Berth Line Set Up Advice
The advice on this page is general in nature and more concerned with pointing out some common problems that can lead to line breakage or other damage.
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Here's some general information on Mooring lines
All Lines need to be of a sufficient rating (strength) and need be protected from sharp edges and chaffing.  
No fibre rope is immune to cutting or wear
  All moored vessels need to be checked regularly as lines do chafe and wear.  Don't forget to also check the condition and security of cleats, bollards and other fittings!  As well as regular checks, lines and fittings need to be re-checked before and after bad weather  
 
To get the best performance out of your mooring lines -
Firstly lets get an understanding of what each of the different mooring lines does
 
Lines are properly named after what function they perform - the movement they control
 
A for'ard spring does not necessarily need to be on the forward part of the boat
Aft Spring
on Fwd Cleat
Fwd Spring
on Aft Cleat
An advantage of short opposing springs like these (if only using two) is that they can serve a secondary purpose of controlling movement of either end of the vessel away from the berth. For example the bow cannot move very far from the berth unless the vessel can move forward.  You would never leave a vessel berthed with only two lines but an arrangement like this could hold the vessel in place temporarily.  These two would be the first two on.
 
However, there is one big rule
The MAXIMUM angle away from the horizontal for any line under strain, should be 45 degrees in the fore and aft line, this leads to excess line stress, also 45 degrees up to a bow fitting but near perpendicular out from the dock can still be subjected to excessive stress. 
Some boats roll, some pitch, some yaw - ALL BOATS move up and down in some way relative to the dock pontoon Under no circumstances should you have a mooring line which is nearly vertical between the pontoon and the boat - and is tight!! A line like this tries to prevent vertical movement.  That's a sure way to end up with a broken mooring line - or worse!
The simple test of whether your lines are at risk of breaking, or are risking damage to fittings, is to look at them and picture what they are doing.  Your lines should be stopping your boat from moving: forward or backwards along the dock and Out away from the dock.  If your lines are trying to stop any part of your boat from moving up and down or rolling, your set up can be improved.
 
Did you know - Dynamic Loading
VOIDS the Breaking Strain of your rope
 
Here's an example of a pretty effective standard line set up, where the lines are long enough and at a low enough angle to reduce and absorb stress from dynamic loads
The boat is controlled forward and back and there is good control from 'stretching' away from the berth or twisting 'yawing' in the berth
The dotted arrows show the lateral control point created by the two opposing lines working against each other, basically the effect is like an invisible perpendicular line at that point.
 
The problem is that most boats in floating marina berths are just the right size for the berth
Which means that the stern cleat will line up vertically or near vertically above the berth cleat
 
The stern line
will try and
stop vertical
and rolling
movement
Definite
Dynamic Loading,
no question
The Bow line
May try and
stop rolling
movement
Dynamic Loading is very likely
From what we see this is a fairly standard arrangement
 
One solution is to run crossed springs
Stress on the lines has been relieved, but -
The points of 'control' are close to the centre of the boat and this may allow the boat to pivot or yaw excessively in the berth.  Again the dotted arrows indicate where lateral control created by the crossed opposing lines is 'felt', where the invisible perpendicular lines act.
 
The Golden Rules for Mooring Lines
1. Spring lines should not have excessive slack, such as would allow a boat to get a run up from spring to spring.
2. A line should not be more than 45 degrees up from the horizontal.
3. If it is not possible for a line to be more than 45 degrees from vertical, it must not come taught when the boat bobs up and down or rolls.
4. All lines need to be protected from rough or sharp edges.
5. All lines need to be checked regularly and re-checked before and after bad weather.
 
This may come as a surprise, but lines do not simply break because a load greater than their breaking strain has been applied to them.
This is obviously part of it but really, they break because they have been over stretched.

Often when we talk about the stretch factors of various ropes we describe how much stretch they have as though this is always a great advantage - not so.

Depending on the source you refer to Nylon stretches up to 50% of its length at rupture (breaking) compared to Polyester at maybe 35% extra stretch doesn't make it better, just for some things, like anchoring.

If we accept that Polyester stretches to about 35% to breaking point, this means that if we have a line on our boat that is one metre long, and because of the movement of the boat that line can be stretched by just 35 centimetres, it will fail. 

Using Nylon, or any available shock absorbing device will do little more than extend this by a few centimetres.

HOWEVER

If we set up the lines differently.  So that the same type of rope is 5 metres long to do the same job we now need to stretch the rope 175 centimetres (nearly 2 metres), before it will fail.  That's a lot of movement. 
And the load will come onto the rope more gradually, 'less dynamically' dissipating the initial force all the way.

Any boat will roll and bob by 35 centimetres or more, particularly when you consider the boat and dock moving independently and invariably going in opposite directions at some time.

Here's where we need to consider the "real" stretch factor we need to take into account, the % stretch to the rope's Safe Working Load (SWL).  This is the amount a rope can be stretched before it starts to suffer damage. 
With Polyester this is accepted as 15%, 75 centimetres on our 5 metre line (nearly a metre).
With Nylon this figure may be around 25%, still only 25 centimetres on our 1 metre line, every centimetre after this is degrading the rope.

Many stern lines we see are nearly vertical and less than a metre long.  This is a common problem that we do not believe is adequately protected against by conventional methods.
Now there is a solution 
Here's why our New
MoorControl 'Y' Lines are better
'Y' lines also take a lot of confusion out of line
set up caused by varying cleat placement and spacing. 
And when used in conjunction with a MoorControl
TM  System they make tying up easier because they can be set up so that just two eyes need to be looped on the boat for full line security
You can't always have the cleats in the right position.
Now it doesn't matter.

 
In the example below, the 'Y' Line effectively consists of a stern breast line, longer than usual with a spring line spliced into it which, tensions the stern line to hold the boat alongside. (if using just one 'Y' Line an opposing spring is required) When the boat rolls or bobs up and down against the stern line the arrangement of these lines assists in dissipating shock loads through the length of all the lines.  By comparison, the forward 'Y' Lines differ in that they effectively have a breast line spliced into a spring line.
 
Click on image for animation of 'Y' Line action
We've shown a stern 'Y' line on its own with an opposing spring and bow line
 
More information on our Y Lines can be found on our
Mooring line Page
 
The 'Y' Line arrangement can be used fore and aft
And with a variety of cleat/bollard arrangements
(forward 'Y' lines are slightly different to stern lines)
This one above has the spring from the stern line as an 'aft' spring
The bow 'Y' Line is set up as a forward spring
The example above has the function of lines reversed, sprung forward from the rear 'Y' Line
and sprung aft from the forward 'Y' Line.
No centre cleat on boat or dock, the 'Y' Lines are made longer and reach end to end,
in this example sprung aft from the aft 'Y' Line and forward from the forward 'Y' Line
Sprung forward from the aft 'Y' Line and aft from the forward 'Y' Line
 
'Y' Lines make it easy to get the right set up on virtually any floating marina berth
 
Compare the action of standard lines
to 'Y' Lines
The diagram below is an example of a reasonable standard line layout

 
 
The lines shown in red are the active lines, those that are under strain
BUT
The shortest line is still probably only around 2 metres long, requiring only about 30 centimetres of relative movement between boat and dock
to cause failure.  'Y' lines may be an option.
 
For temporary lines this is an adequate set up

Just two are capable of holding the boat (suitable for temporary mooring)
 
 
Again the line in red is active and under strain
What's the difference between this and a 'Y' line set up?
This line is now subjected to Dynamic Loading!
 

The inside 2 lines can hold the boat, but not as well as the outside lines
 
 
Even though both lines are loaded, their geometry doesn't make for great control
 

In the real world berths are usually just the right size for the boat so we don't have the luxury of a distant stern cleat
 

The temptation then is to put lines straight UP to or straight OUT to the boat's cleat or bollard.  Now we're trying to stop roll or bob. WRONG
These lines are certain to be subjected to Dynamic Loading!
 
Now look at the action of the 'Y' Lines

This set up has the springs secured to a dock cleat
 

The forward line to 'B' prevents the boat moving forward.  The stern cannot swing out unless 'D' can swing forward in an arc.  The aft spring line is only under tension because the stern line to 'D' is trying to straighten
 

The lines work the same way from the bow but will allow slightly more movement due to the extra length needed in the Y line at the bow
The 'Y' line still has the ability to reduce or cushion Dynamic Loading!
 

If no dock cleat is available, both 'Y' lines can be secured to a second cleat or bollard on the side of the boat
 

This time the line to 'C' stops the boat moving forward and unless 'D' can move forward it cannot move out.
 

With the wind on the right angle and strong enough 'C' and 'B' could move out together but only until the line to the rear dock cleat from 'C' takes strain and stops 'C' moving out
 
In any of the 'Y' Line examples above doubling up for peace of mind can be done, conventional springs can be added.
And additional bow and stern lines as long as they have sufficient slack so as not to take tension while the 'Y' lines are in tact, they must hang slack just short of the water.
 
Spring lines should be kept reasonably tight to prevent the boat getting a "run up" from slack take up to slack take up.
Every possible circumstance or combination has not been shown -
the examples are to demonstrate the purpose and function of the lines
 
For a recommendation and quote for lines to suit your application - go to our
'Mooring Line Page'
 
For conventional lines we recommend lines with a soft spliced eye (loop) on one end and an anti fray finish such as a sailmaker's whipping on the other end.
This way, on for example a vessel berthed bow in, the for'd spring
(that stops boat moving for'd) is belayed to the berth cleat with the spliced eye (loop) able to be quickly dropped over the boat's cleat or bollard, to limit for'd movement and position the boat at a predetermined place in the berth (adjusted with the belayed end).
The Aft Spring is fitted to the berth by "threading" the eye through the hole in the berth cleat and doubling the loop back over the horns of the cleat. The straight end is now ready for you to use to tension against the for'd Spring to hold the boat snugly and prevent it moving back and forward.
From there it is really personal choice whether to fit the bow and stern lines to the berth with a belay and put the eyes to the boat, or the other way around. Unlike the Springs, the bow and stern lines don't need to be (and shouldn't be) tight. They need to allow a range of movement depending on the characteristics of the boat.
Splicing all your mooring lines directly to berth cleats, with drop over loops does not allow for re-tensioning.
 
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The advice on this page is valid only for floating marinas, and is of a general nature only.
If in any doubt seek advice from your Marina Manager or local boat club