40 ft boat, plow anchor, 40 ft of water
| plow (CQR) anchorresets well, needs weight to dig in | 44 lb |
|---|---|
| Chain sizeworking load about 5,400 lb | 3/8" |
| Chain lengthone boat length minimum, 30 ft floor | 40 ft |
| Rope size | 5/8"nylon three-strand |
| Total rode at 7:140 ft of water + 6 ft bow height | 322 ft |
| Total rode at 5:1calm, crowded anchorage only | 230 ft |
| Rope to carrytotal rode less the chain | 282 ft |
- Boat length
- 40 ft
- Anchor type
- plow
- Water depth
- 40 ft
Anchor weight is the least important number here
A 44 lb plow is the right size for a 40 ft boat, but weight is what holds an anchor on the bottom only until it sets. After that, holding power comes from the fluke area digging in and from the pull staying horizontal — which is what scope and chain are for.
An oversized anchor on a short rode holds worse than a correctly sized one on a long rode.
Scope is measured from the bow roller
At 40 ft of water, 7:1 scope means 322 ft of rode — because the height of your bow above the water counts too. That is the step people skip, and it is why a boat that thinks it is at 7:1 is often nearer 6:1.
In a crowded anchorage in settled conditions, 230 ft at 5:1 will usually hold. It is not what you want when the forecast turns.
Chain earns its keep in the last few feet
The 3/8" chain here does two jobs: it resists chafe on rock and coral where rope would part, and its weight keeps the pull on the anchor shank horizontal. Add a snubber — it takes the shock loading out of an all-chain rode and it is the cheapest part of the whole system.
Notes
- Scope is measured from the bow roller, not the waterline. Forgetting the 6 ft of freeboard on a 40 ft boat is how people think they are at 7:1 when they are closer to 6:1.
- This is a working anchor for an overnight stop in settled weather. A storm anchor goes up one or two sizes, and no chart substitutes for watching the forecast and leaving early.
- An all-chain rode holds better at low scope because the catenary keeps the pull horizontal, but it also shock-loads the boat in a chop. Add a snubber — it is the cheapest part of the system and the one that saves the windlass.
Nearby sizes
- 38 ft boat, plow anchor, 40 ft of water
- 42 ft boat, plow anchor, 40 ft of water
- 36 ft boat, plow anchor, 40 ft of water
- 44 ft boat, plow anchor, 40 ft of water
- 40 ft boat, fluke anchor, 40 ft of water
- 40 ft boat, claw anchor, 40 ft of water
- 40 ft boat, spade anchor, 40 ft of water
- 40 ft boat, plow anchor, 30 ft of water
- 40 ft boat, plow anchor, 25 ft of water
Read more
- "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.
- 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.
- 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.
- Anchoring a 24-Foot Boat: The Questions the Chart Cannot SeeTwo 24-foot boats can need different anchors. Length is the index every chart uses and the one variable that tells you least about the load.