Mooring Lines

I learnt just about all there is to know about rafting boats with our gameboat & mothership operation!

The high winds we experienced on the
Australia Day weekend from ex-cyclone Oswald, were a wake up call for many owners regarding their mooring line set ups. While a lot of the old timers and experienced boaters have seen this before, you only need to walk around the marina to see who wasn’t prepared by the poor state of their mooring lines – or what’s left of them! The forecast issued some 24 hours earlier for Moreton Bay waters was E to NE 40 to 45 knots, possibly reaching 45 to 50 knots at times. As if that wasn’t bad enough, they added possible thunderstorms with gusts to 75 knots. When I saw this forecast I immediately contacted all my clients and told them I would be at the club within the hour, doubling lines and taking down biminis etc.  On arrival I assumed the marina would be bustling with concerned owners doing the same.  I spent the best part of that day at the club and I was amazed at how few people turned up. Instead, the task was left to our marina manager and a handful of helpers who were doing the rounds, adding additional lines to some of the more poorly moored boats. Thankfully, this preparation helped reduce the amount of damage and being on hand during the height of the winds the following day was vital, as many lines were wearing
through and needed to be doubled up and replaced. Not to mention the fenders
popping and squeezing out of position.

So it is probably timely that we take a look at the basic ground rules for a well moored boat.  I gained my experience with mooring boats through years of rafting gameboats alongside motherships. It wasn’t uncommon for us to have a couple of 48 footers alongside in 30 knots on the outer reefs off Cairns. At high tide, when the sea had a chance to build, these boats would be pitching wildly alongside for days and even weeks! It was in these conditions that I learnt the importance of quality mooring lines, how to set them up, and how quickly they can wear and break!

But of course, mooring in a secure harbor such as Manly is far less extreme, but with heavy wind and surge, the principles and lessons learnt are similar.

I doubled up and added additional lines to all my clients boats ahead of the expected weather.

Basic mooring line set up.

The basic minimum lines required are a bow, stern and two springs. As a rule of thumb, the bow and stern lines should be at least half the length of your boat or longer if possible. The fore and aft springs should be at least as long as your boat.
Obviously it is the bow and stern lines that adjust the distance you set the boat from the dock. I find the longer you can make them the better to allow for maximum stretch, but this isn’t always possible. You can’t run them too far forward and aft as they loose their ability to pull the boat in towards the dock. So they often end up short and of course in certain conditions they will jerk tight causing wear, particularly through the fairleads, and possibly loosen and damage cleats. They need to allow for the boat’s movement up and down, without jerking, if possible. Running the stern line across to the far stern cleat to lengthen the line is a good tip.
The spring lines are crucial when mooring as they stop movement fore and aft, and because they can be set long, they absorb the jerking well. You’d be amazed at how often people think they are unnecessary when rafting or mooring. You should use spring lines even at the fuel dock in my opinion!
I appreciate having long springs isn’t always an option due to cleat arrangements on your boat or pontoon. Those short little springs so many owners use are in most cases fine in a calm marina, but if there is surge like we experienced during the recent big blow then they will do more damage than good, if too tight and short. The longer, the better for spring lines!

Rope choice

Choosing what rope to use has many variables including budget, stretch, cleat size, ability to withstand UV and so on, but even more important is that the breaking strain must suit your boat’s weight and windage under the worst conditions you are likely to encounter.
I believe the best option is to own two sets of mooring lines. Leave a set of mooring lines permanently set at the right length on the pontoon. Have a loop spliced in the boat end as this is always helpful when friends help you berth. Keep another set of quality lines stowed for use when rafting up or berthing when away. As a side note, a problem we encountered when doubling up lines ahead of the recent blow was the absence of spare lines on many of the boats.  A second set is very handy – you can never have too many quality lines onboard!


I don’t have the space here to elaborate on all the types of suitable mooring ropes and set ups, their pros and cons or their breaking loads in this article so you need to ask a professional or do some research online. However, below is some very basic information on the more commonly used ropes.


Silver Rope – Silver is probably the most commonly used for mooring lines. It’s inexpensive, lasts well, offers some stretch and is easy to splice. Its down side is the lower breaking strength for its diameter. So for boats with small cleats it might pay to consider nylon or polyester lines which offer significantly more strength for their diameter. It’s also pretty rough and ready on hands and the eye so if presentation is important (which it should be), again, nylon or polyester are better choices.


Polyester Rope – Polyester comes in 3 strand which enables people to splice it themselves however the most popular is the braids. Characteristics include low stretch and high abrasion resistance, soft feel and they are not affected by water. The down side is you’ll need the splicing done by a professional.


Nylon Rope – The multi plait nylon is a great choice if looking for a quality mooring line. Characteristics include good stretching and recovery capabilities, abrasion resistant, good knot holding and coiling and high strength for diameter. It is probably the pick but is the most expensive and again requires professional splicing.


Just a word of caution regarding factory spliced mooring lines, bought off the shelf. The splices are often much shorter than I would recommend and I have seen some let go.

What diameter of rope is suitable?

Sizing again is difficult to cover given the variables to each boat’s length and weight. For example, a 50 foot timber cruiser with flybridge and clears is vastly different in weight and windage to a carbon racing yacht of the same length. Also, the diameters can vary significantly as silver has a much larger diameter for the same breaking strength of nylon or polyester. So use common sense, research or ask a professional for advice and then it doesn’t hurt to upscale to the next size to cope with a serious weather event.



Mooring line check list


  1. Longer the lines, the better to allow stretch and absorb shock which helps avoid chafing and damage to cleats.
  2. Keep springs tight to avoid movement fore and aft, that’s what they are there for.
  3. Bow and stern lines should not be too short or tight to avoid jerking.
  4. Ensure your lines are of a suitable breaking strain. Consider weight, windage and extreme weather.
  5. I suggest a spliced loop on the boat end and an adjustable end on the pontoon.
  6. Have a second set of lines stowed for when away and when double lines are required in extreme weather.
  7. Ensure cleats onboard and on the pontoons are up to the task.
  8. Set lines to avoid chafing. Slide sections of hose or stitch leather over vulnerable points.
  9. When extreme weather is forecast make preparations by doubling up lines and take down clears and biminis to help reduce windage
  10. Have quality fenders and check regularly during extreme weather – they do pop and squeeze out of position easily!


Rafting up

Rafting up is always a fun way to socialize when down the bay. But it is also a classic scenario for damaging boats. It doesn’t take long for a flat anchorage to suddenly change on the turn of the tide and before you know it, trying to separate the boats can become a dangerous operation. Basically the theories are similar to your pontoon berth. However, when you are at anchor you generally will hang into the wind. Experiment with the tension of the aft spring. By having it slightly tighter you can sometimes set it to allow the boats to sail apart reducing the bumping and wear on your fenders. Also be aware of masts or outriggers clashing if you get some roll. Try and offset these. If you have more than one boat rafting up, a good idea is to share the load by running an additional long bow and stern line from the outside boat to the anchor boat. Also, it goes without saying but watch the weather, and ensure you have plenty of chain out to withstand the additional weight. It is often a much wiser choice to separate and anchor off before bedtime!


Peter Jenyns


An example of a poorly moored boat. These lines are old and undersize. Thankfully someone added another line before she broke away.

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