To meet aquaculture demands, modified aquaculture vessels usually have several cranes added on the main deck, and the cranes are high enough to block the navigation bridge visibility. The middle crane and the crane at the front form scattered blind sectors, and the angle between the two blind zones is smaller than 5°. With the conventional drawing method, the legal requirement for the bridge visibility can’t be met, while if the requirement is to be met by changing the crane layout position, then the ship functions will be affected. In order to solve this problem of the angle being smaller than 5°, a method is proposed in this paper, that’s to combine the two zones while ensuring the function realization of the cranes on the main deck, so that to increase the angle between the two blind zones to larger than 5°, and meet the legal requirement on visibility. This method can be applied to ships with similar deck layout with that of aquaculture vessels.