Wave forces acting on slender cylinders are normally estimated using Morison equation (1950). When a structural member is near the free water surface, it experiences the slamming force. Wave slamming on horizontal members of any ocean structure is crucial to its design. API Recommended Practice 2A-WSD (2000) recommends slamming coefficient Cs equal to n for circular cross sectional members near the still water level. The horizontal cylinders in the inter tidal zone for Port craft jetties are subjected not only to slamming force in the vertical direction and horizontal direction but also berthing force in the horizontal direction. If two cylinders are kept in close spacing, then the load on each member will be different compared to force on a single member kept alone. In this paper, the results of investigations of the effect of tidal variation on slamming forces are reported. The comparison of single circular member and twin circular members with c/c spacing varying from two to four times the diameter of cylindrical member in random waves is also included in this paper. The slamming coefficient is found to be not a constant value and it varies with respect to the spacing between the cylinder and free water surface, the incident wave height and wave period.