How Long Should Your Anchor Line Be?
Ian Fortey Updated on February 19, 2023. In Boatsby
There is a general rule of thumb that your anchor line, also known as an anchor rode, should be in the neighborhood of 7 to 10 times the depth of the water in which you’re dropping the anchor. Some boaters will offer up more specific guidelines however, as do some organizations. For instance, according to the United States Coast Guard you’ll want to have 5 to 7 times the depth of the water, plus the length from the surface of the water to where the anchor is attached to the bow.
Longer line is definitely called for in rougher seas so if you’re trying to decide between 7 times or 10 times and you know bad weather is brewing, you’ll want to lean towards that 10 times to increase your anchor’s ability to maintain its hold. This goes for most anchor types such as plow anchors or flukes.
Anchor Line Length
As quoted above, many boaters or boating organizations will suggest you use a length of line that is 7 to 10 times the depth of the water you’re anchoring your vessel in. Many sailors carry between 200 feet and 250 feet on board their vessel which would allow them to anchor in water that ranges from 20 feet deep to 35 feet depending on how they follow those guidelines.
If you were following the USCG guidelines at the lower end of the scale and had 250 feet of line on your vessel, you’d be able to anchor yourself in about 50 feet of water, give or take.
Anchor Rode, Anchor Chain and Anchor Rope
People tend to use the words anchor line, anchor rode and anchor chain pretty interchangeably and often they do mean the same thing in that context though each does have a specific meaning. Specifically, a chain and a rope are pretty obvious, but a rode is what you get when you combine your chain with the nylon line on an anchor swivel to make a single line or rode. All of these parts together are sometimes called your ground tackle.
That said, you can use chains as well as nylon rope for your anchor line and, in fact, should use both. There’s a good reason for mixing up your anchor line like this and you should be aware of why to use both chain and rope, where to use them and, of course, the length you want to use as well.
Big ships pretty much exclusively use chains. When a megayacht drops anchor, it’s coming down on a big galvanized or stainless steel chain. Most of us are going to make use of an anchor rode that combines a nylon rope with a chain, however. Pure chain lines are really only necessary for the largest and heaviest of vessels.
Like the anchor line in general, there’s a general rule for how much anchor chain you want on your anchor line which is one foot of chain for every one foot of boat. That means if you have a 35 foot fishing boat, you should have 35 feet of chain. Sounds like a lot, right? You’d want even more in rough waters or if you plan to moor in place for a longer period of time, with the ideal length of chain being one foot of chain for every 6 feet of rope which could potentially be very long relative to your boat.
For larger boats, many boaters find that this amount of chain is actually a bit much and they may reduce it by as much as 50% just to ensure there’s room on the boat to actually store the chain.
One thing to keep in mind here is that the length of the chain is separate from the length of the line. So if you want to use a nylon rope that is seven times the water depth , you’ll want to attach that length to a chain that is the length of your vessel or, at the very least, 50% of the length.
According to the United States Coast Guard you’ll want to have 3 to 6 feet of something like a galvanized chain between your anchor and the fiber line that extends the rest of the way to the boat. This is, as you can see, considerably less than many others might recommend. The choice at the end of the day is yours and many boaters won’t use a chain at all but we do recommend it. If you ever have a nylon line cut by rocks and you lose your anchor as a result, you’ll know why that chain is a good idea.
Additionally, a longer length of chain ensures that the rode remains horizontal for a greater length. That helps ensure your anchor is less likely to be pulled up and pulled free as a result.
One of the reasons you want more chain rather than less is that it can actually help compensate for having a smaller anchor. Many new boaters tend to be surprised by how small and light their anchors are relative to their boat. They work thanks to some physics, not just sheer mass.
If you have a smaller boat, you may not have room for a massive anchor. So using a smaller anchor, one that only weighs 10 pounds or so, can still work if you increase chain length beyond the bare minimum. Longer chain decreases the angle at which you’re anchored. The chain keeps the anchor at an angle that provides a stronger hold. A shallow angle is ideal while the closer you get to 90 degrees, or straight up and down, the less holding power your anchor will have.
More chain is also ideal if you’re in a tight space. Say you’re anchoring among many other boats and don’t have a lot of room to drift, more chain will help anchor you in a tighter space so you don’t drift as much and risk running into others.
All of this said, there are also potential dangers to too much chain. Longer lengths of chain run the risk of getting snagged up in rocks or other debris that it’s incredibly hard to pull loose from. It’s not unheard of for an anchor rode to have to be cut loose because the chain got so tangled up on the bottom that it couldn’t be pulled loose at all.
What’s the Chain For?
The point of your chain is actually to protect your anchor line. The chain will attach directly to the anchor so it’s going to hit the sea floor with the anchor. The galvanized steel will be able to stand up to being pulled over things like rock, coral, sand and other debris which, over time, would destroy your nylon or other rope lines.
Another reason for the chain is that it’s heavy. This weight helps get your anchor angled the way you want it to by pulling it down to the seabed once it’s been dropped. Instead of just the base of the anchor hitting as it might if it were dropped on just a rope line, the chain sinks and will drag the top of the anchor down as well, increasing the likelihood of the anchor embedding itself faster and more efficiently.
Now, when the current or the wind moves your boat and your anchor line pulls on the anchor, instead of the rope pulling directly up on the anchor, it will pull on the chain which then pulls horizontally on your anchor. That means it will be far more likely to stay where it is rather than coming free and allowing your boat to begin to drift.
The reason you use the one foot to 6 foot ratio for bad weather or for long periods of time is that it can help your boat get the best angle along the rode between you and the seabed where you’re anchored. At too steep of an angle your anchor will experience more tension and be more likely to pull free.
The rope you use is subject to some variables just like the chain is. Again, the Coast Guard says 5 to 7 times the depth of the water and other sources say 7 to 10 times. There are laid ropes and braided ropes and ropes made of everything from nylon to cotton to polypropylene and even Kevlar.
Anchor rope needs to be long to prevent your anchor from pulling free too easily. Consider how easy it would be to lift an anchor that is sitting right at your feet versus dragging one towards you from twenty feet away that is half dug into the ground. Even if one of the flukes of the anchor immediately below you is set, the tension of pulling straight up will loosen it much more easily than if the line is at an angle dragging it through mud or rocks that may actually end up setting it more firmly, which is, of course, the point of the anchor in the first place.
Each kind of rope has some benefits and potential drawbacks. Polypropylene line is very cheap so you won’t drop a ton of cash buying it but it also wears out really quickly, too. It’s susceptible to UV radiation so it will degrade as it sits in the sun. It can cut your hands up pretty bad too, and I wouldn’t recommend it for anchor line.
Nylon rope is probably the most recommended anchor line because it’s strong and resilient. It can stretch up to 40% which is what makes it ideal for your anchor line because as wind and currents move your vessel, it needs that give. A stiffer line with less stretch will be subject to more stress and more likely to break under conditions that the nylon rope can withstand.
I recommend nylon rope as well for the above reasons. Honestly, I’ve never actually tried something like dacron or Kevlar which I’m sure is very tough. Regardless of material, you’d still need approximately the same length for your anchor so in that regard the material doesn’t make a difference. Instead, the different materials mostly offer benefits in terms of endurance, buoyancy and so on.
In addition to length, it’s also worth noting you may need to adjust the rope diameter of your anchor line. Again, we have another general rule here that a lot of boaters will go by to determine they have rope not just long enough but thick enough to hold.
One standard boaters go by is to use ⅛” of rope for every 9 feet of boat. So if you have an 18 foot boat, use a quarter inch line. For a 36 foot boat you’d use a half inch line. In general it’s a good idea to always defer to the larger and stronger if you’re not sure what the right size is, of course. Better to go with a little overkill than not have enough.
The Bottom Line
There are several schools of thought regarding the length of line that is ideal for your anchor but the bare minimum is five times the depth of the water in which you’ll be anchored. The United States Coast Guard goes as high as 7 times and many others will recommend 8 times to as much as 10 times your depth. This ensures that even if you start dragging anchor across the sea bed, the horizontal pull will keep you more secure rather than uprooting your anchor.
Though an anchor line can be either all rope or all chain, a good anchor rode should be both with the rope portion meeting the above requirements and the chain being at least 3 to 6 feet and up to as much as one foot of chain per one foot of boat length. This length of chain will attach directly to the anchor shank.
Many boaters tend to store at least 200 feet of anchor line on their boat and up to about 250 feet. The number will definitely vary depending on which standard measurement you choose to go by and the depth of the water in which you want to anchor. That said, it’s always a good idea to have too much line rather than too little. Even if you anticipate only anchoring in very shallow water, if there were to be some kind of emergency you never planned for, having more line available to anchor in deeper waters is always a good idea.