Over a couple of summers, I swam laps at a local pool. I wore swim trunks and used Mares AvanteQuatro dive fins (they are paddle style) and an AquaLung Hawaii2 mask with snorkel. I calculated that my max sustainable speed in knotts was just under 3 knotts. I could sustain this swim for 15+ minutes or so. I flutter kicked only and broke the water surface tension ahead of me by keeping outstretched arms, hands clasped together just out of the water. I could NOT have achieved this rate on SCUBA (even without water resistance) because I was WAY OVERBREATHING what an average regulator could supply.
I work in a hospital intensive care unit where I deal with ventilated patients. I have 10years experience seeing adult breathing response patterns. An otherwise healthy adult, with normal lung function (in other words, without lung infections or chronic lung disease) will experience an oxygen demand deficit/lag when they go from resting to stressed (somewhat comparable to a swimmer or runner doing a sprint). Adrenalin flows, metabolism increases, then the body/respiratory system tries catching up. This lag takes about 45seconds to a 1 ½ minutes to start; and about the same length of time after coming back to rest to recover.
I experimented with this while SCUBA diving in tropical clear water. I do a 100ft moderate sprint. By the time I get to about 75ft my respiratory rate has increased to the point where, if I continued, would quickly cause me to overbreath my regulator (You know that feeling of air starved underwater?). Then upon resting, it would take the compunctual one minute to recover.
Over the six years I have been diving, I estimate that maybe I could sustain an underwater swim against a half (0.5) knot current, if I were in my best athletic shape; I speculate I might possibly succeed against a one (1) knot current for short periods (like my 100 foot sprint experiments); that one&ahalf (1.5) knot currents would be unmanageable to sustain any kind of headway. Too easy to overbreath my regulator.
Out here in California in the Pacific ocean we have kelp. For me, swimming against a current which causes kelp to be 20-25 degrees off vertical, respiratorially, is a manageable current; kelp at 45degrees off vertical, I cant sustain swims against current; kelp being pushed flat towards the bottom is a real howler of a current, time to thumb the dive. This California cold-water experience is in wetsuits only. The few times I have dived drysuits, the increased drag slowed me down considerably. This increased drag in drysuit diving is a major reason why I am partial to wetsuits (much more streamlined and efficient in water).
IMHO: max finning on SCUBA is a half (0.5) knot sustained - without current.
