On the Boat

I've heard this game under many different aliases, but I first heard of it as 'on the boat', so that's what I'll be calling it. Basically, it's like this--

Person 1: I want to take a piece of butter on the boat.
Mod: You can take the butter onto the boat.
Person 2: I want to take a flower on the boat.
Mod: You can't take a flower on the boat.
Person 1: I want to take a letter on the boat.
Mod: You can take a letter on the boat.

And so on. The point is, you have many shots at guessing what you can take on the boat and what you can't, and this is moderated by a certain rule. In this case, the similarity between butter and letter is that they have a double-consonant. Abiding by such a rule, a flower can't be taken on the boat, but a ball could. In the end, the game is 'won' when someone correctly guesses the rule, which only the moderator knows.

So I'll start, and then the person who guesses the rule correctly is the next moderator.
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Hint: You can take a fish on the boat.
You can't take a whale onto the boat.

I want to take a clownfish on the boat.

You can't take a clownfish on the boat.
You can take a sheep on the boat.

Does it have something to do with one being a fish and one being a mammal?

Can I take a wish on the boat?

Usagi !! wrote:

Does it have something to do with one being a fish and one being a mammal?

Nope. There is no gimmick related to sea creatures whatsoever.

Metroid-Life wrote:

Can I take a wish on the boat?

No, you can't take a wish on the boat.
You can take a moose on the boat.

Can I take a deer on the boat?

Azure wrote:

Can I take a deer on the boat?

Yes! You can take a deer on the boat.

I'm sure you guys have guessed it by now.

Can I take some beer on the boat?

Knell wrote:

Can I take some beer on the boat?

No. You can't take beer onto the boat.
You can take children onto the boat.