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PostPosted: Tue Feb 21, 2012 8:39 am 
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I've been having issues with my rudder off and on since getting my boat six months ago.

As I've dissected the rudder system and the control lines in greater and greater detail, I've found that the knots used on the control lines are not appropriate and in general not safe for long term use.

The most widely used knot is the overhand knot http://en.wikipedia.org/wiki/Overhand_knot. The key problem with the overhand knot is it's strength. It causes a 50% reduction in line strength due uneven wearing and stretching. Over time, this will increase until the line FAILS.

Much better would be the figure eight knot http://en.wikipedia.org/wiki/Figure-eight_knot_%28ropes%29. It causes a 20% reduction in line strength.
or
The blood knot which is ideal for slippery line like spectra or monofilament line and causes a 20% reduction in line strength.

The bowline, double bowline, double fisherman's knot, carrick bend, sheetbend, and double sheetbend could also be considered.

I found that overhand knots were used in the running length of a line merely to shorten the line. This is something that a knot should NEVER be used for because it weakens the line. If it has to be done, at least use a knot appropriate for the use and that does the least damage.

I think that with all the sailing experience Hobie has they would know better.

I have ordered new spectra cord and will be replacing all of the existing rudder line. I think I will also install a turnbuckle in the system to tension the lines

Disquieted,

j

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PostPosted: Tue Feb 21, 2012 8:59 am 
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I agree with you 100%, however in Hobie's defense, I suspect the strength rating on the lines far surpasses that which is necessary so any reduction in strength due to poor knots is mostly a non-issue.


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PostPosted: Tue Feb 21, 2012 9:56 am 
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... perhaps if this were a Pottery forum and vendor tied a box up with a sloppy knot - but it being a sailing boat ...

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PostPosted: Tue Feb 21, 2012 10:12 am 
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Tom Kirkman wrote:
I agree with you 100%, however in Hobie's defense, I suspect the strength rating on the lines far surpasses that which is necessary so any reduction in strength due to poor knots is mostly a non-issue.


It is true that the initial strength may far surpass the needs of the boat, however a knot is a destructive thing. It slowly breaks the line down, until the line fails. It creates high stress zones that far exceed the actual load, focusing the entire load on relatively few fibers in the line, while wearing on itself, destroying fiber though friction, and creating a focal point for wear from outside sources.

Cut though an overhand knot that has been in heavy use and you should be able to see the effects I've described.

Knots, properly used, are fine. I have several in use on my boat, but they are located where they are easy to inspect and easy to replace. The steering system is neither.

j

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PostPosted: Tue Feb 21, 2012 11:45 am 
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kayakman7 wrote:
I found that overhand knots were used in the running length of a line merely to shorten the line. This is something that a knot should NEVER be used for because it weakens the line. If it has to be done, at least use a knot appropriate for the use and that does the least damage.

Gotta agree. If you must use a knot to shorten a line, the Alpine Butterfly Knot is best IMHO. Very popular with climbers and those dudes are seriously motivated to look after their lines.

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PostPosted: Tue Feb 21, 2012 12:02 pm 
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chrisj wrote:
kayakman7 wrote:
I found that overhand knots were used in the running length of a line merely to shorten the line. This is something that a knot should NEVER be used for because it weakens the line. If it has to be done, at least use a knot appropriate for the use and that does the least damage.

Gotta agree. If you must use a knot to shorten a line, the Alpine Butterfly Knot is best IMHO. Very popular with climbers and those dudes are seriously motivated to look after their lines.


That's funny, I have an alpine butterfly knot tied in my barber hauler. It's also ideal for placing a loop in the middle of a line with unequal loading.

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PostPosted: Tue Feb 21, 2012 12:28 pm 
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kayakman7 wrote:
It's also ideal for placing a loop in the middle of a line with unequal loading.
I use them to loop the ridgeline of my camping hammock over the support poles. Classic example of three way loading.

Image

They're also great for isolating a section of damaged line - just tie the knot so that the damaged section is part of the loop.

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PostPosted: Tue Nov 05, 2013 12:30 pm 
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chrisj wrote:
kayakman7 wrote:
I found that overhand knots were used in the running length of a line merely to shorten the line. This is something that a knot should NEVER be used for because it weakens the line. If it has to be done, at least use a knot appropriate for the use and that does the least damage.

Gotta agree. If you must use a knot to shorten a line, the Alpine Butterfly Knot is best IMHO. Very popular with climbers and those dudes are seriously motivated to look after their lines.



Long reach back for this one .. and not entirely sure how I got to this thread but

That knot is brilliant !! I can't believe I've never seen it before having spent a fair amount of time clipped in

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PostPosted: Tue Nov 05, 2013 4:13 pm 
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Sometimes we have to choose between building boats and making better knots. We have expert knot guys and experts at getting the job done in a production setting.

And, Tom is correct. Our Spectra control lines are way, way over their required strength to do the intended job. In addition, knots under low loads do not likely to decrease strength as one would under maximum loads.

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