Wave forces on slender horizontal and vertical cylinders are normally estimated using Morison equation (1950). When a cylinder is near the free surface, it experiences the slamming force. Wave slamming on horizontal cylinders of any ocean structure is crucial to its design. API Recommended Practice 2A-WSD(2000) recommends slamming coefficient Cs equal to π for circular cross sectional cylinders near the still water level. The shape of the member (circular, rectangular or square) is also expected to alter the values of Cs. The horizontal cylinders in the inter tidal zone for Port craft jetties are subjected not only to slamming force in the vertical direction but also to berthing force in the horizontal direction. If two cylinders are kept in close spacing, then the load on both cylinders will differ compared to force on a single cylinder. The effect of tidal variation on slamming forces needs thorough investigation. The comparison of single circular cylinder and twin circular cylinder with a clear spacing equal to diameter of cylinder in regular waves is discussed in this paper.