Cockleshell
/ˈkɑːklʃel/
Definition 1 of 2
Pro Tip 1/3Size Connotation
Cockleshell implies the boat is small and possibly fragile. 
During the competition, they were given a cockleshell to navigate the narrow streams.
Pro Tip 2/3Historical Reference
'Cockleshell' can evoke images from the 'Cockleshell Heroes,' a WWII mission. 
Our adventure in the tiny cockleshell felt like we were the modern Cockleshell Heroes.
Pro Tip 3/3Metaphorical Use
The term can be metaphorical for anything small and insufficient. 
Their budget for the project was a cockleshell, hardly enough to succeed.