Krylov about ship unsinkability

A letter to Admiral Makarov

(from Chapter 16 of Professor Krylov's Navy)

Your Excellency! This is how I understand ship unsinkability.
1) It is often said that “ship unsinkability is provided by partitioning the hold into compartments.” This is inaccurate. The ship reserve buoyancy provides unsinkability. Reserve buoyancy is in turn the volume of the above-water part of the ship, bounded by the upper watertight deck. Partitioning of the hold into compartments is one way to utilize reserve buoyancy.
2) Besides buoyancy, it is necessary to provide for the ship stability. This is achieved by coordinating partitioning of the above-water parts with partitioning of the hold and by arranging appropriate system of flooding the compartments to right the ship. Only such righting provides ability to use the entire reserve buoyancy. The bilge system is powerless in controlling the holes. When partitioning the hold and the above-water parts, we must be guided by calculations of the effect of flooding the compartments on the list, trim, and stability. The principle of partitioning should be that buoyancy is lost prior to stability—in short, that the ship sinks without capsizing.
3) Any damage to the freeboard causes corresponding reduction in reserve buoyancy and stability of the ship. The desire to provide this reserve in a battle led to change in the ship armor. Before, the purpose of the armor was seen in covering the machinery, boilers, and generally vital parts of the ship. To provide buoyancy, the presence of unarmored freeboard was considered sufficient. The development of the rapid-fire artillery forced changes to the armor, considering as its main purpose: to ensure reserve buoyancy and stability of the ship.
4) The natural development of the first type of armor led to concentration of all the vital parts of the ship in her middle, covering this part with the thickest possible armor over the least possible area.
5) The second type, conversely, requires covering the largest possible area of sideboard, with the same thickness everywhere or even thicker at the ends.
6) In practice, both systems are often combined, covering the middle part of the ship along the waterline with the thicker armor and the rest of the sideboard with the armor of the equal or almost equal thickness everywhere.
7) Any armor can be pierced by a gun of a proper caliber within limits of certain angles of impact and range; hence the opportunity to equalize probabilities: having superiority in artillery over the more powerfully armored adversary, to inflict on him in the same time the same total area of the holes as is expected to receive from him. Thus, the question of the battle between armor and artillery as it relates to unsinkability can be reduced to numerical calculations of probabilities and the expected value of the area of the holes, similar to the calculations of pension funds and other insurance enterprises.
8) Rational armoring must be in certain correlation to the partitioning of the hold into compartments; this latter to the radius of destruction from the torpedo hole.
9) Until now, in designing the warships, for the most part, the same stability calculations were made as for the sailing vessels. When considering such important quality as survivability or unsinkability of a ship, not calculations, precise and defined, but general considerations sufficed—to put it bluntly, conversations. Many shortcomings arose. For example, on some vessels, the mess deck partitioning in the number of compartments, does not correspond to the hold partitioning. Damage to the deck and to the freeboard causes excessive decrease of stability; there are many small compartments in the hold, 10 tons of volume or less, next to the compartment of 800 tons. The centerline bulkhead in the boiler room is made without doors, so after ramming in the middle, the battleship will capsize before the crew manages to think about what to do to prevent the ship’s loss. On other vessels, shipbuilders have fallen into opposite extreme, not making the centerline bulkhead at all, as if forgetting that this is one of the main ship ties. All this happens because shipbuilders do not trust calculations and do not establish basic principles for them, so assessment of the requirements for the warship is absent. Any rational design should be based on number and measure. However, we must remember that awareness of shortcomings is the first step in correcting them.
I do not know how the foregoing will correspond to the content of your lecture. In any case, I am entirely at the disposal of Your Excellency.
With the deepest respect and sincere devotion, I have the honor to be Your Excellency’s obedient servant,
A. Krylov

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