Anchoring & Docking
What size dock lines should I use, and which is better - 3-strand or double-braid?
How do I size an anchor rode for my boat?
How much chain should I have?
There are a number of factors to consider when choosing dock lines. First, let’s review safe working loads. The safe working load of a line is typically assumed to be 20% of its breaking strength. Since most of us have neither the math nor the desire to calculate the loads a dock line might experience in use, it's handy to have a reliable reference that tells us what we need. The West Advisor has an article that offers useful information about choosing the right size dock lines for your boat - https://www.westmarine.com/WestAdvisor/Dock-Lines
It is important to choose your line sizes correctly, because too much stretch can be dangerous. If you exceed the safe working load of a stretchy line often enough, it will lead to fatigue and failure. If the line snaps, things can get broken and people can get hurt.
At the other end of the size spectrum, while it is true that bigger is stronger, as you go larger, the line does not have to work as hard, so it stretches less. You gain strength, but by sacrificing the stretch element that was the reason to choose nylon in the first place. Don’t lose track of the fact that you want a strong line that stretches.
Now let’s look at stretch. Nylon is typically the fiber of choice for dock lines, because by its nature it has more stretch than polyester. Stretch is good for dock lines because it keeps your boat’s fittings (and dock hardware) from shock loading as the boat shifts in its slip.
A popular question is, “which is better, 3-strand or double braid?” The answer requires you to consider what you want the line to do.
3-strand has 12% stretch at 20% of its breaking strength. 3/8” New England Ropes 3-strand (because not all ropes are created equal) has a breaking strength of 4250 lbs. 20% of that is 850 lbs. Over a 100’ run, it would stretch 12’ at its maximum working load! Therefore, in 25’ at the maximum safe working load, you could see 3’ of stretch! On longer runs, this amount of stretch could become unproductive.
This is where double braid can be useful. Double braid has approximately half the stretch, so in longer runs, relying on the stretchy nature of nylon instead of the stretch in construction will keep your boat from surging too much.
Another aspect to consider in docklines is that tying a knot in a line reduces its safe working load by 25-40%. Thusly, using a bowline to tie a loop in your 3/8” dockline can reduce the line’s safe working load from 850 lbs to 510 lbs.
A splice provides a means of creating a loop in a line while preserving the safe working load. An alternative to a splice is to wrap the line a number of times around a piling and then secure it to the working length with half hitches. If you intend to use this method, it is important to allow for it in your calculations for the length of your dock lines. A single loop around a 12” diameter piling will use more than 3 feet of rope!
The West Advisor suggests that transient bow and stern lines should be about 2/3 of your boat’s length and that transient spring lines should be equal to your boat’s length. This is a good place to start for measurements, but you must also consider your favored methods of tying up. If you have raw line and are planning to splice it, remember to allow for the splice and the size of the loop. If you are putting multiple turns around a piling, the paragraph above shows how quickly that can eat up a lot of line. Lastly, there’s probably going to be a cleat hitch and a stopper knot somewhere too.
The purpose of spring lines is to limit your boat’s ability to move forward and backward while tied up. Spring lines should always be fairly taut. In our home slip, I have one spring tied to the outermost piling of our slip, pre-measured to about the length of the boat, and with a spliced eye ready to drop over a cleat as the boat enters. This way, any guests unfamiliar with handling lines don’t need to worry about cleat hitches or whether or not the boat is going to hit the dock. When the spring goes taut, the boat is right where she needs to be.
The spring that pulls opposite your first spring can either be preset, or tensioned to make your first spring taut once you are in the slip. It is important to have two springs pulling opposite each other, or else you are requiring your bow and stern lines to do double duty. The reason for having long spring lines is to compensate for any tidal effect without them getting too tight. Also, if you make them short and a wake rolls through your slip, it will work the lines and fittings.
Having checked the boat’s motion fore and aft, let’s look at the bow and stern lines. Bow and stern lines limit your boat’s motion side to side. I set up my bow and stern lines on the side opposite the dock first. The springs are keeping the boat from moving fore and aft, so all I have to do is make sure that when the bow and stern lines on the opposite side go taut, the boat can’t hit the dock. Remember to allow for stretch and tide. I like to set my lines so they are horizontal at mid-tide. That way, the boat only gets farther away at high and low tide. Once this is accomplished, it is just a question of attaching the bow and stern lines on the dock side, and making sure that they go taut before your boat reaches the pilings on the far side. Lastly, pull each bow and stern line one at a time and make sure that the lines check you before an end can clip a dock or piling. Having achieved all this, the springs should be snug, and there should be some slack in the bow and stern lines.
For side tying, once again the springs are long and taut. I hang a single cylindrical fender a little off horizontal at the widest part of the boat. I try to run my stern line from the outboard cleat to the dock, to give it the longest run possible. I leave enough slack in it so the boat can pivot on the fender and the bow can swing in to within a few feet of the dock. I set the bow dock line so that if I pull on the stern line, the bow line goes taut when the stern is a comfortable distance to step to the dock. Just like in a slip, the springs are taut to keep the boat from wandering fore and aft, and the bow and stern lines are slack, but not slack enough that the boat can get herself in trouble.
Everyone has a favorite style of anchor, and no amount of debate is going to change their mind. That’s okay. As long as it fulfills the basic requirements of what makes an anchor and is suited for the bottom type, it’s really the anchor rode and anchoring technique that determine if you are going to stay put, or if you are going to wake to find that your boat went on a voyage while you slept.
What makes a good rode? Good scope is the first thing to consider in making a good rode. Many folks say that scope is the amount of rode you put out relative to the depth of the water where you are anchored. It is that, plus the height to your bow from the water’s surface, plus any additional tide remaining to come in over the period of time you are planning on staying anchored. As an example, let’s say you need a scope of 7 to 1 (7:1) to stay put, and you just used the water’s depth to calculate this. If you anchored in 5 feet according to your depth gauge, you would need a mere 35 feet of rode. Or would you? If you count the 3 feet from the water to your bow, and the 2 feet remaining in the tide, at high tide, your scope will be 3.5 to 1 (3.5:1)! I don’t think any anchor manufacturer boasts that their anchor will hold with that kind of scope. While 70 feet may sound like a lot, when I’m trying to picture if we’ll fit in a crowded anchorage, instead of trying to picture what 70 feet looks like, I picture two 35 foot boats end to end. I find that much easier to visualize.
When considering scope, it is best not to skimp. The West Marine Advisor recommends 7:1 for scope using a combination of rope and chain, and 4:1 for an all chain rode. Don’t go short just because it’s supposed to be a calm night. It’s not about seeing how short you can anchor and in the morning still be where you dropped the hook. Probability will eventually catch up to you. Minimizing the opportunities for the unexpected to happen allows you to relax better. Big accidents are usually a combination of small mistakes.
Attachment to the Anchor
A shackle is the typical method of attaching a chain to an anchor. When selecting the shackle, look at the maximum working load of your selected chain. Conventional galvanized shackles are typically the weak link in ground tackle. Our anchor choices always have an oval slot for the shackle attachment, which allows the shackle jaw to fit through. Then the pin goes through the chain. When selecting a shackle, I go for the biggest one with a pin that still fits through the chain.
Any screw fittings should be restrained in some way. I have used seizing wire (done carefully to avoid catching nylon if the rope were to play over the shackle), plastic wire ties, and red Loctite (if there is no hole on the pin to seize).
On the subject of swivels, if you are using a windlass to deploy and retrieve your anchor, swivels are essential. Over time, the rode will store twist for a variety of reasons. The swivel gives the rode a means to dissipate that twist. Without the shackle, you could end up with the rode hockling and jamming the windlass from inside the anchor locker during deployment.
Be wary of swivels. Make sure the working load is in line with the rest of your rode. Do not get confused with the breaking strength. A safe assumption is that the working load is 20% of the breaking strength.
Modern anchors are designed to pull horizontally. If the angle of pull changes, it encourages them to break out. Therefore, the first duty of your rode is keep your anchor’s shank parallel with the bottom. Having chain attached to the anchor achieves this quite well.
Some folks feel this can be achieved with a short length of really heavy chain, shackled to a long length of nylon rope. There are two downsides to this approach. The first is that if the anchor has set well, breaking it out while lifting the chain can be an exercise, because you have all of the heaviest part of the rode concentrated in a short distance. Second, if the conditions get choppy, a bouncing boat can easily pick up what you thought was a heavy chain. What you thought of as heavy is really quite light compared to the displacement of your boat. After all, the boat can easily carry you and all of your stuff!
A good alternative to a short length of heavy chain is a long length of lighter chain. The long length of lighter chain makes it easier for you to pick up in the morning, but harder for the boat to lift the anchor’s shank in a squall. As a thought experiment, consider which is harder; holding a 20 pound weight close to your chest, or holding a 10 pound weight at arm’s reach. A long length of lighter chain also means that in a lively seaway the nylon portion of your rode might spend less time on the bottom, as the boat is able to lift a portion of the chain, thusly reducing abrasion to the rope. The West Marine Advisor has a good table for selecting the right chain size for your boat. I usually go with a length of chain equal to the length of my boat rounded up to the nearest 5’.
On larger boats, or boats with sufficient buoyancy forward to support it, an all chain rode is an option. It is important to consider whether your boat has the displacement in its bow to support the weight of the rode, or you will end up compensating by adding weight to the stern. Boat designers will tell you that keeping weight out of the ends will make for a better performing boat and a more comfortable ride.
For Grace, we chose the compromise of a chain and nylon rode. Even without the rode in the locker, her long overhangs mean we have a lot of weight at the ends of the boat that is not supported by water. We carry a second rode, but to keep the weight off of the bow it lives in one of the quarterberths until it is needed.
Nylon Rode and Snubbers
It is important to match the right size of nylon to the chain. Choose too small a diameter rope, and you run the risk of increased wear due to the line’s constant flexing and stretching caused by loads above its anticipated working range. Choose too large a rope, and you defeat the advantages of nylon’s stretchy qualities. Since it doesn’t approach its working range, the line is less inclined to stretch. For instance, an “O” ring and a rubber band are made out of the same material, but it’s a lot easier to stretch the rubber band. Once again, the West Marine Advisor has a good table for choosing the right nylon rope to go with your chain. I prefer to use manufacturer and distributor’s recommendations as a starting point for decisions like these. Since they are making and marketing the products, it stands to reason that they want to see it used appropriately.
There are a number of different choices available in the construction of nylon rope. I have only used 3-strand for anchor rodes. I prefer its simplicity and the availability in addition to its stretchy nature. In recent years, I have turned away from using a thimbled eye and shackle to secure it to the chain, and have come to favor a rope to chain splice instead. I feel the rope to chain splice looks more tidy and, more importantly, it removes a piece of redundant hardware from the ground tackle.
If you are using an all chain rode, the snubber plays at least two important roles. It takes the load of the ground tackle off of the windlass, and it provides the stretch that keeps the boat motion from breaking out the anchor. In that regard, to me it seems that 3-strand would be the best choice for a snubber, since you would get the most stretch in the shortest run. Use a snubber hook designed for the job. Running the line through a link, and cleating both ends is going to lead to chafe. Using something like a carabiner could subject it to loads outside its safe working load. Tying a bowline reduces the safe working load of the line by approximately 40%.
I have no personal experience anchoring with windlasses. I understand that a swivel from the anchor to the chain is considered important. Some manufacturers I have spoken with have told me that their gypsies do not like using nylon double braid, so if you are inclined toward double braid after your chain, check your manual. If you have specific questions about your windlass, the manufacturer’s tech help is often very happy to help. They want satisfied customers. It sells windlasses.
Making It All Work
Before we anchor, we have a snack. Since anchoring can sometimes be stressful, a snack can take the edge off.
When we anchor, Suzanne handles the anchor, and I handle the engine. I bring the boat into the wind, and slowly kill the headway. She already has the anchor ready to run. When the boat is where I want the hook, I tell Suzanne. I put the engine in neutral and call out the depth. She lowers the anchor until it touches bottom. As the bow blows off, she pays out more rode. She does not let the rode run free, since this could end up with a heap of chain on top of the anchor. Since it is noisy for me in the cockpit, if she needs me to use the engine, she turns and faces me before speaking, then tells me what she needs. Typically, slow astern on and off does the trick. Remember that when backing at a slow speed, the rudder has almost no effect on steering, since there is very little water moving over it. If Grace wants to put her stern to the wind, I ask Suzanne to snub the rode, and that straightens the boat out. Both of us try to make sure we communicate our needs clearly and succinctly.
When she gets past the chain, Suzanne counts full arm-lengths of the rope. She considers every arm-length to be 5’. She pays out the rode as the boat takes it away from her until she gets to a length approximately 7 times the depth plus the height to the bow. She then asks me to back on it as the rode goes taut. As I throttle up, we both pick targets with something prominent a good distance behind them and off our opposite beams. As long as the two objects remain in line with each other, it means the anchor has set. If the nearer object appears to be moving forward, the anchor is dragging. If so, we pick the whole rode up and try to reset. It’s not worth trying to get a dragging anchor to grab. You don’t know why it didn’t grab. It could be that it just didn’t dig in yet, or it could be that a loop of chain fouled it. Maybe you found a tree limb. At best, if it does grab, you’re probably not going to sleep well. At worst, you’ll be re-anchoring in the dark of night.
As with many things in sailing, good communication between crewmates is essential.
One thing Suzanne has taught me is if the anchor breaks out after you’re anchored the boat motion will change. If the anchor is holding, the boat basically aims into the swell, and you feel a comfortable fore and aft rocking motion. Typically a drifting boat will want to lie beam or stern to the wind. If the boat begins rocking side to side, this may indicate that the anchor is not holding and the bow is trying to turn away from the wind (and succeeding). This would be a good time to check your anchor.
In a perfect world, everyone would be able to anchor so that their swing radius would not overlap anyone else’s swing radius. This is rarely the case. Oftentimes, the best you can get is being your radius from the nearest boat. When you enter an anchorage try to avoid crossing close to the bows of anchored boats. Their rodes are down there. If the crew is aboard, they’re probably watching you. Don’t make them nervous. It is okay to pass close astern of anchored boats. Just watch out for lines or people in the water.
When picking a spot to drop the hook, I look for similar boats with similar ground tackle. I try to avoid anchoring among all chain boats, as their arc of swing will be different than mine. I also stay away from catamarans and powerboats, since they move differently at anchor than my monohull. Something else to bear in mind is that they often tend to anchor in water more shallow than most sailboats can handle.
When picking a spot to anchor, if space is limited, it often works to drop your hook close astern of someone already anchored. That way, you will be the length of your rode away from them when you are done. I you were going to anchor in front of someone, you would have to anchor more than twice your anticipated rode in front of them to not end up swinging overtop of their anchor. If you end up swinging over someone’s anchor, it may make their departure in the morning tricky.
If I see folks sitting in the cockpit of a boat near where I plan to anchor, if it doesn’t look like
I’m interrupting, I have occasionally tried to inquire to the amount of rode they have out. This has met with mixed results. It seems polite, but can get confusing pretty quick with the engine thumping away.
Remember that the boats that are already anchored picked their spots for the safety of their boats and the comfort of their crews. Try to respect that while you aim to achieve the same for yourself.