Calibrated Anchor Chain - General Information
Calibrated chain is essential if you have a windlass fitted on your yacht or if you are considering a windlass in the near future.
Calibrated means that each link is manufactured to the same dimensions within a given tolerance.
Windlass gypsys are generally designed and manufactured to be compatible with a given size and calibration of chain.
When the dimensions are close but not a direct match, it can be difficult to detect without a practical trial.
The problem then normally occurs after a short length has been through the gypsy under load.
The difference in size between the chain link and the pocket on the gypsy eventually leads to a jam or a jump.
A lot of information is available on the internet regarding the calibration of windlasses.
This information may come from the manufacturer or even from a fellow sailor.
This is a very good guide and could well be accurate.
However, there are some ‘caveats’ which need to be taken into account e.g.
Windlasses are normally offered with a choice of different chain sizes and calibrations.
Any markings or stamps on the gypsy itself may help in this respect.
Windlass manufacturers have changed their specifications over the years, and the details of those changes are not easily available without much research.
If you are not 100% sure of the provenance of your yacht, windlass or gypsy, then the gypsy may have been replaced at some time.
The replacement could be a different calibration.
There are only two main calibrations for chains manufactured in Europe: DIN766 and ISO4565.
The good news is that the dimensions for 6mm, 8mm and 12mm are identical.
10mm is more difficult because the dimensions are different for DIN766 and ISO4565.
Both 10mm calibrations are very commonly used in Europe.
Be aware that selecting the wrong calibration, particularly in 7mm or 10mm, on the vast majority of windlasses will result in ‘jamming’ or ‘jumping’ under load.
7mm is also tricky because the dimensions are sufficiently different to create problems on most windlass gypsys.
To make matters worse, 7mm ISO4565 is not generally available from any calibrated anchor chain marine manufacturer.
US Calibrations are entirely different to European DIN766 or ISO4565, and they will generally only work on their US matching gypsy. US Calibrated chain is not readily available in Europe. You can replace your US-calibrated chain with a European calibration, but the prudent course of action will be to replace the gypsy to match.
For information on how Jimmy Green Marine can help you select the right chain for your windlass, please go to
Calibrated Anchor Chain - determining the calibration of your Anchor Chain