MacGregor Hatch Cover
Spare Parts Supplier

The first is one sentence with a whole parts list behind it: forces are to be carried by the steel structure only, and the packings are to be compressed so as to give the necessary tightness effect for all expected operating conditions. So the packing seals and does not carry, and what keeps the load off it is the bearing arrangement round the coaming. The maker says the same from the other side: the panels are supported on adjustable and replaceable pads all round the coaming periphery, so that weight is not taken by the seals. Pad and packing are one system with two references, and a pad worn or adjusted down changes the compression on the packing.

The second decides whether there is a pad to order at all. The maker's pad literature is direct: bearing pads transfer the weight of the cover and any cargo it carries into the hull while still letting the hull flex in a seaway, so their replacement has to be considered carefully. It records that older covers were built with steel-to-steel pad fittings rather than replaceable pads, and offers upgrading such a cover to a replaceable pad system as a job in its own right, one reason given being that it removes hot work on board. Where a replaceable pad is fitted, the families divide into low-friction sliding pads and non-sliding flexible pads, and the maker states that its own self-lubricating polymer pad, sliding against a stainless mating plate, can replace most existing load-bearing pads — naming two other builders' pads it replaces.

The third is the securing devices, the requirement most often missed. They are to bridge the displacements between cover and coaming caused by hull deformation, and individual securing devices on one cover are to have approximately the same stiffness characteristics. A cleat of a different design on one corner therefore changes the stiffness distribution rather than merely fitting. Where rod cleats are used, resilient washers or cushions are to be incorporated, which makes the rubber part of the cleat and not an accessory. Where cleating is hydraulic, a positive means is required to keep it mechanically locked closed if the hydraulics fail.

The consumables are the straightforward half. Packing sections and retainers, wedges, resilient washers and cushions, hoses and fittings, cylinder seal kits, filter elements, drain non-return valves: each has a measurable profile and a stated material, so a verified alternative route can be reviewed on them where a buyer's approval requirements allow, with dimensional data and material documentation checked at RFQ stage. On packing the material is the harder half of the question, because the requirement ties it to the cargo carried and to the deformation the joint has to absorb rather than to a dimension — a profile that measures correctly in the wrong compound is still the wrong item. An OEM-route review can be asked for on the same lines instead.

The other two kinds go differently. Securing devices, stoppers and anti-lifting devices are matched to the approved arrangement, their material is stated on the ship's drawings, and the same-stiffness requirement makes a single cleat of another design a class question rather than a fit question; those go to an OEM-route review and we say so before pricing. A cover built with welded steel pad fittings that is to receive replaceable pads is not a supply line at all but a conversion, with drawings, class-approval documentation, hot work and a dock behind it — and it is quoted as that. Vessel Core is an independent spare parts supplier and names the route against each line, so a requisition holding a packing set, a cleat and a pad upgrade is answered as three.