Free surface effect
A mechanism causing watercraft instability from moving liquids in partially filled compartments.
It refers to the tendency of liquids, and unbound aggregates like seeds or gravel, to move in response to changes in a craft's attitude.[1] A watercraft can become unstable and capsize due to the mechanism known as the free surface effect.[2] A tank that is not completely filled is termed a "slack tank", whereas one that is completely filled is called "pressed up".[1]
Quick Facts
- Field
- Naval architecture and maritime safety
- Related regulation
- SOLAS Convention and International Code on Intact Stability
- Affected vehicles
- Watercraft
- bulk cargo or liquid tanker semi-trailers and trucks
- and aircraft
Facts from the source article.
Key facts and history
The first International Convention on Load Lines, adopted in 1930, was based on the principle of reserve buoyancy.[3] The IS Code included fundamental principles such as general precautions against capsizing and the effect of free surfaces.[3] Cargo vessels reduce the free surface hazard by employing many small bulk compartments or liquid tanks rather than a small number of large ones.[4] Minimizing the effect can also be achieved by ensuring individual compartments or tanks are either nearly empty or completely full.[4]
To maintain a full tank at all times, hydraulic tankers pump water in to displace the lighter oil.[4] Under the SOLAS Convention and the International Code on Intact Stability, international regulatory requirements apply to all ships to reduce the free surface effect.[5] The primary regulations for safe ship design are SOLAS chapter II-1, the 1966 Load Line Convention and its 1988 Protocol, the 1969 Tonnage Measurement Convention, and the International Code on Intact Stability, 2008.[3]
What the cited sources add
The Intact Stability Code states that freeboard provisions ensure adequate stability and avoid excessive stress on the ship's hull from overloading.[3] Ships carrying timber deck cargo are assigned a smaller freeboard because the deck cargo provides protection against wave impact.[3] The damage control plan required by SOLAS regulation II 1/19 provides officers with information to prevent progressive flooding and recover stability.[3]
References
- Wikipedia, "Free surface effect" (CC BY-SA 4.0), which cites: "Ship inspection maritime guide." (original not read by us) en.wikipedia.org
- Wikipedia, "Free surface effect" (CC BY-SA 4.0), which cites: E.Lewis, Editor, Principles of Naval Architecture, 2nd. Rev., 1988 (The Society of Naval Architects and Marine Engineers), page 93ff (original not read by us) en.wikipedia.org
- "Intact Stability Code", International Maritime Organization. facts only, no text reused. imo.org
- Wikipedia, "Free surface effect" (CC BY-SA 4.0), which cites: Morrell, "Oil Tankers", Simmons-Boardman Publishing Company, 1931, p. 305&306 (original not read by us) en.wikipedia.org
- Wikipedia, "Free surface effect" (CC BY-SA 4.0), which cites: "Intact Stability Code", International Maritime Organization (we also read that source) en.wikipedia.org
Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article Free surface effect (contributors), used under CC BY-SA 4.0; this entry is available under the same licence. Other sources were used for facts only; no text or images are copied from them.
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