Advice and information
Everything we know about marking and using an anchor chain.
Written by people who make chain markers for a living, for people who anchor. None of it requires you to buy anything.
Why mark your anchor chain?
If you're new to boating you may wonder why experienced owners, captains and crew place so much importance on knowing exactly how much chain is going out. The answer is simple: knowing how much chain you've deployed lets you set the correct scope, and scope is what keeps the anchor in the ground.
What is anchor scope?
Scope is the ratio between the depth of water and the length of chain deployed. Too little chain and you reduce the anchor's holding power and increase the risk of dragging. Too much and you risk swinging into the boats around you. The right amount helps the anchor set properly and holds better.
Marking the chain won't tell you how much chain you should let out — that's your call, and it depends on depth, wind, tide and how close the neighbours are. What marking does is let you put out the amount you intended, accurately. Without it, that's genuinely hard to judge: especially at night, in poor weather, or short-handed.
Proper anchoring is a safety issue
Boats move constantly even at anchor, so it matters to you and to everyone anchored around you. Safe anchoring practice is regularly emphasised by the RYA, maritime training providers, yacht management companies and safety authorities worldwide — and knowing your deployed chain length is one of the most consistently overlooked parts of it.
How to measure your chain size.
Chain size refers to the wire diameter — the thickness of the metal a link is made from — not the length or overall size of the link. That's the single most common mix-up we see.
With callipers
The most accurate method. Measure the side of several links and take an average. Bear in mind that older chain may have slightly deformed links from the loads it has carried, so your readings may not land on an exact round number.
With a rule or tape
Measure the diameter of one link side as accurately as you can, then use the nearest standard size. If you land between two sizes, ring us — we can usually settle it over the phone, or from a couple of photographs.
Measure five links, not one
Take five different links, avoiding any joining link, and average them. One reading off a worn link will send you to the wrong size.
What is calibrated chain?
Calibrated marine chain is made to specific dimensions — wire diameter, pitch and width — so it will be gripped correctly by the gypsy or wildcat in your windlass. For metric chain the codes to look for are DIN766 and ISO 4565; you'll also see EN818. Our markers are toleranced to fit all three, so a marker may sit slightly loose on some chain. That doesn't affect how it performs.
Above 12mm the tolerances get wide enough that a stocked marker no longer fits reliably, which is why everything from 13mm upwards is custom made.
Anchor chain length conversions.
A reference for converting between metres, feet, fathoms, shackles and cables — useful for scope calculations, marking up a chain, and translating whatever unit the previous owner used. Read each row as "one of this equals…".
| 1 unit of… | Metres | Feet | Fathoms | Shackles / shots | Cables | Nautical miles |
|---|---|---|---|---|---|---|
| Metre | 1 | 3.28 | 0.55 | 0.036 | 0.0054 | 0.00054 |
| Foot | 0.3048 | 1 | 0.167 | 0.0111 | 0.00165 | 0.000165 |
| Fathom | 1.8288 | 6 | 1 | 0.0667 | 0.00987 | 0.000987 |
| Shackle / shot | 27.432 | 90 | 15 | 1 | 0.1 | 0.0148 |
| Cable | 185.2 | 607.6 | 101.2 | 10 | 1 | 0.1 |
| Nautical mile | 1852 | 6076.1 | 1012 | 100 | 10 | 1 |
Our guide plates can be supplied numbered in metres or in feet — pick whichever your depth sounder speaks.
Colour sequences — best practice.
Whatever you use to mark your chain — paint, cable ties or markers — there are four things worth thinking about first. We designed our sets around all of them.
1. Put an anchor marker just above the anchor
A simple point, and one we're constantly surprised people don't think about. Put your first marker the same distance up the chain as your bow roller is above the water. When you see that mark coming up you know the anchor is about to break the surface, so before it comes aboard you can:
- Clean off any weed or mud
- Check it isn't swinging around and about to damage the bow
- Orientate it, if yours has a habit of coming up the wrong way
- Slow the retrieval down before anything hits anything
How our sets help: every guide plate has a first position you can mark with an "A" for the anchor.
2. Keep it as simple as possible
We have built some genuinely complex sequences for customers, but marking a chain usefully doesn't need to be complicated. A common sequence is red, yellow, blue, white, green — repeated as necessary.
The traditional way sailors remember it:
Rub Your Balls With GreaseRed · Yellow · Blue · White · Green
How our sets help: we'd rather you didn't have to remember anything. With fifteen colours available you can give every position its own colour and skip sequences entirely.
3. Don't use single links to count distance
Some people mark one link, then two links, then three. The problem is obvious the first time a marker is lost or fades: the whole system falls over, and you can't tell "two" from "three" with one missing. If you do mark this way, at least double it up — so "one" is two marked links, and "two" is two marked links, two blank, two marked.
How our sets help: a unique colour at each position removes the problem, and with five markers of each colour, one coming out still leaves the position perfectly readable.
4. For long chain, use repeating intervals
On a long chain, consider a unique colour at the major intervals and one shared colour for everything in between. For example:
Orange always means "you're at a five", and the unique colours mark each ten. How our sets help: we can put together custom sets for all chain sizes, so any sequence you like is buildable.
Our recommended full order
If you'd rather just use ours, this is the order we supply and the order the guide plate assumes:
Red · Yellow · Light blue · White · Light green · Pink · Orange · Royal blue · Ivory · Forest green · Magenta · Auburn · Purple · Brown · Olive
Fitting instructions.
No degreasing, no masking, no drying time, no waiting for weather. You need a screwdriver. If you're using the guide plate, keep the tab at the top of the rack.
Fitting the chain markers
- Break the two opposite halves of the marker off the rack and place one either side of the chain link. One half has a protrusion, the other a cavity and the screw hole.
- Press them together firmly to make sure they are aligned.
- Place the supplied screw into the hole.
- Screw into place with a suitable screwdriver until the screw bites. Do not over-tighten.
Markers can be removed and relocated later if you need to — undo the screw and it comes apart into two halves again.
Building the guide plate
- Colour tabs go into the plate numbered (or "+") side down.
- Cut the numbers you need off the rack, making sure the ends are clean, and slot them into one column. Press firmly until flush — if they don't sit flush, check both ends are clean, as they're designed to be a tight fit.
- Cut the colour tabs off the marker rack, again with a clean edge, and fit them opposite the numbers you've chosen.
- Mount the plate somewhere it is easily visible while you're dropping the anchor.
Suggested marking sequence: anchor indicator about a metre up from the anchor → mark every 5m from 2–20m → every 10m from 30m upwards → STOP tab near the bitter end so you know to stop paying out.
Best anchoring practices.
Whether you own a small leisure boat, a cruising yacht or a large superyacht, the fundamentals don't change: choose a suitable anchorage, deploy sufficient chain, set the anchor properly, and monitor the vessel while you're on it. Vessel size changes the procedure and the equipment, not the principles.
Poor anchoring results in dragging, collisions, damaged equipment, or simply a rotten night's sleep.
Smaller boats and day cruisers
Generally easier to manoeuvre, and usually needing less chain and lighter ground tackle.
Before you anchor
- Check weather and tidal conditions
- Assess the depth — in a tidal area, allow for how much it will change
- Identify a suitable seabed
- Make sure there is adequate swinging room
Deploying the anchor
- Lower the anchor under control
- Don't throw it overboard
- Reverse slowly while paying out chain
- Confirm the anchor has set before increasing engine load
Common mistakes made by new owners
- Deploying insufficient chain
- Estimating chain length rather than measuring it
- Anchoring too close to other vessels
- Failing to allow for tidal changes
- Not checking whether the anchor has actually set
Cruising yachts
Cruising boats spend longer at anchor and meet a wider range of weather and seabed. Additional things to plan for: wind shifts overnight, higher loads on anchor and chain, larger swinging circles, and clear communication between crew. As chain lockers get bigger and more chain goes out, knowing the deployed length matters more, not less.
Large yachts and superyachts
The principles are identical; the consequences of getting it wrong are considerably larger. Professional crews plan the anchorage in detail, assess seabed suitability, calculate swinging room, check forecasts, note nearby vessels and hazards, and agree emergency recovery procedures.
Clear communication between bridge and foredeck is considered essential. Crew should be able to report anchor status, chain lead angle, direction of pull and amount of chain deployed — which is one reason professional vessels use clearly marked chain and dedicated identification systems.
The spring chain checklist.
Your anchor chain is a lot more than "what we put down to stop for a sandwich". It is one of the most crucial pieces of safety equipment on board — it's what keeps the boat where you left it while you're asleep, and in an emergency it may be the only thing that does.
It also lives in the worst conditions of anything on the boat: salty, wet, and shut in a damp locker at the bow. It suffers more than the rest of your equipment, and it deteriorates quietly. Pull the whole chain out, lay it on the deck or the pontoon, and work through this list.
- Remove any twists or rotations in the chain.
- Inspect for corrosion or rust — including whatever length was still in the locker after you hauled the rest out.
- Pay attention to all the links, looking for any bent, cracked or excessively stretched. Those reduce the chain's load-bearing capacity.
- If you use a chain and rope combination, check the joint and the full length of the rope for frays or twists in the strands.
- Inspect where the chain attaches to the boat. It should be strong — but you must still be able to cut it loose quickly and safely.
- Inspect the shackles connecting chain to anchor. Properly secured, no bending, cracking or loosening.
- Inspect the gypsy or wildcat in the windlass for broken teeth or distortion.
- Check the wiring running from the helm to the windlass, looking for corrosion anywhere along it.
- Ask yourself when the windlass was last serviced. Is it due a once-over?
- While the chain is out, refresh the markings so they're clear and obvious for the season.
Checking it consistently means you find problems while they're still problems, rather than in a rising wind at two in the morning.
My size isn't here!
If your chain size isn't listed, or you're not certain what you have, don't guess and don't give up — this is genuinely routine for us.
- Have a look at how to measure your chain first — it's often a case of the link length being measured instead of the wire diameter
- Send us the dimensions using the form and we'll confirm what fits
- Or just ring 01202 070916. We can usually identify a chain from a couple of photographs and a rule
Between 13mm and 70mm we custom build anyway, so an unusual size is not a problem. Larger, heavier-duty or unusually long chain — we've quoted for 78mm stud link on a commercial vessel — is a conversation, not a dead end.
Tell us what you've got
We'll come back with the size that fits and what it costs.
Q&A
Technical questions about chain and markers. For questions about ordering, shipping and returns, see the FAQs on the home page and the returns policy.
I have 3/8" chain. Which size should I buy?
The 10mm markers. Imperial sizes map across as: 1/4" is 6mm, 5/16" is 8mm, 3/8" is 10mm, 1/2" is 12mm, 5/8" is 16mm, 3/4" is 19mm and 1" is 24mm.
Will they go through a windlass?
Yes. The markers have been designed and tested to pass through a windlass without interfering with its function or jamming it. This was particularly important during design, because the gypsy is where a marker is most likely to be subjected to wear.
I have a really long chain — can you help?
Yes. Typical sets are sold to leisure boaters with chains up to about 120m and up to fifteen marked positions. If you have a longer or heavier-duty chain, or want to mark more positions than that, get in touch and we'll build a set for it.
What is the guide plate for?
Rather than memorising your colour sequence or keeping a laminated card by the windlass, the guide plate is a permanent cross-reference you mount where you can see it. If you're ordering four or more colours it comes with a set of numbers letting you mark from the anchor through to 50 in intervals of 5, then up to 100 in intervals of 10.
One is included with every pre-packed kit. Spares are £4.58.
I'm not sure what size chain I have.
The size is the diameter of the metal within the link, not the size of the link as a whole. Measure it accurately with callipers, or reasonably well with a rule or tape — see how to measure your chain.
Our markers are designed to fit DIN766 and ISO 4565 chain, which can vary slightly in link length or width but will be a set size to pass through the boat's windlass. If you're uncertain, get in touch — a couple of photographs and testing a few sizes usually settles it.
What is calibrated chain?
Chain made to specific dimensions so it will pass correctly through a windlass built for that size. There are three common calibrations — DIN766, ISO and EN818. Our markers are made with tolerances to fit all three, so they may be slightly loose on some chain. That does not affect performance.
What colour sequence should I use?
Ultimately it's up to you, and we'll build whatever you ask for. If you'd like a recommendation, our colour sequence guidance sets out the four things worth considering and the order we supply as standard.
I don't know the length of my chain.
The only way to know for certain is to haul it all out and measure it — which is messy and hard work, especially with the boat on the water. If you know roughly, buy a set you think will cover it: if you don't use the last couple of rows on the guide plate, just leave them empty.
Why is 13mm and above custom made?
Because calibrated chain of the same nominal size genuinely isn't the same size. DIN766 permits a spread of up to 6.2mm in the inner width of a 14mm link, and we've measured customers' 14mm chain anywhere from 15.7mm to 21mm. A standard marker would fit some of it and get punched out of the rest. The full explanation is here.
Still got a question?
Ring us. You'll get Quinton.
Office hours are 08:00–17:00. If nobody picks up it's because we're making something — leave a message and you'll get a call back.