Frank says:
Volume does play a big role in buoyancy.
I wish I could attached a picture to show the mathematical proof...
Dean says:
What an unnecessarily confusing and uninformative answer.
In advanced maths you learn that the shortest correct answer is THE correct answer.
The simple answer that anyone can understand is volume DOES equal buoyancy minus the weight of the board.
eg: A oard has 40Litres volume, is 5kg in weight, it therefore has 35kg of floating capacity "while stationary".
On a wave though, its a different thing because now the surface area makes a difference and the board shape.
oli says:
Density AND volume combined, give the buoyancy PRECISELY, in any liquid of a known density. Basic hydrostatics. She should stick to spaceships. They all float in space regardless of volume; easy.
Joe says:
Agree with the earlier comments regarding volume, and suggest that this article is revised.
When you consider that the weight difference between PE board and an epoxy board is small relative to the weight of water displaced by the board, density in surfboard design is likely to have less impact than volume.
Alex says:
Everyone has made some valid points but is missing part of the whole picture.
When an object floats, the buoyant force (up) is equal to the weight force (down) due to gravity. Those forces “cancel” each other out, causing the object to neither accelerate up nor down. In other words, the object “floats”.
The upward buoyant force is proportional to the submerged volume of the object (Archimedes’ Principle). When an object is dropped on the surface of the water, it sinks until its submerged volume generates adequate buoyant force to counteract the weight force pulling it down. So in general the weight to volume ratio (density) is important.
However, the confusion with surfing comes about because the “object” consists of surfboard AND surfer. Since the surfboard weight is typically only 5 to 10% of the surfer’s weight, the surfboard weight does not have a large influence on overall floatation (although it is important for maneuverability). However, more volume will allow board and surfer to sink less, creating less drag, and increasing paddling speed.
Volume distribution is also important. Volume is equal to surface area x depth. Remember that the buoyant force is proportional to the submerged volume. So, a board with a larger surface area does not need to sink as deep in order to generate the same buoyant force (less drag, more speed).
If the board is really small, even when completely submerged it does not generate adequate buoyant force to keep the board/surfer afloat. Therefore, part of the surfer must also sink under water, generating additional buoyant force for everything to stop sinking. By then, there is a LOT of drag, and paddling technique and timing becomes very important.
Jeff says:
Why not specify "sinking weight" - how much weight/force does it take to sink the board in salt water? It is easy for anyone to visualize what this means, not too hard to measure, and takes into account volume and density.
Tone says:
Surely considerations 2 (surface area- described as length and width) and 3 (thickness) equal volume. So basically after rubbish in volume the article finishes with "consider materials used then:volume...
8 Comments
Scott says:
Very informative article - thanks!
Frank says:
Volume does play a big role in buoyancy. I wish I could attached a picture to show the mathematical proof...
Dean says:
What an unnecessarily confusing and uninformative answer. In advanced maths you learn that the shortest correct answer is THE correct answer. The simple answer that anyone can understand is volume DOES equal buoyancy minus the weight of the board. eg: A oard has 40Litres volume, is 5kg in weight, it therefore has 35kg of floating capacity "while stationary". On a wave though, its a different thing because now the surface area makes a difference and the board shape.
oli says:
Density AND volume combined, give the buoyancy PRECISELY, in any liquid of a known density. Basic hydrostatics. She should stick to spaceships. They all float in space regardless of volume; easy.
Joe says:
Agree with the earlier comments regarding volume, and suggest that this article is revised. When you consider that the weight difference between PE board and an epoxy board is small relative to the weight of water displaced by the board, density in surfboard design is likely to have less impact than volume.
Alex says:
Everyone has made some valid points but is missing part of the whole picture. When an object floats, the buoyant force (up) is equal to the weight force (down) due to gravity. Those forces “cancel” each other out, causing the object to neither accelerate up nor down. In other words, the object “floats”. The upward buoyant force is proportional to the submerged volume of the object (Archimedes’ Principle). When an object is dropped on the surface of the water, it sinks until its submerged volume generates adequate buoyant force to counteract the weight force pulling it down. So in general the weight to volume ratio (density) is important. However, the confusion with surfing comes about because the “object” consists of surfboard AND surfer. Since the surfboard weight is typically only 5 to 10% of the surfer’s weight, the surfboard weight does not have a large influence on overall floatation (although it is important for maneuverability). However, more volume will allow board and surfer to sink less, creating less drag, and increasing paddling speed. Volume distribution is also important. Volume is equal to surface area x depth. Remember that the buoyant force is proportional to the submerged volume. So, a board with a larger surface area does not need to sink as deep in order to generate the same buoyant force (less drag, more speed). If the board is really small, even when completely submerged it does not generate adequate buoyant force to keep the board/surfer afloat. Therefore, part of the surfer must also sink under water, generating additional buoyant force for everything to stop sinking. By then, there is a LOT of drag, and paddling technique and timing becomes very important.
Jeff says:
Why not specify "sinking weight" - how much weight/force does it take to sink the board in salt water? It is easy for anyone to visualize what this means, not too hard to measure, and takes into account volume and density.
Tone says:
Surely considerations 2 (surface area- described as length and width) and 3 (thickness) equal volume. So basically after rubbish in volume the article finishes with "consider materials used then:volume...