Duncan Loop in lieu of eye splice or bowline? - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
 Not a Member? 

Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


Reply
 
LinkBack Thread Tools
  #1  
Old 04-05-2011
patrickstickler's Avatar
Rhumbunctious
 
Join Date: Dec 2008
Location: Espoo, Finland
Posts: 150
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
patrickstickler is on a distinguished road
Duncan Loop in lieu of eye splice or bowline?

When one does not have time to make a proper eye splice, common practice is to use a bowline; but, a bowline halves the strength of the line and is thus suboptimal, however convenient.

There is a popular fishing knot, called the duncan loop, which is purported to preserve 95% of the line strength, and I'm wondering if anyone has used, or has any opinions about its use in lieu of a splice, as it can be quickly tied without tools, and can even be used with a thimble to prevent chafe.

The key difference that I can see between a duncan loop and an eye splice or bowline is that the loop will almost surely constrict with use over time, and as such, under significant load it's really more of a bend than a loop, but if a thimble is used, that could be a non-issue.

Though that raises the question of whether a thimble might reduce the strength of the knot, and perhaps a perfectly round thimble might be better than the typical teardrop shape.

Here is one tied with 10mm line:



Given that it is as strong as an eye splice, and can be made more quickly than a splice and without tools, one might wonder why splice at all? Cosmetic arguments aside...
__________________
...
If a man speaks at sea where there is no woman to hear, is he still wrong?
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

-
Cruising the Baltic in 'Merihiisi', a 1979 Westerly Berwick Ketch
Reply With Quote Share with Facebook
  #2  
Old 04-05-2011
Senior Member
 
Join Date: Feb 2010
Location: Narragansett Bay
Posts: 8,687
Thanks: 10
Thanked 113 Times in 107 Posts
Rep Power: 6
Minnewaska will become famous soon enough Minnewaska will become famous soon enough
If that is tied as I understand, the eye will slip closed under load. That is impractical to get it back off in many circumstances.

I'm unfamiliar with the declaration that the bowline halves the strength of the line. Any references?
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Jeanneau 54DS

In the harsh marine environment, something is always in need of repair. Margaritas fix everything.
Reply With Quote Share with Facebook
  #3  
Old 04-05-2011
zz4gta's Avatar
I don't discuss my member
 
Join Date: Aug 2007
Location: Chesapeake Bay
Posts: 2,420
Thanks: 0
Thanked 16 Times in 16 Posts
Rep Power: 7
zz4gta is on a distinguished road
I do believe that it greatly weakens the line, but by 50% is a bit of a stretch. I'd like to see some break testing to back that up.

This knot looks like a slip knot. Getting very tight with a load and very hard to untie. It will also not work for a halyard unless the sail wasn't at full hoist, and it looks bad. Doesn't offer much. It would hang up on shrouds as much as a bowline with being harder to untie. And most jib sheets are much larger than they have to be, so breaking one is rare.
__________________
Merit 25 # 764 "Audrey"
Reply With Quote Share with Facebook
  #4  
Old 04-05-2011
Senior Member
 
Join Date: Jun 2005
Location: New Orleans
Posts: 1,826
Thanks: 4
Thanked 21 Times in 19 Posts
Rep Power: 10
nolatom will become famous soon enough
been through a court proceeding last year with a rope expert, who opined that a bowline takes about 25% of the strength off a poly mooring rope. 50% seems high.

And the bowline not only won't slip, but is much easier than a round turn and two (or more) half-hitches to "break" and untie afterwards.
Reply With Quote Share with Facebook
  #5  
Old 04-05-2011
Boasun's Avatar
Senior Member
 
Join Date: Feb 2007
Location: New Orleans, LA
Posts: 3,056
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 9
Boasun will become famous soon enough Boasun will become famous soon enough
Am a retired Boatswain Mate; Now that may or may not make me an expert on anything, but I'am a student of most things and still learning.
Have seen it referenced on the Bowline that it reduced the strength of the line to about 54%. Checked with another retired BM and he said about the same thing.
The bad thing about "Experts", is that they stop learning after they think they know everything, and end up knowing very little.
__________________
1600 Ton Master, 2nd Mate Unlimited Tonnage

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Maritime Instructor
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

S/V Rapture
Reply With Quote Share with Facebook
  #6  
Old 04-05-2011
Senior Member
 
Join Date: Feb 2010
Location: Narragansett Bay
Posts: 8,687
Thanks: 10
Thanked 113 Times in 107 Posts
Rep Power: 6
Minnewaska will become famous soon enough Minnewaska will become famous soon enough
Very interesting.

Knot Break Strength vs. Rope Break Strength
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Jeanneau 54DS

In the harsh marine environment, something is always in need of repair. Margaritas fix everything.
Reply With Quote Share with Facebook
  #7  
Old 04-05-2011
Boasun's Avatar
Senior Member
 
Join Date: Feb 2007
Location: New Orleans, LA
Posts: 3,056
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 9
Boasun will become famous soon enough Boasun will become famous soon enough
Quote:
Originally Posted by Minnewaska View Post
Minnewaska's data is acceptable to me on this... 63% is a tad better then the 54% that I've quoted.
__________________
1600 Ton Master, 2nd Mate Unlimited Tonnage

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Maritime Instructor
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

S/V Rapture
Reply With Quote Share with Facebook
  #8  
Old 04-05-2011
AdamLein's Avatar
Senior Member
 
Join Date: Nov 2007
Location: Coquitlam, BC
Posts: 1,866
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 7
AdamLein will become famous soon enough
Interestingly, there seems to be some disagreement as to know the Duncan Loop is tied. This version clearly shows a slip-knot:



Yet I just watched a video that shows the initial loop being made in the standing part, which of course would prevent the knot from slipping:

http://www.videojug.com/film/how-to-...bJQ36w&cad=rja

However I don't know if this knot has the same strength as the slipping version. Actually I don't know if the slipping version has the strength that is claimed in the OP, but I have heard 50% for the bowline many times.
__________________
s/v Essorant
1972 Catalina 27
Reply With Quote Share with Facebook
  #9  
Old 04-05-2011
PaulfromNWOnt's Avatar
Senior Member
 
Join Date: Aug 2010
Location: Fort Frances, ON, CA
Posts: 342
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 4
PaulfromNWOnt is on a distinguished road
So what we should gather from all of this discussion is that rope selection should be based on the knotted breaking strength as opposed to the single line breaking strength.
Reply With Quote Share with Facebook
  #10  
Old 04-06-2011
Bilgewater's Avatar
Hmmm
 
Join Date: Jul 2008
Location: Campbell River, British Columbia
Posts: 514
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 7
Bilgewater is on a distinguished road
Quote:
Originally Posted by patrickstickler View Post
When one does not have time to make a proper eye splice, common practice is to use a bowline; but, a bowline halves the strength of the line and is thus suboptimal, however convenient.

There is a popular fishing knot, called the duncan loop, which is purported to preserve 95% of the line strength, and I'm wondering if anyone has used, or has any opinions about its use in lieu of a splice, as it can be quickly tied without tools, and can even be used with a thimble to prevent chafe.

The key difference that I can see between a duncan loop and an eye splice or bowline is that the loop will almost surely constrict with use over time, and as such, under significant load it's really more of a bend than a loop, but if a thimble is used, that could be a non-issue.

Though that raises the question of whether a thimble might reduce the strength of the knot, and perhaps a perfectly round thimble might be better than the typical teardrop shape.

Here is one tied with 10mm line:



Given that it is as strong as an eye splice, and can be made more quickly than a splice and without tools, one might wonder why splice at all? Cosmetic arguments aside...
That is the equivalent of a Prusik Knot. We use this at work under extreme loads. We use it for many purposes but quite often it's used as a sacrificial line (sac line) in order to take the weight off the main line. In other words we will tie it on another line which is under extreme load, then release the load and this sac line will take the full weight without slipping. It's a very useful knot but I always put in one more turn (4 in total). Your photo shows 3 turns prior to the half hitch. From experience, that knot if rubbed against a hard edge or corner will definitely cause it to slip and in your case, constrict but with a thimble that wouldn't happen. I would question that without a constant load, the half hitch may just work it's way loose....just a thought.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Impulse III
Truant Pilothouse
Reply With Quote Share with Facebook
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Main halyard tackle in lieu of winch jcalvinmarks Gear & Maintenance 10 01-13-2011 12:28 PM
Duncan Marine auleta General Discussion (sailing related) 0 04-22-2008 11:42 AM


All times are GMT -4. The time now is 11:28 AM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012