The GZ curve is quite powerful to the point of maximum GZ (0.700m at 65.9º), particularly in the range 0º to 20º heel. This indicates that she has good form stability and should be able to carry her sail area well for her size. The GZ at 30º is 0.475m.
Though this is a theoretical GZ curve in flat water, it is useful for assessing the basic dynamic stability of the boat. In reality, under seaway conditions, dynamic stability may be greater or smaller than indicated, depending largely on the shape of the lee bow wave. if there is a “hole” in the wave amidships as when the boat is travelling near waterline speed, this will lessen stability. If there is a crest amidships, then stability will tend to be greater. And the action of the waves themselves will also affect stability.
The loads in the spars and rig are calculated using the GZ at 30º. Though the GZ continues to rise as the boat heels, the sails will be spilling wind at angles beyond 30º and so it will not just be the sails and spars that are causing the boat to heel. There are also built in safety factors that we apply when calculating the spar and rig sizes to allow for knockdown situations.
A note about Displacement: Displacement is the weight of water the boat displaces at any given flotation waterline. It is therefore the same as the all-up weight of the boat floating on that waterline. It is often quoted with the boat floating at the Datum Waterline (DWL) or a specific Load Waterline (LWL) – but obviously varies depending on the amount of gear and personnel aboard.
|LWL/∇1⁄3||4.72||A cruising yacht needs greater volume available for stores, gear, equipment and comfortable living and will therefore displace more than a race boat of the same waterline. ∇ = Volume of Displacement|
|Sail Area/Wetted Surface||2.42||Between 2.0 and 2.5 for practically all yachts, with a mean value of 2.25. Sail area is main + 100% foretriangle.|
|Sail Area/∇2⁄3||19.11||15 - 22 for practically all yachts, with a mean of 19. Higher values indicate emphasis on light-weather performance|
|Ballast/Displ.||41%||Generally sailboats of this type are between 35% and 45%.|
|Dynamic Stability Factor||41.3||ISO Ocean is >40, which means she just sneaks in to Ocean, but we class her as Offshore.|
|Deck Edge Immersion||About 45º||Not a ratio - but useful to know.|