| This page is fairly technical ... but in 2005 the Catalac 8M was my new boat and calculating it 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 |
| Catalac 8M / 9M Specifications | ||
| Parameter | Value | Description |
| 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., 4.17 m |
Beam overall |
| Bcl | 10.41 ft. 3.17 m | Distance between hull centerlines of a catamarn 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 catamarn 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). |
| Displacement | 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. |
