use the crab.
you put it in the water
get the crab from the living quarters
You use it to lasso a pipe in the underground below the "hot hatch."
you go all the way to the right and the top is red
on the hot hatch on the hub place all the way on the right
There are no windows that open inward on Steamworks Island. There is a skylight in the City Hall that can be opened with the Multi-Tool. You go out the hatch above Zack's room in the living quarters, to reach the Mech Crank on the vines.
its in the museum on mainstreet of steamworks island :)
It's Steamworks Island #14th Island
(The solution is at the related question "How do you beat Steamworks Island")
the crab on steamworks island is next to the living quarters
You go to Steamworks and head to the museum and there is the Deogen
The robot crab is full of cold water, which you can use to cool down the Hot Hatch at the Hub on Steamworks Island. However, you will need Sprocket the Robot to help you. Find the robot at the Living Quarters to the far left of the main part of the island. Jump on him to get him and Sully's door key. Using the Steam Generator (trash bin at the Cantina), open Sully's door and find Sprocket. Ringing the bell on the counter will awaken him. Take him and the crab to the Hot Hatch at the Hub. Use the robot crab and Sprocket will drop it on the Hatch, cooling it down so you can go underground. That is the only use for the crab.