Question: I recently ran an encounter on a "restaurant boat" where my players had to obtain info from a noble on board. They successfully bluffed/bribed/sneaked their way on board. Certain areas of the ship were off limits to guest, such as the crew's quarter's, the captain's cabin, and the lower deck with rowers moving the ship along.

My players found a somewhat quiet spot on deck. They proclaimed they wanted to sneak past the guests, who were busy with eating/socializing/etc., into the forbidden areas. One of them cast *pass without trace*, and I asked them to all roll for Stealth. No one got less than 19 on their Stealth check (after modifiers). They then proceeded to "sneak" past guests into the upper areas (not forbidden per se) and then further into "Staff Only" areas.

How do I adjudicate this?

Obviously, they pose as guests, no weapons or armor on, so they would just blend into the crowd and then, in an opportune moment, sneak past a door/curtain/rope barrier. But they are still moving in plain sight of at least a dozen NPCs. The NPCs can probably see them, but they do not *perceive* them.

The same problem would arise for me if they wanted to escape someone following them in a dense marketplace or in a crowded tavern. How can you Hide/roll for Stealth in a crowd of - admittedly uninterested in you - NPCs?

Answer: 
Stealth was most likely the wrong choice
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Stealth implies that you are impossible to see. If you succeed on your stealth attempt, you are hidden, if you fail, you are not hidden.

Your players aren't actually trying to be hidden, anybody can see them, they simply don't register them as *somebody who shouldn't be there*.

Blending in with the crowd really shouldn't require a stealth check at all. It might, however, if you like, entail any of the following:

* Persuasion: To get other guests to cooperate if they at some point figure out things are fishy.
* Deception: To bluff their way past guards who are suspicious about the players actually being guests
* Performance: Deception works great for pretending to be a guest when you are not, but performance could also work, depending on who you ask.

None of these things require stealth, because you aren't trying to be unseen, you're trying to blend in.

Stealth doesn't enter the ordeal until they actually try to go somewhere a normal guest would not be allowed. The moment they want to pass into Staff Only areas and the guards would react if a normal guest did that, then they have to actually use their stealth skill, and they would obviously have to do so in a way that makes sense, you can't stealth your way through a door in plain sight, regardless of how well you rolled.

Blending into a crowd to escape from somebody else is a completely different thing than blending into a crowd to not stand out. Once your target no longer has line of sight to you, you can try to stealth. If you succeed, the target no longer knows where you are and you can keep moving in the crowd until they have direct line of sight of you again, at which point you are no longer hidden and the chase most likely continues.

It's the difference between:
"I need to hide in the crowd because I'm a wanted man and if I'm spotted they will arrest me!" and "I need to blend in because I don't want to look out of place and get asked questions by nosy guards."
A Charisma (Deception) vs Wisdom (Insight) check
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I'm guessing that you're referring to a *certain location* in Storm King's Thunder. If I'm right, the book suggests the following on page 216:

> 
>  The adventurers might try to replace one or more of the workers [of the Grand Dame] [...] A character who wants to get aboard in this fashion must **succeed on a Charisma (Deception) check contested by Captain Storn's Wisdom (Insight) check**. A character who wins the contest can board the ship without raising suspicion.
> 
> 
> 

The informational text on this page is talking about getting on board from the docks while it is tied up between trips, not getting into the *CREW ONLY* sections of the ship while it is underway and entertaining guests onboard but I think the Charisma (Deception) vs Wisdom (Insight) check works for both situations.

It might not be the Captain's Insight they are trying to oppose but that of whomever sees them attempting to access the off limits areas. This could be a crew member or the pit boss Pow Ming).

Even if I'm totally wrong on the campaign, I think the recommendation is still universally applicable.