Joining two long tow lines - how to do it ?

[sarabande]

Some pretty detailed discussion with an experienced sailing friend has recently explored some possible answers - all with advantages and possible disadvantages.

Scenario
Boat A needs a tow in rough conditions, and needs to join two purpose-made lines together to pass to towing boat B.

One suggestion is that both ends of the lines should be prepared with small soft eyes, and then be joined with a Swiftlink.

Another is to join the lines at the prepared eyes with dyneema wraps and anti-chafe.

And a third is to use a hard eye at one end of each tow rope and then use a decent shackle like a tested lifting Crosby in each hard eye to join the warps.

I have reservations about using knots to join tow lines, as the forces are likely to be in the order of several KNewtons, and chafe is a strong possibility, as is the load jamming the knot - unless someone knows of a rope-to-rope knot that will definitely undo after really heavy loads ?

Does anyone have any idea what sort of forces are involved in towing , say, a 6 tonne boat in rough weather ? 20 to 30 KNewtons (2 to 3 tonnes force) ?


How best to join the bits of cordage ?

 

[LittleSister]

Re: Joining long two lines - how to do it ?

If you want to be sufficiently prepared in advance to be talking about prepared eyes and specialist shackles, wouldn't it be easier just to have a single very long rope?

 

[William_H]

Re: Joining long two lines - how to do it ?

That is right Little Sister. For a towing situation you are more likely to be trying to use what is available for tow rope. If indeed the rope available is too short you must join ropes together. Ropes which will usually have just a plain end.
I would use 2 bowline knots. Bowline can be undone if it has been under load. Chafing may be a problem on the faying surfaces of the ropes in the knots. Hopefully your tow will not be that long in time if it is then check occasionally for chafe and if necessary retie the bowlines with chafe in a different place. olewill

 

[zoidberg]

Re: Joining long two lines - how to do it ?

Would the congregation not consider that the OP's 80m. of 22mm multiplait nylon ( ? ) should be quite sufficient for towing a 6-ton sailboat? Or, if snatch loads were a concern, then the basic technique of dangling a heavy tyre or an anchor from the middle of the line should solve that problem.....?

 

[Kelpie]

Re: Joining long two lines - how to do it ?

A sheet bend is the usual way of joining two lines. Less chafe than a pair of bowlines. Can be harder to undo after very high loading.

 

[GHA]

Re: Joining long two lines - how to do it ?

Spliced loops, soft or hard with soft or hard shackle would get my vote. Stronger than knots.

https://web.archive.org/web/20160318230212/http://www.bethandevans.com:80/load.htm

 

[savageseadog]

Re: Joining long two lines - how to do it ?

A sheet bend is the usual way of joining two lines. Less chafe than a pair of bowlines. Can be harder to undo after very high loading.

I tend to use double sheet bends instead of a standard sheet bend as the knot tends to be less tight, easier to undo after loading and more more secure or at least looks more secure.

 

[john_morris_uk]

Re: Joining long two lines - how to do it ?

On the size of lines used for a tow, is loss of strength really a concern? 65% of hugely strong becomes quite strong but still strong enough.

It’s the snatch loads you’ve got to watch out for in my experience.

I agree with double sheet bend.

If you are going to use bowlines where there’s a possibility of chafe, use a turn on the loop you thread through. (If you follow me..)

 

[GHA]

Re: Joining long two lines - how to do it ?

On the size of lines used for a tow, is loss of strength really a concern? 65% of hugely strong becomes quite strong but still strong enough.

It’s the snatch loads you’ve got to watch out for in my experience.

I agree with double sheet bend.

If you are going to use bowlines where there’s a possibility of chafe, use a turn on the loop you thread through. (If you follow me..)

No mention of line material or diameter - dynamic loads can go through the roof. Better to do the best you can if there is time IMHO.

 

[Kelpie]

Re: Joining long two lines - how to do it ?

Yes I generally use a double myself if it's for anything important.
I'd never had one jam on me until a few weeks ago when I used one on some heavy ropes at work that were being hauled by a hydraulic capstan. A pair of bowlines doing the same job have never jammed.

 

[guernseyman]

Re: Joining long two lines - how to do it ?

I would use a Hunter's Bend which is quick to tie, if you use the quick method. A round turn on each rope placed back to bank, then the two ends passed through in opposite directions. Depending on how you put the turns back to back you get either a Hunter's Bend or a Zeppelin Bend, reckoned to be the strongest bend of all.
Both knots can jam, but you normally have more time to untie than to tie.

 

[neil1967]

Re: Joining long two lines - how to do it ?

Slight thread drift, but do many people carry a dedicated towing line? We took a tow from a very obliging Dutchman a few years ago when we got a ball of rope around our prop off Calais (no wind). He has a line he keeps for towing and I've been wondering if I should do the same in case I can return the favour to someone else. What length/size of line would be appropriate - we have an Oyster 406 so we won't be towing anything too big.

 

[Plum]

Re: Joining long two lines - how to do it ?

I carry a long line suitable for towing but if i needed to join two I would vote for two of those already mentioned: the double sheetbend or the hunters bend. Both are very secure and weaken the line far less than bowlines.

Www.solocoastalsailing.co.uk

 

[fisherman]

Re: Joining long two lines - how to do it ?

Double sheet bend, used for attaching pots to backline and usually possible to release after lots of strain. But you could use spliced or bowline eyes, bound together with multiple turns of smaller cordage, which can be cut later, but often the end is so far from the strain it never goes tight. We join some net ropes like this using eye splices and (lots of) 5mm braided twine, it runs through the hauler and doesn't snag.

 

[GHA]

Re: Joining long two lines - how to do it ?

. the double sheetbend or the hunters bend. Both are very secure and weaken the line far less than bowlines.

Do you links to any load test data for that?

Double braid polyester seems you're better off with a bowline -

https://web.archive.org/web/20160318230212/http://www.bethandevans.com:80/load.htm

Average breaking strength as a % of rated strength(10 tests of each knot for 3 different lines)​

[TABLE="class: style62, width: 426, align: center"]
[TR]
[TD="class: style33, width: 54, align: center"]Bowline[/TD]
[TD="class: style33, width: 86, align: center"]Figure 8 Loop[/TD]
[TD="class: style33, width: 55, align: center"]Buntline[/TD]
[TD="class: style33, width: 118, align: center"]Double Sheet Bend[/TD]
[TD="class: style33, width: 113, align: center"]Double Fisherman[/TD]
[/TR]
[TR]
[TD="class: style33, align: center"]74%[/TD]
[TD="class: style33, align: center"]73%[/TD]
[TD="class: style33, align: center"]74%[/TD]
[TD="class: style33, align: center"]61%[/TD]
[TD="class: style33, align: center"]67%
[/TD]
[/TR]
[/TABLE]
2. The sheet bend slipped in all three lines. These are new lines, and more slippery than used ones, but it still suggests the sheet bend may not be very reliable (see tests of alternatives below in the "specialty knots" section).

 

[Plum]

Re: Joining long two lines - how to do it ?

Some pretty detailed discussion with an experienced sailing friend has recently explored some possible answers - all with advantages and possible disadvantages.

Scenario
Boat A needs a tow in rough conditions, and needs to join two purpose-made lines together to pass to towing boat B.

One suggestion is that both ends of the lines should be prepared with small soft eyes, and then be joined with a Swiftlink.

Another is to join the lines at the prepared eyes with dyneema wraps and anti-chafe.

And a third is to use a hard eye at one end of each tow rope and then use a decent shackle like a tested lifting Crosby in each hard eye to join the warps.

I have reservations about using knots to join tow lines, as the forces are likely to be in the order of several KNewtons, and chafe is a strong possibility, as is the load jamming the knot - unless someone knows of a rope-to-rope knot that will definitely undo after really heavy loads ?

Does anyone have any idea what sort of forces are involved in towing , say, a 6 tonne boat in rough weather ? 20 to 30 KNewtons (2 to 3 tonnes force) ?


How best to join the bits of cordage ?

Regarding max load on towline, my 21hp engine in my sailboat produces a theoretical bollard pull of 230kg. If i use all available thrust to drive my boat through a heavy sea at 4 knots then another boat would have to apply the same force via a towline if my engine stopped. Obviously, you need to allow for snatch (x3?) and apply a safety factor (x2?) That would mean i would need a towline with a breaking load of approx 1.4tonnes.

Www.solocoastalsailing.co.uk

 

[kalanka]

Re: Joining long two lines - how to do it ?

I agree with double sheet bend but the photograph above gives the wrong idea IMO - the tails seem minimally short.

I would tie the knot with long tails and seize or cable tie each tail to the standing part.

 

[Vegable]

Re: Joining long two lines - how to do it ?

Nobody's mentioned a Carrick Bend. I would have thought that would be the ideal knot to use?
Mike

 

[AntarcticPilot]

Re: Joining long two lines - how to do it ?

I would use a carrick bend, which according to Ashley is one of the strongest bends available, and is specifically recommended for joining anchor warps. It is also very easy to undo while remaining secure. There are two ways of using it; one is to tie the knot and leave the ends free; on taking a tension the knot will collapse into it's stable form with a long bight at each end of the knot; pushing those sideways will open the knot. The other is to seize the ends to the standing parts so it remains in the under-over pattern used to tie it ; this is what Ashley recommends for anchor warps. If in a hurry I would use the former; both are very secure and very strong.

If there is time to prepare I would suggest a spliced eye in each rope and then thread them through each other, reef knot style. That CANNOT come undone, short of the splice failing, and should remain reasonably easy to undo.

The majority of classic knots will remain easy to undo after being under load - it was part of the selection processs that made them classic knots! However, in come cases you do have to know how they come undone easily.

Incidentally, the bowline and sheet bend are structurally the same knot, so there is little advantage in linking two bowlines. The double sheet bend is no stronger than the single one, but is less likely to slip with modern materials.

 

[lw395]

Re: Joining long two lines - how to do it ?

I would use bowlines, with the bights formed into a reef knot where they meet. I think this cuts chafe.
Carrick bend is the proper thing, particularly if you have a frigate with a proper capstan to drag it around, but I would avoid any knot I wasn't very, very familiar with in this situation.
Bowlines seem to work adequately well with any rope. But I'd add a half hitch or a lashing as Fisherman says if I thought the knot was not lying tight because the rope was very big or stiff.
One advantage of bowlines is that you can add the second rope while the first bowline is dropped over the cleat or sampson post.