Info What is the "best" fin?

[tursiops]

There are actually two sets of graphs. You are correct that the first set only measures thrust as a function of kicking frequency, but the second set of graphs measures thrust as a function of the toque delivered to a kicking leg (simulating muscle exertion) that is generating the thrust. It seems reasonable to assume that VO2 consumption would be proportional to muscle exertion.

As stated at Efficiency & Geometry — Truefin
<Testing VdotO2 is rather involved, and as Pendergast noted, VdotO2 may be effected by divers "consciously or unconsciously" altering "their ventilation independently of their VdotO2". For this reason, the Truefin machine tests correlating input power with both kicking frequency and fin thrust may be considered objective tests while omitting human interaction.>

From:
https://www.researchgate.net/publication/10677199_Evaluation_of_fins_used_in_underwater_swimming

< The physics of underwater swimming with fins is complicated, as demonstrated by the
data from the present study showing fins with very different designs can have similar energy
costs of swimming (Attack vs Apollo). Some fin comparisons are reported for swimming at
slow speeds with measurements of air consumption, however due to the low ventilation, the
diver can consciously or unconsciously alter their ventilation independently of their VdotO2.
This invalidates these types of studies. This point was emphasized in this study as the reliability
of ventilation and velocity was very low (r = 0.54), while the reliability of VdotO2 and velocity
was very high (r = 0.94). Fins designed on the basis of physical principles for airfoils or
propellers do no necessarily lower the energy cost of swimming (Apollo vs Appolo taped). This
demonstrates that, based on our current understanding of the physics of underwater swimming
with fins, theoretical models have to be evaluated empirically as was done in this study. >

One thing I am not clear on though is that in the Pendergast paper, the O2 and CO2 fractions in the expired gas were determined using a calibrated mass spectrometer, so why does it matter if the diver alters their ventilation, they are still measuring O2 consumption. But evidently at slow speeds VO2 tests are unreliable.

Joe Maresh

I thought the point in those papers was that a swimmer could somewhat alter their VE, but the VO2 and VCO2 were fixed by their energy needs and metabolism.

 

[Truefin]

I thought the point in those papers was that a swimmer could somewhat alter their VE, but the VO2 and VCO2 were fixed by their energy needs and metabolism.

I think you are correct,, it is just that at low exertion levels VO2 tests are unreliable. I don't know what is considered 'low exertion level' however. Even with the machine tests we conducted, when you are down to 20 kicks per minute or so, all the graphical data is somewhat superimposed.

 

[tursiops]

I think you are correct,, it is just that at low exertion levels VO2 tests are unreliable. I don't know what is considered 'low exertion level' however. Even with the machine tests we conducted, when you are down to 20 kicks per minute or so, all the graphical data is somewhat superimposed.

One major problem in all this "fin testing" is that fin differences only begin to show up in the extremes, like how long can you sustain maximum thrust and how much O2 does that require? It may be fun engineering to rank highly for these kinds of tests, but most diving and most divers really don't care; they want to use minimal energy to get somewhere, and if it takes a little longer, fine. They want to be able to deal with a current, but prefer to get out of it rather than fight it, so the goal is good thrust for just a little while. They do not have, in general, massive leg muscles, so large, stiff fins are not desirable even if they deliver maximum thrust if you can actually kick with them. So the whole game is inside the margins, by which i mean how do you take a 130 pound woman with only modest legs and give her a fin that she can kick for an hour and not get worn out? Thus, the trend toward split fins, which are much easier on the legs and ankles, but fail most "high power" tests. I think a different metric is needed that aims at the average diver, not the super-divers, like meters per minute per liters O2 per minute......speed versus O2 required. Less thrust per liter O2 is OK, if there is sufficient speed to counteract the occasional current.

 

[Truefin]

One major problem in all this "fin testing" is that fin differences only begin to show up in the extremes, like how long can you sustain maximum thrust and how much O2 does that require? It may be fun engineering to rank highly for these kinds of tests, but most diving and most divers really don't care; they want to use minimal energy to get somewhere, and if it takes a little longer, fine. They want to be able to deal with a current, but prefer to get out of it rather than fight it, so the goal is good thrust for just a little while. They do not have, in general, massive leg muscles, so large, stiff fins are not desirable even if they deliver maximum thrust if you can actually kick with them. So the whole game is inside the margins, by which i mean how do you take a 130 pound woman with only modest legs and give her a fin that she can kick for an hour and not get worn out? Thus, the trend toward split fins, which are much easier on the legs and ankles, but fail most "high power" tests. I think a different metric is needed that aims at the average diver, not the super-divers, like meters per minute per liters O2 per minute......speed versus O2 required. Less thrust per liter O2 is OK, if there is sufficient speed to counteract the occasional current.

All good points. From our perspective we needed objective tests while refining the design, and that required a machine and computer. We went after efficiency as the priority, and nothing we tested was better in efficiency. Keep in mind Truefin has no stiff elastomeric rails, and is highly flexible up until the angle of attack is rigidly enforced with the artificial spines. That is why it is easy to kick slowly, and yet if you kick it fast it will never collapse.

 

[tursiops]

All good points. From our perspective we needed objective tests while refining the design, and that required a machine and computer. We went after efficiency as the priority, and nothing we tested was better in efficiency. Keep in mind Truefin has no stiff elastomeric rails, and is highly flexible up until the angle of attack is rigidly enforced with the artificial spines. That is why it is easy to kick slowly, and yet if you kick it fast it will never collapse.

I understand the objective of your design, but have trouble visualizing just how it would feel and perform. As to travel, no, I don't want to take the spines out and roll it up. I see the large fin is just under 24 inches long, not counting a heel strap; that is a bit longer than my Deep 6 Eddys and about the same as my Dive Rite XTs, so I see no travel problem with them. You say you only have the L size; your sizing chart make your L sound a lot larger than the L of either of my other fins. What is the size of your L foot pocket, and when might you have a Medium fin. Will the Medium be overall smaller and lighter?

 

[Truefin]

I understand the objective of your design, but have trouble visualizing just how it would feel and perform. As to travel, no, I don't want to take the spines out and roll it up. I see the large fin is just under 24 inches long, not counting a heel strap; that is a bit longer than my Deep 6 Eddys and about the same as my Dive Rite XTs, so I see no travel problem with them. You say you only have the L size; your sizing chart make your L sound a lot larger than the L of either of my other fins. What is the size of your L foot pocket, and when might you have a Medium fin. Will the Medium be overall smaller and lighter?

It does feel different because you don't expend any energy flexing the rails. Performance is excellent, even with the human speed tests. A couple of the very stiff fins were nearly as fast during flutter speed test, but they were strenuous to kick.. Being able to remove the spines and roll the fin up was only a secondary consideration. I would just lay them assembled and flat in a suit case, but you could fold them up in a back pack if need be. The spines are removable if you want to customize the fin to your preferred kick,, with Green spines during the frog kick the fins stay flat as a board when you frog kick away for example yet flex toe down the same as Blue spines for good flutter kicking, or asymmetrical spines set up if you have trouble twisting your ankle during frog kick with Blue spine at big toe and Green spine at little toe,, or yellow spines if you have a long flutter kick, etc.. Most will just use Blue spines, and the customization option just yields marginal changes. Kind of complicated to explain it here.
Truefin size Large is nearly the same foot pocket size as ScubaPro Seawing Nova Large, for example.
We don't have a time frame when Medium will be available, but it will be months, maybe even six months. Yes, medium will overall be smaller and lighter, yet accept the same spines as all other Truefin sizes. Without the spring heel straps, Truefin is around 3.1 pounds per fin, but in salt water (without straps) it is only negative 0.5 ounces. Buoyance table at online manual at truefintechnical.

Joe Maresh

 

[tursiops]

Truefin size Large is nearly the same foot pocket size as ScubaPro Seawing Nova Large, for example.

That means nothing to me. Width? Height?
Right now my M8.5 fits comfortably in my Large Deep 6 or L DR XT.....with either a TUSA hard-sole bootie or a pair of Converse Chuck Taylors. But it looks like I'll bounce around inside your L foot pocket.

 

[Truefin]

That means nothing to me. Width? Height?
Right now my M8.5 fits comfortably in my Large Deep 6 or L DR XT.....with either a TUSA hard-sole bootie or a pair of Converse Chuck Taylors. But it looks like I'll bounce around inside your L foot pocket.

It's hard to give numbers that are meaningful because of all the weird geometry and drafts involved. I wear a size 9 and use a bootie that has a pretty good sole on it, and the fin fits, but I would like the fin to be a little smaller. I don't recall what the thickness was of the bootie I used, and they are at a different location now. I know of one user that had a size 13 and they worked, but he may have had a thin bootie I guess. We need to expand the size chart to provide better sizing information. Unfortunately, I would say the Large is too big for you.

 

[Pearlman]

Absolutely at least until I find a good price on the super nova.

seriously they are really good fins, they have the canted blade angle like the GoSport That makes them easier to flutter kick and really good with frog kick, they have replaced my Jets as my go to cold water fin.

I read many reviews both here on this forum and other places before I settled for the Go Sport (more for overall packing length but not entirely), and not one review asserted that the Novas are good for Frog Kick, but only great for flutter - a reason why I rejected them. So is your comment about the Nova Gorillas or the original Nova?

On my recent trip last month, a diver was unhappy with his FFs that he got to the point that he asked for advise about his kicking technique, and was advised to get rid of them.

 

[Guille G]

The very best fins ever are yellow Avanti Quattro+s, because I like them and I say so and I am a person on the internet so it must be true