1 Stability criteria in the intact condition

A multihull craft, in the intact condition, should have sufficient stability when rolling in a seaway to successfully withstand the effect of either passenger crowding or high speed turning as described in 1.4. The craft's stability should be considered to be sufficient provided compliance with this paragraph is achieved.

1.1 Area under the GZ curve

The area (A1) under the GZ curve up to an angle Θ should be at least:

A1 = 0.055 x 30°/Θ (m.rad)

where:

Θ is the least of the following angles:

.1 the downflooding angle:
.2 the angle at which the maximum GZ occurs: and
.3 30°.

1.2 Maximum GZ

The maximum GZ value should occur at an angle of at least 10°.

1.3 Heeling due to wind

The wind heeling lever should be assumed constant at all angles of inclination and should be calculated as follows:

	(m)	(see figure 1)
	(m)	(see figure 1)

Figure 1 Intact stability

where:

P_i ^footnote	=	500 (Pa)
A	=	projected lateral area of the portion of the ship above the lightest service waterline (m²)
Z	=	vertical distance from the centre of A to a point one half the lightest service draught (m)
Δ	=	displacement (t)

1.4 Heeling due to passenger crowding or high speed turning

Heeling due to the crowding of passengers on one side of the craft or to high speed turning, whichever is the greater should be applied in combination with the heeling lever due to wind (HL2).

.1 Heeling due to passenger crowding

When calculating the magnitude of the heel due to passenger crowding, a passenger crowding lever should be developed using the assumptions stipulated in 2.10 of this Code.

.2 Heeling due to high speed turning

When calculating the magnitude of the heel due to the effects of high speed turning, a high speed turning lever should be developed using the following formula:

where:

TL	=	turning lever (m)
Vo	=	speed of craft in the turn (m/s)
R	=	turning radius (m)
KG	=	height of vertical centre of gravity above keel (m)
d	=	mean draught (m)

1.5 Rolling in waves

The effect of rolling in a seaway upon the craft's stability should be demonstrated mathematically. In doing so, the residual area under the GZ curve (A2), i.e. beyond the angle of heel (Θh), should be at least equal to 0.028 m.rad up to the angle of roll Θr. In the absence of model test or other data Θr should be taken as 15° or an angle of (Θd - Θh), whichever is less.