Gorgeous quilt! One of the patterns on my "must do" list.
I'd go with a dark blue thin border to set off the center. Then a medium light blue border. Do you have enough to do a border in your sashing pattern? That between two dark thin borders would be lovely.

Beautiful!

that is really beautiful... and I love your blue fabric! any of the borders would look great, but I like the idea of the white border to make the blocks look like they are floating

What shows up here as dark blue is actually a dark purple. I only have 1/2 yd of that left, but did see that Joanns still had some of that the other day. I have 1 yd each of the blue/purple stripe and white tone on tone. I bought all of these fabrics over 7 yrs ago, should still be able to find the white. But doubtful I can find the blue/purple stripe. Thanks for all the compliments, it has been in my UFO pile for a long time.

Very pretty so far!

Lovely quilt!!

I vote for a small dark blue piping (withouth cording) as close to your dark blue as possible to make the pattern pop. Number 2 looks like it is a teal that pulls out the color in the blocks, so that would be a good next border. Lastly, I would do more dark blue for the final border and binding. A good rule of thumb is to go from narrow to wide with the borders.

Oh my, so very pretty.

I just love that pattern. Thanks for posting. You've inspired me to do one soon!

I like the darker of the two.

Storm at Sea was my first real quilt. Yours is lovely. Great piecing!