28 Eng. Guideline on Special requirements for dredging materials

Special requirements for dredging materials

 

1 Conditions to be fulfilled for assignment

1 - Conditions to be fulfilled for assignment of a freeboard which is less than the statutory minimum freeboard

1.1.1 The regulations are applicable to hopper dredgers, i.e. ships fitted with bottom doors, or to ships having similar means by which the cargo can be speedily dumped, e.g. split-barges.

1.1.2 Operational limits:

1. Restricted zone, normally not exceeding 15 nautical miles from the harbour, or occasionally along the coast if this zone does not impair with the restricted zone "15 miles from a harbour".
   
   
2. A greater navigation zone, e.g. parts of the North Sea.
   Reduced freeboards are not permitted on an international voyage. 
   
   

1.2 - Freeboard less than statutory minimum freeboard in the navigation zone mentioned in 1.1.2 (a).

1.2.1 The freeboard may be reduced to ½ (table B).

1.2.2 For ships of over 100 metres in length the freeboard may be reduced to ½  (Table B-60) or ½ (Table B-100).

In the latter case the damage calculations required by ILLC 1966 have to be carried out for the ship with statutory minimum freeboard.

1.2.3 The bottom doors should be operable from the bridge even when the main source of power fails.
The bottom doors should be positively activated.

1.2.4 The cargo releasing arrangement should operate within 1 minute after being activated.

The bottom doors should be opened completely within 3 minutes, this means that the time necessary from the start until bottom doors completely opened, should not exceed 4 minutes.

If the main source of power fails, the emergency source of power should be sufficient for operating the release arrangement within 15 minutes instead of 4 minutes.

1.2.5 In addition to 1.2.4, the cargo release arrangements on ships assigned a freeboard of ½ (Table B-60) or ½  (Table B-100) should be capable of jettisoning sufficient cargo within 4 minutes to enable the requirements of 1.2.2 (damage calculations) to be complied with.

If the main source of power fails, the emergency source of power should be sufficient to fulfil the requirement within 15 minutes.

A loading trial at sea will be required to prove the efficiency of the arrangements provided for the jettisoning of the cargo within the required time.

1.2.8 The strength of the ship should be shown to be adequate at the draught associated with the decreased freeboard.

For the stability of the ship, see 3.

1.2.11 A draught indicator should be fitted on the bridge, indicating the draughts amidships and at the draught marks.

1.2.13 The weather conditions will be specially considered in each case and will depend of the size of the ship, class-notation, bow-height, a.s.o..

1.3 - Freeboard less than statutory minimum freeboard in the navigation zone mentioned in 1.1.2. (b).

1.3.1 For ships of over 75 metres in length and operating in the navigation zone mentioned in 1.1.2 (b), the freeboard may be reduced to ½  (Table B).

For ships of over 100 metres in length the freeboard may be reduced to ½  (Table B-60) or (Table B-100).

1.3.2 The ship should comply with the requirements of 1.2.2 - 1.2.14 inclusive.

1.4 - International Load Line Certificate and International Load Line Exemption Certificate.

B = assigned reduced freeboard
BZW = fresh water freeboard

 

2 General requirements

2 - General requirements concerning covers on sea-inletchests and bilge arrangements

3 Stability requirements

3 - Stability requirements

3.1 The stability calculations are to be carried out for hopper dredgers, etc, engaged in the transport of sand and gravel.
The following calculations are not applicable when the cargo consists of stones.

The calculation method is based on the calculation of cross-curves of stability (KN-levers) for the ship assuming that the hopper is closed, at the top as well as cross-curves of stability for the hopper itself also assuming that the hopper is closed at the top.

3.2 Definitions

	=	specific gravity of the cargo in t/m3;
	=	resulting righting lever in m.;
	=	righting lever for liquid cargo in m.;
	=	righting lever for solid cargo in m.

3.3 Required righting levers (static stability arms).

3.3.1 The stability calculations are generally to be carried out for cargoes with specific gravities between 1.00 t/m³ and 2.2 t/m³.
In all cases the displacement of the ship in the upright position shall be equal to the maximum displacement with the cargo space completely filled or equal to the displacement, corresponding with the assigned reduced working freeboard, whichever is the least.
Depending of the shape of the cargo space it may be necessary to investigate the stability of the ship in the early stages of loading.

3.3.2

1. If the specific gravity of the cargo (average value) is equal to or less than 1.4 t/m³, then the righting levers are to be calculated assuming that the cargo is in a fluid state,
   thus:
   
   
2. If the specific gravity of the cargo is greater than 1.4 t/m³, but less than 2.0 t/m³, then the righting levers are to be calculated as follows:
   
   
   
   
3. If the specific gravity of the cargo (average value) is equal to or greater than 2.0 t/m³, then the righting levers are to be calculated as follows:
   
   
   
   

3.3.3 The intact stability characteristics of the ship shall be shown to meet at least the following criteria after taking into account in the manner described in 3.3.2 (a), (b) or (c) the effect of the free surface of the cargo:

1. the righting lever shall be at least 0.20 metre between the angles of heel of 25 degrees and 35 degrees;
   
   
2. the vanishing angle shall be at least 50 degrees.

3.3.4 Ships operating with hold spaces open.
For liquid cargoes the spillage of saturated cargo and water overboard as well as the penetrating of water into the cargo space shall be taken into account.
The cargo surface shall be assumed to remain horizontal (i.e. parallel to the sea level) and to be touching the top of the hatch coaming; spillways are not to be taken into account.

3.3.5 For cargoes of high density where the spoil level does not reach the top of the hopper coaming (at maximum draught), penetrating of water should be taken into account.
In that case a layer of water should be assumed on top of the spoil in the hopper up to the upper edge of the hopper coaming.

In that final condition the maximum allowable draught should not be exceeded.

The influence of a layer of water can be neglected if the dimensions of the spillways are sufficient to discharge the total amount of water within 15 minutes.

If the hopper is only partly filled penetration of water should be taken into account when calculating the righting levers when assuming that the cargo is in solid state.

3.3.6 ships operating with hold spaces closed.
Spill out of cargo and/or penetrating of water is not to be taken into account.

3.3.7 In a ship fitted with bottom doors at either side of the ship the heeling effect, should the doors on one side fail to open, shall be calculated as follows:

1. the ship is assumed to be loaded to the load waterline corresponding with the reduced working freeboard, the cargo space is assumed to be completely filled with cargo;
   
   
2.  
   1. if a centreline bulkhead is fitted in the cargo space 30 percent of the cargo at one side of the bulkhead is assumed to be discharged;
      
      
   2. if no centreline bulkhead is fitted in the cargo space 20 percent of the total cargo is assumed to be discharged at one side of the centreline of the ship;
      
      
3. in the condition of equilibrium after discharging the cargo as indicated under (ii)(a) or (ii)(b) the angle of heel shall not exceed 25 degrees and the righting lever curve shall have a minimum range of 30 degrees beyond the position of equilibrium with a maximum righting lever of at least 0.1 metre within this range.

Appendix

Appendix

1 Liquid spoil in open hoppers

1 - Calculation of stability levers with liquid spoil in open hoppers

1.1 The hydrostatic particulars and the cross-curves of stability for the ship as well as for the hopper should be calculated by means of a computer program.

1.2 Nomenclature and basic data required (See Figure A)

	=	righting lever for liquid cargo, in m;
ys	=	height of intersection of waterline and ship's centreline to baseline, in m;
yh	=	height of intersection of spoil level in hopper and ship's centreline to baseline, in m;
	=	mean specific gravity of spoil, in t/m3;
	=	height of the centre of gravity of the ship, above the baseline with stores etc., but without spoil, in m;
	=	displacement of the ship, loaded, in seawater, in t;
	=	displacement of the ship with stores etc. but wihtout liquid in het hopper, in seawater in t;
Vh	=	volume in the hopper up to spoil level, in m3;
Vw	=	volume in the hopper up to water level after the penetration of the water, in m3;
Vmax	=	maximum volume of hopper up to the top of the hopper coaming at various angles of heel, in m3;
	=	KN-lever for the ship with hopper closed, in m;
	=	KN-lever for hopper up to spoil level only, in m;
	=	KN-lever for hopper up to level of penetrated water, in m.

The cross-curves of stability (KN-levers) should be calculated, assuming that the hopper is closed at the top and that the bottom doors are closed.
Cross-curves to be calculated at 5, 10, 15, 20, 30, 40, 50 and 60 degrees.

 

1.3 The following data should be submitted in graphical form;

yh	at various angles of heel as ordinates and Vh as abscissae;
ys	at various angles of heel as ordinates and ship's volumes as abscissae (with hopper closed);
	as ordinates and Vh as abscissae
	as ordinates and ship's volumes as abscissae, and
Vmax	as ordinates and the angles of heel as abscissae

See Figures B and C.

 

1.4 Calculation of arms of statical stability (righting levers)

1.4.1 Determine if spoil will spill over the hopper coaming, i.e. if the volume of the cargo in upright position is greater than V_max for the particular angle of heel.
If not, the total displacement is not changed from that in the upright position, then proceed as indicated in 1.4.3.

If spoil will spill over the hopper coaming, proceed as indicated in 1.4.2.

1.4.2 Determine for the given V_h (=V_max) the value of y_h from the graph, Figure B.

Determine for the displacement  the value of y_s from the graph, Figure C.

If y_h> y_s, proceed as indicated in 1.4.3;

if y_h < y_s, proceed as indicated in 1.4.4.

1.4.3 Calculation of the righting levers when water will not penetrate y_h> y_s.

Determine for the given V_h the value of from the graph, Figure B.

Determine for the given the value of  from the graph, Figure C.

Then the righting lever is:

1.4.4 If y_h < y_s, water will penetrate into the hopper, then:

Determine the new value of y_s based on .
Repeat this calculation, until the difference between the assumed y_s and the calculated y_s is neglectible small, then equilibrium is reached.

Now proceed as indicated in 1.4.5.

1.4.5 Calculation of righting levers when y_h < y_s

With the values of , V_h and V_w the following data can be calculated;

 = f (), Figure C
 = f (V_h), Figure B
=  f (V_w), Figure B (identical to  = f (V_h), where V_w = V_h)

Then:

Usually y_h < y_s occurs only at large angles of heel.

2 Righting levers for hoppers wich are closed at the top

2 - Calculation of righting levers for ships with hoppers which are closed at the top.

Spill out of cargo or penetrating of water through the spillways is not to be taken into account.

The hydrostatic particulars and the cross-curves of stability should be calculated, taking into account that the hopper is closed at the top and assuming that the bottom doors are closed.

Calculation of the righting levers (see also 1.2 of the Appendix).

Determine the value of for the given  .
Determine the value of for the given V_h.

Then:

 

Figure A-1

 

 

Figure A-2

 

 

Figure A-3

 

 

Figure A-4

 

 

Figure B

 

 

Figure C

• Informatietype: Informatie voor uitvoering
• Documentsoort: Technische richtlijn
• Toegangsrechten: Extern
• Identificatie: PUC_1330_14
• Versie: 1
• Datum beschikbaarheid: 22-11-2012
• Geldigheid van: 01-11-1980
• tot en met: 31-12-2001
• Wijzigingsdatum: 24-11-2016
• Titel: 28 Eng. Guideline on Special requirements for dredging materials
• Organisatie: Inspectie Leefomgeving en Transport
• Taal: Nederlands
• Onderwerp: Veiligheid / Safety
• Hoofdtaak: Koopvaardij / Merchant Shipping
• Thema: Zeevaart / Seagoing ships / Information / National Instruments - (Informative) / Technical guidelines