This is a common misunderstanding. As an example, I recently surveyed a 60ft steel yacht in Greece. I asked about registration documents and was told that the only one that the previous owner had given him related to a different vessel. Not only were the weight and all the dimensions different, but it also said that it has two engines, when his yacht only had one.<\/p>\n\n\n\n
I studied the document and explained to him that it was in fact the same vessel. The registration said two engine sets but, as I pointed out, only one shaft. The 6 cylinder Ford was for propulsion and the four cylinder Perkins was the generator. Both counted as an engine set for registration purposes and the engine numbers proved it. That still left the issue of the vessel\u2019s dimensions.<\/p>\n\n\n\n
The purpose of a tonnage measurement is to determine the dues that a vessel has to pay when navigating a port or waterway. It is logical that it should be based on the commercial potential of the vessel. Those capable of carrying the greatest volume of cargo have to pay the highest dues. The tonnage measurement is a calculation of the weight of cargo a vessel can theoretically carry, it has nothing to do with the weight or displacement of the vessel itself.<\/p>\n\n\n\n
The measurements are intended to calculate the internal dimensions of the hull and convert that into tonnes based on one tonne per cubic metre of cargo space. The original principal was to calculate the hull volume and then deduct working spaces such as engine room, steering space, crew quarters, tankage etc. Shipping authorities around the world calculated this in different ways according to local rules. This resulted in merchant vessels sometimes having up to twelve different ratings dependent on which port or waterway was charging them for passage.<\/p>\n\n\n\n
In 1969 the International Maritime Organisation ratified the whole issue into one internationally accepted process and defined two different methods of measurement. For vessels over 24 metre Load Line Length a full hull volume measurement with deductions for working spaces has to be carried out. This is called the Assigned Formal Tonnage Measurement. For vessels under 24 metres Load Line Length, which means the majority of pleasure vessels, a Simplified Measurement was established. This is simply 0.16 x the overall length x beam x depth of the hull. This does get a bit more complicated when there are different weather deck levels.<\/p>\n\n\n\n
Load Line Length is defined as the length between the forward most part of the stem and the front of the rudder stock. This is measured at 85% of the minimum moulded depth of the hull parallel to the waterline. My clients vessel had been built in 1965 in Australia and had a Maltese registration, so the full Load Line Length method with deductions had been used. It was no surprise that none of the apparent measurements, tonnage, length, engines etc appeared to match the boat he was buying. Medusa Marine are approved tonnage measurers for all Red Ensign flag states.<\/p>\n","protected":false},"excerpt":{"rendered":"
This is a common misunderstanding. As an example, I recently surveyed a 60ft steel yacht in Greece. I asked about registration documents and was told that the only one that the previous owner had given him related to a different vessel. Not only were the weight and all the dimensions different, but it also said […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[57],"tags":[],"_links":{"self":[{"href":"https:\/\/medusamarine.co.uk\/index.php\/wp-json\/wp\/v2\/posts\/3122"}],"collection":[{"href":"https:\/\/medusamarine.co.uk\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/medusamarine.co.uk\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/medusamarine.co.uk\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/medusamarine.co.uk\/index.php\/wp-json\/wp\/v2\/comments?post=3122"}],"version-history":[{"count":3,"href":"https:\/\/medusamarine.co.uk\/index.php\/wp-json\/wp\/v2\/posts\/3122\/revisions"}],"predecessor-version":[{"id":3163,"href":"https:\/\/medusamarine.co.uk\/index.php\/wp-json\/wp\/v2\/posts\/3122\/revisions\/3163"}],"wp:attachment":[{"href":"https:\/\/medusamarine.co.uk\/index.php\/wp-json\/wp\/v2\/media?parent=3122"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/medusamarine.co.uk\/index.php\/wp-json\/wp\/v2\/categories?post=3122"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/medusamarine.co.uk\/index.php\/wp-json\/wp\/v2\/tags?post=3122"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}