Buoyancy?

"An article on floswimming.org by Chris Brammer"

Buoyancy?
Chris Brammer Profile
June 13, 2009

FINA has yet to provide any sound reasoning as to why some suits are banned and others are not. Where in the manufacturing of suits is the line drawn and what exactly does that line differentiate? BlueSeventy suits "may trap air when worn by a swimmer" and that is why they are banned? Well they may not. Does this mean that for all of the suits that were approved this air trapping effect has been ruled out? I cannot fathom how they were able to quantify this “air trapping” as it is surely dependent on the shape, texture, and position of the swimmer in addition to the permeability of the suit material. The issue of permeability has been put off until later, as John Leonard stated in his interview with GM. How then, knowing for sure that the LZR and others do not trap air and not knowing of the suit’s permeability, did FINA create this list of banned suits? Buoyancy is one variable that Professor Hanson ..err Manson has supposedly measured and is at the center of recent discussion. Therefore, I wish to define buoyancy and discuss some of the issues that FINA and the independent research group hired to evaluate the suits are faced.
Buoyancy is only part of what makes an object float or sink in a fluid. Buoyancy is equal to the weight of the fluid displaced by a submerged object, and is proportional to the object’s volume. However, it is the summation of an object’s weight (downward force) and it’s buoyancy (upward force) that determines if it will sink or float. An object that is completely submerged in water will float if it’s dry weight is less than it’s buoyancy and, alternatively, an object will sink if it’s weight is greater than its buoyancy.
To put it in other terms, if an object’s weight to volume ratio (it’s density) is less than the density of the fluid in which it is submerged, then the object will float. If we wish to decrease our density relative to the fluid to improve “floatability” then we can decrease our weight, increase our volume, or some combination of both. For example, a lean-bodied swimmer who normally sinks needs only to take a big breath of air (thus increasing volume and decreasing density below that of the water) and he/she will float. In the case of suits, if the density of the swim suit is less than the density of the swimmer, then the density of suit+swimmer will be less than the swimmer alone and he or she will have a larger buoyancy. The increase in buoyancy can work to make a swimmer sink less or float more depending on their individual body density. The problem is that the greater difference in density the suit is compared to the swimmer, the more relative effect it will have. In other words, although a given suit will increase buoyancy the same amount for everyone, the effect of this change on “floatability” will be different depending on the individual’s initial density.
FINA states that a “swimsuit shall not have a buoyancy effect of more than 1 Newton (100g).” What does this mean exactly and why 1 Newton? Is it that a suit (by itself) shall not have buoyancy greater than 100g?If that is the case, then a suit measured to have a volume of 100ml will also have a buoyancy of 100g and the majority of our suits would not be compliant. Is it that a suit alone shall not have a net upward force (downward weight plus upward buoyancy) of 100g? I interpret FINA’s rule to mean a suit when worn by a swimmer shall not cause a net increase in upward force more than 1 Newton (100g). But as I said above, just because a suit increases buoyancy 100g for all who wear it, that does not mean that each swimmer enjoys the same effect. So how has Professor Manson proposed to address this issue?
In addition to an unequal effect on “floatability”, where this additional buoyancy is acting on the swimmer is also of concern. If the resultant buoyancy does not act through the swimmer’s center of mass, then the body begins to rotate. In a typical swimmer, resultant buoyancy is directed closer to the head than the center of mass (through which the subject’s weight acts). This torque causes the body to rotate in the direction of the feet toward the pool’s floor. The greater distance between the downward force of weight and upward force of buoyancy, the faster the body will tend to rotate. If we were able to shift the resultant buoyancy closer to the center of mass (perhaps with a leg suit of low density), then the effect would be a slower sinking of the legs and improved body position (less energy is required of the swimmer to keep his legs up). The problem here is that it is entirely possible that these new swim suits do not result in a net upward force (and therefore pass the 1 Newton test) but may shift the resultant buoyancy closer to the center of mass with the effect of decreasing leg rotation toward the pool’s floor. How can we account for this?
The independent research group hired to evaluate the suits have yet to disclose their results and, perhaps more importantly, their methodology. When (or if) this occurs we may gain greater insight as to how a suit is or is not approved. However, buoyancy is not the only variable of concern as I have yet to mention about material permeability to air and water, both of which have the potential to affect performance. Further, the variables of resistance, compression, and body alignment, among others, have been identified as potential players in the task of swim suit evaluation. Some would say the enormous task FINA faces is of their own doing, but it is too late to point fingers. We cannot change the past. We must now focus on gathering as much information on the What and How of tech-suits so that we may make reasoned decisions for the future.