i want to do my rudder blade like this :

http://www.hobie-cat.net/img/produits/accessoires/lame_safran_fleur.jpg

it's possible to put a thin cotton\nylon tissue under the epoxy layer to show the pattern and protect?
it's like laminate the carbon or not?
after a good polish it should be shine and perfect.......

Those blades are made with the colors in the mold. They first lay down a layer of clear gel coat, then the colored material (sometimes vinyl graphics when small, other times painted), and then the composite board is laid up. I'm not sure what the best method is to do something like this after the board has been made.

I've buried vinyl using clearcoat. I'm sure you could do the same with tissue or cloth. The trick may be how you glue the graphic down. Maybe spraying a little clear first then lay the graphic down. Then bury it with the clear. A craft store may have some tips on attaching the graphic.
Couple ideas anyway.

Sufboard glassers have been doing this forever. Contact one of them. Say, didn't Hobie make surfboards...for like, 30 years? Ask their surfboard division, if it still exists.

Internal graphics in a surfboard-like construction uses something called "rice paper" that the graphic is screen printed onto. A surfboard is constructed by core first, glass, rice paper and then the finish coats of resin I think. Rice paper becomes clear when wetted with resin.

Not sure of the process with the euro blades, but I assume it is similar.

i had a freind who refinied his decks on an older(wooden decks) 505 like this, he used this god-aweful plad cloth. Musta thought the boat had more character after that. But it looked to me like it was just painted over with resin. He must have dones something creative to hold the cloth down tight though to get the nice finish he got.

There are the thick clear resins, like used on bars or tables. Experiment and let us know what happens. I wonder if the photo graphics would be the way to go. Put that on like vinyl then bury that in clear.

If I recall, that polyester is pretty heavy...

Those "decoupage" tabletop deals are epoxy. Polyester does not work well.

I was at the Performance Catamaran factory last April and they were doing what you want just like Jake described. The material that went down right after the clear gelcoat was a printed fabric. I don't know the material but I thought it was a polyester. I think they had some problem with a nylon (I'm not sure of this) that looked like carbon fiber. They showed me some neat material that looked like woodgrain! I thought the teak would make a cool looking boat! They said they just sarted with clear gelcoat, decorative cloth and then the normal layup of glass-foam-glass. I saw some examples of daggerboards done this way.

if that rudder were a surfboard, i'd say that was a fabric inlay. the fabric is from the fabric store and is applied and trimmed prior to the glass job.
i don't know how log lasting fabric is if you don't burry it with glass. just a clear coat isn't enough on a surfboard, even if you use rice paper instead of fabric.
these days you can print your design on special paper like rice paper with an inkjet printer and fiberglass that in. the ink can fade tho.
for an existing rudder, sand off about as much material as you expect to add in the new process....good luck with that. your rudder is going to come out heavier and thicker if you add layers. plus the new layers could pop off if the rudder flexes much.