Tug vessel classification and design: safety, stability and notations 30 March 2021 • 13:00-13:45 BST

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Presentation documents:Page 2: Lawren Best, Robert Allan LtdPage 11: Scott Baker, SvitzerPage 25: Kerrie Forster, The Workboat AssociationPage 53: Capt Mike Morris, United Kingdom Maritime Pilots Association

Escort Stability and IMO Tug Stability CriteriaLawren Best – Director of Design Development

Introduction and Background

1. Robert Allan Ltd. is a firm of internationally-recognized Naval Architects in Vancouver, Canada. Since 1930, we have built a reputation for innovative designs for vessels of almost all types, primarily high-performance tugs of which over 1200 tugs built to our designs

2. Presenting Escort Design Information in a Useful Manner to Operators

3. IMO Tug Stability Limit Angles

Escort Tug Stability Free Body Diagram

Overturning

Restoring

Hydrodynamic

Hydrostatic

Thruster

Presenting Design Information in a Useful Manner to Operators

1. Designers, Charterers, Owners, Class, Tug Masters are all looking for different information

2. How to inform the owner and tug master of steering and braking force values and translating these into Towing System Load Ratings (TSLR)?

3. Most critically: How to inform the tug master of the safe operational stability limits?

Escort Tug Safety Placard

• All new Robert Allan Ltd. Escort Tugs issued Escort Safety Limits Placards and designed with electronic inclinometers

• 160+ Escort Reports

generated so far and

growing weekly

IMO 2020 Tug Stability Criteria

• IMO has now implemented Tug Stability Criteria which was previously introduced by BV and adopted by LR, ABS and others

• Class harmonization of criteria through IMO is a great improvement! Adoption by individual Flag States is in progress

• Implements some of the practical elements by incorporating longitudinal position of tow points not clearly defined by previous tow stability criteria.

• As more tugs are designed under this criteria additional research is undertaken to ensure highest possible level of safety is always maintained

• Similar to Escort Stability, IMO Self-Tripping

Criteria is relative measure of righting energy

vs. heeling energy

• Robert Allan Ltd. introducing Limit Angle guidance into future designs as criteria is very dependent on downflooding angle

• ƟRLA = RAL Limit Angle. Bollard pull of future designs will be established according to this angle. The angle of downflooding in the worst-case condition must be greater than ƟRLA

• Discussions and research also underway on IMO Tow Tripping Criteria

Limit Angles for IMO Self Tripping Criteria

Area A > Area B

ƟRLA

Illustration of Dependence on Downflooding point height

• Stability criteria are calculated using Static stability calculations

• Tug heeling is highly Dynamic behavior and so there is Danger with relying on additional stability at large angles of heel to pass criteria

• Industry should not use increased DF Angle as opportunity to unsafely increase BP in tugs

Lawren BestDirector of Design DevelopmentLbest@ral.ca

In Summary:• Escort Tug Safety Placards are now industry best practice• IMO Tug Stability Criteria a definite improvement, but safety improvements possible

29 MARCH, 20211

ITS TUGTECHNOLOGY WEBINAR WEEKTHE OPERATOR’S PERSPECTIVE

29 MARCH, 2021

THE 30-YEAR LIFECYCLE REQUIREMENTS OF THE NEXT GENERATION OF TUGS

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THANK YOU

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The 30-year lifecycle requirements of the next generation of tugs

Key design innovations for harbour and coastal towage

Designing seafarer-centric tugs

How many different work scopes are there in towage?

How many different (grouped) types of tugs are there?

What are the synergies?

Examples outside of our industry

What are the synergies?

Design principals

Height

Height

Height

Height

Height

Height

Every day is a new opportunity to change

Capt Mike MorrisChairmanUKMPA

•Tug design and stability - from an end users' perspective.

What do Ships Pilots want from a Tug ?

POWER

• The power to bring a ship up within a short time in order to prevent an incident.

• Power to arrest the ship in cases

where the engine is stuck ahead

(Milano Bridge) or total engine

failure.

Manoeuvrability

• The ability to shift position relatively quickly depending on command or circumstances. ie Escort Towage

30 Year Lifecycle ?

Seafarer Centric Tugs?

•Thank you for your Attention