I am up to mission 30 in the GTA V story mode. The next mission I'm meant to do is mission 31 which is the mission where you have to steal the submersible. I for some reason can not get past this point. I've done shooting practice with Franklin and have finished flight school with Michael. I've done every single mission for every single character including the side missions. I've seen videos for completing the Heist setup and apparently there is meant to be a HS on the map for Trevor but for me there doesn't seem to be anything except side mission. Either I'm stupid and blind or the game is glitched. Or both.
The last part of the Merryweather Heist will open up for play after you complete several other missions as various characters, such as The Long Stretch, Hood Safari, and the third FIB mission. In order to complete the third FIB mission, By the Book, you need to receive a phone call while playing as Michael or Trevor (not Franklin). Please switch to one of those characters and make sure that your in-game phone is not off, so you don’t miss mission-triggering notifications.
Yo, this really works. So I've been doing all the side missions for hours and nothing but, when I switched to online and then back to Trevor I got texts from "Brad" and Wade concerning the heist instantly. I hope this saved anyone from scrapping their multiple hours of gameplay to start from scratch.
I've had the same problem and I've sussed it woop it's took me forever but good good.
Ok so I choose the easier option for the merry weather heist of going in quietly. It told me I had to do flight school with Michael. It was a pain in my ass but I managed to get through doing a medal for each lesson. I then got lost and starting doing all side missions etc and couldn't work out where next to go as nothing showed on my map of what to do next. But the tip is this. Complete flight school with Michael. Then save and switch to Trevor. Look for your message from Wade saying he will look for info on sub and then call him via his message. It goes to answer machine and will shortly be followed up with a txt saying seen the sub etc and then a H will appear on the map to start the prep.
So for anyone trying to figure this shit out like i did after playing the story again... i know you want to save lesters missions for LAST... you gotta do the very first one to get Franklin his mansion and progress the story. just throw all your money into BET on BAWSAQ. after that you should be good. after that you can wait till the end. took me forever to figure/find that out. Hope this helps