Use of three-dimensional technology to construct ergonomic patterns for a well-fitting life jacket of heterogeneous thickness

Abstract

To produce a life jacket that fits users both comfortably and stably, we developed a life jacket pattern based on the three-dimensional (3D) shape of the human body, with foam flotation material of different thicknesses used in different sections to achieve the required buoyancy and facilitate movement. We created a nonstandard life jacket for water sports that can adopt free design for canoeing and kayaking. Engineering design process and 3D technology were used to create the ergonomic 3D life jacket, which comprised an inner pattern, a polyethylene (PE) foam pattern for proper buoyancy in water, and the outer pattern. We developed a layering method for achieving the heterogeneous thickness of the life jacket and its outer pattern considering the ergonomic aspects of the 3D human body curvature and movability. The pattern expansion length was calculated to enlarge the outer pattern of each panel covering the varying thicknesses of life jacket and spacing for torso flexion. The calculation formula for this length was useful in increasing or decreasing the life jacket’s buoyancy, which was affected by the PE-foam thickness. Human-subject wear tests were performed in air and water to evaluate the developed life jacket. The developed life jacket had improved functionality. Significant differences (P ≤ 0.01) existed between the newly developed and conventional life jackets in air, in terms of the overall comfort, freedom of rowing movement, and fits in the chest and waist areas. Significant differences (P ≤ 0.05) also existed in water in terms of the overall fit and prevention of separation from the shoulder due to buoyancy.

Keywords

life jacket pattern production three-dimensional technology functional design lines canoeing and kayaking

Given the increase in the number of humans enjoying water-borne leisure activities, there is an increasing need for more advanced safety equipment. In water sports, the life jacket is an essential safety item for protecting the wearer in the event of potentially fatal accidents. Devices for preventing drowning are known by different names in Europe, the USA, and Canada, such as life jackets, buoyancy vests, flotation aids, and personal flotation devices (PFDs).¹ Wearing an appropriate life jacket (or PFD) was found to reduce the rate of drowning mortality;^2–5 however, their usage rates are not particularly high.^6,7 According to the US Coast Guard’s recreational boating statistics for 2010, almost 75% of the victims of all fatal boating accidents drowned, and of those, 88% were reported as not wearing a life jacket.⁸ Some of the victims from among the reported fatalities would not have lost their lives if they had been using appropriate safety equipment.⁹

However, life jackets currently used for water sports are still lacking in terms of their fit to the shape of the human body as well as the freedom of motion that they allow. The most common reasons stated for not wearing a life jacket while participating in recreational boating are based on the participants’ perceptions that life jackets are bulky, uncomfortable, and unfashionable and that they add weight, restrict movement, and interfere with the performance of the activity concerned.^10,11

According to Article 1177 of the UL (Underwriters Laboratories Inc., US) standard, a life jacket can be designed in either of two ways: standard or nonstandard.¹² A standard life jacket is required to comply with all performance requirements specified in the UL 1177 or ISO12402 standard. In contrast, a nonstandard life jacket should be more user-friendly (i.e., it should be less bulky and should not restrict movement), while also permitting the amount of buoyancy required for the intended application.

This study focused on nonstandard life jackets used for water sports, particularly canoeing and kayaking. A nonstandard-type life jacket can be freely designed; therefore, the goal of this study was to improve the fit and comfort of this type of life jacket—which is better suited to canoeing and kayaking—by the application of three-dimensional (3D) technology. Because the 3D shape of the human body is not considered in the design of current two-dimensional (2D) flat-pattern life jackets, wearers of these jackets still experience problems of poor fit, discomfort, and restricted movement. The advantage offered by the 3D pattern examined in this study is that a series of 3D lining patterns and the outer layer, which precisely reflect the 3D shape of different layers of polyethylene (PE) foam and body movement, can be created directly from the 3D shape of the human body.

The objective of this study was to develop a 3D life jacket for canoeing and kayaking that reflects the ergonomic aspects of a human body’s shape and movement by using 3D-technology-based products made of flat textiles, instead of the conventional molded-type jacket. In this way, we set out to improve the life jacket by enhancing its fit, mobility, appearance, and ease of adjustment. Unlike a 3D molding approach, the 3D shaping approach of using flat textiles is easily adaptable and it allows the attachment of accessories via sewing. Therefore, if we can construct an ergonomic pattern with a good 3D fit by using flat textiles, the range of applications of sewn-type life jackets will become much wider than that of molded-type jackets. The key tasks of this study were as follows: (1) application of the ergonomic body lines of a standard human body to the seams of 3D modular patterns; (2) adjustment of the thickness of each module on the basis of its appearance and function; and (3) development of the corresponding patterns for a PE foam of different thicknesses, as well as development of its cover and outer layer, while maintaining the 3D fit, safety, and ease of movement of the life jacket.

Experimental method

Functional design process of the life jacket

Figure 1 shows the overall design process used in this study. Pattern development was performed in three steps. In the first step, the 3D inner pattern for the lining of the life jacket was developed using a standard 3D body and functional design lines. A standard 20-year-old-male body was used for the design of the 3D life jacket. Table 1 lists the body measurements taken from the standard male body. The plot of the curvature can be mathematically defined on the 3D scanned body surface at each point as in Figure 2. Locations of color change, which indicate positions where the sign of the curvature changes from concave to convex, are useful in selecting design lines for improved fitting. The design lines were drawn directly on the 3D human body by using the 3D modeling program RapidForm XOR (INUS Technology, Korea). Then, each panel was cut using the “Trim” tool for a 3D mesh and exported as a .dxf file to produce a flat pattern by using the 2C-AN program, which was custom-developed in our laboratory.¹³ Figure 3 shows an example of flattening of a panel for a piece of the inner layer. Each developed panel was then combined to construct a tight-fitted 3D lining pattern.

Figure 1.

Overall design process for an ergonomic three-dimensional (3D) life jacket.

Figure 2.

Design lines for the three-dimensional (3D) ergonomic life jacket, obtained using curvature plot at points on a standard 3D human body.

Figure 3.

Creation of a two-dimensional pattern by flattening of the upper front panel obtained from the three-dimensional scanned surface using the 2C-AN program.

Table 1.

Mean and standard deviation of dimensions for standard 20-year-old-male body (data from SizeKorea 2010). Unit: cm

Measurement	Value (SD)	Measurement	Value (SD)
Height	173.5 cm (5.5)	Hip circumference	94.5 cm (4.7)
Chest circumference	95.6 cm (6.2)	Neck circumference	36.9 cm (2.0)
Waist circumference	77.7 cm (7.9)	Waist back length	41.9 cm (2.4)
Waist circumference (omphalion)	79.8 cm (8.0)	Waist back length (omphalion)	46.7 cm (2.4)

In the second step, the spacing and layering of the PE foam over the lining were developed in consideration of the shape of the body and the movement of the wearer. In this study, several PE foam sheets of 5 mm thickness were used to achieve the required level of buoyancy. To ensure comfort of the wearer, the thickness of each panel was adjusted by considering the ergonomic aspects of the human body. At the same time, the thickness of the panel around the chest region was increased in order to accommodate a well-developed chest.

In the third step, the outer pattern was developed on the basis of the required thickness of the PE foam and the curvatures of the corresponding body parts. To develop the outer pattern, the inner pattern was differentially enlarged by an amount equal to the pattern expansion length that was calculated from the length of the inner pattern, height of the PE foam, and radius of curvature of the 3D human body. The length and curvature were measured by RapidForm XOR. The outer fabric of the life jacket was a 1-mm-thick stretchable neoprene laminated with jersey. To determine the optimal reduction rate of the stretchable outer pattern made of neoprene, fabric stretch percentages were measured according to the standard test method for “stretch properties of knitted fabrics having low power” (ASTM-D2594, 2012).¹⁴ The optimal reduction rate of the outer pattern was calculated based on Ziegert and Keil’s method.¹⁵

Evaluation

The 3D experimental life jacket, based on a standard 20-year-old-male body, was evaluated in actual wear tests in air and water that were performed using 21 male subjects. Out of these, 16 male subjects with an average age of 24.4 years (SD: 2.94), height of 174.0 cm (SD: 3.54), and chest circumference of 94.1 cm (SD: 3.03) were recruited to evaluate the comfort and fit of the life jacket in air. All of these dimensions were within one standard deviation of the corresponding means for the standard 20-year-old male body (Table 1). Each subject wore two types of life jackets—the newly developed 3D life jacket and a conventional 2D life jacket—and then performed several types of movement (shoulder joint flexion, extension, adduction, abduction, and hyper-adduction; waist flexion and extension; and sitting and standing), including a rowing motion. Both these life jackets were evaluated in terms of overall comfort, fit in the chest area, fit in the waist area, and freedom of movement when rowing. The remaining five male subjects, with an average age of 24.2 years (SD: 1.64), height of 179.4 cm (SD: 4.82), and chest circumference of 96.0 cm (SD: 4.18), were recruited with the aim of evaluating the performance of the two life jackets (new and conventional 2D) in water, in terms of aspects such as the overall fit, freedom of movement in water, prevention of separation from the shoulder owing to buoyancy, and overall comfort. These subjects performed the standing stroke, backstroke, and freestyle with the two life jackets. All five subjects had 3–5 years of experience as professional swimming instructors. Subsequently, feedback was obtained from them by using a seven-point Likert scale ranging from 1 = extremely dissatisfied to 7 = extremely satisfied. SPSS 18.0 software was used to perform statistical analysis of the collected data. A paired t-test was used to compare the average differences between the two types of life jackets.

Results

Functional design lines and 3D inner pattern

The design lines were drawn directly onto the 3D human body by considering the anatomy of the torso, the movement of the neck/arm, and the flexion of the upper body required for canoeing and kayaking. Figure 2 shows the design lines used to create the design panels over the traditionally defined curvature plot produced for the life jacket by RapidForm XOR. The locations where the signs of the surface curvature change were noted as being appropriate as the seam lines, so as to fit the curved shape of the body more closely by sewing blocks of separate panels together. The neckline area was designed such that it was high enough to prevent slippage from the torso owing to buoyancy in water and thin enough to allow for a wide range of bending and rotation motions of the neck, while preventing the bottom of the chin from touching the life jacket. Therefore, a neckline panel was inserted to accommodate PE foams differing in thickness near the neckline from those on the torso. To facilitate the flexion and extension of the torso, a horizontal cutting line was used under the sternal area where the curvature changes from positive to negative, as indicated in Figure 2. The side panel line was inserted on the basis of the curvature plot, where the foam layering was omitted for ease of rowing motion and benefit of extension from the stretchable outer layer. To facilitate the movement of the scapula, the cutting line for the upper part of the back was located inside the scapula.

The shoulder width was reduced to allow for arm movement when rowing; the armhole was located beyond the deltoids. Figure 4 shows examples of the movement of the shoulder joints. Figure 5 shows the 3D inner layer pattern and prototype of the lining of the life jacket, which were derived directly from the 3D standard male body.

Figure 4.

Observation of movement of upper arm to determine size of panels for canoeing and kayaking.

Figure 5.

Inner layer pattern and prototype lining of the life jacket.

Layering method for PE foam

In this study, the edge of the PE foam in each module was tapered to facilitate bending and provide a natural appearance, as depicted in Figure 6. The length of the outer foam decreased on account of the tapering edge of the boundaries. Figure 7 shows a 3D image of the PE foam layered over the chest area. The boundaries of the second and third foam layers were reduced by 5 mm each to produce smoothly tapered profiles. The thickness of the panels, the layering angle of each panel, and the spacing between the panels were all determined to realize an aesthetic appearance as well as functionality of the life jacket.

Figure 6.

Breakdown of panels to enhance mobility (note that the panel edges are tapered).

Figure 7.

Layered polyethylene (PE) foam sheets in the chest area.

Initially, we used four layers of 5-mm-thick PE foam for the chest panel and three layers for the abdomen panel, as shown in Figure 8. To realize an aesthetic and healthy appearance, more layers were used in the chest area than in the abdomen. The number of foam layers may be increased to attain more buoyancy. Subsequently, we introduced spacing between the chest and abdomen panels by considering the maximum bending angles of the thoracic and lumbar vertebrae, that is, 135°, to prevent interference between these panels (Figure 8). To provide space during bending, the outline of the first layer of the PE foam was displaced 3 mm from the sewing seams of each inner lining, resulting in 6 mm of spacing between the two panels. With this 6 mm spacing between the two panels, the problem of blocking during bending due to thick foam was eliminated (Figure 8). Figure 9 schematically shows how PE foam sheets might be layered for the panels of different body parts. Figure 10 shows a sample pattern of PE foam sheets and actual photographs of the PE foam layering over the lining.

Figure 8.

Relation between chest and abdomen panels depending on spacing between seam lines. (a) Blocking occurs when no spacing is added between the chest and abdomen panels. (b) Smooth bending motion is possible with 6-mm spacing.

Figure 9.

Schematic of possible layering of polyethylene sheets for panels of different body parts (the length of the upper sheet was reduced by 0.5–1.5 mm).

Figure 10.

Polyethylene foam sheets and their actual layering over the lining.

Development of the outer pattern

The outer pattern was enlarged based on the inner pattern by using the global average radius of curvature.^16,17 This parameter, which represents the overall characteristics of the curved plane, is obtained by creating a circle that passes through three points spaced 2–5 cm apart, as shown in Figure 11. Each of 22 curves was drawn from the center point of a panel to the midpoint of an outline of that inner panel to calculate the amount of enlargement of the outer layer from the initial lining, as illustrated in Figure 12. Figure 13 shows an example that illustrates the relations among the 3D nude body, length of the lining, layered PE foam, and outer pattern by using curve 9 in Figure 12.

Figure 11.

Example of measurement of global average radius of curvature by using three points along the chest by RapidForm XOR.

Figure 12.

Locations of 22 curves used for measurements to obtain expanded outer pattern. L1 and the radius of curvature along L1 on these 22 curves were observed.

Figure 13.

Cross-sectional image of the three-dimensional human body, layered polyethylene (PE) foam, and outer pattern. H: height of foam; R: radius of curvature; L1: length of baseline, inner pattern; L2: decrease in length of PE foam (1 cm in this case); L1′: L1 – L2; L3 = $\frac{H}{R} \times L 1$ ; L4 = $\sqrt{(L 2 + L 3) 2 + H 2}$ ; A: pattern expansion length = L1′ + L4 – L1 = L4 – L2; P: point along outer layer where the arc parallel to L1 is of the same length.

The measurements included the length of the inner pattern (L1), the height of the PE foam (H) and the radius of curvature (R) for 22 curves of the human body. If we denote P as the point on the outer layer from which the arc drawn along the outer surface is of the same length as L1 and denote L2 as the decrease in length from P to achieve a smooth look (in this case, 10 mm), the total length of the outer pattern is (L1 – L2) plus L4 (i.e., the length of the oblique side of the PE foam). The radius of the circle (R) and the angle θ (in radians) are obtained by selecting three points along arc L1 (i.e., L1 = Rθ). L3 is the naturally expanded length resulting from layering and is defined as the distance from point P to the point on the outer layer through which the radius of the inner circle passes when extended, as indicated in Equation (2). The enlarged arc length (L1 + L3) was obtained from the height (H) of the PE foam and the radius and arc length of the inner circle (R and L1, respectively) as follows:

L 1 = R θ

(1)

L 1 + L 3 \approx (R + H) θ when R >> H

(2)

L 3 \approx (R + H) \frac{L 1}{R} - L 1 = \frac{H}{R} \times L 1

(3)

L2 and L3 are known from the radius of the body curvature (R); furthermore, the additional height resulting from the foam, H, and the initial lining length

L 1

are also known. Hence, we can obtain L4 approximately by the Pythagorean theorem:

L 4 \approx \sqrt{(L 2 + L 3) 2 + H 2}

(4)

Therefore, the length of the pattern expanding amount (A) was

A = L 1' + L 4 - L 1 = L 1 - L 2 + L 4 - L 1 = L 4 - L 2 = \sqrt{(L 2 + L 3) 2 + H 2} - L 2 = \sqrt{(L 2 + \frac{H}{R} \times L 1) 2 + H 2} - L 2

(5)

Hence, from the length of the baseline (L1), the length reduction of the PE foam (L2), the height of the desired layers of the PE foam (H), and the radius of the body curvature (R), we obtain the length enlargement (A) for the corresponding outer pattern. Table 2 presents the enlargement (A) values for each curve to create the outer pattern. In fact, the thickness of the PE foam sheets could be increased further to 3 cm to provide a higher level of buoyancy if desired, as indicated by the values on the right-hand side in Table 2.

Table 2.

Length of each segment for creating the outer pattern. Unit: cm

	No	H	R	L1	L2	L3	L4	L1′	A	H	L2	A
Front	1	0.5	8.35	2.79	0	0.17	0.53	2.79	0.53	1.0	0	1.05
	2	0.5	62.03	7.05	0	0.06	0.50	7.05	0.50	1.0	0	1.01
	3	0.5	14.3	2.73	0	0.10	0.51	2.73	0.51	1.0	0	1.02
	4	0.5	11.55	7.66	0	0.33	0.60	7.66	0.60	1.0	0	1.20
	5	0.5	8.28	8.03	0	0.48	0.70	8.03	0.70	1.0	0	1.39
	6	2.0	22.03	10.39	1.0	0.94	2.79	9.39	1.79	3.0	1.50	2.68
	7	2.0	24.58	8.31	1.0	0.68	2.61	7.31	1.61	3.0	1.50	2.41
	8	2.0	13.03	8.14	1.0	1.25	3.01	7.14	2.01	3.0	1.50	3.02
	9	2.0	8.53	9.89	1.0	2.32	3.87	8.89	2.87	3.0	1.50	4.31
	10	2.0	19.04	10.95	1.0	1.15	2.94	9.95	1.94	3.0	1.50	2.90
	11	1.5	38.14	8.14	0.5	0.32	1.71	7.64	1.21	2.5	1.00	1.93
	12	1.5	11.35	7.25	0.5	0.96	2.09	6.75	1.59	2.5	1.00	2.60
	13	1.5	70.00	7.35	0.5	0.16	1.64	6.85	1.14	2.5	1.00	1.80
	14	1.5	25.36	7.95	0.5	0.47	1.79	7.45	1.29	2.5	1.00	2.07
Back	15	1.0	14.30	13.83	0	0.97	1.39	13.83	1.39	2.0	1.00	2.55
	16	1.0	104.22	7.11	0	0.07	1.00	7.11	1.00	2.0	1.00	1.30
	17	1.0	24.17	9.39	0	0.39	1.07	9.39	1.07	2.0	1.00	1.68
	18	1.0	6.98	7.56	0	1.08	1.47	7.56	1.47	2.0	1.00	2.75
	19	1.0	16.95	15.34	0	0.91	1.35	15.34	1.35	2.0	1.00	2.45
	20	1.0	134.20	11.17	0	0.08	1.00	11.17	1.00	2.0	1.00	1.32
	21	1.0	9.67	14.44	0	1.49	1.80	14.44	1.80	2.0	1.00	3.46
	22	1.0	34.02	7.68	0	0.23	1.03	7.68	1.03	2.0	1.00	1.47

H: height of foam; R: radius of curvature; L: baseline length depending on distribution of the inner pattern; L2: decrease in length of polyethylene foam; L3 = $\frac{H}{R} \times L 1$ ; L4 = $\sqrt{(L 2 + L 3) 2 + H 2}$ ; L1′ = L1 – L2; A: pattern expansion length=L1′ + L4 – L1 = L4 – L2.

In consideration of the stretchable nature of the 1-mm-thick neoprene laminated with a single jersey, the outer pattern was reduced by Ziegert and Keil’s method as follows. The percentage of fabric stretch (S) was calculated using the length differences between the reference size and the size after it was stretched using a 500-g weight, which were 4.5% and 6.5% in the widthwise and lengthwise directions, respectively. Then, the pattern reduction rate (P) was calculated as indicated in Equation (6). In this study, the applied percentage of fabric stretch (A) was 66% in the widthwise direction and 50% in the lengthwise direction, according to a suggestion in a previous study.¹⁸

Patternreductionrate (P, %) = Percentageoffabricstretch (S) \times Appliedpercentage offabricstretch (A)

(6)

Widthwisepatternreductionrateofneoprene used (P_{W}, %) = 4.5 % \times 66 % = 2.97 % ≒ 3 %

(7)

Lengthwisepatternreductionrateofneoprene used (P_{L}, %) = 6.5 % \times 50 % = 3.25 % ≒ 3 %

(8)

According to Equations (6)–(8), the widthwise (P_W) and lengthwise (P_L) pattern reduction rates of neoprene were about 3% each. Since subjects did not want tighter fit in air than the one with 3% pattern reduction, the pattern reduction rate of 3% was selected although the life jacket was relaxed a bit in water, that is, a 3% pattern reduction rate was within the optimum range of pattern reduction for the neoprene life jacket with a PE foam sheet. The size of the outer fabric pattern was then reduced to 97% of the original size of the pattern in both directions. Figure 14 shows the inner and outer patterns and a prototype of the life jacket.

Figure 14.

Comparison of three-dimensional (3D) inner and outer patterns (a) and prototype of the newly developed 3D life jacket (b).

Results of the subject wear test

Table 3 presents the results of wear tests conducted in air to evaluate the efficacy of the newly developed 3D life jacket in comparison to that of a conventional 2D life jacket. The conventional life jacket chosen as a control is a representative model of the kind currently available in the market, as shown in Figure 15(a). Both its inner and outer patterns are identical 2D flat patterns. The buoyant material inserted in the conventional 2D life jacket is a single block of foam and, therefore, it does not properly follow the 3D shape of the human body. In this work, our subjective evaluation in air was focused on comfort, fit, and movability while wearing the two types of life jackets. The evaluation results showed that the newly developed 3D life jacket was rated more highly in terms of overall comfort (5.69) and freedom of rowing movement (5.75) than the conventional 2D life jacket. The fits in both the chest area (4.63) and the waist area (5.00) were also improved in the case of the newly developed 3D life jacket. Significant differences were observed in the overall comfort (paired t-test: t = 6.351, df = 15, P ≤ 0.000***), freedom of rowing movement (paired t-test: t = 6.953, df = 15, P ≤ 0.000***), the fit in the chest area (paired t-test: t = 2.853, df = 15, P ≤ 0.012*), and the fit in the waist area (paired t-test: t = 3.359, df = 15, P ≤ 0.004*) between the two types of life jackets. These results demonstrate that the newly developed method of 3D design improves the fit and comfort of the life jacket, as a result of which it is better suited to water sports such as canoeing and kayaking owing to reduced restrictions on the wearer’s movement or lesser discomfort caused by the fit.

Figure 15.

Conventional two-dimensional life jacket (a) and newly developed three-dimensional life jacket (b) used in the wear test.

Table 3.

Paired evaluation of experimental life jacket and manufactured life jacket (out of water) (n = 16)

Evaluation item	3D experimental life jacket		Manufactured life jacket		t	df	P-value
Evaluation item	Mean	SD	Mean	SD	t	df	P-value
Overall comfort	5.69	1.01	2.94	1.18	6.351	15	0.000***
Fit (chest area)	4.63	1.09	3.25	1.29	2.853	15	0.012*
Fit (waist area)	5.00	1.32	3.44	1.26	3.359	15	0.004*
Freedom of rowing movement	5.75	1.00	2.56	1.26	6.953	15	0.000***

P < 0.05; ***P = 0.000.

Seven-point Likert scale (1 = extremely dissatisfied, 7 = extremely satisfied).

Table 4 presents the results of the wear test conducted in water. In this case, we lay emphasis on the performance of the life jacket in terms of its fit, comfort, and movement as affected by the buoyancy of water. The test results showed that the newly developed 3D life jacket was given a higher rating than the conventional life jacket in terms of the overall fit (6.0), freedom of movement (6.0), prevention of separation from the shoulder due to buoyancy (5.8), and overall comfort (5.8). Significant differences were observed in the overall fit (paired t-test: t = 4.000, df = 4, P ≤ 0.016*) and the prevention of separation from the shoulder due to buoyancy (paired t-test: t = 2.994, df = 4, P ≤ 0.040*) between the two types of life jackets.

Table 4.

Paired evaluation of experimental life jacket and manufactured life jacket (in water) (n = 5)

Evaluation item	3D experimental life jacket		Manufactured life jacket		t	df	P-value
Evaluation item	Mean	SD	Mean	SD	t	df	P-value
Overall fit	6.00	1.00	4.40	1.14	4.000	4	0.016*
Freedom of movement	6.00	1.00	3.80	1.48	2.750	4	0.051
Prevention of separation from shoulder due to buoyancy	5.80	0.45	3.60	1.52	2.994	4	0.040*
Overall comfort	5.80	0.84	3.60	1.52	2.557	4	0.063

P < 0.05.

Seven-point Likert scale (1 = extremely dissatisfied, 7 = extremely satisfied).

The newly developed 3D life jacket, which is based on 3D technology in order to maximize the consideration of 3D characteristics of the human body, has improved functions both in and out of water; this results in more enhanced activity and safety of the wearer.

Discussion

In a recent survey on the use of life jackets among recreational boaters, deterrents to wearing a life jacket consistently included not only problems of fit and function but also poor appearance. Although the test subjects said that current inflatable life jackets were handy, they had some apprehension that the jackets would malfunction when they would actually be required. The higher cost of inflatable life jackets and the maintenance of CO₂ cartridges are regarded as problems for potential users, and many boaters suggested improvements to the design of non-inflatable life jackets.¹⁹ The motivation to improve life jackets by using conventional textile materials is supported by these current needs of potential users.

For improved 3D fitting and an appealing appearance, design lines were directly selected on the 3D surface of the human body, initially by using the curvature plot. Breakdown of the patterns by design lines is necessary because the thickness of the life jacket should be different in each panel for achieving the required appearance and function. For example, by separating the front panel between the chest and the abdomen, we can emphasize the chest by including additional layering of the PE foam while keeping the thickness around the abdomen much thinner than that around the chest. A healthy look comes from a well-developed chest, a thin waist/abdomen, and an appealing appearance. PE foam sheets of different thicknesses can also be applied to the neckline and back of the life jacket. In our improved life jacket, the side panel was composed solely of two layers of extensible neoprene, which maximized extensibility and allowed a thin appearance around the waist. The extensible side panel was highly efficient in accommodating wearers of different body dimensions.

The accuracy of the direct development of next-to-skin patterns from a 3D body has been verified within a 5% margin of error.^13,20,21 However, in addition to the innermost lining, all other layers should also follow the curved form of the human body. Therefore, in this study, 5-mm-thick layers of PE foam, instead of blocks of foam, were used to enhance compliance. In addition, the length of the PE foam was reduced by 0.5 cm with each additional layer that increased the thickness of the PE layering. An intensive ergonomic approach is necessary for patterning the outermost layer because this layer should not only cover 3D shapes of different thicknesses but also take into account the spacing between thick PE foam layers so that body movement remains unrestricted. To avoid collisions between thick PE foam layers in neighboring modules, 6-mm spacing is recommended between the chest and abdomen panels, considering the bending angle of the upper body during rowing.

The outer pattern was developed by considering the spacing between the sewing lines, the 3D shape of the panel, the height of the PE foam, and the length reduction of the foam. We also established Equation (5) to obtain various expansion patterns of the outer layer depending on variables such as the thickness and length reduction of the outer PE foam, as well as the radius of curvature of the body location. This equation can be used to construct other kinds of thick protective and functional clothing with heterogeneous thickness, such as body armor and heavily padded jackets.

If the neckline and armhole line are too large, the body may separate from the life jacket by slipping through these holes as a result of the buoyancy of the life jacket in water. To prevent this, comparably narrow necklines and armholes were designed in this study. The larger the body area covered by the life jacket, the greater should be the ergonomic attention paid to its design. Therefore, a neckline panel was inserted with fewer layers of PE foam to facilitate the movement of the head and neck around the neckline. The shoulder width and armhole line were also optimized so as to prevent interference with the circumferential movement of the arm. Side panels made of two layers of outer materials offered a more favorable appearance and better extension for subjects of various body dimensions. The decreased thickness of the side panel allowed for reduced friction with the arm during movement.

Conclusion

In this study, the engineering design process was implemented for developing a well-fitted 3D life jacket with an improved fit, appearance, movability, and comfort for recreational water sports such as canoeing and kayaking. With the aim of improving the safety of life jackets in water, 3D technology was adopted to construct a contoured life jacket, which was designed to prevent its separation from the wearer’s body in water. Other design features, such as seam lines for each panel with different thicknesses, were considered with a view toward improved fit and function to facilitate the movement of the wearer and create an appealing appearance. An equation for expanding the outer layer such that it can cover panels of different thicknesses was obtained and verified using variables such as the radius of curvature of the panel, thickness of the PE foam, and reduction of the outer length of the foam.

The newly developed 3D life jacket was highly rated by human subjects for canoeing and kayaking, where the ergonomic design lines of varying thickness offered fit, movability, and comfort during movement in both air and water. In addition, a prototype of the newly developed 3D life jacket made of stretchable neoprene and side panels without PE foam improved the range of the life jacket owing to the lack of an additional size-control module. The newly developed 3D life jacket is expected to offer a higher level of safety for dynamic water sports owing to the improved fit and movability of the upper body. The buoyancy of the life jacket could be increased further by increasing the number of layers of PE foam. The proposed design process could also be used to tailor ergonomic life jackets according to gender and age group.

Footnotes

Funding

This research project was supported by the Sports Promotion Fund of Seoul Olympic Sports Promotion Foundation from Ministry of Culture, Sports and Tourism (2011–2014).

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