This page is fairly technical … but in 2005 the Catalac 8M was my new boat and calculating performance characteristics satisfied my curiousity.
Essentially this page displays crucial data which is used to calculated max speed and stability for the Catalac 8M / 9M (same hulls). The data can be used in the context of hull design or racing handicaps. There’s no way a Catalac 8M (or most cruising catamarans for that matter) can be mistaken as a racer.
The link to my hull design formula page can be found here.
Catamaran Hull design page
Catalac 8M / 9M Specifications
| LOA | 27 ft / 8.23 m | Length overall |
| LWL | 25.5 ft / 7.77 m | Length at waterline |
| SA | 400 sq. ft. 37.16 sq. m | Total sail area of the Main and Jib – 100% fore-triangle area only |
| BOA | 13.67 ft / 4.17m | Beam overall |
| Bcl | 10.41 ft / 3.17 m | Distance between hull centerlines of a catamaran or the distance between outrigger centerlines for a trimaran. Unless provided by the Designer it will be approximated by the formulas: Catamaran (Bcl = Boa-Bh) for a trimaran (Bcl = 0.95*Boa). |
| Bh | 3.26 ft / .99 m | Distance between hull centerlines of a catamaran or the distance between outrigger centerlines for a trimaran. Unless provided by the Designer it will be approximated by the formulas: Catamaran (Bcl = Boa-Bh) for a trimaran (Bcl = 0.95*Boa). |
| Displ | 2.8 LT | Displacement — Designer’s target weight for a boat expressed in tons or, lacking that information, the actual weight divided by 2240 lbs. |
| 6272.00 lb | ||
| 2844.93 kg | ||
| Bcl/Lwl | 0.41 | Ratio of Beam at the hull centerlines (Bcl) to the waterline length (LWL). For catamarans, this should be 40% or greater to avoid wave interference between the hulls and subsequent drag rise at speeds approaching hull speed. |
| Lwl/Bh | 7.82 | Waterline length to the beam ratio of a single hull of a catamaran or the center hull of a trimaran. 16:1 High Performance Racer; 12:1 Racer; 10:1 Racer/Cruiser; 8:1 Cruiser. The narrower hull will be faster, . The fuller hull will be slower, but carry more payload for a given boat length. |
| PI-C | 0.64 | PI-C : A Classic indicator of a measure of relative speed potential of a boat. It takes into consideration Sail Area, Displacement and boat Length at Waterline. The higher the number, the faster speed potential for the boat. PI-C = 0.5*SQRT( (Lwl*SA)/(Disp*2240) ) |
| BSpd | 7.74 Knots | Base Speed is an empirically-derived indicator of the speed a given boat could average over a 24 hour period under a variety of conditions. It can be used to compare speed potential of one or more boats and has been used for handicapping boat races involving a variety of boat types. “Base Speed: A Simple Measure for Estimating Multihull Performance”, Multihull International,No. 225,(APR’89) pp.108-110. Base Speed=1.7*(Lwl^0.5)*(SA^0.352)/((Displacement*2240)^.253) |
| BN | 1.09 | The Bruce Number is a power-to-weight indicator for relative speed potential for comparing two or more boats. It takes into consideration the sail area of the main and jib, no overlapping sails, and the displacement. Chris White, “The Cruising Multihull”; 1997 International Marine, Camden, Maine, states that a boat with a BN of less than 1.3 will be slow in light winds, and a boat with a BN of 1.6 is a boat that will be reefed often in offshore cruising. Derek Harvey, “Multihulls for Cruising and Racing, 1991, International Marine, Camden, Maine, states that a BN of 1 is generally accepted as the dividing line between so-called slow and fast boats. Bruce No. = SA^0.5/(Displacement*2240)^.333 |
| SA/D | 18.82 | The SA/D ratio is similar to the Bruce Number, giving a power-to-weight ratio type figure for comparing two or more boats. Higher numbers indicate faster boats for a given length. However in this ratio, unlike the Bruce Number, main and genoa or any combination of sail area can be used. When comparing any two boats one should ensure that both the SA and displacement, including planned payload, are equivalent, to get a realistic comparison. SA/D = SA/(Displacement*2240/64)^.666666667 |
| Texel | 146 | The Texel Rating provides handicap numbers for widely varying boats sailing together in a race. The formula is essentially the inverse of the Base Speed formula with constants applied to make the numbers useful. The Texel Rating permits the calculation of time to sail a given distance. Thus, a boat with a higher Texel Rating can be expected to take longer from start to finish of a race than one with a lower TR. TR = 100/(0.99*(Lwl)^0.3*(SA)^0.4/(D)^0.3)*K in which K is a correction for catamarans vs. trimarans, based on the equation, K = 1/(0.19*SA^0.4/D^0.36+0.91). If K is greater than 1, use the calculated value. If K is less than one, use the value 1. K is always one for trimarans. |
| SI-CM | 2.44 | This figure is an indicator of the resistance of a boat to sideways capsize for comparison with other boats. This formula only considers static Forces, not dynamic forces such as hull shape, wind, and waves. Therefore it should be considered a “Figure of Merit”. “Theory and Statistics for Cruising Multihulls” by Calvin Markwood, Multihulls Magazine, Vol. 23, No. 2, (MAR/APR 1997), pp. 51-59 Article. The higher the number, the more resistance to sideways capsize. SI-CM = 1000*((Displacement*Loa*Bcl)/((SA)*(SA+15*Loa)) |
| SSpd | 22.34 Knots | The Stability Speed figure is an indicator of the wind speed at which the windward hull of a catamaran, or the main hull of a trimaran, will begin to lift. This formula only considers static Forces, not dynamic forces such as hull shape, wind, and waves. SSpd = 8.23805*((0.5*Bcl*Disp*2240)/(SA*Hce))^0.5 Multihull Designs” by John Shuttleworth Yacht Designs, 1998, p. 37. |
