Calculation

Hull and stability factors

Great Dane 28 is relatively heavy and stiff, which means she will be slower, but comfortable offshore and will go well in rough seas. With a good ballast, she has a very good stability, even being more on the slim side. Her long roll period for a boat that size indicates a stable vessel, together with a large angle of vanishing stability (AVS) and a relatively good comfort factor.

Based on Lh = 8,54 m, Lwl = 6,4 m, Bmax = 2,44 m, Bwl = 2,2 m (0.9*Bmax), Draught = 1,45 m, HD = 0,5 m (Guess), Displacement = 4195 kg, Ballast = 1798 kg, Sail area = 36,7 m2, Power = 18 HP. Calculation found on www.boatdesign.net thanks you to Guillermo Gefaell.

Length/Beam ratio (Lfl+Lh)/2B = 3,06 ;
Ballast/Disp Ratio = 0,43 ;
Displacement/Length Ratio D/L = 446,35;
Sail Area/Disp. Ratio SA/D = 14,34 ;
Power/ Disp. Ratio HP/D = 1,94 HP/ton ;
Hull speed HSPD = 6,14 Kn ;
Potential Maximum Speed PMS = 6,43 Kn ;
Velocity Ratio VR = 1,05 ;
Capsize Safety Factor CSF = 1,53 ;
Motion Comfort Ratio MCR = 38,49 ;
Angle of Vanishing Stability AVS = 138 º ;
Heft Ratio HF = 1,61 (OK over 1) ;
Roll Period T = 3,77 Sec ;
Roll Acceleration Acc = 0,04 G's (Malaise 0.1+) ;
Stability Index SI = 1,54 (Comfort: 1 – 1,1)

AVS is the angle of heel at which a boat capsizes (a larger ° is thus preferred). Lightweight ocean production boats are now coming out with AVS of 110°. Anything added to the boat will reduce that, since it's placed above the center of gravity (radars, genoa furlers, and so on). On the other end of the scale is the Contessa 32 with an AVS of approx 152° and she was one of the only small boat to survive and finish the deadly race Fastnet in 79'. So our 138° AVS is pretty good for our 28 footer.

The comfort factor represent a kind of livability offshore. It generally favors bigger boats on which people will generally feel more comfortable, except with smaller boat that have a heavy displacement and narrower beam!

The capsize factor (CSF) is a measurement developed after that sadly '79 Fastnet (beam is compared to displacement) to determine whether a wave would capsize a boat). Values less than 2 are supposed good, the lower the better (1 is a minimum and boats with values over 2 are not considered suitable for ocean races). But considering the actual result of the race, particularly the Contessa 32 finishing (and ahead of larger boats), some of the boats capsized must have had better CSF numbers than the Contessa's 1.77. I really don't know what it really means…

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