EVALUATION OF FINS USED IN UNDERWATER SWIMMING

Study Research Team: 

David Robert Pendergast- Dept of Physiology and Biophysics

Joseph Mollendorft          - Dept of Bioengineering, Aeronautical Engineering, Aerospace Engineering

C Logue 

S Samimy

 

 

 Key Points of Interest in the Study and how they relate to Indigo’s DEFIANT 

 

Fin selection is most often made on the basis of the diver’s perception of the effectiveness of the fin. Divers 

invariably ranked fins as powerful which did not correlate with the objective evaluation of these fins. 

 

Strain and pressure on the legs does not trhttps://clicktotweet.com/P45Uxanslate to a powerful or efficient fin. Ideally, a fin that is easy to kick yet produces a large amount of thrust is ideal. The stacked benefits of DEFIANT length, width, open toe design and power stroke Stiffeners combines to create this very scenario.

 

An excellent area to pick up efficiency in fins is to increase resistance in the power stroke and lessen it during the recovery period.

 

 DEFIANT’s power stroke stiffeners work on the top of the fin. They are fixed at the points near the foot but attach in a floating fashion at the front positions. Because they are on top they must stretch on the power stroke, engaging more resistance and creating more thrust. As humans, the recovery stroke is by far the weakest movement we have in our kick cycle. On DEFIANT’S recovery stroke the floating design allows the stiffeners to disengage and walk forward in their mounting position, reducing resistance and conserving energy.

 

Fins based on splits and airfoils designs, or those with vents, ridges or trauths do not increase efficiency or thrust.     

 

 

Click the twitter icon to tweet this message.

 

 

 

 

 

DEFIANT is based on engineering and science. We didn’t add things to make you feel like you have a technological advantage. We added in things that work, and nothing feels better than truth that performes.

 

Long, rigid fins do not provide more thrust.

 

The notion that a lot of resistance equalls efficiency is incorrect. DEFIANT utilizes all of the available thrust surface by allowing the fin towork under your feet. Its open toe foot pocket transfers the load from your toes and weaker muscle groups back toward your heel and stronger muscle groups. 

 

 

The bottom line is that the perception of a good fin and the science of a good fin are not aligned... and divers pay for the misunderstanding. DEFIANT provides many advantages and efficiencies that have to be felt to be understood. We are all a little different, with different body types, dive types and swim styles. DEFIANT allows you to tune the fin to your type and style as well as change it up for new and different.

 

ABSTRACT

Underwater swimmers use fins which augment thrust to overcome drag and propel the diver. The VdotO2 of swimming as a function of speed, velocity as a function of kick frequency, maximal speed (v), maximal oxygen consumption (VdotO2) and the maximal thrust were determined for eight fins in 10 male divers swimming at 1.25 m depth in a 60 m annular pool. A theoretical analysis of fin cycles was also performed. VdotO2 increased as a second order polynomial as a function of velocity; VdotO2 = 0.045 + 1.65B V + 1.66 (2) V2 (r2 = 0.997), VdotO2 = 0.25 + 1.03 V + 1.83 V2 (r2 = 0.997) and VdotO2 = -0.15 + 2.26 V + 1.49 V2 (r2 = 0.997), for least, average and most economical fins respectively. Kick frequency increased linearly with velocity and had a unique movement path (signature), giving theoretical values that agreed with the measured thrust, drag and efficiency. In conclusion, virtually all thrust comes from the downward power stroke, with rigid fins kicked deep (high drag), while flexible fins are kicked less deep but with higher frequency (low efficiency). Kick depth and frequency explain the performance of the eight tested fins, and should be optimized to enhance diver performance. 

 

 

Fins used in underwater swimming

 

EVALUATION OF FINS USED IN UNDERWATER SWIMMING

D.R. PENDERGAST1,2, J. MOLLENDORF1,3, C. LOGUE1,2, AND S. SAMIMY1,3 

 

Center for Research and Education in Special Environments1 

Departments of Physiology and Biophysics2 and Mechanical and Aerospace Engineering3 Schools of Engineering and Medicine and Biomedical Sciences 

University at Buffalo, Buffalo, NY 14214 

 

Pendergast DR, Mollendorf J, Logue C, Samimy S, Evaluation of fins used in underwater swimming. Undersea Hyperb Med 2003; 30(1): 55-71 - Underwater swimmers use fins which augment thrust to overcome drag and propel the diver. The VdotO2 of swimming as a function of speed, velocity as a function of kick frequency, maximal speed (v), maximal oxygen consumption (VdotO2) and the maximal thrust were determined for eight fins in 10 male divers swimming at 1.25 m depth in a 60 m annular pool. A theoretical analysis of fin cycles was also performed. VdotO2 increased as a second order polynomial as a function of velocity; VdotO2 = 0.045 + 1.65B V + 1.66 (2) V2 (r2= 0.997), VdotO2 = 0.25 + 1.03 V + 1.83 V2 (r2= 0.997) and VdotO2 = -0.15 + 2.26 V + 1.49 V2 (r2= 0.997), for least, average and most economical fins respectively. Kick frequency increased linearly with velocity and had a unique movement path (signature), giving theoretical values that agreed with the measured thrust, drag and efficiency. In conclusion, virtually all thrust comes from the downward power stroke, with rigid fins kicked deep (high drag), while flexible fins are kicked less deep but with higher frequency (low efficiency). Kick depth and frequency explain the performance of the eight tested fins, and should be optimized to enhance diver performance.

active drag, oxygen consumption, efficiency, underwater swimming, thrust, SCUBA

 

INTRODUCTION 

 

Underwater activities are quite common and include sport, commercial and military divers. Although the tasks of these groups vary widely, one common factor in underwater swimming is the use of fins for propulsion. Fins come in a wide variety of shapes, materials and designs, which are reported to affect their performance. The performance of divers using fins is impacted by the energy cost of swimming, as it determines their 

breathing-air use, and thus their dive time, oxygen exposure and thermal status, as well as potential fatigue. 

The energy cost of swimming is determined by the average velocity of forward progression and the ratio of the power required (including drag and internal and kinetic power) to the mechanical efficiency while actually swimming (active)(1). The diver must generate a force equal and opposite in direction to the drag. Some studies have determined drag by towing underwater swimmers passively (2, 3, 4). Further studies were needed because passive drag grossly underestimates active drag (5), the fins used in these studies were not adequately described, and VdotO2 was not determined uniformly. 

Two techniques have been published to determine active drag and efficiency (6,7,8), but only one includes the effects of a leg kick (6), and this methodology has not been applied to underwater swimming. The type of fin selected by the diver, along with his/her technical ability, are major determinants of drag, internal and kinetic work, and efficiency. The energy cost of underwater swimming at or near the surface has previously been reported (9, 3, 10, 11) and the values ranged from 1.3 to 2.5 l/min while swimming at speeds of 0.5 to 1.2 knots, maximal VdotO2 of 3.1 to 4.2 l/min and rapid fatigue at higher speeds. In another study VdotO2 was not affect by depth (1.8 to 54m)(12). It has also been shown that the energy cost of swimming was negatively correlated with fin surface area, but not flexibility, while maximal speed was negatively correlated with flexibility (13, 14). More recently it was reported that fin selection affects VdotO2 by as much as 25%, with large, heavy, rigid fins requiring the highest VdotO2 and smaller less rigid fins less (5). A previous study has suggested that the venturis and vents in fins did not affect their economy (13). 

A firm conclusion about the best types of fins cannot be made from previous studies, and many new fins designs have been marketed based on various physical characteristics without supportive data. To date, no clear understanding of the effects of the characteristics of fins on the energy cost of underwater swimming is available. Previous theoretical work has applied flow over a thin and flexible waving plate of finite chord leading to a progressive wave of given wavelength to imposed transverse oscillatory movements of swimming in slender animals like fish and eels (15, 16, 17, 18). This analysis yields theoretical estimates of thrust, the power required for maintaining motion and the energy imparted to the fluid, and allows calculation of propulsive efficiency. More recently, the waving plate theories have been applied successfully to fins (19) and to surface swimmers 

using legs, and when they use fins as well, to calculate economy, total mechanical work, propelling efficiency and mechanical efficiency (1). It is our hypothesis that fins of different designs used during underwater swimming could be evaluated using the wave plate theories to determine the effectiveness of specific fins in producing thrust, and thus propelling efficiency, and the required energy cost of swimming. 

The purposes of this study were to propose quantitative methods and to evaluate commercially available fins, with different physical characteristics, that are widely used in diving. Fins of various sizes, materials, flexibilities, and designs were tested for the energy cost of swimming, maximal and sustained speeds, and thrust. A theoretical analysis, using the Lighthill model (16), combined with measurements of drag and drag efficiency for selected conditions was done in an attempt to provide further input to the understanding of fin 

performance. 

 

METHODS 

 

Subjects 

 

The subjects for this project were recruited from the local community. Ten male divers were studied. The divers were all SCUBA certified instructors or professional divers and had been diving for between 3-15 years and self-reported 100 hrs/yr of diving. The average ages of the subjects were 32 ± 3.8 years, heights 182 ± 6 cm, weights 90.86 ± 9.28 kg, and body fat 12 ± 4 % (determined by underwater weighing).

 

Protocol 

 

The University’s Institutional Review Board approved the pr