The rules that use the vocabulary item "boat" are:

<ship_class-creatable-sing>

attack boat flotilla

fishing boat

missile attack boat

missile boat flotilla

<ship_class-not_creatable-sing>

attack boat flotilla

fishing boat

missile attack boat

missile boat flotilla

<ship_class-not_creatable>

attack boat flotilla

attack boat flotillas

fishing boat

missile attack boat

missile boat flotilla

missile boat flotillas

<ship_class-not_creatable-pl>

attack boat flotillas

missile boat flotillas