What Size Anchor Do I Need? Boat Anchor Buying Guide by Bottom and Boat Size
Quick answer: Pick the anchor style for your usual bottom first (fluke for sand and mud, a modern scoop or plow for mixed bottoms, grapnel for rock), then pick the size from the manufacturer's chart for your boat length and weight, and size up if you are between sizes or anchor in wind and current. Pair it with chain and nylon rode and let out 7:1 scope in normal conditions. For example, an aluminum Fortress FX-11 with 15 feet of 1/4 inch chain and 3/8 inch nylon is rated by Fortress for boats up to 32 feet.
The right anchor holds your boat where you put it, on the bottom you actually anchor on. The wrong one drags, and dragging ruins a sandbar day at best and puts a boat on the rocks at worst. Anchoring is a system: the anchor, the chain, the rope and how much of it you let out all work together. This guide covers how to match anchor type to the bottom, how to size it, how to set up the rode, and which anchors we recommend.
Step 1: Match the anchor to the bottom
- Sand and firm mud: fluke (Danforth style) anchors set quickly and offer excellent holding for their weight. Lightweight aluminum flukes like Fortress are very popular for this reason.
- Soft mud: flukes still work well, especially with the fluke angle opened up or mud palms fitted where the design allows.
- Grass and weed: plow, claw and modern scoop anchors with a sharp, weighted tip penetrate weed better than flukes.
- Rock and coral rubble: grapnels hook into rocks and are common on small boats and kayaks. Use a trip line so you can retrieve a fouled anchor.
- Mixed bottoms: a modern scoop or high-holding-power anchor is the most versatile single choice.
- Very shallow flats: shallow-water anchor pins and poles hold a small boat in a foot or two of water without a rode.
Step 2: Size by boat length, weight and conditions
Every manufacturer publishes a sizing chart, and you should follow it for the specific model you buy. As a rough guide, typical starting weights look like this:
| Boat length | Aluminum fluke (lightweight) | Steel fluke | Steel plow, claw or scoop |
|---|---|---|---|
| Up to 18 ft | About 3 to 5 lb | About 5 to 8 lb | About 4 to 9 lb |
| 18 to 27 ft | About 4 to 7 lb | About 8 to 14 lb | About 9 to 15 lb |
| 27 to 33 ft | About 7 to 10 lb | About 14 to 22 lb | About 15 to 25 lb |
| 33 to 40 ft | About 10 to 15 lb | About 22 to 35 lb | About 25 to 35 lb |
Heavy boats, boats with lots of windage like tall cruisers and pontoons, and anyone who anchors overnight or in strong current should go one size up. An anchor that is a little too big is cheap insurance; one that is too small is not an anchor.
Step 3: Set up the rode
The rode is everything between the anchor and the boat. A good rode does as much for holding as the anchor itself.
- Chain at the anchor: a length of chain keeps the pull on the anchor shank low and horizontal, helps it set, and resists chafe on the bottom. Common practice is at least 6 to 15 feet on small boats and roughly one foot of chain per foot of boat length on cruisers.
- Nylon rope: three-strand or braided nylon stretches to absorb shock loads. Typical sizes are 3/8 inch for boats to about 25 to 30 ft and 1/2 inch for larger boats, with chain sized to match.
- Shackles and swivels: use galvanized or stainless shackles sized to the chain, and mouse (wire) the shackle pins.
Our anchor rode and chain guide covers chain sizes, rope types and how much you need.
Step 4: Use enough scope
Scope is the ratio of rode length to the depth of water plus the height of the bow above the water. Use about 7:1 for normal anchoring, 5:1 as a minimum in calm conditions with an all-chain rode, and 10:1 when a blow is coming. In 10 feet of water with a bow 3 feet above the surface, 7:1 scope means about 91 feet of rode. Too little scope is the most common reason anchors drag.
Step 5: Carry a backup
Experienced boaters carry two anchors: a primary sized for the boat and a second, often a different style, for a different bottom, a stern anchor at the sandbar, or as a spare if the first is lost. A lightweight aluminum fluke makes an excellent backup because it stows flat. If you anchor often on a larger boat, an anchor windlass makes retrieval far easier.
Common anchoring mistakes
- Too little scope, especially in deeper water.
- No chain, which lets the rope lift the anchor shank and pull it out.
- Wrong anchor for the bottom, such as a fluke in heavy weed.
- Not backing down to set it. Always set the anchor with gentle reverse before relaxing.
- Undersizing to save weight or money.
Our picks for boat anchors
All in stock at Boat Supplies Direct.
Complete anchoring systems
Fortress FX-7 Complete Anchoring System for smaller boats, or the Fortress FX-11 Complete Anchoring System, which includes chain, 250 ft of 3/8 inch nylon and mud palms for boats up to 32 ft.
Lightweight aluminum fluke anchors
Fortress FX-16 and Fortress FX-23 for larger boats and as storm or backup anchors, or the value-priced Fortress Guardian G-11.
High-holding-power anchors for mixed bottoms
Ankerplex Stainless 5 kg, for boats to 21 ft or the Ankerplex Stainless 8 kg, for boats to 30 ft, both stowing flat.
Shallow water and small craft
Panther Water Spike for 16 to 22 ft boats for flats and sandbars, or the YakGear 3.3 lb Grapnel Kit for kayaks and rocky bottoms.
Swivels, snubbers and retrieval
Quick SW10 Stainless Anchor Swivel, the Davis AnchorSnubber, and the Attwood Anchor Lift System for easy hand retrieval.
Frequently Asked Questions
What size anchor do I need for a 24 foot boat?
It depends on the anchor model, boat weight and conditions. As a starting point, many 24 ft boats use roughly a 5 to 7 lb aluminum fluke or a 10 to 15 lb steel anchor; confirm with the manufacturer's chart and size up for wind and current.
What is the best all-around boat anchor?
A modern scoop or high-holding-power anchor handles the widest range of bottoms. In mostly sand and mud, a fluke anchor offers outstanding holding for its weight.
How much anchor rode should I let out?
About 7 times the depth of the water plus the bow height in normal conditions, 5:1 minimum in calm weather with all chain, and up to 10:1 in strong wind.
Why does my anchor keep dragging?
The usual causes are too little scope, no chain, the wrong anchor for the bottom, or an undersized anchor. Fix scope and chain first.
Do I need chain on my anchor?
Yes. Chain keeps the pull on the anchor low so it sets and stays set, and it protects the rope from chafe on the bottom.
Should I carry two anchors?
Yes. A primary plus a backup of a different style covers different bottoms, stern anchoring, and the day you have to cut a fouled anchor loose.
This guide is general information. Always follow the anchor manufacturer's sizing chart, local regulations on anchoring and protected seagrass or coral areas, and good seamanship practice. Conditions vary, so size up when in doubt.
