Noun
One of the crooked timbers which are scarfed together to form the lower part of the compound rib of a vessel; one of the crooked transverse timbers passing across and over the keel.
Source: Webster's dictionaryBetween each futtock the planks were lapped in normal clinker style and fastened with six iron rivets per plank. Source: Internet
The lower part of the side stay consisted of ropes looped under the end of a knee of upper futtock which had a hole underneath. Source: Internet