in the constrictor family, they are_very_very_very hard to undo.

Francis

 

[peterdevlin]

Alpine butterfly??

can be tied one handed:

Respect!

I would really struggle to tie an alpine butterfly with 1 hand. But agree this would be great to tie the new line into.

 

[wormster]

Alpine butterfly??

can be tied one handed:

Respect!

I would really struggle to tie an alpine butterfly with 1 hand. But agree this would be great to tie the new line into.

opps i meant that it can be formed around the hand, meaning that if you learned to do it blindfold, you could do it in any vis conditions.

 

[peterdevlin]

Alpine butterfly??

can be tied one handed:

Respect!

I would really struggle to tie an alpine butterfly with 1 hand. But agree this would be great to tie the new line into.

opps i meant that it can be formed around the hand, meaning that if you learned to do it blindfold, you could do it in any vis conditions.

;-)

 

[docfunk]

Yep I would use an alpine flutter by.
My party trick was to tie one(and a bowline),one handed in my pocket

 

[Steve_T]

Alpine butterfly? Great if you have the slack, if not then no chance.
I would go with Francis, a constrictor knot with a few half hitches added, no chance of slipping in either direction and will not come undone.

 

[Dep]

In the existing line put a half hitch into it with one hand to make a loop...
Then thread the end that you are carrying into it up through the loop and then around the main line and back out of the loop. "as in lake-frog-tree"
The end result is essentially the same as a bowline but tied with two separate bits of line.
It won't move up and down and shouldn't come undone although a safety knot on the free end might not be a bad idea I guess.

 

[Steve Robinson]

Sounds good but pulling on the existing line to make a half hitch runs the risk of pulling it into a line trap or causing it to abraid on a sharp edge.

 

[AMW]

As long as the line is secure a range of knots and cable tie methods can be used.

This is a junction that is fine (better  than it looks) not my work but fine to use.

Andrew.

 

[Dep]

Sounds good but pulling on the existing line to make a half hitch runs the risk of pulling it into a line trap or causing it to abraid on a sharp edge.

You only need a few inches of slack to do as I described.
Otherwise if it's that critical then larksfoot the diver's new line onto the existing line and use a safety knot to secure it so it doesn't come undone.
BUT, unless  you have some form of hitch or loop in the existing line it will slide up and down.

If your main line does not permit a few inches of movement without risk of abrasion then something is very wrong!
I'm not a diver myself but surely divers swim along holding onto these lines as guides? and this would add a much greater pull than what I suggested for a knot.

 

[AMW]

holding onto these lines as guides? and this would add a much greater pull than what I suggested for a knot.

You should never pull on a line, just let it run through the hand with minimum pressure on it.

Andrew.

 

[Dep]

holding onto these lines as guides? and this would add a much greater pull than what I suggested for a knot.

You should never pull on a line, just let it run through the hand with minimum pressure on it.
Andrew.

Understood, thanks.
I reckon you would be ok with gently teasing out a very small loop as I suggested, it will be a one-off event and will release the slack in the main line once the knot is tied.

 

[Peter Burgess]

Ah, Dep, you should have consulted out mutual cave diving acquaintance before offering help on this! 
You know the onw who practices by crawling around under bushes.

 

[MSD]

If the line concerned is hawser laid, twist the line to open the lay and poke your line through. Take an extra turn and tie a bowline. MSD

 

[Pitlamp]

I'm not convinced a lot of the above advice fits with CDG best practice. Most UK divers prepare the reel beforehand so that there is a safely tied loop in the start of the line - the reel is then passed through the loop to attach it to an existing line. The idea is that you don't need to tie ANY actual knots underwater - as any required knots are likely to be much more secure if tied in advance on the surface. Knots tied underwater have a long history of being insecure! The above method results in a "hero loop" (as climbers call them) - or is it a lark's foot?  (I can never remember.)

Anyway, once the branch line is attached in this fashion and then laid out it CANNOT become detached from the line it was looped onto.  So then the only problem is that it can travel along the previous line and thus perhaps not follow a safe route through the sump. As folk have said above, adding zip ties will then prevent this travel. However another way is to secure the junction to a decent belay (e.g. a large rock) so that you don't have a floating junction.

It's generally held to be good practice to try and avoid tying any knots underwater if possible.

 

[Steve Robinson]

Pitlamp, your sound advice regarding primary belays is much appreciated.

What can you advise for when you are "completing" a line-lay to create a T-Junction with another line that you come across on your travels?

Ta, Steve

 

[Pitlamp]

Sorry Steve - I only got back from working away just now and I'm a bit busy at the moment. I'll try and put a few ideas on here soon . . . .

 

[Pitlamp]

. . . got a bit of time, so here are a few ideas.

Firstly, how you create a junction to complete a new loop may well depend on various factors such as how quickly vis is lost, depth (affecting narcosis and deco time build up), temperature of the water (influencing manual dexterity), amount of gas available, likely future currents, availability of convenient belays, what belaying devices you are carrying, etc, etc. 

In particularly difficult circumstances you may opt for a somewhat temporary arrangement which can be improved on a future dive.  But remember that those "difficult circumstances" are also likely to make life awkward in future if the junction fails, leading to loose line.  For example, a quick method (if there's no time to do a proper junction) might be simply to zip tie the lines together then continue reeling out beyond until you find a proper belay.  This would leave the lines in a safe condition for other visitors, which you could then improve on the next dive. The downside is that you would temporarily have a 4-way junction.

Anyway, for what it's worth, here is a method I like to use. I'll refer to the line you are laying as the "new line" and the line you are joining onto (to create a T junction) as the "in situ line".

1. As you approach the in situ line, place a temporary "OUT" marker on the new line.
2. About 30 cm before you reach the in situ line tie a small overhand loop in the new line.
3. Pass the entire reel around the in situ line several times.  If possible do this at a line tag on the in situ line as this will make surveying more accurate.
4. Secure this "wind around" area temporarily with a zip tie.
5. Pull off 2 m of slack from the reel then cut the reel off.
6. Secure remaining line on reel and clip to in situ line out of the way.
7. Use the 2 m tail of new line to tie in to the overhand loop in the new line (which you tied earlier, 30 cm before the junction). Any sensible knot will do - feed the line around to create a reef knot or tie a simple sheet bend.
8. "Lock" the knot just created with a few half hitches (using up the rest of the "tail" of new line).
9. "Lock" the half hitches by adding a couple of zip ties.
10. You should now have a small triangle of line.  The sides of the triange can be drawn in if desired with further zip ties to tidy the whole thing up. 
11. Belay the junction - e.g. by hero-looping a snoopy around the coiled area on the in situ line before attaching this to a boulder, flake, silt screw or drop weight.
12. Collect your reel, remove your temporary "OUT" tag and survey out along the new line.    13. Write your dive log A.S.A.P. to inform everyone else about the new line junction.
14. Consider installing a permanent "OUT" tag on a future dive, to indicate the easiest way out from the junction, if appropriate.

There are a few other things to think about. If vis is not easily disturbed you might consider travelling a short distance along the in situ line in each direction to identify the optimum place to create your new junction. If you find there is enough slack in the in situ line you might consider making an overhand loop in the in situ line instead of in the new line as described above. Your new line might also be used to create gentle tension in the in situ line, thus making the whole area safer (provided this does not pull the in situ line away from a safe course - or from a potentially useful belay for the whole junction).

These are just my ideas and you may well get better ideas from other people. Give it a go and let us know how you get on. You might well come up with something better.