The Koftjalk was only built in Groningen until around 1925. The type is recognizable by the heavy, hollow schooner bow and the bowsprit that lies on this bow (sea tjalks sail with a jib boom next to the bow).
Koftjalks do not have a set edge, but a fixed raised edge, which is only interrupted at the bollards and the stern. The ships often had large masts. The mainmast was sometimes fitted with a topmast. Between the top and the gaff the topsail, often equipped with a topable yard for downwind courses, could be hoisted. The standing rigging was carried out with weaving lines and sometimes equipped with scab plating to prevent the sails from wearing out. Due to the construction for seagoing, many ships were built under class, for example Class A4K-Grote Kustvaart of the Germanischer Lloyd
The lateral surface was then considerable and this resulted in strong bonding of the ship.
The skipper could more or less reduce the drift by deploying the daggerboard deeper, but then the risk of breaking the daggerboard became very high. So the skipper kept sweating. Many swords have been broken in battle and many a ship has therefore remained at sea, often with all those on board. Due to the flat bottom, the ship became stuck close to the beach in the event of a stranding. As a result, the ship could often be easily abandoned when the tide was falling. Sometimes the ship refloated itself when the wind decreased and the tide was quite high. In this way, small-scale coastal shipping constituted a heavy existence full of risks.
The engine did improve this somewhat, but it is also the reason that the koftjalks were no longer built; tjalks don't run that fast on the engine. They were replaced in this industry by the schooners and clippers.
In fairly good weather koftjalks were excellent ships with reasonable sailing and earnings; they were not fast but they were solid. Before the wind it always went well, because the head was well supported by the full bow. But cruising in high winds was a tough one. In very strong winds the skipper had to reef. Not only the sails, but also the swords had to be 'reefed' if the forces for the sword were not to become too great. It was always bad with an empty ship.
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