Diving Performance - Beyond Drag (article Series And Discussion)

[REVAN]

I did some testing. So far, all I have is data with the OMS BCD. This video shows the calibration swims to show repeatability with the tests done last year with the experimental streamlined kit. Then it shows the streamlined kit data shown previously with the Pilot SR-1 fins. Then I show the new data with the OMS BP/W with the Pilot SR-1, Rocket and Apollo Biofin Pros.


Summary: The BP/W kit doubles the drag of a diver, whereas the streamlined kit only increases the drag of a diver by 15%. In cruise, rocket fins have about half the thrust efficiency of the Pilot SR-1 fins. Add those two together, and my streamlined system will have about 3.5 times the efficiency at cruise speeds compared to someone in a BP/W plus Rocket fins.

 

[Eric Sedletzky]

Nice work!

 

[undrwater]

For slow cruising speeds, what's the comparison of effort between the pilot and bio fins?

 

[REVAN]

For slow cruising speeds, what's the comparison of effort between the pilot and bio fins?

That's a little harder to define and I should really do more testing to get a good number. The Biofins have such a light feeling kick that it is hard to gauge a stroke that puts in an equal amount of work over time. As pointed out in the video, to get the Biofin loaded with what feels like the same leg force in the stroke, I got a very quick stroke. That makes it hard to match the cadence. I ended up with fairly large kicks to fill it in, but what I should have done to get equal power is to keep the amplitude the same and add a pause the kick cycle to equal the cadence. However, that kind of intermittent duty cycle can impact the fin efficiency also. Like I said, it can get complicated.

In this case, I got 1.6 knots with the Pilot SR-1 fins and 1.5 knots with the Biofins for cruise speeds. If we assume the power input was the same, the Pilot fins would have to be about 20% more efficient. I just don't have much confidence in assuming that the power input was the same.

I know that the Biofin Pros are not very good for frog kicking and the other wierd things the DIR guys want their fins to do, but they are actually pretty good for performance in a flutter kick. The main drawback is that they cramp my feet. The Rocket Fins may have already set me up for the cramp (I know they have messed me up before), but by the time I did the sprint with the Biofin, my right foot was hurting pretty bad where it always does when I use scuba fins. I think that is the big advantage of the Pilot fins. They have awesome foot and arch support and are very comfortable even if I have to work hard.

Also, the sprint with the Biofins left me feeling so winded that it took me 3 to 4 times longer to recover than with the sprint I did using the Pilot fins. With the Pilots, my breathing would calm about 30 seconds or so after the sprint. It seemed like I was still breathing heavily a couple minutes after the sprint with the biofins. That could get expensive on the air consumption if I was still on the regulator at depth. However, the fact that I could tap into that high level of power and get that extra speed is certainly noteworthy, if not downright impressive.

Side Note - I initially got into designing and building my own fins because of the foot cramps I usually would get from most scuba fins. I always make fins that are very comfortable as well as having good performance.

 

[REVAN]

With the Pilots, my breathing would calm about 30 seconds or so after the sprint. It seemed like I was still breathing heavily a couple minutes after the sprint with the biofins.

After thought on this -
My gut feeling is that I was putting more power into the cruise with the biofins as a result of the larger amplitude kicking. If that is true, a part of that increased recovery time would likely be from being more depleted at the start of the sprint. The sprint was the last run I did. With these fins, I only did one sprint as I just felt too tired to do a second one.

 

[ronscuba]

Great job. Thanks for doing the test and publishing the results.

 

[Eric Sedletzky]

That's a little harder to define and I should really do more testing to get a good number. The Biofins have such a light feeling kick that it is hard to gauge a stroke that puts in an equal amount of work over time. As pointed out in the video, to get the Biofin loaded with what feels like the same leg force in the stroke, I got a very quick stroke. That makes it hard to match the cadence. I ended up with fairly large kicks to fill it in, but what I should have done to get equal power is to keep the amplitude the same and add a pause the kick cycle to equal the cadence. However, that kind of intermittent duty cycle can impact the fin efficiency also. Like I said, it can get complicated.

In this case, I got 1.6 knots with the Pilot SR-1 fins and 1.5 knots with the Biofins for cruise speeds. If we assume the power input was the same, the Pilot fins would have to be about 20% more efficient. I just don't have much confidence in assuming that the power input was the same.

I know that the Biofin Pros are not very good for frog kicking and the other wierd things the DIR guys want their fins to do, but they are actually pretty good for performance in a flutter kick. The main drawback is that they cramp my feet. The Rocket Fins may have already set me up for the cramp (I know they have messed me up before), but by the time I did the sprint with the Biofin, my right foot was hurting pretty bad where it always does when I use scuba fins. I think that is the big advantage of the Pilot fins. They have awesome foot and arch support and are very comfortable even if I have to work hard.

Also, the sprint with the Biofins left me feeling so winded that it took me 3 to 4 times longer to recover than with the sprint I did using the Pilot fins. With the Pilots, my breathing would calm about 30 seconds or so after the sprint. It seemed like I was still breathing heavily a couple minutes after the sprint with the biofins. That could get expensive on the air consumption if I was still on the regulator at depth. However, the fact that I could tap into that high level of power and get that extra speed is certainly noteworthy, if not downright impressive.

Side Note - I initially got into designing and building my own fins because of the foot cramps I usually would get from most scuba fins. I always make fins that are very comfortable as well as having good performance.

The other thing you have to really be carefull of working that hard and getting winded at depth is CO2 loading. That can be a disaster and can result in some really nasty stuff happening. A reg only can give you so much gas and when CO2 gets out of hand it can result in a feeling of overbreathing a reg, of just not being able to get enough air no matter how hard you breath. When that happens it can cascade downwards quickly into a severe panic situation. It can happen to the best divers, nobody is immune. Getting out of it takes a hell of a lot of nerve management and calming techniques.
Most people concentrate on the inhale worrying that they aren't getting enough O2, which can lead to shallower and shallower quick panting breaths making the problem worse. The trick is to concentrate on the exhale and to blow off as much CO2 as you can. Excess CO2 is what gives you the feeling that you are starving for air, not a lack of O2. This means deep controlled breaths and stopping physical activity until the problem resolves.
Just thought I'd throw this into the conversation for those that may not know the effects of CO2 and hard work at depth.

 

[REVAN]

Yes, the CO2 is a very real danger. I'm pretty sure that if I restricted the speed to 1.8 knots (same speed as the other fins), the Biofins would be better than the Rocket fins for efficiency and reduced CO2 buildup. However, exercising restraint is important to not get into these extreme power states, because it is possible with these fins.

Maybe this is why the split fins get a bad reputation for using them in strong currents. It's not because they don't have speed, it's because you can tap into power and speed that other fins restrict and inadvertently create an unsafe CO2 condition if you are not careful. One massive CO2 hit at depth could really sour someone on the splitfin, as it is really an uncomfortable situation. Without testing in a controlled environment they would not understanding the difference between fin performance and the CO2 issue. If the speeds are regulated properly, the situation may be observed positively, instead of negatively.

 

[John C. Ratliff]

Revan,

I did a dive a just over a week ago to try using my Hammerhead Unit in current. The Clackamas River is running high right now, which some pretty stiff currents. I had my GoPro on my helmet, recording the dive. Unfortunately, at age 70 I was towing a "Diver Down" buoy and flag, and because of the dolphin kick got the line tangled in my legs, and so was unable to do much of a test. That's why I haven't been posting recently.

I'll download the video, and get a few stills and maybe a bit more. I used the Hammerhead Unit last year, and got some video of it being used in the river, but I haven't had time to edit it yet.

Some of the video I shot of salmon deaths is being used in a hearing next week that I'm testifying about, concerning water temperature and the ability of salmon to survive in warm river temperatures. So that has taken more of my time in the last few weeks too.

I like your video above, and will watch it a few more times. There are a couple of considerations we may be able to play with later to gather more and better data on physiological load and different fin configurations, and different tank/scuba configurations, and those are breathing rate, heart rate, and air consumed. Some of that can actually be gathered from your video (breathing rate, for instance). Knowing the amount of air consumed can also be translated into oxygen consumption.

Eric Sedletzky,

I have been interested in your information on CO2 loading, and will be doing a bit of reading about it. But a couple of things from my experiences may interest you too. A lot of the problem, in my opinion, is not the regulator or the exertion, but the way some divers breathe. If you are cruising, as Raven was in some of his video, you should not build up a lot of CO2 in your system. Cruising means that your breathing rate is sustainable for a long period of time. Sprinting is another story. But for CO2 loading to become a problem, sometimes it is the type of breathing people are doing. In one Basic Scuba thread about breathing, one diver stated that he/she could last a long time on a tank, by tanking only small breaths. This, in my opinion, can lead to problems with CO2 retention by re-breathing a significant portion of our exhaled breathe that is captured in our lung's dead air spaces. Full, deep breaths tend to alleviate this by reducing the percentage of the breath that this dead air space represents. You pretty much hit it by stating:

Most people concentrate on the inhale worrying that they aren't getting enough O2, which can lead to shallower and shallower quick panting breaths making the problem worse. The trick is to concentrate on the exhale and to blow off as much CO2 as you can.

But there is a need to use good regulators, with good exhalation characteristics and breathe deeply too.

SeaRat

 

[Eric Sedletzky]

I

Yes, the CO2 is a very real danger. I'm pretty sure that if I restricted the speed to 1.8 knots (same speed as the other fins), the Biofins would be better than the Rocket fins for efficiency and reduced CO2 buildup. However, exercising restraint is important to not get into these extreme power states, because it is possible with these fins.

Maybe this is why the split fins get a bad reputation for using them in strong currents. It's not because they don't have speed, it's because you can tap into power and speed that other fins restrict and inadvertently create an unsafe CO2 condition if you are not careful. One massive CO2 hit at depth could really sour someone on the splitfin, as it is really an uncomfortable situation. Without testing in a controlled environment they would not understanding the difference between fin performance and the CO2 issue. If the speeds are regulated properly, the situation may be observed positively, instead of negatively.

I'm no expert on split fins, but the way I always understood them was that if you over kicked them they actually performed worse. There is a sweet spot apparently, not too much force and not too little, and they don't work well with a wide full kick from the hip, they work best with a knee to ankle flip like someone would have that has weak legs. An instructor explained to me once that split fins were good for people who had horrible technique because they were one of the only designs that actually worked for bicycle kickers. That might explain their quick popularity when they first came out. It's also kind of sad.