Click on the above pictures to enlarge them. Click on the link below to read about the author. This is a 1956 Dell paperback with interesting cover art by someone named Maguire.
Here is information on Robert Maguire and pictures of many more of his paperback covers. Click on them to enlarge them.
http://www.ramaguirecoverart.com/gallery_covers.php
This cover is really great in that it is not at all clear exactly what is happening. What is she scared of? Is it a hurricane that is coming? Is it a recently discovered oil slick? And what is he up to? None of the above of course. Below you will find a description of the story but I suspect it will be hard for the book to be as good as this cover.
http://en.wikipedia.org/wiki/Charles_Williams_(U.S._author)
Here is more about this author and his books.
http://www.mysteryfile.com/GM_Williams/Williams.html
And finally here is a bit about the real story of this book.
"In Charles Williams' Gulf Coast Girl, Shannon Macauley--a tall, blonde ex-showgirl--hires Bill Manning--a diver, sailor, and writer--to help her husband escape from gangsters. The husband had stolen a cache of diamonds from the gangsters, but lost them in a plane crash in the Gulf of Mexico. He survived, but the diamonds sank with the plane. Despite Bill's efforts, which include killing one of the thugs, the escape plan fails. The gangsters kill the husband, framing Shannon for his murder. They then force Shannon to give them directions to the site of the plane crash and force Bill to sail a boat to the site and try to salvage the diamonds. Bill and Shannon fall in love during the voyage. But their future is bleak because even if they escape, they will still be hunted--hunted by the gang who still want the diamonds and hunted by the police for two murders. The ending is clever and surprising--and I, for one, didn't see it coming, even though Williams dropped hints along the way."
--pigeye
