The form and method of construction
The Captain Cook memorial stone stands in the centre of a four-walled square tower. The stone has an inscription on all four sides, read through a wide semicircular arched portal in each wall of the tower. The tower stands on a man-made grass covered tump, surrounded by a shallow moat. When built in 1780, the moat excavated in clay and puddled with the clay, would have held water, representing the sea surrounding the great navigator, on an appropriate peak. It would also have prevented invasion and damage by cattle, without the visual intrusion of a hedge or fence.
The tower would be structurally unstable if its foundations were perched on the top of an artificial clay mound. The “invisible” foundations are supported below general ground level (probably) in clay with flints at about the level of the moat bottom.
Rough measurement and calculation shows that the volume of the moat is approximately equal to the volume of the mound, which was designed to mask the clumsy wide base walls of the tower, necessary for a low ground pressure. Calculations show that if the tower were founded on the top of the mound, the pressure on the ground would be one ton per square foot. Although the weight of the tower is much increased by the heavily stepped base walls, their greater width, and hence base area, reduces the pressure on the ground to half a ton per square foot. The heavy clay at this level would be adequate to support this pressure indefinitely, particularly if maintained at a constant moisture content by the water retained in the moat.
Without visual inspection from an excavation, this theory is proved correct by the total absence of settlement, which would be evinced by major cracks and deformity in the visible part of the tower.
Description of the visible parts
There is a flat roof four feet below the castellated parapet; this is a later addition, meanly timbered, covered with zinc sheet draining into a gutter inside the south parapet, and reached by open-riser softwood steps. The opening for these, through the flat roof, is sheltered by a flat-topped canopy level with the parapet capping bricks.
The parapet may have been rebuilt when the roof was constructed; the capping bricks are cement-mortared.
The walls are eighteen inches thick flint, all quoins and arches are brick, and there is a four-course brick string below the castellations.
The tower floor is two feet above the top of the mound, and is paved with large square limestone slabs.
The lime/sharp sand mortar which bonds all the flint and brick below the top string course is in very good condition and there is no serious deterioration.
Faults and method of repair
- The SW corner has suffered from saturation by water overflowing from the blocked gutter hopper above it. This has leached out some of the lime, which has allowed the sand in the cement to slump slightly; the visible result of this is a one-inch bulge (at the mid height) to the south and west, i.e. approx. one and a half inches resultant diagonal in a SW direction. Provided that the rainwater continues to be channelled down below and not down the wall there will be no further movement. Hence make sure that the pipe is free of obstruction and firmly fixed to the wall at the top and firmly secured to the spigot below the gutter. There should also be a bend at the bottom into a below-the-grass drain down the bank of the moat.
- The joint between the stair roof and the parapet is leaking. Major holes in the bricks should be filled with mortar and the felt/brick joint should be sealed with a tape or mastic.
- All the cracks in the outside flaunching should also be sealed.
- Repair the zinc cladding by gluing or soldering on a zinc patch: (SW & NW corners). Solder zinc strip over gap between wood and zinc at top of stairs.
- Repair the inside wood stringers; put risers on to the bottom step of the stairs.
- Treat furniture beetle infestation at top of steps and brush all of the wood to the bottom with preservative.
- Clean algae from the stone memorial post by scrubbing with cold water; when dry, repaint with black. Treat with algaecide.
- Apply sodium chlorate to cracks between paving stones and point with hydraulic lime putty.
- Cut down the trees and hedges. Cut the grass once a year. Repair the moat lining (clay puddle) and fill with water. Remove the fence surrounding. Make the footbridge more attractive with a spring-loaded wicket gate to keep animals out.
The tower is generally in a sound structural condition and will stand indefinitely, if it is not wilfully damaged by visitors and has regular minor maintenance.