Office of Marine Safety

Stability and FloodingStability and Flooding

Eric Stolzenberg

Presentation OverviewPresentation Overview

• Stability• Flooding progression• Impact of physical rudder loss• Effects of astern travel

Vessel ConfigurationVessel Configuration

OSV Ranger

Fishing Vessel Alaska Ranger

HoldRudderMachinery Spaces

Factory Deck

Fo’c’sle Deck

Wheelhouse

Ramp Freezers Processing Area

Trawl Deck

StabilityStability

• Stability criteria– Intact stability: capsizing– Damage stability: flooding

• Stability requirements– Necessary for vessel certification– Incorporate stability criteria

Vessel Intact StabilityVessel Intact Stability

• Owner monitored stability– Not required– Intact stability through T&S booklet– Damage stability not monitored or required

• Postaccident Coast Guard MSC review– Stability test confirmed– T&S booklet met requirements– Intact stability met requirements

Intact Stability MarginIntact Stability Margin

• Large stability margin prior to sinking• Downflooding points located aft

– Engineroom intake vents– Aft trim conditions at deeper drafts

quickly reduced the margin

Flooding ProgressionFlooding Progression

Flooding Progression — ProfileFlooding Progression — Profile

Aft Fish Bin(Freezer)

Flooding Progression — PlanFlooding Progression — Plan

Watertight Bulkhead

Watertight Bulkheads

Flooding Rate VerificationFlooding Rate Verification

• Coast Guard scenarios– Estimate 5 minutes to flood rudder room– Estimate 50 minutes for water to reach

switchboard

• Electrical switchboard– Will short if flooded– Vessel loses electrical power

• Loss of rudder flooding rate roughly corresponds to event timeline

RudderRudder

Upper Rudder Assembly

Lock Nut

Starboard Rudder

Hull

Thrust Bearing

Rudder Stock

Vessel Traveling AsternVessel Traveling Astern

• Exacerbated flooding– Increased rate– Decreased distance to downflooding

points– Increased pressure on hatches and

doors• Prevented crew from entering liferafts

Stability and Flooding SummaryStability and Flooding Summary• Vessel had adequate intact stability• Most likely encountered rudder loss• Would not have sunk if flooding contained

to rudder room• Sank from uncontrolled progressive

flooding• Astern travel accelerated flooding

Office of Marine Safety

Propulsion SystemPropulsion System

Eric Stolzenberg

Presentation OverviewPresentation Overview

• Causes of astern travel• Propulsion system overview• Propulsion system modification• Means to stop travel

CPP System OverviewCPP System Overview

Propulsion System LayoutPropulsion System Layout

Port main engine

Stbd main engine

Gear

GearPropulsion Shaft

Propulsion Shaft

Propeller

Propeller

Hydraulic pumps

Main Switchboard

Spindle Torque ForcesSpindle Torque Forces

Hydrodynamic Lift

Centrifugal Force

HubRotation

SpindleAxis

Net Spindle Torque

ASTERN

Rolls-Royce

CPP HubCPP Hub

Rolls-Royce

CPP System ModificationsCPP System Modifications

Main Switchboard

Stbd CPP Hydraulic Pumps

Port CPP Hydraulic Pumps

Stbd EnginePort Engine

Consequences of ModificationsConsequences of Modifications

Port PropellerStbd Propeller

Astern Travel SummaryAstern Travel Summary• Causes

– CPP pump modifications affected system redundancy

– Astern travel resulted from electrical power loss

– Engines were still turning propeller shafts• Stopping astern travel

– No means to control blade pitch– Crew could have secured engines to stop

shaft