Show Freeboard is defined as vertical distance measured at the ship’s side between the summer load line (or service draft) and the freeboard deck. The freeboard deck is normally the uppermost complete deck exposed to weather and sea which has permanent means of closing all openings, and below which all openings in the ship’s side have watertight closing.
If you’re unfamiliar with maritime terminology, as many across the nation are, then you’ve probably never heard of the term freeboard. Because you’ve never heard of it, you’ve also probably never considered how important it is when determining the safety of a vessel on certain waterways. In today’s post, we’d like to explain what freeboard is to illustrate why you should consider it before operating a vessel. For those who don’t know, freeboard is the distance between the waterline and a ship’s upper deck. This measurement is important when operating a vessel on certain waterways, particularly on large lakes and salt-water bodies, where sizeable waves are possible. If a ship’s freeboard is too low, a sizeable wave could wash over the ship’s deck, causing it to take on water and potentially sink in the process. Now that you know what freeboard is, you understand its importance when operating vessels on certain bodies of water. You may even be able to think of a few ship accidents in which inadequate freeboard was to blame, such as the Argo shipwreck, which had ties to New York because of the ship’s owner, a tug and barge businessman who operated a fleet around New York. When ship operators fail to take into consideration a ship’s freeboard, they inevitably put their crew in danger. As some shipwrecks have shown, crew may be seriously injured or even killed when a ship sinks after taking on too much water. In cases like this, surviving crew members and the families of those crew members who have been lost may have grounds to collect civil damages courtesy of the Jones Act. It’s important to point out, however, that filing a maritime claim for compensation can be challenging, which is why it’s a good idea to seek legal counsel right away if you believe you have a claim for damages. Source: Maritime.about.com, “Freeboard: What it Means and Why it’s Important,” Paul Bruno, Accessed Dec. 1, 2015
Freeboard is a common term used in vessel operations. Freeboard is the smallest vertical distance between the waterline and the freeboard deck (generally the upper deck) along the length of the vessel. The term ‘smallest’ is of significance, as the height of the deck above the vessel’s baseline may vary along the length of the vessel due to sheer – this leads to difference in the vertical distance between the deck and the waterline at different points along the vessel’s length. Freeboard of a ship ‘f’ in picture above (Source: Wikipedia) A higher freeboard indicates a higher reserve buoyancy of the vessel, which is the volume of the spaces above the waterline. This lends better stability to the vessel, but leads to higher weight of the vessel. Vessels with more openings on the deck (i.e., susceptible to more rapid flooding) are expected to have higher freeboard, while vessels which have the deck with minimum or no openings (like tankers) are expected to have lower freeboards. In this article, we will understand the what, why, and how of freeboard calculation for a vessel. Freeboard Calculation – considerationsThe calculation of freeboard is carried out as per the International Convention on Load Lines, 1966, as Amended by the Protocol of 1988 – Annex I – Regulations for Determining Load Lines. Thinking about the basic purpose of assigning freeboard to a vessel, we can find out what factors or calculations will go into play when determining it. The basic purpose while assigning the right freeboard is to ensure that the vessel has sufficient reserve buoyancy. Thinking in basic terms, what factors or items can contribute to the reserve buoyancy of a vessel?
Tabular Freeboard (Regulation 28 of ICLL)The approach to freeboard calculation as laid out in ICLL 66 is to first calculate the standard freeboard that is attributable to the vessel. The ICLL 66 provides standard tables for the minimum freeboard needed, depending on the length and type of ship. There are two types of ships recognized:
The typical table is shown below:
Consideration for some Type-B ships:
The Standard Ship, and corrections to freeboardWe can see that the freeboard varies with the length of the vessel. It is noteworthy that the above tabular freeboards are provided for a standard ship. A ‘standard ship’ means a ship:
block coefficient Cb and length of the ship). This also means that any ship which deviates from the ‘Standard ship’ in any of the factors specified above, will need some adjustment to the tabular freeboard. These adjustments are called ‘corrections’. These corrections are listed below:
The standard ship has a block coefficient of 0.68. If Cb is greater than this the freeboard must be increased. This is needed to ensure that the same percentage of reserve buoyancy is maintained for the ship with higher block coefficient. Basically, the ship with higher Cb will be a fuller ship, and will need more reserve buoyancy [Ref 3]
The loadline markFrom the above process, the Summer freeboard of the vessel can be calculated. The summer freeboard is used to calculate the summer loadline of the vessel. The Summer Loadline is marked on the vessel as a ‘Loadline Mark’. It is indicated by the upper edge of the line which passes through the centre of the ring and also by a line marked S. There are multiple other loadlines of the vessel, depending on its area of operation. For sailing ships, only the Fresh Water and Winter North Atlantic loadlines are to be shown, apart from Summer Loadline. These additional lines are:
That brings us to the conclusion of this article. We have explained all the considerations in calculating the freeboard, and also explained why each of them is needed. Hope this was of use to you. Please do spend some time in exploring our product on Freeboard calculation: FBD the freeboard calculator References
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