Bulbous Bow questions

Greetings,

I was touring the Oceanco website recently. I see that on some of their designs, say 100 meters or more, that some vessels have the bulbous bow, (e.g. "DP002") and some don't (e.g. "Titan"). These ships are of similar size, power and cruising speed.

I am aware that the bulb creates a low pressure zone and can assist in reducing drag (thus helping reduce fuel consumption) and also there are ancillary benefits such as reduced noise, etc. What considerations and or operating parameters would induce a designer/builder to choose a bow bulb or not? Approximately, at what point do the efficiencies kick in; at what point is the bulb addition counter productive?

thanks in advance for any replies

thank you