Maugan,
I *really* love sailing.
Diamonds and gold are not my thing.
Now, I don't know how long you guys have been dating and sailing together, but unless it has been for over two years, don't get her the harness as her sole birthday gift.
Dude, just don't do it.
The dinner is nice and all, but get her something to go along with it that is not, well, practical. This does not mean you have to spend a lot of money on it. Get her something for herself. Not all jewelry comes with a high price tag, you know.
One of the best gifts I ever got is a necklace made of a black rounded faux-leather rope (of small diameter- suitable for a necklace) that has some small silver beads on it and the "center piece" is a small shackle. He made it. And it is absolutely perfect. Cost hardly anything and it is very cool.
Get her something to go along with the harness -
Tracie