WARNING
Be VERY careful with Navionics in the Yasawa's. In many places they are dead wrong...eg they don't show the commonly used, and marked, channel into the Blue Lagoon from the E, just a big reef, and the reefs they show don't often correlate with reality 
ADVICE
Get hold of paper chart F5 and make good use of the Mk1 eyeball.
Cheers
Alan