Defining criteria for the minimum diameter of surfaces upon which tensioned chain bears was addressed by both analysis and experiment in this study. This is the only known study of chain tensioned over an ungrooved curved surface. The problem is of interest in many applications, including sizing of tanker bow chocks for SPM hawser chafing chains.
The complex interaction of forces between chain links is difficult to precisely define. The analysis was simplified by making certain assumptions about how forces act between interlocking chain links and how stresses are distributed in the chain link, and by ignoring plastic deformation. The analysis showed that, for surface diameter to chain diameter ratios of 7 or greater, maximum stresses are not significantly greater than those experienced in straight tension.
In the experimental program, stud-link chain specimens were loaded to failure in tension around pins having various surface diameters. The chain generally broke in links which were not in contact with the surface as often as in links which were in contact, depending on the geometry of contact between the chain and the surface. Breaking strength of the chain decreased very little for surface diameter to chain diameter ratios as low as 6. Even for smaller ratios, significant reductions in strength were produced only when the chain links were arranged in unfavorable attitudes against the surface.
The strength of chain tensioned over a curved surface is of vital interest in ocean engineering and naval architecture because chain is used in many ways to anchor, moor, lift, and secure. Anchor chain is tensioned against curved surfaces on anchor windlasses, chain stoppers, and hawse pipes. Lifting chain bears on curved surfaces under loads, such as pipe. In towing and mooring, chafing chain passes over a curved fairlead and may be secured around bitts.
A number of general recommendations have been made in the past regarding the safe diameter of surfaces over which chain is tensioned. Study of the problem and review of the recommendations indicate little is actually known about the strength reduction of chain on curved surfaces. The few recommendations which have been based on studies apply only to grooved surfaces, such as chain windlasses and sheeves, and no studies have been done of chain over ungrooved curved surfaces.
In this study, a basis was sought for recommendations for the surface diameter of chocks through which chain passes. Such chocks are used on the bow of large tankers to pass the SPM bow hawser chafing chain.
Analysis of the stresses in a chain tensioned over a curved surface is more complex than it first appears. Three cases of chains tensioned over curved surfaces are illustrated in Figure 1. Case 1 is that of an ungrooved surface, such as a chock. The chain links lie at angles to the surface, alternatively lying to one side and then the other, with all links bearing against the surface. This is the case of primary interest in this study.
