There aren’t a lot of people around that can withstand the force of Shanks’ haki uncontrolled. The best good example who’s around would be Beckman, but if Shanks is dealing with handling his haki, Beckman would be handling the crew, so he’s out.

The other option? Mihawk. Earlier on in their duels, Mihawk finds out about Shanks’ conundrum; he was spending so much energy keeping it in check that he was an absolutely shit fighter that day, and Mihawk pressed the issue long enough until Shanks spilled the details.

Mihawk’s proposed solution: use their duels, when safe/out of range of the crew, as a way to release some of that pressure valve for his haki. Gets Shanks under control, and Mihawk has a decent level of resistance to it. As time goes on, Shanks is comfortable letting more and more of it go after Mihawk proves it won’t absolutely knock him out, which does wonders for his wellbeing. (Mihawk gets hit with how beautifully terrifying Shanks can be, and then chooses to not process that for a good long while.)

An additional option that pops up later down the road: sometimes, the above happens but without a duel, if things are really bad. Beckman takes over for an afternoon, and Shanks and Mihawk take Hitsugibune out to a nearby deserted island so Shanks can absolutely let go. At that level, it’s not a great idea to involve dueling or weapons. Shanks also isn’t a fan of the crew seeing him lose that degree of control; Mihawk realizes how big of a sign that is for Shanks’ trust in him. Often ends in Shanks falling asleep on or near Mihawk with his haki still active. (It’s like a very strong mental weighted blanket, albeit Mihawk will never say that out loud.)

Additional third option: there’s very fun possibilities here for when they actually get into a relationship, but that’s its own post, haha.