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Arctic Vessels: Anti–fouling and Other Traditional Ship Bottom Covering Concepts
by Sven Johansson, CM 2013
The term ‘anti–fouling’ – may for land locked persons signify "preventing" foul language – obscenities – but for mariners it is a very important factor to maintain "ship–shape" – not just for smart looks but to the get best and efficient ships speed through the water.
The oceans are full of life and some life forms fasten themselves to any solid enough surface below water – or burrowing worms will destroy ships wood planking.
Any marine growth on the ship’s hull increases friction and slows down the speed – therefore ships "bottoms" are most often painted in a red copper colour because of copper–based anti–fouling paint. High concentration of copper powder in the paint is poisonous to marine life. However, copper sheeting is ideal for use as an anti–fouling substance as it is a natural material and an essential element required for normal growth by all plants and animals when at low concentrations.
Copper sheathing being repaired on the hull of the North Star of Herschel Island by the author. (Photo from Nauticapedia collection.)
In wooden hull sailing ships the best form of anti–fouling was by copper sheeting nailed to the wooden hull. In fact the copper sheathed wooden clipper ships were the fastest sailing ships. On long voyages copper paint on the was effective only for half a year, whereas copper metal sheeting would last much longer – an important factor important when outbound and homeward bound could last for years.
For Arctic seafaring in wood-planked ships – Australian greenheart sheeting was needed for two reasons. Firstly, when navigating in ice – whether broken up multi–year ice or thin newly frozen ice the softwood fir ships planking could not withstand rubbing against hard ice. Secondly, if frozen–in over the winter in polar ice, a ship without "double planking" and with thick tar paper (Irish ships felt) in between experienced a mystical freezing action of "pulling out the caulking" installed between each layer of planking causing the ship to sink during the following spring thaw. It is not known if the caulking is actually pulled out by the freezing action or if the wood planking ‘shrinks’ at very low temperature opens up the hull a few millimeters between the planks for water to enter.
I personally saw this happen with the Tilirak at Inuvik NT – where she was frozen in over the winter in a Mackenzie Delta channel. At spring thaw she filled with water and had to be pumped out and repaired for the next summer’s navigation.
A wood ship fit for Arctic duty should have a double planked hull. Australian greenheart (also called ironbark) is the best wood to use. It is so hard and dense that it will sink in water just as quickly as metal. Since the ice may freeze 6 to 9 feet (2–3 metres) thick over one winter the greenheart sheeting must go from one ft above waterline down to the keel to protect when frozen in solid ice over the winter. The outer greenheart sheeting is not watertight. There is also caulking installed in the inner fir planking layer. To prevent the caulking from being pulled out by freezing strong, thick Irish ship’s felt is installed on the inner fir planking in a continuous layer of tar so that the double planking will be watertight regardless of –50C winter temperatures.
North Star of Herschel Island having her bottom scraped while careening. (Photo from the Nauticapedia collection.)
Arctic navigation has another peculiar attribute. In windless relatively warm late summer days, while in heavy pack ice, the multi–year pack ice has had all the salt leached out and is composed mainly of fresh water. When it starts to melting a layer a few millimeter thick of freshwater concentrates on the surface of the salt Arctic Ocean water. That layer can be a few degrees below the freezing temperature of freshwater. In that situation a thin layer of freshwater ice forms. Such thin ice is knife sharp and will damage soft wood planking creating holes on both sides of the boat’s/ship’s bow. The stem commonly has a metal band forward that breaks the thin ice. The time it takes to penetrate the planking depends on the thickness of the wood planking.
This situation of thin freshwater ice forming on saltwater can also occur in freezing air temperature in British Columbia’s costal fjord–like inlets. Therefore wood-hulled fish boats and similar craft usually have gum wood ice protection on the waterline. Gumwood is dense and hard enough to be used as ice sheeting however I consider that it is second grade relative to greenheart ironbark.
Modern icebreakers can have a steel hull thick enough to withstand working in ice – however the hull material for wintering frozen–in over the Arctic winter is not simple in favor of the steel hull. Water freezing in a bucket or barrel will expand with enough force that the ice rises upward in the centre. A steel hull of less strength than that of an icebreaker can experience the expanding force of Arctic ice powerful enough to cause "wash–boarding" on the sides of ships that are frozen–in over the winter. There is no give at the ships ribs that are rigid whereas the steel plating between ribs is made concave by the pressure of the expansion of the solid ice. At the spring thaw the concave areas do not spring back and if the ship is winter frozen–in for a number of years the concavity between each rib will increase each winter until the ship’s side takes on the visual shape of a rough washboard.
Interestingly, a wooden ship properly constructed for Arctic service is not at risk for ‘wash boarding’ because wood has a innate springiness and will resume its original form at spring thaw.
Ship anti–fouling has also an interesting electric component. Dissimilar metals in salt water actually generate an electric current that corrodes the "less noble" metal. To prevent becoming a short–circuited battery copper and iron must be electrically isolated from each other. In steel hulls there must be non–conducting undercoats between the two metals. In wooden hulls there must be thick tar paper bedded in tar between the iron fastenings (nails in the planking) and the copper sheeting. Today there are many new colors of anti–fouling for all different metal hulls, especially for aluminum craft – some blue, green etc. but red is the traditional anti-fouling colour.
I personally have had first hand experience with using copper. In 1978 at Victoria British Columbia I copper sheathed the wooden hull of the sailing ship North Star of Herschel Island. To my knowledge she is the only copper sheathed ship still afloat in Canada. The copper sheeting made her independent from expensive annual haul–outs for new anti–fouling painting. Inspections and maintenance is done by careening on any smooth tidal beach.
The 57 foot North Star of Herschel Island built in the winter of 1935–36 at the George W. Kneass Shipyard in San Francisco at the highest specifications for Arctic navigation. The specification read: "with all that entails". She is double–planked with 7/8 inch Australian Greenheart outer sheeting with thick Irish ship’s–felt between. She has been squeezed by solid ice expansion when frozen–in over several winters but sprang back each time. She even has a small bay at Baillie Island in the Beaufort Sea named after her – "North Star Harbour" as a result of a frozen–in wintering there when severe Fall ice conditions prevented her owner, Fred Carpenter, from going from Aklavik NT to Sachs Harbour NT until the following Fall. During the winter at North Star Harbour her crew on board trapped marten for furs on the mainland instead of usual Arctic white fox on Banks Island NT. From North Star Harbour the next summer they returned to Aklavik and traded the marten fur for supplies and successfully reached Sachs Harbour before the next freeze–up.
The best way to winter a vessel of that size in the Arctic is hauling out on a beach – as marine haul–out facilities never existed until there were Caterpillar tractors. The original technique showed the skill and ingeniousness of the local mariners. Vessels too large to be beached by muscular power were "walked" sideways on two smooth logs lubricated by sealskin. Block, tackle and hand winches anchored by "dead men" (with buried anchors) in the permafrost for hauling out or on the ice for launching were used. With the vessel listing inward towards the beach the forward end was first winched 3 to 4 feet in – on one log – then the stern end winched on the other log – and so on "walked" out until the keel was above the water line.
The navigation season in the high Arctic is only 2 to 3 months ‘short’ and with little marine life in the cold water anti–fouling paint is never needed. The North Star of Herschel Island never had an anti–fouling painted bottom until 1973 when I sailed her from Tuktoyaktuk, in the Western Arctic into Pacific Ocean where anti–fouling is obligatory. After thirty years the copper sheeting is still fully effective as an anti–fouling mechanism.
The Author: Captain Johansson skippered the first successful west to East Transit of the Northwest Passage in a yacht (the Belvedere). He lived as a guide, reindeer hereder, mariner in the Arctic Islands for many years, living on the schooner North Star of Herschel Island. He is a Member of the Order of Canada.
To quote from this article please cite:
Johansson, Captain Sven B. (2013) Arctic Vessels: Anti–fouling and Other Traditional Ship Bottom Covering Concepts. Nauticapedia.ca 2013. http://nauticapedia.ca/Articles/Ship_Bottom.php
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