Hold Mass Curve and Local Loading Criteria

The hold mass curve is the maximum allowable and minimum required mass of cargo and double bottom contents in a cargo hold, expressed as a function of the draught at the mid-hold position, and it is the limit that actually governs a dense bulk cargo. IACS Unified Requirement S1A requires it in the loading manual of a bulk carrier of 150 m and above, together with an equivalent curve for any two adjacent holds against the mean draught in way of them, and requires the approved loading instrument to check both.

The limit moves with draught because the net vertical load on the double bottom is the difference between the downward weight of cargo and ballast in way of the hold and the upward buoyancy, which depends on draught. The practical consequence is that the allowable cargo mass in a hold falls as the mean draught falls, so the tightest moment in a loading is often an intermediate stage rather than the final condition. Ballast still carried in the double bottom and hopper wing tanks in way of the hold is deducted from the allowable cargo weight.

The full article will cover the local loading diagram, the reading rules for single and adjacent holds, the relationship to the tonnes per square metre tank top figure that UR S1A reserves for cargoes other than bulk cargoes, and the flooded-condition criteria that cap the intact curve.