At [Fig. 49] is shown a buoyant mine. The only difference in the mooring of this and the one before described, is that instead of resting on its anchor on the ground, it is moored at a certain distance above its anchor d, to which it is secured by a chain e.
[Fig. 50] represents an electro contact mine. M is the mine with circuit closer enclosed, a the wire mooring rope, d the mushroom anchor, and b the electric cable leading from the mine to the disconnector D.
The mushroom sinker or anchor, which is undoubtedly the most effective of all other forms of mooring anchors used for the purposes of anchoring submarine mines, is shown at e, Fig. 49; the legs are added for use on rocky or hard bottoms, under which circumstances the weight of the anchor should also be increased.
For ground mines the form of sinker shown at d, [Fig. 48] is employed; it is of an oblong shape, and hollowed out in the centre to allow of its being lashed close up to the mine.
Large blocks of stones with their bases slightly hollowed are useful as extempore moorings, so also is the one shown at [Fig. 51], which consists of a strong heavy wooden shaft a, with a number of wooden arms b, b attached to its base; this form of extempore sinker was considered very efficient by the American authorities.
The wooden weighted platform, which was described at [page 56], is also a very useful form of extempore sinker.
For dead weight moorings, pigs of ballast, heavy stones, &c., may be used.
The weight of the anchor or sinker for mooring submarine mines is a very important consideration. It will depend on the amount of buoyancy of the mine, on the strength of current, and on the nature of the bottom, also whether the mines are to be hauled down to, or moored with the anchor.
Stotherd uses the following formula: