Slide 1

ENHANCING SAFETY

UNDERSTANDING

UNDERKEEL CLEARANCE

Captain Jonathon PearceBusiness Development Manager

VIII Foro Latino Americano de Practicos

Cancun, 2015

Slide 2

The GuidelinesThe Design and Use

Component

Slide 3

PIANC WG 49Harbour Approach Channels

Design Guidelines

Slide 4 Channel Depth factors

2.1

Slide 5 Manoeuvrability Margin (MM)

“Therefore, only motions which affect the lowest average position of the

bottom of the ship need be taken into consideration in the calculation of

MM (= depth – draught – squat – heel). For this reason, it is an

independent check which should always apply in channel design (and

operation)”

“this check of MM is separate from calculations of Gross UKC that

includes the wave response allowance”

Ship factors include … (f) Net UKC. Separately, a manoeuvrability margin is

checked such that a minimum clearance under the ship (between the

seabed level and the lowest average position of the ship) is provided

The limiting value of MM depends on ship type, channel dimensions and

alignment, and ship traffic (including whether one-way or two-way).

A minimum value of 5% of draught or 0.6 m, whichever is greater, has

been found to provide adequate MM for most ship sizes, types, and

channels.

Slide 6 Muddy Channel - Nautical Bottom

Approach

(PIANC WG30) defined the nautical bottom as “the level where

physical characteristics of the bottom reach a critical limit beyond

which contact with a ship’s keel causes either damage or

unacceptable effects on controllability and manoeuvrability.”

This guideline is

implemented

through full

analysis and

complemented

by pilot

experience of

actual ship

handling.

Slide 7

The PortThe Workplace

Component

Slide 8 Bathymetry

High Density Bathymetry

Slide 9 Bathy Nodes

DUKC®

Bathymetry

Nodes

Dividing the channel

into sections for

accurate analysis

Slide 10 Channel Segment

14.8m BC

Declared Depth

15.7m Max

Channel Section

300m to channel boundary

100m segment

MM 15.0m for 300m x 100m section

Channel Boundary

Scale exaggerated by 25x for emphasis

Slide 11 Overlays – PPU Chart

Overlays

High resolution sounded

depths

Minimum

depth

10m x 10m

overlay grid

DUKC®

Bathymetry

Nodes

Compare DUKC® minimum

keel elevation to overlay grid

cell depth

Methodology High-resolution bathymetry of

transit area

Create 2D Grid overlay (10m x 10m)

Compute DUKC® predictions of

minimum keel elevations

In each grid cell compare the

(nearest adjacent) predicted keel

elevation with the depth at this

location

Mark each grid cell as “pass” or

“fail” (go/no go)

Produce real-time overlay (Web)

Promulgate overlay to users

ECDIS/PPU

Slide 12 Hydrodynamic model

Slide 13 Tidal Datums

Slide 14 Complex Tidal Regimes

12:00 18:00 00:00 06:00 12:00-1.5

-1

-0.5

0

0.5

1

1.5

Wate

r level relative to A

HD [m]

Recorded water level across Prince of Wales Channel 15/16 May 2007

booby

goods

hammond

nardana

ince

Slide 15

Turning Points

Residuals Lags

Predictions

Measurements

Tidal Residuals

Slide 16 Predicted UKCM Tidal Plane

Slide 17

VesselsThe Economic

Component

Slide 18 Ship Size

Slide 19 Theory – Stability

Slide 20 Ship Motions Unique to each Vessel

Slide 21 Calculating Ship Motions

Slide 22 Vessel Spectra

Slide 23

Wave TheoryThe Enviroment

Component

Slide 24

Waves

Slide 25 Idealised wave spectrum

Slide 26 The AWAC

Acoustic Wave and Current bottom-mounted

measurement device

Wave Measurement

AWAC is designed to measure wind/swell

waves

0.5-30 second period

Slide 27 WaMoS radar images

Slide 28 Wave theory – Wave period and height

• Wave period relates to wave length.

• Commonly used wave periods:– Tp: Peak period

– Tz: Zero-crossing period

– Tm: Mean period (=average)

• Significant Wave Height Hs

• Stands for significant wave height.

• Corresponds well to visual estimate of wave heights.

• Average of largest one third of waves over a certain period of time.

• Also known as H1/3

Slide 29 Wave Spectra

• A statistical representation of a stationary sea

state

0.0

2.0

4.0

6.0

8.0

1 0.0

1 2.0

0.0 0 0.0 5 0.1 0 0.1 5 0.2 0 0.2 5 0.3 0

F requency [Hz]

Wa

ve

en

erg

y [m

2/H

z]

20 s 10 s 5 s 4 s6.7 s 3.3 s

peak

TP

FFT rapidly converts a time series

signal to a representation in the

frequency domain, a spectra

Units are m2/hz v hz, convert

spectral density to m by integrating

hence related to area under the

curve

Parameters\ specifically

Spectral density can be interpreted

as the total variation or variance of

sea-surface elevations over

frequencies

Also equals 4 x SD: standard

deviation of sea surface elevations

Hmo is typically 5-10% larger than

Hs by Longuet-Higgins 1980

Sea swell split often picked at

around 8s when deriving wave

paramters from spectra, strictly

speaking..