CB/T 3837-1998
Technological Requirements for Ship Upgrading or
Launching Relying on Air-Bags
Scope
The present standard prescribes
the requirements
on ship launching
or upgrading
by
means of air-bags and the relevant equipments;
the requirements
on launching procedure,
falling down from docking biock, shifting of ship and the safety measures for launching and
upgrading etc.
The present standard is applicable to launching and upgrading of ship relying on air-bags,
2 Reference standards
The articles of the follO\ving standard, if once quoted by the present standard, shall
constitute a pm1 of it and be in full effect at the time of issuing. All the standards can be
revised and all the parties that use the present standard should discuss how to use the latest
edition of the following standards:
CBIT 3795-1996
Air bag for ship up to or down to launching way
3 The requirements of launching ship and relevant equipment
3.1
Ship
3.1. I The engineering
work under waterline
shall wholly be finished,
especially
those
equipments,
valves and others that are to be installed at the openings under ship waterline.
The installation should be approved by inspection.
3.1.2 An the burrs, welding beading and the like on the ship bottom or appendages should be
ground away.
3.1.3 All the welds on the shell plate ( i.e. nevv' welds for the ship repaired ) must pass
inspection and tightness test.
3.1.4 The main dimensions of the ship should be measured up and the mark of load line must
pass inspection.
3.1.5 All the paint work of the shell plate has been finished.
3.2
Rampway
3.2.1 The ramp way on which the air-bags will rolling should be cleaned and be dear of sharp
ends such as iron nail.
3.2.2 The ramp way should be leveled and the level error from left to right should be less than
80 mm. The ground caved in should be filled up and the ground bearing capacity should be
relatively equalized.
3.2.3 The ramp way may be of mud land, sanded land, sands or concrete, however, its bearing
capacity should be twice as big as the working pressure of air-bags.
3.2.4 The slope of ramp is to be determined according to the size of the launching ship and is
generally no bigger than 1/7. In the range of the whole length of the ramp way, the shape may
be of multiple combination with slope line, arc line and others. However, the ship bottom
shouldn't contact the ground even when the air-bags are at their lowest working height.
3.2.5 The ramp way should extend into water for certain length.
3.3
Air-bag
3.3.1 Air-bags should pass the inspection according to the regulations of CBIT 3795. They
have to take no load airfilIing test every time before it is used to
launch or to upgrade a ship.
The test pressure of filling air should be 1.25 times of working pressure of the con-esponding
diameter.
3.3.2 For conventional ships the quantity of rolling air-bags can be calculated by formula (1):
where: N is the quantity of roIling air-bag. in pieces;
Kl is constant, Kl = 1.2---1.3;
Q is the weight of launching ship, t:
g is acceleration of gravity, mls2;
Cb is the block coefficient of launching ship;
R is the allowable bearing force per meter of air-bag length, kNlm, see table 3 in the
standard CBIT 3795-1996;
Ld is the contact length between ship bottom and air-bag body at the midship section,
m;
Nl is the quantity of air-bag replaced continuously, in pieces; normally it takes 2~4
pIeces.
3.3.3 The center distance of two neighbouring air-bags should meet the needs of .structural
hull strength, and avoiding overlapping of rolling air-bags as well. As a rule, the center
distance may be checked by using formula (2) and (3):
where: L is the length of launching ship, m;
N is the quantity of rolling air-bag, in pieces~
D is the nominal diameter of rolling air-bag, m.
For ship with fine ends, the counting length L is the length overall subtracted by the
length of fine ends that are unsuitable for cushioning with air-bags. If the ship has special
needs on structural hull strength, the center distance between two neighbouring air-bags may
be arranged according to the actual conditions.
3.4 Winch
3.4.1 In general, a slo"v winch is to be selected, its veering speed is about 9---13m1min.
3.4.2 The slip force of launching ship and the hauling force of winch wire are shown in figure
1 and can be calculated by formula (4) and (5):