Spade anchor size chart
| — Spade anchor by boat length — | |
|---|---|
| 10 ft boat1/4″ chain | 8 lb |
| 12 ft boat1/4″ chain | 10 lb |
| 13 ft boat1/4″ chain | 12 lb |
| 14 ft boat1/4″ chain | 12 lb |
| 15 ft boat1/4″ chain | 12 lb |
| 16 ft boat1/4″ chain | 14 lb |
| 17 ft boat1/4″ chain | 14 lb |
| 18 ft boat1/4″ chain | 16 lb |
| 19 ft boat1/4″ chain | 16 lb |
| 20 ft boat1/4″ chain | 18 lb |
| 21 ft boat1/4″ chain | 18 lb |
| 22 ft boat1/4″ chain | 18 lb |
| 23 ft boat1/4″ chain | 20 lb |
| 24 ft boat1/4″ chain | 20 lb |
| 25 ft boat5/16″ chain | 22 lb |
| 26 ft boat5/16″ chain | 22 lb |
| 27 ft boat5/16″ chain | 22 lb |
| 28 ft boat5/16″ chain | 24 lb |
| 29 ft boat5/16″ chain | 24 lb |
| 30 ft boat5/16″ chain | 26 lb |
| 32 ft boat5/16″ chain | 28 lb |
| 33 ft boat5/16″ chain | 28 lb |
| 34 ft boat5/16″ chain | 28 lb |
| 35 ft boat3/8″ chain | 30 lb |
| 36 ft boat3/8″ chain | 30 lb |
| 40 ft boat3/8″ chain | 34 lb |
| 50 ft boat7/16″ chain | 42 lb |
| — The four types at one length — | |
| Fluke for a 25 ft boatsand and soft mud | 18 lb |
| Plow for a 25 ft boatmixed bottoms | 28 lb |
| Claw for a 25 ft boatrock, coral and grass | 28 lb |
| Spade for a 25 ft boatalmost everything | 22 lb |
Notes
- Spade, also sold as modern concave. The concave designs — Spade, Rocna, Mantus, Vulcan — set faster and hold harder per pound than anything older. They cost more and they need a bow roller that will take the shape.
- These are working weights, not storm weights. The table holds a boat overnight in ordinary conditions. Anything forecast above about 25 knots wants a second anchor set at an angle rather than a heavier primary, because two rodes at 45 degrees share the load and stop the boat sailing around.
- Scope decides more than the number in this table. The same anchor on 7:1 scope outholds a 50% heavier one on 3:1, every time — the angle at the shank is what buries the flukes. And measure the depth from the bow roller, not the waterline: on a 30 ft boat the bow adds about 5 ft to the triangle.
- Bottom type beats weight. A spade is at its best in almost everything. Where it is wrong, going up two sizes will not fix it — the wrong shape does not set at all, and an anchor that has not set weighs nothing.
- Manufacturer tables differ, and they differ for real reasons: hull form, displacement and superstructure all matter and none of them appear in a length-only chart. Round up if the boat is heavy for its length, carries a tall bimini or flybridge, or lies on an exposed mooring.
The Spade anchor, by boat length
The table above is a starting size, not a specification. It comes from the weight-per-foot figures published by anchor makers, and every one of those tables is a length-only approximation of a question that really depends on displacement and windage.
What the chart cannot see
Two 30 ft boats can want different anchors. A heavy displacement cruiser with a tall superstructure loads its rode far harder than a light open boat of the same length, and neither appears in a chart keyed on length alone.
Round up if the boat is heavy for its length, carries a flybridge or a large bimini, or lies on an exposed mooring rather than in a protected cove.
Weight is the smaller half of holding power
An anchor holds because the flukes are buried, and they bury because the pull at the shank is nearly horizontal. That angle comes from scope, and scope is free. Paying out more rode costs nothing and does more than any upgrade in the chart.
Measure the depth from the bow roller rather than the waterline — the freeboard is part of the triangle, and forgetting it is the usual reason a scope calculation comes out short.
Nearby sizes
Read more
- New-Generation Anchors Against the Classics: What the Concave Fluke ChangedThe difference is not marketing. A concave fluke digs deeper under load where a plow tends to plane, and re-setting after a wind shift is where the gap is widest.
- "Anchor Weight per Foot: The Rule of Thumb, and Where It Breaks"A pound per foot is a rule that works in the middle of its range and fails at both ends, for two different reasons.
- Reading a Modern Scoop Anchor Chart, and What Its Small Print AssumesModern anchor charts look interchangeable and are not. The difference between them is usually one line of small print about assumed wind speed.
- Fluke Anchors: Where They Excel, and the Two Bottoms That Defeat ThemThe fluke anchor has the best holding-to-weight ratio in common use and two well-known failure modes. Both are about the bottom, not the size.