YANMAR Technical Review

Abstract

Yanmar’s flagship products include the EX38A and EX34A fishing cruisers that combine fishing functionality with comfort.
While the EX38A is currently Yanmar’s largest vessel in this category, there is market demand for fishing cruisers of 40 feet or more that feature high livability and comfort.
This led Yanmar to develop the EX47A as a new flagship model that offers the best features for fishing in the EX Series, combining a large deck space and improved rigging tolerance for fishing with spacious living space and storage capacity.

1. Introduction

As a mainstay of Yanmar’s recreational marine lineup, the EX Series of fishing cruisers combine excellent features for fishing with comfortable livability.
The newly developed EX47A is the flagship model in the EX Series. It features the new 594-kW 6GY135W-P1 engine, a long range provided by having the largest fuel tank of any EX model, and comes with more than 40 options, including a shower room and galley to suit a wide range of different needs. This article describes the highly efficient air conditioning design that included an analysis of subjective thermal comfort to improve performance, one of the innovations adopted to equip the new craft with the comfortable living spaces that customers expect from a flagship model.

2. Product Overview

2.1. Styling

2.2. Main Specifications (Table 1)

2.3. Engine (Table 2)

3. Comfort Improvements

3.1. Improved Air Conditioning: Aircon Efficiency – Efficient Air Conditioning Design with Consideration for Subjective Thermal Comfort

While air conditioning has long been a common fitting on marine craft, using an air conditioner for cooling is more difficult on a boat than in an automobile. The reasons for this include the lack of shade at sea that leaves the interior completely exposed to sunlight during the daytime, the presence of many heat-producing devices such as the generator and engine, and the difficulty of installing high-capacity air conditioning systems due to limitations on the amount of electric power and space that can be made available. The EX47A in particular called for action to address inadequate air conditioning, having the largest cabin volume of any model in the series and an interior that is exposed to sunlight through large glass windows on all four sides (Fig. 2). To overcome these challenges, the development project called on the assistance of Yanmar’s Central Research Institute and went about designing the air conditioning in a way that would provide each and every passenger with a more pleasant sense of thermal comfort. This included the use of computational fluid dynamics (CFD) to predict the comfort level of passengers seated in each of the vessel’s seats.

3.2. Standard Effective Temperature (SET*)

Standard effective temperature* (SET*) is a metric used to assess comfort levels. The value is expressed in °C and calculated from six parameters (air temperature, humidity, solar irradiance, air flow, clothing, and activity level). It is used to assess the realistic level of subjective thermal comfort (how hot or cold a person feels) in a way that takes account of the complex mix of environmental conditions influencing comfort. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), the body that defined SET*, specifies that 80% or more of people will consider an environment to be comfortable when its SET* is in the range 22.2 to 25.6°C
As SET* is a suitable indicator for the subjective level of comfort that occupants experience, it is mainly used for building interiors and in air conditioning design, including for assessing the comfort level of living spaces or office environments. It was used in the development of the EX47A to equip the craft with comfortable living space.

3.3. Subjective Thermal Comfort Analysis

The first step was to use CFD to calculation the SET* for the previous model to assess its comfort level for passengers in each of its seats. The table below lists the calculation conditions.

Table 3 CFD Analysis Conditions

The SET* at each seat was calculated assuming a mid-summer day with passengers wearing short-sleeved shirts and trousers and with a metabolic rate commensurate with a seated position. The CFD model for the EX47A was then recalculated to study how best to position and orient the air conditioning vents to bring the SET* for the passengers at each seat down to 25°C or less, the criterion for summertime comfort. Fig. 4 shows maps of air flow and SET* calculation results for the previous model and for the EX47A after the vents had been relocated. These results indicate that the cool air expelled from the vents in the previous model tends to pool in the lower parts of the cabin, resulting in a low value of SET* at foot height. In the vicinity of the skipper’s head, however, air flow is poor and the sunlight coming in through the front glass window raises the SET*, resulting in diminished comfort even when the air conditioning is on. While cooling the neck region through which the carotid artery passes is known to be a good way to lower body temperature, the previous model has a high SET* value in this vicinity.

On the EX47A, in contrast, the results for the relocated vents show that the cool air now circulates and reaches all parts of the cabin, lowering the SET* evenly, including in the vicinity of passengers’ necks.
Likewise, the SET* values at each seat shown in Fig. 4 demonstrate that the seat-specific variability in SET* that existed previously has been reduced and a comfortable cabin space has been achieved efficiently (Fig. 5).

3.4. Sensory Evaluation of Air Conditioning Performance

The improvement in comfort and reproducibility of the analysis results were assessed by conducting sensory evaluation onboard with ten subjects who wore the same amount of clothing and had the same level of activity as in the CFD analysis. The evaluation assessed the subjective thermal comfort at each seat by rotating the subjects and moving seats at fixed time intervals. As the comfort levels reported by the subjects were higher than those obtained from sensory evaluation testing in the previous model, this provided a real-world demonstration of the EX47A’s improved air conditioning performance compared to the previous model.

4. Conclusions

Scope remains for further improvement in the comfort of Yanmar boats, with the use of analysis techniques to improve design quality and the adoption of new internal fittings among the many options available. As the design technique development described in this article also has potential applications in Yanmar products beyond the marine sector, it can help to improve comfort across the entire Yanmar product range. If product development is to deliver products with high added-value that bring customer satisfaction, paying close attention to market needs and other trends is vital. In the future, Yanmar will persevere in its efforts to provide products that delight its customers by taking vigorous steps to implement new technologies and incorporate new internal fittings.