Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Yachts are not forbidden in themselves. They are like any other boat or ship which are used in Halal matters. So, there is no objection to your husbands’ work in a factory that makes luxurious yachts unless these yachts are used in Haram things or mostly used in that which is unlawful.
In such case, it becomes forbidden to make them.
Allah knows best.