The stability of multihull sailing vessels over 6m in length
should be assessed using ISO 12217 - Part 2, which includes a requirement
that the vessel shall float after an inversion without the benefit
of any trapped air pockets other than dedicated air tanks or watertight
compartments. Vessels under 6m are to be specially considered by the
Administration.
11.10.1 A multihull vessel should be provided
with a Stability Information Booklet based on the Administration's
model booklet, giving details of the maximum advised mean apparent
windspeeds for each expected combination of sails that may be set,
as derived from ISO 12217 - 'Part 2 - Small craft - Sailing and buoyancy
assessment and Categorisation sailing boats of hull length greater
than or equal to 6 metres'. These wind speeds should be presented
in knots, and be accompanied by the note, "In following winds, the
tabulated safe wind speed for each sail combination should be reduced
by the boat speed".
11.10.2 For the purposes of the application of
ISO 12217 to coded vessels, the maximum safe wind speed shall be taken
as the lesser of the values calculated by the formulae below, instead
of those given in G.1 of the ISO standard. Both pitch and roll moments
shall be calculated for all vessels.
or
where
|
vW
|
= |
maximum safe apparent wind speed (knots) |
|
LMR
|
= |
limiting restoring moment in roll (newton-metres) |
|
LMP
|
= |
limiting restoring moment in pitch (newton-metres) |
|
A'S
|
= |
area of sails set including mast and boom (square metres) |
|
h
|
= |
height
between the geometric centre of area of A's and the below-water
profile of the hull, with centre/dagger boards lowered and the boat
upright (metres)
|
|
ΦR
|
= |
heel angle at maximum roll righting moment (in conjunction with LMR
)
|
|
ΦP
|
= |
limiting pitch angle used when calculating LMP (in
conjunction with LMP
)
|
|
AD
|
= |
plan area of the hulls and deck (square metres) |
|
b
|
= |
distance
from centroid of AD
to the centreline of the
leeward hull
|
Derivation of the maximum advised apparent windspeeds, and the
Stability Information Booklet, is to be submitted to the Certifying
Authority for approval. Evidence should be provided as to the derivation
of the stability data.
The permitted area of operation
should be determined with reference to the following table, including
the maximum safe apparent wind speed with no sails set (bare poles
condition):-
|
Permitted Area of Operation
|
MCA Code Category
|
ISO 12217 Design Category
|
"Bare Poles" safe wind speed should exceed
|
| Unrestricted
|
0
|
A
|
36 knots
|
| Up to 150 miles from a safe
haven
|
1
|
A
|
36 knots
|
| Up to 60 miles from a safe
haven
|
2
|
B
|
32 knots
|
| Up to 20 miles from a safe
haven
|
3
|
B
|
28 knots
|
| Up to 20 miles from a safe haven in
favourable weather and daylight
|
4
|
C
|
25 knots
|
| Up to 20 miles from a nominated
departure point in favourable weather and daylight
|
5
|
C
|
25 knots
|
| Up to 3 miles from a nominated
departure point in favourable weather and daylight
|
6
|
C
|
25 knots
|
11.10.3 Trimarans operating in Areas 0 or 1 shall
have sidehulls each having a total buoyant volume of at least 200%
of the displacement volume in the fully loaded condition. Trimarans
operating in Area 2 shall have sidehulls each having a total buoyant
volume of at least 150% of the displacement volume in the fully loaded
condition.