Anchor rodes consist of a length of chain, rope or a combination of rope and chain that connects an anchor to a boat. The rope portion of anchor rodes typically consists of a nylon three-strand rope.
Ideally, the rode for your anchor setup should consist of both chain and rope. The chain should be on the end with the anchor. Why use both chain and rope?
First, it keeps the rode from wearing away by rubbing on the bottom of the seafloor as the boat swings. Second, because the chain is heavy, it holds the rode to the bottom so the pull on the anchor is horizontal, which reduces the chances of your anchor unsetting.
What rope material is best?
For most boaters, the best type of rope to use when anchoring is nylon. Nylon has many advantages for anchoring including:
Good shock absorption, light and flexible
Great tensile strength and is the most common anchor rope found in marine stores
Nylon anchor rope more importantly provides elasticity, which helps mitigate shock loads on your anchor and boat. However, the fact that nylon stretches mean that it creates heat and will eventually break down and need to be replaced.
"the fact that nylon stretches mean that it creates heat and will eventually break down and need to be replaced."
However, you will want a strong rope that will absorb the shock from waves and sink, not float. Nylon fits the bill of all of these things.
Braided or twisted rope?
In our experience, generally for recreational boaters, the difference between using twisted anchor rope or braided anchor rope comes down to preference.
Both make excellent choices for an anchor rope but there are some subtle differences between these two styles of rope.
Less stiff and more flexible
Typically stronger than twisted rope
Easier on the hands
Nearly impossible to splice
A lot less stretch than twisted rope.
Easy to splice
Provides good value
Is stretchier than braided rope
Might tend to kink
Stiffer and less flexible
How long should my anchor rope be, and what size?
The rule of thumb is:
You should have 8 ft (2.4 meters) of rope for every 1 ft (0.3 meters) of water you will be anchoring in.
Your rope should be 1/8 inches (3.175mm) in diameter for every 9 ft (2.74 meters) of boat. (3.2mm of rope for 2.7m of boat)
In Singapore, the depths around the coastal areas are less than 30 feet (9.1 meters)
Image courtesy of: National Archives Singapore; Credit: Professor R. D. Hill
Depths near the shores in Singapore (estimates)
East Coast from Marine South to Tanah Merah - Up to 10 ft (3 meters)
Around Tanah Merah - Up to 20 ft (6 meters)
Around SAF Yacht Club - Up to 25 ft (7.6 meters)
Around Changi Beach CP1 to CP7: Up to 8 ft (2.4 meters)
If facing Ubin, CP1 can be up to 20 ft (6 meters) further out
Nearby offshore waters are around 80 ft (24 meters) and no more than 100 ft (30 meters) till beyond the shipping channels.
This means a 28' boat would want at least a 3/8" (10mm) or 1/2" (12mm) diameter rope. Rope is one of those things, like anchors, where bigger normally is better.
"Rope is one of those things, like anchors, where bigger normally is better."
We would advise typically adding 4 - 6mm to the diameter of rope (calculated above) for the best results.
How much anchor chain do I need, and what size?
With the rope, you should also have a smaller length of chain between the rope and the anchor. This chain will help prevent your rope from rubbing against the seabed and more importantly, creates the optimal angle between your rode and the seabed.
The general rule of thumb is that you want approximately 1ft (0.3m) of chain for every 1ft of boat. So a 20ft (8.5m) boat would ideally required 20ft of chain.
But of course in the event it is not feasible to keep that much chain onboard due to the sheer weight or space needed to allow this ideal chain amount, in these situations you should have at least 10-15ft (3m to 4m) of anchor chain for the reasons shared above.
"This chain will keep your rope from rubbing against the seabed and also creates the optimal angle between your rode and the seabed."
What type of chain do I need?
If you're not using an anchor windlass, there is not much to consider!
Any chain that you can buy at a marine store that follows the size rules above should be adequate and ensure that it is galvanized. If you are not using a windlass, you can simply attach your rope to your anchor using a shackle in between (ideally your rope will have an eye and/or thimble spliced into one end to make attaching a shackle easy.
If you are using a windlass, it would be best to consult the windlass manufacturer on which chain is best suited.