Spanish naval construction in the 18th century

The construction of naus (carracks), gallions and ships of the line was very active in Spain, but during the 16th and 17th centuries the construction was merely empirical, this is, based in experience, intuition and inherited knowledge, without resorting to formal regulations. But during the late 17th century a couple of essays from expert engineers and builders appeared, and during the early 18th century some more were published. During the 18th century, the evolution of the techniques used suffered many ups and downs due to the change of technical criteria, but also to political changes.

Spanish ship of the line of the late 17th century
The first regulation imposed by royal decree dates back from 1720, and it is known as the "Gaztañeta system". This essay detailed the construction of vessels armed with 50 to 80 cannons and frigates armed with 10 to 40 cannons. These early designs were still structurally weak but of good seaworthiness, presenting still the accentuated inclination in the stem and sternpost, which was characteristic of the ships of previous centuries and caused cracks in the structure.

Spanish ship of the line of the early 18th century
The second period was represented by the "Jorge Juan system" and it lasted from 1750 to 1770. This period was marked by an admiration - which sometimes was excessive - for the British construction and its famed vessel HMS Culloden. Jorge Juan brought to his homeland five English masters specialized in hulls, masts and spars and rigging, with the purpose of strengthen these parts in the Spanish ships. He directed very effectively the construction of vessels and the foreign builders, and in 1752 the King approved his system which became regulation.

The following plans of a 60-gun ship of the line and a 22-gun frigate, drawn by Jorge Juan in 1750, show a quality unseen until then. The 60-gun ships were habitual in the Spanish Navy during the first half of the 18th century, but their role was later taken by the 74-gun ships.

60-gun ship of the line from the album of Jorge Juan
22-gun frigate from the album of Jorge Juan
However Jorge Juan had to modify some methods advised by the English builders which were not suitable for the Spanish requirements. For example, the wooden bolts used by the British tended to loosen in tropical waters, causing the ships to literally fall apart. Because of this the metallic bolts made of iron or copper were reintroduced. And however the ship of the line Guerrero, built in 1755 following such system, lasted for 95 years, being the most long-lived ship of her class. A higher longevity was expected from the vessels built in La Habana, because of the higher quality of tropical woods, but curiously the Guerrero had been built in Ferrol.

And as a turn of events, the outstanding knowledge of Jorge Juan would later be adopted by the foreign nations. His essay "Examen Marítimo", published in 1771, was quickly translated to French and English. Maybe this was his requital, for an arbitrary political decision had Jorge Juan destituted in 1769. The Spanish court became influenced by the French and hence the French builder Francisco Gautier would take the place of Jorge Juan, starting so the third period, which was the most unfortunate one.

The French system reduced the beam for the sake of speed. This caused the ships to lose stability and with vivid winds the leeward battery was easily flooded and hence rendered unusable. The nefarious effects of this would be seen in Trafalgar some decades later. In tests effectuated in 1766 between the ships San Juan, of French system, and San Genaro it was seen that this latter was faster, despite of her heavier tonnage and lesser sail area.

Following the death of Gautier, the fourth period started when Romero Landa was appointed in 1784. This one made a new regulation and constructed the 74-gun ship San Ildefonso, which was of very good qualities. Consequently, seven similar 74-gun ships and another three of 64 guns were built following the same methods. The fifth period was simply a further perfectioning of the right ideas posed by Romero Landa. To this last period belonged, among others, the aforementioned 74-gun ship Montañés, built in 1794.

The following drawing, originally made in 1790, shows the 112-gun ship of the line Santa Ana. The excellent qualities of this ship made her a reference model for the subsequent 112-gun ships of the line built for the Spanish Navy. During wartime her crew exceeded one thousand men and during peacetime the huge 36-pounder cannons were replaced by the more manageable of 24 pounds.

110-gun ship of the line Santa Ana (1790)

Technical details

The most discussed aspect during the century was the length/beam ratio whose values were: 3.43 (Garrote, 1690); from 3.5 to 3.62 (Gaztañeta, 1720); from 3.62 to 3.67 for ships of the line and from 3.69 to 3.78 to frigates (Jorge Juan, 1752); 3.84 (Gautier, 1770); 3.73 (Romero Landa, 1785); 3.73 (Retamosa, 1794). The best results were achieved with the values from 3.65 to 3.67 and finally with 3.73. The length, as a principle, should be as great as possible to accommodate a higher number of cannons, but it was limited by the size of the wood. In 1720 the width of gun ports was 0.86 meters with a separation between them of 2.296 meters. To reduce the length without reducing the number of cannons, gun ports were adjusted to 0.83 meters and the separation to 2.232 meters, which allowed to save 1.72 meters in total.

The beam had a minimum size, imposed by the space for cargo and the recoil of the cannons, but as we have seen an adjusted beam would be detrimental for a warship. A more complex attribute, because of its three-dimensional nature, is the block coefficient, this is, the ratio between the volume of the careen (the underwater hull) and that of the imaginary parallelepiped which would circumscribe it. The values used were 0.61 for 100-gun ships, 0.56 for 74-gun ships and 0.5 for frigates. As we can imagine, the value is higher as more "paunchy" the hull is.

Now let us see some standard values for the different classes of warships; these are: length of the lower gun deck, beam, average draught, height of the main mast from the waterline, tonnage and displacement.

For an exceptionally large first-rate ship of the line of 120-130 cannons, the values are: 59.40 meters, 16.12 meters, 7.78 meters, 63 meters, 2163 tonnes and 4902 tonnes. The only ship of this type would be the Santísima Trinidad.

For a standard first-rate ship of the line of 112 cannons, the values are: 59.40 meters, 16.12 meters, 7.37 meters, 62 meters, 2112 tonnes and 4770 tonnes. The displacement was notably higher than that of the British counterparts - including the famous HMS Victory - which had less armament.

For a standard first-rate ship of the line of 94 cannons, the values are: 54.8 meters, 15.60 meters, 7.22 meters, 59 meters, 1600 tonnes and 2800 tonnes.

For a third-rate ship of the line of 74 cannons, the values are: 53 meters, 14.50 meters, 6.80 meters, 57 meters, 1500 tonnes and 2750 tonnes.

For a frigate of 58 cannons, the values are: 41.70 meters, 11.95 meters, 5.37 meters, 45 meters, 990 tonnes and 1730 tonnes.

Another interesting measure is the distribution of weights in a ship of the line, which was: 62.5 percent for the hull, 11.2 percent for the ballast, 10.2 percent for victuals (for three months), 8.9 percent for artillery pieces, 3.6 percent for boats and spare materials, 3 percent for masts and spars and 1.8 percent for the crew. This is of course a rough estimation and the most variable element was the ballast, which in some case reached 60 percent.

The qualities demanded from these vessels were somewhat contradictory, for the faster ones due to their slenderer hulls were deficient for steering and balance. To improve stability every vessel needed ballast, but this brought the lower gun ports nearer to the water. In Spain, from 1750, the qualities were generally well balanced, keeping the lower gun ports at distance from the water and avoiding abrupt movements in pitch and roll, which reduced the risk of dismasting. In the last years of the century speed reached up to 14 knots in the best conditions, but generally it was 10 knots.

As aforementioned in the first part of this article, the Santísima Trinidad was a notorious exception. This ship, originally of 120 guns and three decks, was designed by the Irish naval architect Matthew Mullan, who undoudtedly ignored the methods recommended by Jorge Juan. To improve stability in this deficient ship the decks were lowered from 1 to 1.5 feet and sheathed with planks of one feet in thickness, but the problem did not improve much, and with winds of just 5.5 knots the largest ship of the Spanish Navy heeled so much that the distance from the lower gun ports to the water was only 87 centimeters, causing the well known flooding. And to make the problem worse, someone decided to add a fourth gun deck, while the Minister of Marine, Juan de Lángara, recommended to reduce the armament to only 90 cannons.

Now it is time for some arcane knowledge about the ribs which shaped the hull of these ships. To better understand this aspect I have provided the following contemporary drawings which are very clear. In the first one we can see how the keel, which was built with the strongest woods (oak or teak) was made of several pieces assembled by junctions of a particular shape. Along the keel were crossed the ribs, which given their size were necessarily formed by several pieces. Apart from this, the ribs were composed of two attached bodies, with the seams between pieces alternated; otherwise it would be impossible to obtain the required resistance. All of these details can be seen in the drawing.

Hull structure explode of a ship of the line
The following drawing shows the main structure and ribs of a 74-gun ship of the line, which is ready for receiving her secondary ribs. Two of these were allocated on each space between main ribs, giving a total of 64 ribs, which was the number set by regulation on the late century.

Main ribs of a 74-gun ship of the line
In Spanish construction, the two bodies were fully annexed and secured by iron bolts, whereas in British construction the two bodies were separated one inch by means of wooden dices crossed by wooden bolts, which gave as result a lighter but less resistant hull. There was a maximum distance between ribs in warships - at least in the overwater hull -, which was of about 13 centimeters to prevent cannon balls from passing through. The timber which lined the hull had a thickness of up to four inches in the central part and less in the ends. The external lining plus the ribs and the internal lining would give a thickness of about 60 centimeters, in the thickest parts of the hull.

Finally, the two branches of a part of the ribs were linked by the beams, whose purpose was to support the decks and specially the artillery pieces, which with an average weight of two to three tonnes were not little thing. Beneath the lower gun deck, which supported the highest weight, the distance between beams was from 0.69 to 1.50 meters, while in the upper decks it was from 1.70 to 1.76 meters. The distance between the deck and the lower face of a beam was 1.78 meters in the lower gun deck and somewhat less in the upper decks. The beams alone could not endure the weight, so they were assisted by corbels in the ends and by pillars in the center.

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