Chain is the key to anchor hold...The chain keeps the anchor flat to the bottom so it doesn't lift up and pull loose.. The chain should be at least as long as the boat and on small boats, longer is better. For the mixed sand and rock bottom at Catalina island, I found the claw grabs better...
...Recently had the same problem at Catalina island...engines quit one after the other, although I refilled the half-empty tank prior to launching. Turned out to be water in the Sierra fuel filters from boat sitting for 7 months. Drained both filters, refilled them with new gas and engines...