Find a local shop that specializes in boat lettering. Most have a photo-book showing examples of their prevous designs. If you find something that looks close, they can make any changes you might think of.
I found my shop at the winter boat show. Looked through their book, and found a couple of ideas. I had an initial idea, and after the boat show, we emailed back and forth a few times, with both the shop and I trying a few different things, until we finally came up with a nice design.
Some shops will sell you the sign and you can apply it yourself. I have done this in the past, but with my last design, it was so large and so complicated that I left it to the pros.
Sometimes you'll pay a little more, but you will be sure to get what you want that way.
This was my original idea, and I was about to go with it with an on-line sign shop, but there just seemed to be something missing, and I felt we could do something better.
My decision to work with the sign shop is when I saw the moon and cloud graphic used on a different design in their photo book at the boat show, and I instantly knew that was the graphic to use when I saw it:
After working with the sign shop, trying different fonts, position of the text, and graphics, it ended up looking like this:
I have to stress this was a collaboration between the sign shop and me; starting with my idea, and they added their experience as to what they thought would improve it.
For instance, the boat name is actually a lyric from a Moody Blues song (an old Rock group old-geezers are familiar with), and the font I wanted was one I found on a Moody Blues album, so I thought it would be appropriate.
But as it turned out, the sign shop suggested another font, and it had a kind of "I dream of Jeanie" look to it, which blended well with the boat name, and that is what we went with. I would have never thought of it.
The sign shop was even to match the lettering colors to the new striping that I was putting on the boat. A local sign shopw will often even come out to your boat and color-match the graphic to your boat's striping or canvas.
In contrast, you are sometimes limited in the fonts available from the on-line sign shops, but they often can work with you as well.
Some of the on-line shops have a designer on their web page where you can try different fonts, arch patterns, shadows, and so on. If you try those, you can at least get an initial idea of what you want and then go from there.