The Sirius 40 DS Sailboat
Specs & Key Performance Indicators

The Sirius 40 DS, a fractional sloop, was designed by Marc-Oliver von Ahlen and built in Germany by Sirius-Werft GmbH.

Published Specification for the Sirius 40 DS

Underwater ProfileVarious keel and rudder options

Hull Material: GRP

Length Overall: 42'4" (12.90m)

Waterline Length: 36' 7" (11.17m)

Beam: 13'5" (4.08m)

Draft: Depends on keel option: Fin keel (4 options), Twin keels or a lifting keel.

Rig Type: Fractional sloop

Displacement: 25,574 lb (11,600kg)

Designer: Yachtdesign v. Ahlen

Builder: Sirius - Werft GmbH (Germany)

Year First Built: 2015

Published Design Ratios for the Sirius 40 DS

1. Sail Area/Displacement Ratio: 16.2

  • Less than 16 would be considered under-powered;
  • 16 to 20 would indicate reasonably good performance;
  • Over 20 suggests relatively high performance.

2. Ballast/Displacement Ratio: 29.7

  • Under 40: less stiff, less powerful
  • Over 40: stiffer, more powerful

3. Displacement/Length Ratio: 232

  • Under 100: Ultralight
  • 100 to 200: Light
  • 200 to 275: Moderate
  • 275 to 350: Heavy
  • Over 350: Ultraheavy

4. Comfort Ratio: 32.6

  • Under 20 indicates a lightweight racing boat
  • 20 to 30 indicates a coastal cruiser
  • 30 to 40 indicates a moderate offshore cruising boat
  • 40 to 50 indicates a heavy offshore boat
  • Over 50 indicates an extremely heavy offshore boat

5. Capsize Screening Formula: 1.8

  • Under 2.0 (the lower the better): Better suited for ocean passages
  • Over 2.0: Less suited for ocean passages

read more about these Key Performance Indicators...

Summary Analysis of the Design Ratios for the Sirius 40 DS

1. A Sail Area/Displacement Ratio of 16.2 suggests that the Sirius 40 DS will, in the right conditions, approach her maximum hull speed readily and satisfy the sailing performance expectations of most cruising sailors.

2. A Ballast/Displacement Ratio of 29.7 would usually mean that the Sirius 40 DS would have a tendency to heel excessively in a gust, and need to be reefed early to keep her sailing upright in a moderate breeze.

However, as she has much of her ballast concentrated in a bulb at the foot of the keel, she's likely to be considerably stiffer than her published Ballast/Displacement Ratio might suggest. This applies to the fin and twin keel versions but presumably to a lesser extent with the lifting keel option.

3. A Displacement/Length Ratio of 232, tells us the Sirius 40 DS is a moderate displacement cruiser, which means she'll carry all your cruising gear without it having a dramatic effect on her performance. Most of today's sailboats intended for offshore cruising fall into this displacement category.

4. Ted Brewer's Comfort Ratio of 32.6 suggests that crew comfort of a Sirius 40 DS in a seaway is similar to what you would associate with the motion of a moderate bluewater cruising boat - a predictable and acceptable motion for most seasoned sailors.

5. The Capsize Screening Formula (CSF) of 1.8 tells us that a Sirius 40 DS would be a safer choice of sailboat for an ocean passage than one with a CSF of more than 2.0. 

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