Section 2 Pressure Adjusting Factors

201. General

Final design pressure is adjusted by a set etc.

of factors according to design, craft type and location,

202. Design category factor, ÝǼÆ

The design category factor ÝǼÆ , defined in loads due to sea with design category.

Table 4.1, takes into account the variation of pressure

Table 4.1 Values of ÝǼÆ

according to design category

203 Dynamic load factor,

1. General

The dynamic load factor

ŸÆĂ

ŸÆĂ

is considered to be close to the single amplitude acceleration meas-

ured at the craft centre of gravity at the relevant frequency for a certain period of time. This fac-

tor is the negative acceleration supported by the craft, either while slamming in an encountered

wave at speed or falling from the crest of a wave into its trough. g is the acceleration due to gravity (9.81 mĤsË).

ŸÆĂ

is expressed in gs where 1

2. Dynamic load factor

ŸÆĂ for planing non-sailing craft in planing mode

The dynamic load factor for planing craft running in planing mode shall be determined from Equation (1) or Equation (2).

ÄBÄ

à Ë× A Ë

Æ

Æ

ŸẄX G ŊĦĖËF JËŊ ×A Ğ ŊĦŊĒĖF×FÈŊGØŊĦĖF× ŶJ

ÄǼÆ

(1)

where,

V : for non-sailing craft, the maximum speed in calm water declared by the manufacturer, with

the craft in ŶÄǼÆ conditions. This speed shall not be taken as <

ËĦĖÈĬJÄBÄ .

AÆ : the chine beam, measured at

12215-5 Fig 1)

ŊĦĖĬJÄ BÄ

forward of its aft end, in metres (See ISO

ØŊĦĖ : the deadrise angle at

ŊĦĖĬJÄ BÄ

forward of its aft end (See ISO 12215-5 Fig 1), not to be

taken < 10°, nor > 30°, in degrees,

Where Equation (1) gives an Where Equation (1) gives an used.

ŸÆĂ value ≤ 3.0, the value given by Equation (1) shall be used.

ŸÆĂ value > 3.0, that value or the value from Equation (2) shall be

Ÿ ŊĦÈ×à (2)

ÆĂ G JĦËĒŊ

ŶÄǼÆ

In any case,

ŸÆĂ need not be taken > 7.

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3. Dynamic load factor ŸÆĂ for sailing craft and displacement non-sailing craft

For sailing craft, ŸÆĂ

is not used for pressure determination. It is only used in the calculation of

ÝÄ for which purpose the value of

ŸÆĂ

shall be taken as 3. For non-sailing craft where ŸÆĂ, de-

termined using Equation (1), is < 3.0 from Equation (1), a value of 3.0 shall still be used for cal-

culation of ÝÄ .

4. Longitudinal pressure distribution factor ÝÄ

The longitudinal pressure distribution factor ÝÄ takes into account the variation of pressure loads due to location on the craft. It shall be taken from Fig 4.2 or calculated from Equation (3).

ÝÄ is a function of the dynamic load factor defined below for non-sailing craft.

ËG ŊĦËÈĒ× ŸÆĂ Ż Ż

ÝÄ G JŊĦÈ

JÄ Ğ ŊĦËÈĒ × ŸÆĂ but not taken > 1 for JÄ

≤ŊĦÈ (3)

ÝÄ G Ë for

Ż JÄBÄ

BÄ BÄ

IŊĦÈ

where

ŸÆĂ is determined in accordance with 1 to 3, but for the purposes of determination of ÝÄ , shall not be taken < 3 nor > 6;

ŸÆĂ

Ż JÄBÄ

is the position of the centre of the panel or middle of stiffener analysed proportional to

Ż

ÄBÄ, where

JÄBÄ

= 0 and 1 are respectively the aft end and fore end of ÄBÄ.

where

Ż is the longitudinal position of the centre of the panel or middle of stiffener forward of

aft end of

ÄBÄ in

ŶÄǼÆ

conditions, in metres.

The overhangs waterline.

fore and aft shall have the same value of ÝÄ as their respective end of the

Fig 4.2 Longitudinal pressure distribution factor ÝÄ

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204. Area pressure reduction factor

1. General

The area pressure reduction factor panel or stiffener size.

ÝAĄ

ÝAĄ

takes into account the variation of pressure loads due to

ÝĄ × ŊĦË× ŶÄǼÆ Ŋ

Ǽ

ÝAĄ G JA ŊĦĖ

ĦËÈ

(4)

where

ÝĄ is the structural component and craft type factor:

ÝĄ G ËĦŊ

for bottom side and deck panels and stiffeners of planing non-sailing craft operating in planing mode;

ÝĄ G ËĦÈ G

G Ė

Ė× ËŊ × Ẅ

for bottom side and deck panels of sailing craft, displacement non- sailing craft and planing non-sailing craft operating in displace- ment mode;

ÝĄ G Ë G Ë×

G Ė

ËŊ ×ŶŹ

for bottom side and deck stiffeners of sailing craft, displacement

non-sailing craft and planing non-sailing craft operating in ment mode;

AǼ is the design area, in square metres:

AǼ G FŶ× ẄF × ËŊG È for plating, but shall not be taken > ËĦÈ× ẄË × ËŊG È;

G È Ë G È

displace-

AǼ G FŶŹ ×ZF × ËŊ

for stiffeners but need not be taken < ŊĦĖĖ × ŶŹ × ËŊ ;

Ẅ is the shorter dimension of the panel, in millimetres; Ŷ is the longer dimension of the panel, in millimetres; Z is the stiffener spacing, in millimetres;

ŶŹ is the unsupported span of a stiffener, in millimetres.

2. Maximum and minimum value of ÝAĄ

ÝAĄ

shall not be taken > 1 and at less than the values given in Table 4.2.

Table 4.2 Minimum values of ÝAĄ

J

ÄBÄ BÄ

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205. Hull side pressure reduction factor ÝC

The side pressure reduction factor ÝC interpolates the pressure of the hull side between the (bottom) pressure at waterline and deck pressure at the top edge (see Fig 4.1).

C G Y (5)

ÝC G JC

where

C

Y

is the height of top of hull or hull/deck limit above the fully loaded waterline, in metres;

is the height of centre of panel or middle of stiffener above the fully loaded waterline, in metres.

206. Superstructure and deckhouse pressure reduction factor ÝÅÃĀ

The superstructure and deckhouse pressure reduction factor craft type by Table 4.3.

ÝÅÃĀ

is defined according to location and

Table 4.3 Values of

ÝÅÃĀ for superstructures and deckhouses

207. Light and stable sailing craft pressure correcting factor for slamming ÝÅÄÅ

The light and stable sailing craft pressure correcting factor

ÝÅÄÅ

takes into account higher slamming

pressures encountered on light and stable sailing craft when sailing upwind (i.e at an angle of up

to 90° off true wind). It is defined below.

- In design category C and D:

- In design category A and B:

ÝÅÄÅ G Ë

Ė

- ÝÅÄÅ G Ë if ŶÄǼÆ I ÈÄBÄ

- ÝÅÄÅ G

Ļ ËŊĂCÀAB Ĥ ÈŊ × ÄBÄ ŊĦÈ ŁŊĦÈ JĦĖĖ ŶÄǼÆ Ŋ

if ŶÄǼÆ ≤ ÈÄBÄ Ė

but shall not be taken < 1 (6)

where

ĂCÀAB Ĥ ÈŊ

is the maximum righting moment lever taken at a heel angle not > 60°, with all stability

increasing deĿ vices such as cantinM g keels or water ballast at their most effective position, in fully loaded condition, measured in metres.

If the maximum righting lever occurs at a heel angle > 60°, the value at 60° shall be taken. The crew shall be considered in upwind hiking position in the calculation of the above ĂCÀAB Ĥ ÈŊ .

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