[willy]

parish check the search engine for this subject, been discussed a few times including with me.
the jist of it is this, you can remove it with chemical stuff of different manufactures with varied degrees of difficulty for all of them. but with all of them it is a ball bustin time consuming job and you need to wear eye and skin protection. it is the preferred way to do it if you wish to preserve the general gel coat shine and finish of your original hull.
the other alternatives are to have it soda sand dry ice blasted, obviously less or no work on your part but expensive at least in my area 600 - 1000 on our size boats. other drawback is afterwards you really need to paint the hull with one of the good clear or white barrier coat type paints as the gel coat does not have the same outer finish
you pays your money and you make your choices ;)