There is a small private marina in Luperon and a well-protected anchorage in the big harbor.
In Samana, a 200 slip public marina is under construction with anchorage available in the harbor. Dockage is available at the big pier in Arroyo-Barril just west of Samana. Limited dockage is available at the private pier behind the Cayacoa Hotel in Samana. Permission must be gained from the owner to use this dock.
Protected anchorage with docking facilities is available in Bavaro.
A marina with slips for up to 200' of yacht is planned to built in Punta Cana.
There is a marina in La Romana.
Boca Chica has the Club Nautico facilities and some private dockage.
There is a marina in downtown Santo Domingo.
And further west on the south shore there may be facilities that I'm not aware of.
What has limited yachting in the DR more so than facilities are antiquated marine laws and overzealous enforcement of private yachts cruising Dominican waters by the Marina de Guerre. However, recent changes in the law should make things a lot easier with the facilities under construction providing convenient stopover points.