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Calibrated chain is absolutely 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 so that they are compatible with a given size and calibration of chain.
When the dimensions are close but not correct then it is 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.
There is a lot of information available on the internet regarding the calibration of windlasses. This information may come from the manufacturer or even from a fellow yachtsman. 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 change their specifications over the years and the details of those changes are not necessarily available without a lot of research. If you are not 100% sure of the provenance of your yacht, windlass or gypsy then it is possible that the gypsy has been replaced at some time. The replacement could be a different calibration.
There are only two main calibrations for chain manufactured in Europe: DIN766 and ISO
The good news is that the dimensions for 6mm, 7mm, 8mm and 12mm are identical.
10mm is more difficult because the dimensions are different for DIN766 and ISO.
Both 10mm calibrations are very commonly used in Europe.
Be aware that selecting the wrong calibration, particularly in 10mm, on the vast majority of windlasses will result in ‘jamming’ or ‘jumping’ under load.
US Calibrations are entirely different to European DIN766 or ISO.
Jimmy Green offer US calibration anchor chain in Aqua4 and Aqua7 manufactured by Maggi Catena in Italy by special order.
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 correct calibration