Anchor Holding Power Calculator
The anchor holding power calculator estimates the horizontal load (windage) your boat creates at anchor during high winds. It then calculates the required holding power and recommends an anchor weight based on the design efficiency of your chosen anchor style.
Understanding Anchor Holding Power
An anchor's job is to resist the horizontal force generated by the wind pushing against your boat's hull and rigging (windage). As wind speeds double, the force quadruples. This is why storm anchoring requires significantly more holding power than a calm lunch hook.
How Anchor Styles Affect Weight
Not all pounds are created equal. The physical weight of the anchor helps it penetrate the seabed, but its design determines how much horizontal load it can hold once set.
- Modern Scoop Anchors (Rocna, Spade): Highly efficient. They use a roll-bar or weighted tip to dig deep quickly. They can typically hold up to 45-50 times their own weight.
- Fluke Anchors (Danforth): Very high holding power (up to 35x their weight) in hard sand or thick mud, but they can struggle to reset if the wind or tide shifts 180 degrees.
- Plow Anchors (CQR, Delta): Traditional designs that hold roughly 25 times their weight. They are reliable across many bottom types but require a heavier physical anchor to match modern designs.
The Importance of Scope
No anchor works efficiently if the pull angle is pulling upward. Scope is the ratio of anchor rode (chain/rope) paid out compared to the water depth (plus the height of your bow off the water).
A 3:1 scope will cause an anchor to break out easily. A 5:1 scope is standard for everyday anchoring. A 7:1 to 10:1 scope is highly recommended for storm conditions to ensure the pull on the anchor shank remains perfectly horizontal.