FINNING

Update (01/2020): The motion videos on this page were conducted with '512 as well as '412 vertebrae. After extensive tests to optimize thrust and efficiency, Truefin currently provides Blue '412 spines or Yellow ‘415 as standard spines for Truefin Model 110 which are both considered to perform better overall than ‘512 spines.

Blue '412 spines [4°/12°' vertebra = 20°/60° blade flex ] have 20° 'toe up’ articulation and 60° ‘toe down’ articulation, and Yellow '415 spines [4°/15°' vertebra = 20°/75° blade flex ] have 20° 'toe up’ articulation and 75° ‘toe down’ articulation, versus '512 spines [5°/12°' vertebra = 25°/60° blade flex] which have 25° 'toe up’ articulation and 60° ‘toe down’ articulation.

Additionally, Truefin produces Green ‘012 spines which remain straight in the ‘toe up’ direction (0° ‘toe up’ articulation) so the fin blade remains ‘flat as a board’ during the pushing away frog kick, and flexes ‘toe down’ 60° during the frog return kick. Also, Green spines work very well for flutter kicking, and enables the user to produce significant thrust during the flutter return kick if the user has sufficient strength to do so.

Above photos by: Oahu Dive Guide

Update: 4 December 2022 - Current info about spines:

BLUE SPINES - Power at speed

Blue ‘412 spines have an angle of attack of sixty degrees in the 'toe down' direction, and may be considered to be optimized for relatively short flutter kicks, and enable the diver to deliver high thrust while at speed without having to kick excessively fast. Note that short flutter kicks results in reduced projected area with less drag resistance while at speed underwater.

YELLOW SPINES - Easy kicking

Yellow ‘415 spines - Fins equipped with Yellow spines will have a higher angle of attack of seventy five degrees in the 'toe down' direction. This generally implies that fins equipped with Yellow spines will be easier to kick, yet may require a greater flutter kick stroke length than fins equipped with Blue spines. There is no difference between Yellow spines and Blue spines during the 'toe up' flex direction of twenty degrees. Truefin has had a variety of opinions as to the kicking experience of fins equipped with Blue versus Yellow spines, with some saying Blue spines are better, and others saying Yellow spines are better. As indicated above. there appears to be a correlation between kicking range of motion and preference of spines. For example, users having a long and relatively slow flutter kick may find better efficiency and velocity with Yellow spines, versus users who have a short and relatively fast flutter kick who may have better efficiency and velocity with Blue spines.

GREEN SPINES - Optimized for frog kicking

Green ‘012 spines - During the flutter power stroke kick, there is no difference between Blue spines or Green spines, and the blade will flex sixty degrees 'toe down'. During frog kicking Green spines cause the blade to remain flat (flex zero degrees 'toe up') during the pushing away power frog kick for slightly improved glide distances. During the flutter and dolphin return kicking, a fin equipped with Green spines will remain flat in the 'toe up' direction (during the return rearward kick direction) and enable the user to add propulsion thrust during the return kick stroke if the user has sufficient strength. Because Green spines do not allow the blade to flex in the 'toe up' direction, rapid flutter kicking while exerting force during both the power and return stroke may be a more demanding experience, although the benefit is that greater propulsion speed is possible.

NOTE: For those who have hip, knee, or ankle injuries, Truefin users have reported a reduction or elimination of general soreness and pain while using Truefin, as compared to the soreness users typically experienced at the end of a diving day while using the traditional fin of their choice.  These positive reports involved Truefin equipped with Blue spines as well as Yellow spines.  Truefin has had no reports in this regard, pro or con, while using Green spines although it is expected equipping Truefin with Green spines would also result in generally a less strenuous kicking experience during flutter kicking. If Truefin had to make a recommendation as to the best spine to install if a user has some type of leg injury, Yellow ‘415 spines are an obvious choice simply because Yellow spines have a higher angle of attack.

Kicking Styles

Flutter kicking

In general, the faster the user kicks Truefin during the flutter power and/or power and return stroke, the greater the propulsion speed, although note that form drag resistance increases linearly with velocity as the user's body moves through the water (wave drag resistance increases with the square of the velocity but velocities of a diver are generally too low for wave drag to be a factor).

In addition to providing efficient thrust at different kicking frequencies (slow and fast) due to rigid spine enforcement to the optimum angle of attack, efficiency is also gained with Truefin because in a given flutter kick power stroke, the angle of attack is rapidly formed shortly after initiation of the power stroke, and the angle of attack is maintained for a longer duration during the acceleration and deceleration phases of the power kick. With a spineless fin, thrust is only maximized at mid stroke portions of the power flutter kick stroke.

Regarding stresses on the user’s knees while flutter kicking with fins, Truefin produces more thrust than modern high tech fins despite Truefin being slightly shorter by several inches, and this reduced blade length of Truefin minimizes knee stress because the angle of attack of Truefin is formed closer to the user’s knee (the shorter fin length results in less moment of force or torque on the users knees and hip).

Generally, the best flutter kicking technique involves hip-generated movement. Minimize bending of the knees (bicycle kicking) which generates turbulence and displaces water in inefficient directions.

During slow to moderate flutter kicking frequencies, it is recommended to relax the user’s ankles during the flutter return stroke as this promotes blood circulation in the foot and ankle and minimizes muscle cramps. To further reduce the likelihood of muscle cramps, keep your body hydrated and well-nourished

Note: current production includes Blue '412 spines

ABOVE : Real time very slow kick of Truefin Gen 4 with Blue ‘412 spines (Blue ‘512 spines were cancelled).

BELOW: GEN4 - fast flutter kick

Modified Flutter Kick and Shuffle Kick

Truefin is perhaps an ideal fin to perform a modified flutter kick because the user may rapidly and directly push the blade rearward without concern of the blade collapsing. Shown below is a slow modified flutter kick with Truefin Model 110 Gen3 with '412 spines. A shuffle kick may also be performed which is similar, however the knees generally do not move, and most or the motion is from the ankles pivoting, with the heel and toes moving.

Below: Drifting with Truefin.

Note, normally a diver would not kick much while drifting, however it appears in this case either the diver had poor trim with heavy legs which necessitated some kicking to prevent collisions with the ocean floor, or there was also some cross current occurring pushing the diver down the hill. Generally, strong ocean currents can be dangerous, and Truefin machine test results indicate Truefin is capable of providing higher thrust than any other scuba fin on the market. A correlation with high thrust is high efficiency, because due to the fact that at a given leg muscle effort Truefin produces more thrust than all other scuba fins on the market, this implies that for a given amount of thrust Truefin requires less leg muscle effort than all other scuba fins on the market. The greater efficiency of Truefin was confirmed during the machine tests when plotting torque sensor data with thrust load cell data. Refer to: Machine Test Results GEN3

Frog kicking

Flutter kicking typically involves constant movement which may be undesirable because there is no rest phase for Scuba divers, and also flutter kicking tends to disturb sediment at the bottom of a sea floor or inside a cave, where as frog kicking generally does not disturb bottom sediment. For these reasons many divers prefer to frog kick where a kick and glide phase occurs at a relaxed pace while maximizing dive time. During frog kicking, Truefin Blue '412 spines flex up twenty degrees (20°) during the power 'pushing away' phase, and during the return stroke the fin blade flexes 'toe down' up to sixty degrees (60°). The best technique while frog kicking with Truefin is to glide to nearly a stop while returning the fin stroke, then pause briefly after the return stroke to allow the blade to flatten prior to pushing rearward and executing the frog kick power stroke. If Truefin is equipped with Green spines, the frog kick is more efficient because the blade will remain flat during the pushing away power phase of the frog kick.

[EDIT NOTE: - Insert video of asymmetrically equipped fin engaged in frog kicking]

Dolphin kicking

During dolphin kicking with Blue '412 spines Truefin is highly efficient and significant thrust is possible while pushing water down during the power stroke while the blade flexes 'toe down' sixty degrees (60°). The twenty degrees (20°) blade flex in the 'toe up' direction during the return or recovery kick phase may also contribute to propulsion.

Side kicking

During side kicking or breast stroke kicking, the twenty degrees (20°) 'toe up' blade flex limitation with Truefin Blue '412 spines improves efficiency during the power away kick, while during the forward return phase of the side kick the blade advantageously flexes 'toe down' sixty degrees (60°) while minimizing return kick resistance.

Reverse and helicopter kicking

You can back kick without fins simply by backwards movement generated by your legs only. In fact, many instructors will first teach back kicking while not wearing fins. During reverse or back kicking while wearing fins, generally the traditional recommendation is for the side walls or side rails of scuba fins to be used for backward propulsion while the fin blades are kept parallel with the water surface or the sea floor, and while a relatively rapid backward side slicing motion of the fin occurs. The side rails of Truefin are similar in size or side projected area as the relatively large side rails of traditional stiff technical fins.

A second method (not recommended for Truefin due to lost motion while the spines articulate toe down) of reverse kicking involves twisting the tips of the fin and pulling backward while bringing the toes to the knees, and while presenting as much of the blade face to the water as possible at a constant angle. In this manner, during initiation of the reverse kick the feet should be turned out with knees together, and execute the reverse kick while separating the knees and keeping the knees a low as possible.

Helicopter kicks may also benefit from the side projected area of the fin rail, however the main thrust forces while performing a helicopter kick are best produced by alternating between right and left foot during a pushing and pulling motion with the fin blades, and while presenting the fin blade at the broadest presentation against the water as possible depending on the user’s ankle flexibility. During this kick, the knees are typically bent almost ninety degrees, and the more the blades can be turned and presented to the water, the more efficient the helicopter kick.

Truefin is perhaps not optimum for precision movement due to the spine articulation before lockup, however the Monprene rails and blade do have some bending resistance, so a consensus opinion regarding Truefin performance during precision maneuvering as compared to a fin with an extremely rigid blade is not currently understood. The primary objective in the design of Truefin was to develop a fin which would have the highest efficiency and highest thrust of all fins on the market in order to minimize air consumption during periods of moderate to high exertion. Machine tests and subjective diving tests have indicated we achieved that goal.

Surface swimming

During surface swimming with Blue '412 spines, and particularly while swimming face up while on the user's back, the highly flexible nature of Truefin toward the sixty degrees (60°) 'toe down' flex limit is efficient and minimizes splashes, while blade flex in the twenty degrees (20°) 'toe up' direction enables the user to exert limited propulsive forces if desired during the rearward return direction of a surface flutter kick. In most circumstances of endurance surface swimming however, during the flutter return kick the user is encouraged to relax the user's ankle and allow the fin blade to follow the streamline of the water. For a more relaxed and efficient surface swim, orientate your body on a slant while keeping your legs and fins fully submerged.

* * * * * * *

Production has started (9/2022) of Green '012 spines, and Yellow '415 spines, where Green '012 spines would flex 'toe up' zero degrees (0°), and flex toe down approximately sixty degrees (60°) [0°/12°' vertebra = 0°/60° static blade flex]; and Yellow '415 spines would flex 'toe up' twenty degrees (20°), and flex toe down approximately seventy five degrees (75°) [04°/15°' vertebra = 20°/75° static blade flex].

Green '012 spines and Yellow '415 spines are available as a separate purchase.  Currently Blue ‘412 spines are installed, however consideration is being given to install Yellow ‘415 spines at the factory depending upon the consensus of the diving community. Estimated cost is $10 per complete spine of Blue, Yellow, or Green spine geometries, or $40 for a set of four complete spines.  

Note that static blade flex is different from dynamic blade flex with regard to effective 'angle of attack' while kicking and moving underwater.

BELOW: A 'real time' clip illustrating how the spines articulate while being dragged across a steel table top (a horizontal plane). Note that the Yellow spine has a greater angle of attack versus the Blue spine during the power flutter kick, and the Green spine remains flat during the power frog kick. Blue and Green spines have the same angle of attack during the power flutter kick.

UPDATE (January 2022): Production has been changed to Blue ‘412 spines with WHITE chassis. Divers generally preferred a white chassis because the fins are more visible in dark water (the white pattern of shapes protruding out of the bottom of the foot platform). Also, some users appreciated the ability to white balance cameras at depth in water.

Green '012 spines are particularly efficient when frog kicking. If desired, a user may use a Blue '412 spine at the inside rail, and a Green '012 spine at the outside rail (Blue spine at Big toe) in order to minimize leg twist or canted ankle rotation required during an efficient frog kick or modified frog kick. Note: This creates a right and a left fin. Other kicking styles such as when performing sculling or scissor kicking may also benefit with asymmetrical right versus left 'toe up' flex configurations, and there should be little effect during the return flutter kick ('toe up' flex) because typically the user does not cause vertebrae collisions to occur during the 'toe up' flutter return kick, and the 'toe down' flex of 60° is the same for Blue '412 and Green '012 spines.

A Blue '412 spine has been assembled with a Green '012 spine for asymmetrical blade flex in the 'toe up' direction during canted frog kicks, while the blade flexes symmetrically in the 'toe down' direction sixty degrees. As indicated above, recommendation is for the Blue spine to be next the the user’s Big toe during canted frog kicks.

In the photo above, the blade is fully flexed in the toe up direction, while a blue and a green spine has been installed for asymmetrical blade flex for optimal canted power frog kicks. Note that this configuration creates a right and a left fin.

ABOVE and BELOW: Fins produced with blue substrates (factory error) are being held in inventory and have not been released to the consumer market. Based upon current consensus white substrates are preferred due to higher visibility and the ability to white balance cameras.

BELOW: Fins with white substrates

In general, Yellow '415 spines may be utilized in order to provide the easiest kicking experience. Also, while considering your typical flutter kicking style, as noted earlier, keep in mind that Yellow '415 spines may be best for long slow flutter strokes, and Blue ‘412 spines may be best for short fast flutter strokes.

Black fins with a black substrate (chassis), and Black '012, '412, or '415 spines with red springs are available at a discount by special order for US military applications. Minimum quantities may be required for such a production run, however there are plans to produce ‘012 geometry (green) in color black so minimum order quantities may not be necessary. Contact info@truefin.com for details.

For users of Truefin having colored spines and wish to make them black, the above photo is a picture of Truefin with a blue chassis where Blue spines have been painted black. Disregard the dirt and dust on this fin. If the spine surfaces are cleaned properly this may be satisfactory, however molded black spines would be preferable. Custom colors of spines are available at quantities and as a special order.

All active duty military members, reserves, retirees and veterans of the United States Armed Forces and Canada are eligible for a discount on all Truefin products. Contact info@truefin.com for details.

Option to decrease buoyancy of Truefin:

For dry suit divers with floaty feet, up to 1.30 pounds of lead weight per pair of fins (0.65 pounds per fin) may be added to base vertebrae 10000. Without these weights, Truefin size Large is negatively buoyant (sinks slowly) by only one half an ounce (0.52 oz / 15 grams) per fin in salt water (excluding heel straps). If Truefin decides to produce Tungsten weights, the additional weight may be up to about 2.25 pounds per pair of fins. Total weight per fin (not submerged) including spines, and excluding heel straps and excluding weights is 3.10 pounds. Truefin size Large without spines and without heels straps is positively buoyant (floats).

EDIT NOTE: Insert photo of lead weights. Video of lead weight installation: https://www.youtube.com/watch?v=HJyOaXxcsXE or visit Truefin’s YouTube channel.

Future configurations may include one or more colored fins, such as: