The Apla 42, a moderate displacement staysail ketch, was designed by Sparkman & Stephens and built by Apla Yachts in Italy.
Keel & Rudder Configuration: Fin keel with rudder on skeg
Hull Material: Fiberglass
Length Overall: 12.0m (39'5")
Waterline Length: 9.83m (32'3")
Beam: 3.45m (11'4")
Draft: 1.85m (6'1")
Rig Type: Staysail ketch
Displacement: 12,000 kg (26,455 lbs)
Ballast: 4,500 kg (9,920 lbs)
Water Tank Capacity: 401 litres (106 gallons)
Fuel Tank Capacity: 201 litres (53 gallons)
Hull Speed: 8.2 knots
Designer: Sparkman & Stephens
Builder: Apla Yachts (Italy) - no longer in business
Year First Built: 1973
Number Built: 8
I: 14.70 meters (48.25 feet)
J: 4.42 meters (14.50 feet)
P: 13.06 meters (42.86 feet)
E: 4.19 meters (13.75 feet)
Total Sail Area: 71m2 (764ft2)
The following analysis of the design ratios gives an indication of the boat's likely sailing characteristics, but see the 'Notes of Caution' below:
Sail Area to Displacement Ratio (SA/D): 11.66
This ratio indicates that the Apla 42 is somewhat underpowered. A SA/D below 16 suggests that it will not be particularly quick or offer high performance. This is typical for a cruising sailboat designed more for comfort and stability rather than speed and racing performance.
Ballast to Displacement Ratio (B/D): 37.50%
With a B/D ratio of 37.50%, the Apla 42 doesn't quite meet the threshold for a very stiff and powerful boat, which is typically 40 or more. However, it still indicates a decent level of stability and ability to handle some wind, though it may not stand up to heavy wind as effectively as stiffer designs.
Displacement to Length Ratio (D/L): 222
This places the Apla 42 within the "Moderate Displacement" category (200-275). Moderate displacement boats require a balanced amount of sail area to reach their design hull speed and often offer a good compromise between comfort, performance, and load carrying capacity.
Comfort Ratio (CR): 42.71
A Comfort Ratio of 42.71 suggests that the Apla 42 will have a very sedate motion, typically associated with a heavy bluewater cruising boat. This indicates that the boat will be quite comfortable in terms of its motion, which is less likely to induce seasickness even during heavy seas, making it ideal for long ocean passages.
Capsize Screening Formula (CSF): 1.5
With a CSF of 1.5, the Apla 42 is well below the 2.0 threshold, indicating good bluewater capability. Its lower value suggests a design that is resistant to capsizing, with a beam and displacement that contribute well to stability in open ocean conditions.
Summary
The Apla 42 sailboat is designed more for comfort and stability than speed. It's moderate displacement makes it reasonably easy to achieve its hull speed without requiring excessive sail area. The high Comfort Ratio implies a very comfortable and sedate motion, ideal for long-term cruising. While it is slightly under the desired B/D ratio for maximum stiffness, it still offers respectable stability. The low Capsize Screening Formula confirms that the Apla 42 is well-suited for bluewater sailing, making it a reliable choice for ocean passages. Overall, the Apla 42 is a solid choice for cruisers who prioritize comfort and safety over performance.
Here's how to calculate the KPIs yourself - without having to wrestle with the mathematics...
Design Ratios: Notes of Caution...
General Limitations
In summary, while these ratios provide valuable insights into the theoretical performance characteristics of a sailboat, they should be used as part of a broader assessment that includes practical experience, sea trials, and expert advice.
This article was written with the assistance of Gemini, a large language model developed by Google. Gemini was used to gather information, summarize research findings, and provide suggestions for the content and structure of the article.
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