Freeboard
- Parent Category: Technical Articles
- In: Ship construction and Naval Architecture
- 02Dec2009
- Last Updated on Tuesday, 13 September 2011 17:16
- Published Date
- By Master
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Freeboard
The distance between the top of the hull and the waterline. As the ship is loaded, it sinks deeper into the water so the freeboard is reduced. The positioning of the load line mark is aimed at ensuring the freeboard is the minimum necessary for the safety of the ship.
- p/p = length between perpendiculars
- w/l = length at waterline
- o/a = length overall
- b = beam
- f = freeboard
- d = draught (draft)
freeboard means the distance from the waterline to the upper deck level, measured at the lowest point of sheer where water can enter the boat or ship. In commercial vessels, the latter criteria measured relative to the Ship's load line, regardless of deck arrangements is the mandated and regulated meaning.
In yachts, a low freeboard is often found on racing boats, for weight reduction and therefore increased speed. A higher freeboard will give more room in the cabin, but will increase weight and may compromise speed. A higher freeboard also helps weather waves and reduce the likelihood of green seas on the weather deck. A low freeboard boat is susceptible to swamping in rough seas. Freighter ships and warships use high-freeboard designs to increase internal volume and also allowing them to satisfy IMO damage stability regulations due to increased reserved buoyancy.
As per Honkong merchant ship act
"freeboard" means the distance measured vertically downwards amidships from the upper edge of the deck-line to the position at which the upper edge of the load line appropriate to the freeboard is to be marked;
"freeboard deck" in relation to a ship means the deck from which the freeboards assigned to the ship are calculated, being either-
(a) the uppermost complete deck exposed to weather and sea, which has permanent means of closing all openings in its weather portions, and below which all openings in the sides of the ship are fitted with permanent means of watertight closing;
or
(b) at the request of the owner and subject to the approval of the Director, a deck lower than that described in paragraph (a), subject to its being a complete and permanent deck which is continuous both (i) in a fore and aft direction at least between the machinery space and peak bulkheads of the ship and (ii) athwartships, a deck which is stepped being taken to consist for this purpose of the lowest line of the deck and the continuation of that line parallel to the upper part of the deck;
