Having the correct type of mooring system will greatly affect the stability, longevity and performance of your pontoon.
There are 3 main types of mooring systems currently in use for securing pontoons:
A heavy weight which is placed on the seabed and is then connected to the pontoon via a chain or rope.
Anchor mooring systems are very effective in deep-water areas, and where piling is not an option. They can be configured to allow the pontoons to rise and fall with the tidal range and allow a degree of flexibility.
We regularly use 4 different types of anchors, the most appropriate will depend on the specific details of the site:
- Railway Wheels – These make excellent anchors, they are concaved is shape, which allows the wheels to suck onto the seabed to provide excellent hold. They also sit very flat on the seabed, minimising the chance of anything fouling them in shallow water locations.
- Admiralty Pattern Anchors (AP Anchors) – These are traditionally shaped anchors with a very high holding power. They are easy to deploy and recover from the water and work best in systems that incorporate 2 or more anchors as they can be set to pull against each other. Our AP anchors range from 30Kg up to 150Kg.
- Mushroom Anchors – These are a cheaper option compared to an AP anchor, they give good holding power on soft seabed’s (mud/sand). They are also easy to recover making them excellent for temporary installations.
- Concrete Blocks – Concrete blocks are a cheaper option for locations where a large block isn’t going to cause an obstruction e.g. deep water moorings. The downside of the concrete block anchor is, when they are submerged in water their weight is only around 60% of their land weight making it necessary to have larger blocks.
Connecting to the pontoon to the anchors.
Traditionally anchors are attached to the pontoon via chains. We would usually use a few metres of a large diameter heavy ground chain (around 30 diameter links) to help minimise snatch on the anchor. This would then be connected to a lighter weight chain which would run up to the pontoon. This chain should be between 3 and 5 times the depth of the maximum water height.
The chains are connected together with appropriately sized shackles which should always be locked with either locking wire or tie wraps.
A newer system that we are finding very effective is ‘Seaflex’, this is essentially a large bungee that attaches between the anchor and the pontoon which stretches and retracts as the water level changes.
One of the main advantages of this system is that it greatly minimises the movement of the pontoon at low water and also performs very well at stabilising the pontoons in rough conditions.
The anchor layout for each pontoon will vary depending on the system and location. We essentially aim to place an anchor around 30 degrees away from the pontoon along both sides, at distances of no more than 10m apart or often less in rough waters.
The chains/seaflex are then connect to the opposite side of the pontoon, this has a number of advantages:
- It allows the chains to work in a scissor action allowing the pontoon to rise and fall.
- It helps to prevent the pontoon from twisting.
- It keeps the chains much lower in the water around the edge of the pontoon helping to prevent any vessels coming alongside from fouling them.
A stiff arm mooring is a pole that runs horizontally from the bank out to the pontoon that is hinged at both ends allowing the pontoon to rise and fall with water level fluctuations.
Stiff arms work well on pontoons that run parallel to the shoreline, they also tend to be a cheaper option than piling. They hold the pontoon away from the bank, this distance is dependent on the amount of water level fluctuation and height of the bank but is normally at least 2 metres making a hinged gangway essential.
One of the disadvantages of stiff arms is that they restrict access around the inner side of the pontoon but in certain location this can be an advantage.
Piling is undoubtedly one of the most effective pontoon mooring methods. A pile is driven into the ground, the pontoon is then connected to it via a piling guide (hoop).
While allowing the pontoon to rise and fall with the changing water levels piles prevent virtually all horizontal movement of the pontoons adding greatly to their stability.
The locations that piles can be used is restricted, for example deep water and rocky seabed’s prevent piles from being used.
Like all systems piles do have their drawbacks, installing piles tends to be expensive especially if this can’t be achieved from a land based piling rig and a barge has to be brought in. They also look more visible than the other systems as they protrude at least couple of metres up in to the air (at low water the can produce many metre depending on the location).
Every location has a different set of mooring parameters, identifying the most appropriate system will greatly increase the performance of your pontoon.