Utrecht is landlocked and you will probably not find anything there. If your flying in to Schiphol Airport, stop by a news stand and purchase the local boat magazines and check out the adverts. They will probably direct you to locations along the coast, especially the Ijsselmeer area. Probably an hours drive from Utrecht / The Hague. Having said that, this is not the sailing season. With a particularly cold winter the emphasis is more on ice skating than sailing! The Ijsselmeer is also a good place to see their traditional sailboats that are very unique in their design. Good luck