Cargo mound detail – Virtual Dive Trails

Cargo Mound: Intro and components list | Explore the cargo | 3D model

Identification of the individual components was undertaken in 2018. The numbering relates to components marked on the 3D cargo mound.

1-5: Wheels

The most striking feature of the cargo mound are the iron wheels from which the wreck was named. At least three different types of wheel have been identified. The majority of the wheels are eight-spoked cast iron sheave wheels with a square hub. These are all about 1.16m (3.8ft) in diameter with a groove in the outer rim to accommodate a rope or rod. There are 12 of these wheels; only three are completely intact, with some consisting only of dispersed fragments.

There are a number of functions these sheaves could have fulfilled: the obvious ones being lifting or hauling items by rope, or facilitating a change of direction for pump rods in crooked mine shafts.

Six-spoked iron wheel sitting on top of several similar wheels on the seabed — A pile of iron wheels on the seabed

A diver swims over the pile of iron wheels on the seabed — Another view of the iron wheels on the seabed

Reconstruction drawing of a sheave wheel — A reconstruction drawing of one of the iron sheaves found in the cargo mound. On the left is a section, centre face view and on the right a side view. Note the square hub

The most impressive feature of the cargo mound is a large iron wheel rim 3.06m in diameter (10ft), 0.19m deep, and 0.15m wide. This has teeth cast into its outer surface, 0.03m wide, 0.15m long, with a space of 0.05m between tooth faces. There are likely to be 126 teeth, and this is likely to be a gear wheel.

Next to this rim sits a set of iron spokes and a hub which appear to have been intended to fit into the six rectangular sockets cast into the inside face of the wheel rim. The reason for manufacturing this wheel in two parts was probably connected with the logistics of transport, as it is estimated that the wheel rim weighed about 1.5 tonnes and the spokes a further 1.25 tonnes, a combined weight of almost 3 tonnes.

Overhead photo of the cargo mound highlighting the large wheel and the separate spokes — The wheel rim and wheel spokes (highlighted). This is probably a flywheel

A diver swimming over the large wheel at the centre of the cargo mound

Large iron wheel with gear teeth around the rim, on display at East Pool Mine in Cornwall — Large toothed wheel on display at East Pool Mine. This may be similar to the one on the Wheel Wreck, although the presence of teeth have not been confirmed.

Monochrome reconstruction drawing of the flywheel. The image is divided into two parts. On the left shows the flywheel from the side, a large circle with stepped cog teeth. Inside, radiating from a cross-shaped central hub, are six spokes fitting into rectangular slots in the outer wheel rim. To the right of this is the wheel viewed from the front, a thin drawing showing the teeth and estimated thickness of the wheel. This demonstrates how this was part of a gear mechanism. — A reconstruction drawing of the wheel rim and spoke assembly fitted together. The actual depth of the cog-teeth has been estimated.

A smaller wheel lies under the spokes of the large toothed wheel and is only just visible. It has a diameter of 1.02m (40 inches) and is 0.2m thick. It has 42 teeth (one third the number present on the larger wheel), and if designed to work as part of a gear train with the larger wheel, the gear ratio would have been 3:1.

Underwater photo of components on the Wheel Wreck. Yellow arrows point out the almost hidden smaller wheel. A few teeth can just be observed, demonstrating that this wheel was possibly part of a gear train. — The smaller wheel can just be made out under the spokes.

Monochrome reconstruction drawing of the small toothed wheel showing a cross section, a side view of the entire wheel, and a view of the teeth — Reconstruction drawing of the small toothed wheel (SW3). On the left is a section through the wheel, centre is the view of the upper face (the lower face is completely inaccessible) and on the right a side view. The actual depth of the cog-teeth has been estimated

Pumping column components

6. Windbore

Line drawing of a mine shaft showing how the pump pipes were arranged — Click or tap to enlarge

This is the bottom section of the pumping gear. It is an iron cylinder with perforations in the end to prevent stones and debris from being sucked into the pump. This is called a windbore, and the iron pipes it was connected to were called the rising main.

Photograph of wind bore, highlighted to distinguish it from the piles of other machine components — Wind bore (highlighted)

There are three windbores in the cargo mound all stacked next to each other at the eastern end of the cargo mound. The holes in the windbores are largely obscured by the thick layer of iron concretion covering the object. The parallel ridges or fins visible in the centre of the windbore are probably corrosion fins formed as a result of longitudinal cracking of the cast iron, and are thus a post-wrecking feature.

Two large iron pipes sitting on the grass at East Pool Mine — Wind bore on display at East Pool Mine

A monochrome drawing of a windbore — A reconstruction drawing of wind bore. Note the absence of reinforcing fillets around the inner face of the flange. The holes in the pipe and flange are conjectural – on site they are covered with a thick layer of corrosion products.

7-11: Clack pieces

The clack piece (also known as clack valves) is a one-way flow valve incorporated into the pump system to prevent the water from flowing back down the pump pipes (rising main). There was a hinged flap inside the clack valve which closed onto an iron seat, the flap is usually faced with leather to form a watertight seal. They are said to be called clack pieces due to the noise they made as the flap closes. The rectangular opening visible in the photograph is for maintainance of the clack valve – in use it would be covered with an iron door which is missing on this example.

Large pile of iron pipes sitting on the seabed. The clack valve has been highlighted — Clack piece (highlighted)

Line drawing showing how the clack valves would have operated. The arrows show the direction in which the water would move — How a clack valve operates

Two different types of clack pieces have been identified. There are six of the larger clack pieces and eight of the smaller type. The larger have flanges 0.51 to 0.55m in diameter with the outer pipe having a diameter of about 0.43m. The smaller have flanges 0.41 to 0.45m in diameter with an outer pipe diameter of about 0.28m. Both types have a single reinforcing band between the clack door and the far flange.

Black and white drawing from the Perran Foundry catalogue, showing a length of pump piping. — Original advert for a wind bore and clack valve from the foundry catalogue of Williams’ Perran Foundry Co.

A monochrome reconstruction drawing of one of the clack pieces — A reconstruction drawing of one of the clack pieces. Note that the bolt holes in the flanges were not clearly visible on site due to the iron concretion.

12. Rising main

Rising mains are iron flanged pipes used in pumping systems, especially in mines. The term ‘rising main’ is now commonly used but in the nineteenth century these were simply called ‘pumps’ or sometimes ‘pump pipes’.

Thirteen rising mains have been identified on site, and there are probably more concealed within the cargo mound. At least two different diameters of pipe have been observed. The lengths vary between 2.74m (8.98 ft) and 2.77m (9.08 ft).

Rising mains also usually have a number of fillets reinforcing the junction between the outer surface of the pipe and the flanges but none of the rising mains on this site have these fillets. It has not been possible to establish the significance of this absence but it could possibly be a feature related to early pipes or those from a particular foundry. Further work in this area may yield useful results.

Pile of iron pipes on a rock-strewn seabed — The flanged ends of rising mains pipes

Three large cast iron pipe sections lying on the grass at East Pool Mine in Cornwall — Cast iron rising main on display at East Pool Mine

Rising main reused as a mooring post on South Quay, Penzance

Monochrome reconstruction drawing of one of the rising mains — A reconstruction drawing of the 8 inch rising mains – the 10 inch rising mains are structurally similar and of the same length but have a larger diameter. Note that the bolt holes in the flanges were not clearly visible on site due to the concretion. The reinforcing rings are the three bands around the middle of the pipe.

13. Socketed pipes

These pipes are by far the most numerous cargo items present, with about 100 recorded on site – there are probably more in the body of the mound obscured by other items of cargo. The socketed pipes are largely confined to the western end of the cargo mound and are stacked in parallel rows at least three layers deep.

A pile of pipes underwater, with the large wheel rim sitting on top. — The socketed pipes at the western end of the site; note how they are stacked at least three layers deep

These pipes are 1.95m long, with an external diameter of 0.12m and an internal diameter of 0.10m. They have a socket at one end (0.11 long, external diameter 0.16, internal 0.13) which is large enough to accept the un-socketed end of the next pipe with a small gap.

These pipes were probably intended to convey water at low pressure – such as those employed in gravity-driven drainage systems.

A line drawing showing the socketed pipes — A reconstruction drawing of the socketed pipes showing how the pipes would have been fitted together

A photograph showing two presumably 19th century socketed pipes set into a wall in Penzance. One section of pipe fits into the flared opening of the other. — Section of cast-iron socketed pipe forming part of a storm water drain on Abbey Slip in Penzance

14. Iron collars

It was not possible to determine the function of these three items. They are short lengths of cast iron pipe with a wider ring at one end (possibly a flange). They are heavily concreted which precludes any determination of their exact form. They are 0.38m in diameter at the widest point and about 0.275m long. Their close proximity to the three windbores and numerical equivalence perhaps suggests an association with the windbores?

Photograph of broken wheels and circular iron collars on the seabed. The collars are marked with yellow arrows. — Three iron ‘collars’ or very short lengths of iron pipe. They are indicated in the photograph by arrows. The ‘collars’ are 0.4m in diameter. The collar on the left in this image is sat on one of the wind bores.

Archaeological report

The full Wheel Wreck report is available from CISMAS (PDF, 12.4MB).