Chains—small platform extending from the side of the ship on either side to extend the shrouds a bit farther out to better support the mast.The chains platform also provides a place for the leadsman to stand while sounding depth of the water with the lead.
- Forechains-Chains supporting the foremast shrouds.
- Mainchains-Chains supporting the mainmast shrouds.
- Mizzenchains-Chains supporting the mizzen shrouds.
Chains at Wikipedia.