Frequently Asked Questions

Got questions? Find answers to our most popular questions here.

How do I choose the right Knox size for my boat?

Knox sizing depends on boat displacement, windage, and how you anchor — not just length.

As a general guide:

  • Day anchoring / fair weather → standard Knox size
  • Overnight / exposed / liveaboard anchoring → one size up

Many owners choose the next size up for additional margin. That’s normal and supported by the design philosophy. If you’re unsure, we’re happy to recommend a sensible range rather than a single “perfect” size.

Sizing up by one step is common and often beneficial if you:

  • anchor overnight regularly
  • expect changing conditions
  • prefer additional margin
  • cruise unfamiliar anchorages

 

Extreme oversizing beyond one step is rarely useful and can introduce fit, handling, and stowage issues without meaningful holding gains.

No. Holding depends far more on geometry and burial behaviour than weight alone.

Knox is designed to achieve high holding relative to its weight by digging and remaining engaged as load increases. Simply increasing anchor mass without effective burial does not guarantee better holding.

Most do, but bow roller geometry varies significantly between boats — even within the same model.

Key checks are:

  • fluke-to-hull clearance
  • roll-bar-to-pulpit clearance
  • roller width and axle position
  • windlass spacing

We provide templates and visual guides to help confirm fit before ordering. If in doubt, send us a photo of your bow and we can usually advise quickly.

The most useful measurements are:

  • roller width
  • distance from roller axle to bow
  • clearance between roller and pulpit
  • windlass position relative to roller

These determine how the anchor will sit when stowed.

This depends mainly on stem angle. Boats with vertical or plumb bows require closer checking. The 1:1 template or clearance diagram allows you to verify this before purchase.

Roll bar clearance varies widely between pulpits. Most installations work without modification, but this is one of the primary fit checks.

If clearance is tight, a photo usually resolves it quickly.

Yes, if locker dimensions allow. Knox anchors are one-piece and structurally robust, so locker storage is mechanically fine.

However, most installations use bow-roller stowage for deployment convenience.

If you’re unsure:

  1. Measure or photograph your bow setup
  2. Note your boat model and intended Knox size
  3. Send this to us

We’ll confirm whether fit is likely or advise any considerations. There’s no pressure to buy.

Yes. If you’re unsure about size or fit, contact us with your boat details or a photo of your bow. We’ll help you choose confidently.

Why does Knox focus on behaviour under load instead of “fastest set”?

Because anchoring failures rarely occur at the moment of set.

They occur later, when:

  • wind builds
  • direction shifts
  • loads exceed expectations

Knox prioritises predictable behaviour as those loads increase, rather than optimising only for initial setting speed or peak laboratory numbers.

Knox is designed to dig deeper and remain engaged as load builds.

Rather than releasing suddenly when overloaded, it typically maintains seabed contact and manages load progressively.

If forces exceed expected holding:

  • Knox tends to remain buried
  • movement occurs gradually
  • holding is not lost abruptly

 This provides a predictable response instead of sudden breakout.

In sand or mud, Knox typically turns while still buried and resets within about one metre.

This behaviour has been observed repeatedly in testing and real use. As with all anchors, seabed and setup still matter.

It is specifically designed to resist rolling out. The geometry and burial behaviour aim to maintain engagement during directional changes rather than flipping free.

No. Controlled ploughing while buried is different from loss of holding.

Anchors that lose grip typically roll out or break free. Knox movement under overload generally occurs while still engaged.

The slot allows sand and clay to escape as the anchor buries.

This prevents material packing unevenly and preserves the concave fluke geometry needed for sustained holding under load.

No. Structural strength comes primarily from shank and fluke structure, not whether the fluke is continuous. Knox uses thick, high-grade steel and conservative geometry specifically to maintain structural integrity.

Occasionally small stones or debris can lodge in the slot.

This is rare and usually discovered during retrieval. There are no documented cases of holding loss caused by jamming — the typical consequence is minor inconvenience.

Experiments showed that even small changes to the slot significantly reduced holding performance. The open slot is therefore retained as a deliberate trade-off for burial behaviour.

Testing was developed scientifically to produce repeatable comparisons:

  • controlled seabed
  • gradual load increase
  • consistent scope
  • strain-gauged measurement

This allowed behaviour under load to be studied systematically.

Some modern designs did not exist during the original test programme. Testing aimed to understand anchor behaviour broadly rather than rank every future design.

Knox demonstrates very high ultimate holding relative to weight in sand/mud testing. However, performance varies by seabed and setup. No anchor is best in all conditions.

The maximum resistance achieved after full burial under sustained load. Knox focuses on this sustained holding behaviour rather than only initial peak force.

What seabeds is Knox best suited to?

Knox performs best in:

  • sand
  • mud
  • sand-mud mixes

These seabeds allow burial and progressive holding — the behaviour Knox is designed around.

Like most anchors, performance is less reliable in heavy kelp or dense weed.

Kelp stems can occasionally lodge in the fluke slot and prevent full burial. This is uncommon but possible. Where heavy weed dominates, anchoring reliability for any design is reduced.

No anchor can reliably hold in bare rock or large boulder fields without physical hooking. Knox is not designed to hook rock and performs similarly to other burying anchors in these conditions.

No. Reliable anchoring requires a seabed that allows penetration and burial. Rock and dense weed are inherently unreliable regardless of anchor type.

A typical method:

  1. Lower anchor to seabed
  2. Allow boat to drift back while paying out chain
  3. Reach ~4–5× depth
  4. Apply gentle reverse
  5. Increase load gradually to confirm set

This ensures proper burial before relying on holding.

Typical guidance:

  • 3:1 calm conditions
  • 5:1 normal anchoring
  • 8:1+ strong winds

More scope increases holding margin when space allows.

Yes, strongly recommended. A snubber or bridle:

  • reduces shock loads
  • protects windlass and deck gear
  • improves holding behaviour
  • reduces noise

Waves introduce dynamic loading. Chain becomes bar-tight and load spikes can greatly exceed steady wind forces. Shock absorption (snubber/bridle) helps manage this.

After sustained load in sand, the anchor may be deeply buried. Sand stiffens under compression, increasing extraction resistance.

Recommended method:

  1. Motor slowly forward while retrieving chain
  2. Bring chain near vertical
  3. Pause briefly (≈20 seconds)
  4. Allow anchor to release gradually

Avoid high-power “ripping” loads.

Yes. Applying engine power against a deeply buried anchor can create very high loads on chain, windlass, and bow fittings.

No. Holding always depends on seabed, setup, and conditions. Knox is designed to behave predictably and maintain engagement when loads increase, but anchoring still requires judgement.

Confidence. Once properly set in suitable seabed, Knox is designed to remain buried and engaged as conditions change, allowing skippers to rely on predictable behaviour rather than sudden release.

Where do Knox anchors ship from?
  • UK orders: shipped from within the UK
  • EU orders: shipped from the Netherlands distribution centre
  • UK: usually under one week
  • EU: typically 3–14 days depending on destination

The anchor only. Chain, shackles, swivels, and snubbers are supplied separately so owners can configure their preferred setup.

No. Knox anchors are single-piece construction and require no replaceable parts.

High-grade galvanised steel offers:

  • excellent structural strength
  • predictable fatigue behaviour
  • robust weld performance
  • proven marine durability

Stainless anchors can require specialised heat treatment to maintain strength at welds and are often chosen for appearance rather than structural optimisation.

Hot-dip galvanising provides long-term corrosion protection in marine use. Like all galvanised steel, wear can occur over time but does not normally affect structural integrity.

Yes. The design uses:

  • thick shank geometry
  • conservative load assumptions
  • high-grade steel

Structural failure incidence is extremely low.