PORT and Harbor Engineering

Radianta TriatmadjaLecture note 2

Waterway Design

Depth of Waterway

Waterway Design

The depth of waterway depends on the tonnage of the ship and the water.

Following Bernoulli law, the amount of water displaced by the ship equals the weight of the ship. Therefore the more is the tonnage, the deeper is the ship’s draft.

Ships’ draft also depends on the cross section of the ship.

Draft

draft draft50 000 ton 50 000 ton

Ships of the same total weight may have different drafts.

Draft

• Box Coefficient

draft draft50 000 ton 50 000 ton

= Cb

Cb =0.8Cb =0.6

Draft

• Box Coefficient

draft draft50 000 ton 50 000 ton

= Cb

Cb =0.5Cb =0.67

Tonnage

• Displacement tonnage : The weight of water displaced, the physical weight of the ship

• Loaded Displacement : the weight of the ships + loading

• Light displacement : the weight of the ships only

Tonnage

• Dead weight ton : The difference between loaded displacement and light displacement, or the weight of loading (please do not confuse this tonnage with the weight of the ships)

• The weight of fresh water, tools, and fuel are considered as loading

Tonnage

• Gross Registered ton (use for Passenger ships)

Volume of ships space in cubic feet divided by 100

• 1 GRT ~ 2.83 m3

Tonnage

• Net Register Ton (use for Passenger ships)

• Volume of ships (GRT) minus all non earning spaces (machine, bunker, tank, room for staff, tool room, radio and map room, storage room )

Typical ships full load draft of Bulk carrier

Weight (1000 tons) Draft (m)20.99 9.576422.934 10.513823.67 10.235223.96 10.235224.911 9.956626.055 8.056427.48 10.260634.586 10.513835.316 10.969444.477 11.755246.73 12.008448.976 11.527450.055 11.55250.692 11.55252.458 12.059256.672 12.210860.639 12.895

170.418 18.9242

y = 2.1393Ln(x) + 3.6789R2 = 0.9906

0

2

4

6

8

10

12

14

0 10 20 30 40 50 60

Weight (1000 tons) Draft (m)1 4.22 4.95 6.810 8.515 9.320 1030 10.940 11.750 12.4

y = 3.965Ln(x) - 3.1657R2 = 0.8525

02468

101214161820

0 50 100 150 200

Typical tonnage and full load draft of bulk carriers (ore, coal, cement etc)

Dra

ft (lo

aded

)

Dead weight (tons)

Passenger Ships

y = 1.9623Ln(x) + 2.7951R2 = 0.9546

y = 1.6041Ln(x) + 2.6762R2 = 0.9807

0

2

4

6

8

10

12

0 5 10 15 20 25 30 35

Depth required / draft = 1.14

Basin depth for unknown full draft

General Cargo

Weight (x1000) draft depth1 4.2 52 4.9 5.55 6.8 7.58 8 910 8.5 1015 9.3 1130 10.9 1240 11.7 1350 12.4 14

y = 2.3647Ln(x) + 4.308R2 = 0.9807

y = 2.1454Ln(x) + 3.6605R2 = 0.9903

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50 60

Depth/draft =1.14

Depth required 14% more than the draft

Basin depth for unknown full draft

Container Ships

y = 0.08x + 9.1R2 = 0.9877

y = 0.1x + 10R2 = 1

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50 60

Weight (x1000) draft depth20 10.6 12 1.13207530 11.6 13 1.1206940 12.4 14 1.12903250 13 15 1.153846

Depth/draft= 1.13

Basin depth for unknown full draft

Depth of waterway

• The depth of waterway should be deeper than the basin. Provisions should be made for possible pitching, heaving and squat

• Squat Z

2

2

21

4.2F

FL

Zpp

Additional depth due to

• Vertical movement due to wave (heaving)• Vertical movement due to Squat• Vertical movement due to pitching

Required Water depth

Expected vertical movement

Net underkeel clearance

dredging tolerance

Draft (ship size)

Expected sediment accumulation between two dredging campaigns

To b

e dr

edge

d

Sounding tolerance

Keel = bottom

Gross underkeel clearance

How to design waterway depth?

• Define Maximum Ships weight and type• Calculate/predict Ships draft • Define minimum water level• Calculate depth Required (1.15 times

Ships draft) (nominal depth)• Calculate expected sediment

accumulation during two consecutive dredging works

• Calculate total depth required to dredge

What is minimum water level ?

• Sea level is fluctuating due to moon and sun attraction forces and centrifugal forces of the earth during its revolution about its common axis with the moon

• This fluctuation is called tides• Maximum fluctuation occur during spring

tide, while minimum fluctuation occur during neap tide.

Tidal constants

• Tidal waves are periodic due to the driving forces. Yet so many conditions affect the periodicity of the tidal waves. A complete period of tide wave is approximately 19 years. In order to design a harbor one need to know tidal constants in the design area. These tidal constants govern the major water level fluctuations.

Tidal constants

n

ii

ii T

tA1

2cos

40.Air Pelayaran Sebelah Barat Surabaya (Karang Jamuang)

0

4

8

12

16

20

24

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Time

Elev

asi

An Example of Water level Fluctuation

hours

dm

NeapSpring

Discussion• A Harbor designed is given to be discussed. Topics to be

discussed are :2. What is the maximum size of ships that can be served3. The width of the waterway4. During spring tide even larger ships can enter the harbor. What

is the maximum size of the ships during spring tide? Discuss the possibility of allowing such ships to berth in the harbor

5. If the speed of your ships are limited to 10 knots along the waterway, what is the maximum squat ?

6. Do you have any comment other than the topics discussed ?7. Within the next 10 years the harbor will be upgraded to serve

ships of maximum draft 4 meters. What works are needed?