what does the phrase "now I have a raft to throw overboard just for scale mean"
Really need more context. Sounds like "mixed metaphor".
"a raft to throw overboard" usually implies getting ready to abandon ship and preparing a safe escape. "just for scale" usually means [I]to see if it is the right size[I]. Could be the writer means "I am getting ready to get out; let's see if this will work."