Volume Three - The Pontoon Era - Notes on the longitudinal joint of the Penarth dock . . .

The temporary bulkhead in the extension may, when the joint is all bolted and riveted up and found watertight, be completely removed. The permanent bulkhead on the fixed portion must be provided with limber holes, and these will have to be opened. As there is a head of water on the other side of this bulkhead, they must all have the covers knocked off at once to save removing them under water.

The effect of throwing two compartments into one will be to change the trim of the Dock, consequently the different longitudinal divisions should be dealt with consecutively, the trim of the Dock being re-established before each new operation.

Lastly, it may be noted that if all the above precautions fail to give a watertight joint, the two halves of the Dock can be disconnected (assuming them to have been bolted together) and the leaky half docked on the other, and made tight in the dry."

Whichever solution was eventually decided upon for the longitudinal joint the pontoon was delivered to Penarth with the extension attached and not stowed on top of the pontoon as was suggested.

Also the type of packings eventually adopted to ensure a watertight longitudinal joint under all loaded conditions for over half a century remain unknown. General arrangement drawings, detail drawings including a pumping plan and an installation drawing at the dockside were drafted and issued to the Penarth company.

On the 28th January 1909 a letter addressed to the Chairman and Directors of Messrs. The Penarth Shipbuilding and Ship Repairing Company Limited commences “Gentlemen” and provides an interesting insight to the technical challenges of the unique design;

"We have pleasure to enclose a separate letter we have written dealing with some of the technical points in the design of the Dock we propose and also regarding the outline design that was last sent to us for the purpose of basing upon it is a revised tender.

As there are many points in the latter design to which we could not agree as constructors, that is to say, we could not guarantee the strength of the Dock, we very much prefer to adhere to our own design, subject to some modifications we have made in deference to your views. These modifications are referred to in the separate letter and are also indicated in the enclosed plans.