Cal's Evals » CORMORANT CATAMARAN

Release Date: 1/19/2011

Cals Evals Kohler 44 Cormorant

Bernd Kohlers Cormorant is difficult to analyze with the tools normally used on the MDI website for one reasonhis hull cross section is a trapezoid while our tools assume a semi-circular underwater cross section. Nonetheless, a comparison is made below with comments to address this cross section difference.

The following figures show the boat in comparison with 27 other cruising catamarans with waterline lengths from 43 to 44 feet. There are designs by Schionning, Hughes, Barreau, White and others. Averages for the 28 boats are shown in brackets with trend line values for the entire 959 boat catamaran database in parentheses [average (trend line value)].

Length overall: 44.29 feet [44.66 (45.5]

Waterline length: 43.8 feet [43.48 (NA)]

Displacement: 8.85 tons [7.89T (8T)]

Sail Area: 894 sq. ft. [1091 (1155)]

Displacement-Length Ratio: 52.66[47.99 (46)]

Sail Area-Displacement Ratio: 19.52 [26.54 (26.3)]

Beam between hull centerlines: 21.65 feet [19.81 (NA)]

Base Speed: 10.06 knots [11.12 knots (11.4)]

Texel Rating: 135 [120 (116)]

Bruce Number: 1.11 [1.28 (1.30)]

Stability Speed: 26.36 knots [20.57 knots (20.5)]

The boat is featured on Kohlers website at http://www.ikarus342000.com/Comorantpage.htm.

Its calculated Base Speed is below the average for its peers. This may be attributed to the combination of 12% above average displacement and 22% below average sail area. The Sail Area-Displacement ratio shows this best. The sail area listed on the site includes a genoa which improves this performance. The MDI standard for comparison is upwind sails only.

This is probably not a fair analysis of this design. By using the trapezoid rather than the semi-circular cross section, Kohler has optimized the design for higher speeds where wave drag predominates rather than low speed where skin friction predominates. The boat has a very slim waterline length-to-beam ratio of 13.5. To achieve this with a semicircular cross section, the boat would displace in the neighborhood of five tons rather than its 8.85. Considered another way, an 8.85 ton boat with semicircular hulls would have an L/Bh of around 10. So, to do a true comparison, it would be necessary to sail the Cormorant against one of its peers, such as the Dean 441 or the Kennex 445.

A benefit of this design is that a boat with racing-class L/Bh value has much higher than average stability as shown by the Stability Speed.

Kohler states that the hulls are fitted with anti-vortex panels, rather than keels or centerboards, to augment windward performance without increasing draft or encroaching into the hulls. Side-by-side boat comparisons of this feature would also be telling.

Calvin H. Markwood
Engineering Analyst
Multihull Dynamics, Inc.

Contact Cal: multihull.analysis@comcast.net