In order to turn this principle to account, it was decided to depart entirely from the usual flat-bottomed frame-section, and to adopt a form that would offer no vulnerable point on the ship's side, but would cause the increasing horizontal pressure of the ice to effect a raising of the ship, as described above. In the construction of the Fram it was sought to solve this problem by avoiding plane or concave surfaces, thus giving the vessel as far as possible round and full lines. Besides increasing the power of resistance to external pressure, this form has the advantage of making it easy for the ice to glide along the bottom in any direction.
The Fram was a three-masted fore-and-aft schooner with an auxiliary engine of 200 indicated horse-power, which was calculated to give her a speed of 6 knots, when moderately loaded, with a coal consumption of 2.8 tons a day.
The vessel was designed to be only large enough to carry the necessary coal-supply, provisions, and other equipment for a period of five years, and to give room for the crew.
Her principal dimensions are:
Length of keel 103.3 English feet
Length of waterline 119'
Length over all 128'
Beam on waterline 34'
Greatest beam 36'
Depth 17.2'
Her displacement, with a draught of 15.6 feet, is 800 tons. The measurements are taken to the outside of the planks, but do not include the ice-skin. By Custom-house measurement she was found to be 402 gross tons register, and 807 tons net.
The ship, with engines and boilers, was calculated to weigh about 420 tons. With the draught above mentioned, which gives a freeboard of 3 feet, there would thus be 380 tons available for cargo. This weight was actually exceeded by 100 tons, which left a freeboard of only 20 inches when the ship sailed on her first voyage. This additional immersion could only have awkward effects when the ship came into the ice, as its effect would then be to retard the lifting by the ice, on which the safety of the ship was believed to depend in a great measure. Not only was there a greater weight to lift, but there was a considerably greater danger of the walls of ice, that would pile themselves against the ship's sides, falling over the bulwarks and covering the deck before the ice began to raise her. The load would, however, be lightened by the time the ship was frozen fast. Events showed that she was readily lifted when the ice-pressure set in, and that the danger of injury from falling blocks of ice was less than had been expected. The Fram's keel is of American elm in two lengths, 14 inches square; the room and space is 2 feet. The frame-timbers are almost all of oak obtained from the Naval Dockyard at Horten, where they had lain for many years, thus being perfectly seasoned. The timbers were all grown to shape. The frames consist of two tiers of timbers everywhere, each timber measuring 10 to 11 inches fore and aft; the two tiers of timbers are fitted together and bolted, so that they form a solid and compact whole. The joints of the frame-timbers are covered with iron plates. The lining consists of pitch-pine in good lengths and of varying thickness from 4 to 6 inches. The keelson is also of pitch-pine, in two layers, one above the other; each layer 15 inches square from the stem to the engine-room. Under the boiler and engine there was only room for one keelson. There are two decks. The beams of the main-deck are of American or German oak, those of the lower deck and half-deck of pitch-pine and Norwegian fir. All the deck planks are of Norwegian fir, 4 inches in the main-deck and 3 inches elsewhere. The beams are fastened to the ship's sides by knees of Norwegian spruce, of which about 450 were used. Wooden knees were, as a rule, preferred to iron ones, as they are more elastic. A good many iron knees were used, however, where wood was less suitable. In the boiler and engine room the beams of the lower deck had to be raised about 3 feet to give sufficient height for the engines. The upper deck was similarly raised from the stern-post to the mainmast, forming a half-deck, under which the cabins were placed. On this half-deck, immediately forward of the funnel, a deck-house was placed, arranged as a chart-house, from which two companions (one on each side) led down to the cabins. Besides the ice-skin, there is a double layer of outside planking of oak. The two first strakes (garboard strakes), however, are single, 7 inches thick, and are bolted both to the keel and to the frame-timbers. The first (inner) layer of planks is 8 inches thick, and is only fastened with nails; outside this comes a layer of 4-inch planks, fastened with oak trenails and through bolts, as usual. The two top strakes are single again, and 6 inches thick. The ice-skin is of greenheart, and covers the whole ship's side from the keel to 18 inches from the sheer strake. It is only fastened with nails and jagged bolts. Each layer of planks was caulked and pitched before the next one was laid. Thus only about 3 or 4 inches of the keel projects below the planking, and this part of the keel is rounded off so as not to hinder the ice from passing under the ship's bottom. The intervals between the timbers were filled with a mixture of coal-tar, pitch, and sawdust, heated together and put in warm. The ship's side thus forms a compact mass varying in thickness from 28 to 32 inches. As a consequence of all the intervals between the timbers being filled up, there is no room for bilge-water under the lining. A loose bottom was therefore laid a few inches above the lining on each side of the keelson. In order to strengthen the ship's sides still more, and especially to prevent stretching, iron braces were placed on the lining, running from the clamps of the top deck down to well past the floor-timbers.
The stem consists of three massive oak beams, one inside the other, forming together 4 feet of solid oak fore and aft, with a breadth of 15 inches. The three external plankings as well as the lining are all rabbeted into the stem. The propeller-post is in two thicknesses, placed side by side, and measures 26 inches athwart-ship and 14 inches fore and aft. It will be seen from the plan that the overhang aft runs out into a point, and that there is thus no transom. To each side of the stern-post is fitted a stout stern-timber parallel to the longitudinal midship section, forming, so to speak, a double stern-post, and the space between them forms a well, which goes right up through the top deck. The rudder-post is placed in the middle of this well, and divides it into two parts, one for the propeller and one for the rudder. In this way it is possible to lift both the rudder and the screw out of the water. The rudder is so hung that the rudder-stock, which is cylindrical, turns on its own axis, to prevent the rudder being jammed if the well should be filled with ice. Aft of the rudder-well the space between the stern-timbers is filled with solid wood, and the whole is securely bolted together with bolts running athwart-ship. The frame-timbers join the stern-timbers in this part, and are fastened to them by means of knees. The stem and stern-post are connected to the keelson and to the keel by stout knees of timber, and both the ship's sides are bound together with solid breasthooks and crutches of wood or iron.
Although the Fram was not specially built for ramming, it was probable that now and then she would be obliged to force her way through the ice. Her bow and stern were therefore shod in the usual way. On the forward side of the stem a segment-shaped iron was bolted from the bobstay-bolt to some way under the keel. Outside this iron plates (3 x 3/4 inches) were fastened over the stem, and for 6 feet on each side of it. These iron plates were placed close together, and thus formed a continuous armour-plating to a couple of feet from the keel. The sharp edge of the stern was protected in the same way, and the lower sides of the well were lined with thick iron plates. The rudder-post, which owing to its exposed position may be said to form the Achilles' heel of the ship, was strengthened with three heavy pieces of iron, one in the opening for the screw and one on each side of the two posts and the keel, and bolted together with bolts running athwart-ship.
Extraordinary precautions were taken for strengthening the ship's sides, which were particularly exposed to destruction by ice-pressure, and which, on account of their form, compose the weakest part of the hull. These precautions will best be seen in the sections (Figs. 3 and 4). Under each beam in both decks were placed diagonal stays of fir (6 x 10 inches), almost at right angles to the ship's sides, and securely fastened to the sides and to the beams by wooden knees. There are 68 of these stays distributed over the ship. In addition, there are under the beams three rows of vertical stanchions between decks, and one row in the lower hold from the keelson. These are connected to the keelson, to the beams, and to each other by iron bands. The whole of the ship's interior is thus filled with a network of braces and stays, arranged in such a way as to transfer and distribute the pressure from without, and give rigidity to the whole construction. In the engine and boiler room it was necessary to modify the arrangement of stays, so as to give room for the engines and boiler. All the iron, with the exception of the heaviest forgings, is galvanized.