What Size Anchor Does My Boat Need?

We put anchors on boats to keep the vessel safe and secure in a specific location and to manage the boat as best as possible during foul weather. Any old anchor will not suffice. You should have the right anchor – one that is the right size for the boat, that is made to work reliably based on the bed where it will rest, and it must be set properly with the appropriate supporting materials.

An anchor may weigh anywhere from 5 lbs to upwards of 2,000 lbs for non-commercial boats. Knowing how heavy an anchor should be is dependent on factors such as boat length, type of seabed/floor, type of boat. Weather conditions also play a role in determining the appropriate anchor size and type.

Right up there with life jackets, an anchor is a significant piece of safety hardware. Leaving the dock without an anchor is sheer lunacy and you’d be surprised at the number of times this actually happens. Always check to make sure there’s an anchor on board and, if you’re a prudent, savvy boater, you won’t leave the dock without two anchors.

Anchor Size Chart

Because folks like an instant answer, we’ve provided this anchor-sizing table as a resource. However, keep reading for more specific information and factors that will impact your final selection of an anchor. You’ll even see why we recommend having multiple anchors on your boat!

This chart provides information on suitable anchor sizes and types for different sized boats. Use the chart as a resource and in conjunction with the anchor manufacturer’s guidelines. 

Different Types of Boat Anchors

Below, we'll dive into several different types of boat anchors and explain a bit about them. This will help you to understand why some are not useful on larger vessels.

Plough Anchor

A plough anchor slightly resembles a pickaxe in that it has a one-pointed penetration point at the end of the shank. Plough anchors can be hinged or unhinged.

With a hinged plough anchor, the shank can swing back and forth from the giant single, spade-shaped fluke. The hinge allows the chain to have a broader scope of motion. Hinged plough anchors receive mixed results from boaters. Some people think the hinge compromises the integrity of the anchor; others feel the opposite.

Unhinged plough anchors combine the angled, fluke design and weight of the overall anchor to hold a boat effectively. They set fast and are not often impacted by tides or the wind. The unhinged plough anchor will stow easily on common anchor rollers. 

Regardless of hinged or unhinged, the spade-like fluke works well in hard, sandy, muddy, and weedy bottoms. If the bottom is too smooth or loose, a plough anchor may have the tendency to drag on a too-smooth bottom. 

Folding Grapnel Anchor

‍

Perfect for inland and short-term use in areas with little current, a folding grapnel anchor looks like an opened flower with four petals. These four tines can hook to craggy, jagged bottoms, heavy weeds, coral, and stone. They are typically made of galvanized steel which has ample weight and is rust-resistant. 

To use a folding grapnel, prior to putting it in the water, the petal-like grapnels are laid flat. Then a centerpiece is twisted into place. This locks the four tines in an outward position, perfect for gripping.

Typically, a grapnel is used by smaller boats, jet skis, and dinghies. Some boats have a grapnel on board for use as an emergency anchor.

Mushroom Anchor

As the name suggests, a mushroom anchor is shaped like the familiar fungus upside down. Best for waters with a delicate, sandy seabed, the mushroom anchor’s round head becomes buried in the sand. 

They serve as ballast for smaller boats as well as kayaks and canoes. Some are vinyl-coated so as to minimize scratches and scrapes to the boat’s finish. 

Extremely large mushroom anchors are actually used to secure oil rigs, lightships, and dredges, as they become deeply embedded into the seabed and have terrific holding power.

Spade With Roll Bar Anchor

A newly engineered anchor, spades with roll bars offer extra holding power. The fluke’s weight rolls the anchor around the roll-bar so as to pivot the shank’s end.

These anchors tend to dig in fast and securely. Because of the roll bar, the spade anchors with this feature are not ideal for stowing on bow rollers. 

Reef Anchor

Typically made out of aluminum, a reef anchor is uniquely flexible so as to be releasable from the anchored position. The tines actually bend so the anchor works well on rock bottoms, jetties, and reefs. That is because, with the right amount of pressure, the tines bend enough to slip free from the bottom. 

Lightweight and easily stowed, the reef anchor is sometimes handmade and welded by do-it-yourself boaters. Watching a few reef anchor videos on YouTube is a good way to see exactly how these unique anchors work and how to DIY one for your own boat.

One distinction of a reef anchor is that often rather than hoisting them back up when you’re ready to leave, you simply drive the boat forward. This motion pulls the anchor enough to bend the tines, releasing it from its lodging. Don’t forget to bend the tines back into place before you use them the next time!

Claw Anchor / Bruce Anchor

Because they are simply constructed, claw anchors tend to be less expensive than other anchor styles. Shaped like a hand grip, the anchor may tip any which way when deployed and properly set. 

Originally designed to secure oil rigs in the North Sea, smaller versions are constructed of high-grade steel and suitable for most seabeds. A claw anchor is very suitable for an anchor roller platform for convenient stowing, ease of access, and use.

Compared to a plough anchor, a claw anchor will have a wider scoop shape. Like a plough anchor, it isn’t as effective on loose sand bottoms as it is on hard sand, muddy, and even rocky sea bottoms.

Danforth Anchor / Fluke Anchor

Somewhat similar to the plough anchor, because it swings or hinges (at a point called the tripping ring), the fluke anchor’s flukes look like two tall triangles secured to a rod perpendicular to the shaft. This rod, known as the stock, extends beyond each of the triangular flukes.

Referred to as a Danforth or lightweight anchor as well, the fluke anchor is by far the most popular type of anchor. Smaller boats will often use a fluke anchor as their one and only anchor. A fluke anchor is lightweight which is always nice. 

Because it folds flat, it stows nicely and neatly. Flukes anchor well in both mud and sand but not so much in rocky and grassy beds. This is because of the stock – the long metal rod that connects the two flukes. It extends beyond the flukes. The two end points of the rod are prone to fouling on both the rocks and the anchor rode.

For a rough seabed, the gap that is present between the flukes enables better grip-ability. The flukes’ orientation is changeable; however, 30 degrees is the angle recommended for best grip success.

Wing Anchor

A solid one-piece design makes the wing anchor a very popular choice for boat manufacturers’ standard equipment. It has excellent holding power, better than that of a plough anchor, and sets easily on most bottom types. Wing anchors will fit most bow rollers and are also self-launching.

Because a wing anchor has a higher ratio of holding power to weight, boaters can get away with a less weightier anchor than other plow anchors. 

What Factors Do I Need to Consider When Buying A Boat Anchor?

The primary factors affecting an anchor’s suitability for a specific boat includes the size of that boat, the type of boat, and the environment in which the anchor will be used, including the seabed or lake floor and the current. Other considerations include wind conditions and the actual type of anchor.

Most anchors come with size guidelines for use supplied by the manufacturer of the anchor. Make sure you pay attention to this. When in doubt, it is usually a good idea to go up in size. Erring on choosing the larger size when it comes to anchors is rarely an error. 

Seriously, don’t skimp on size. Take it up a size (or two) and know that you’re purchasing extra peace of mind. This will make sleep come a bit easier as you’re rolling back and forth in your bunk when the wind begins to howl your first night away from the dock.

Anchors have a variety of features or factors that make them different from one another in terms of suitability for a boat. Let’s take a look at each of those factors next.

Boat Size

Your boat’s specifications including length and weight (as well as design type) influence the kind of anchor you will need to use. Boats may be the same length but vastly different in weight so boat length alone should not be considered. A boat that weighs 10,000 pounds that is 30’ in length will require more anchor than another 30’ boat that is only 6,000 pounds. 

Review the anchor size chart we have included in this article. Consider boat size and weight of the boat too.   Always check with the anchor manufacturer’s recommendations too. 

Anchor Weight

Relative to the size of the boat, an anchor may be of lighter weight or heavier weight. Measured in pounds, anchors can weigh from 5 lbs (for a jon boat or small skiff/dinghy) to hundreds of pounds for a large recreational boat (sailboat, cabin cruiser) in the 100+’ range.

An anchor must be light enough to be lifted by a person (or anchor lift) from the bottom of the floor. It should be able to be tossed overboard without being so cumbersome as to compromise the boater’s safety. The anchor must be heavy enough to handle the upward pull from the boat.

These days, as anchor design has improved, anchor weight isn’t always the predominant factor, but it certainly remains an important one.

Seabed Type

Because people use watercraft in so many different environments, some discussion of seabeds is needed. Seabeds can be sandy. They can be muddy. Others will be rocky. Others will be weedy. A nice, hard sandy bottom is a terrific place for most anchors to dig securely. 

For boaters who spend time in shallow estuaries or at river deltas, muddy seabeds are the norm. Often, beneath the soft mud, there is a layer of clay or hard-packed sand. This second layer is good because it gives the anchor something to bite into. 

If an anchorage is comprised of a thick, soft, muddy bottom, this can present a problem. It’s challenging for an anchor to dig and take hold in deep mud, leading to dragging which is something no one wants to have happen.

The penetration of the anchor is what fastens it to the floor. Hard sand bottoms are ideal for penetration. Weedy bottoms and soft mud floors are less than ideal for gripping. When gripping is challenged, having a weightier anchor is crucial.

Before making an anchor purchase or when checking the anchor before heading out, give some thought to where you’ll be anchoring and what the seabed is going to be like. 

Holding Power

Holding power is a rating system for anchors. Holding power measures the ability of an anchor to hold a specific weight. Because of the physics of boats on water and the energy that a boat pulling against water can create, holding power needs can fluctuate.

While a boat may be fine on a serene day on the water, the holding power needs might double or triple for that same boat when skies turn dark, winds howl, and water churns violently.

Essentially, holding power ratings result from measuring the pull force an anchor should withstand to keep a certain sized boat in place. Different anchors dig differently. Bottoms of bodies of water vary widely. Anchor shapes fluctuate purposefully. Digging, bottom type, anchor shape. They all affect the tenacity of an anchor’s holding power. 

What is the Recommended Anchor Line Length?

A good rule of thumb is that the length of the line should be at least seven to ten times the depth of the water where you are setting anchor. Anchoring in 10’ of water? Plan on having 70 – 100 feet of anchor line in place.

What is Anchor Rode?

The system that connects the anchor to the boat is collectively referred to as anchor rode. The integrity and sturdiness of the mooring depends on the integrity and sturdiness of the anchor rode. 

The length of the rode is impacted by the upward pull on the anchor. If the boat is directly above the anchor (less rode), then the energy of the boat is going to yank the anchor more easily from its grip. 

With more rode, the energy on the line and chain is distributed and less intense so there is a gentler pull on the anchor. Again, take the depth of the water and multiply it by 7 to 10 times in order to gauge the length of your anchor rode.

More rode typically means better holding. That is because a horizontal pull of the anchor is much much better than a vertical pull. Think of how when you weigh anchor, you get as close to it as possible. 

There is less rode and you’re able to pull the anchor up more easily. When you want your anchor to hold, give it plenty of rode. Otherwise, your anchor may lift up off the bottom or at the very least drag along the bottom.

Does the Weight of an Anchor Matter?

Aside from the previously mentioned weight considerations noted relative to boat length and weight, , one aspect of weight to consider is not the weight of just one anchor but two. It’s a very good idea to have one substantial anchor for normal to rough conditions. 

Having a second anchor, lighter and simpler in design, used for calm water and as a backup anchor is wise. An extra anchor, one of a different weight and/or different type, is a good boating practice.

Do I Need a Chain for my Anchor?

Unless you are a kayaker or on a very small body of water, a chain should be a part of your anchor system. The chain is highly critical for several reasons. 

An anchor with a chain sets much faster and more securely. This happens because the weight of the chain pulls down on the anchor shank. Chains also help the rode lay horizontally, as opposed to being pulled upward, loosening the anchor. 

Chains are protective of the rope (nylon or otherwise, helping avoid sharp things like reefs that can cut the line, resulting in a lost anchor and a boat adrift.

Wrapping It Up

When the need arises, having an anchor that is reliable, sturdy, and correctly deployed can provide peace of mind that is truly priceless. For this reason, anchor size definitely matters. Never skimp on a too-small anchor (or anchors) for your boat, whether you own the boat, or are borrowing it or renting it. 

Check to make sure there’s an anchor on board every time. When borrowing or renting, inspect the anchor to make certain it’s suitable for the location where you’re likely to anchor and for the size of the boat.

As noted previously, when in doubt with anchor size, go up. Increase the weight of the anchor. Be a prudent boater by recognizing the critical safety and security role that is played by your anchor. Respect size and type of anchor for the various seabed environments in which you’ll be boating.