Weight Control

1.0 Introduction

Human intuition is a great asset; it keeps us alive. As humans, we rely on our intuitive understanding of the world, and we extend that intuition into shipbuilding. But every so often, ship science produces a concept so bizarre that our intuition breaks down. Weight control is a prime example. It defies our understanding to believe that a few extra coats of paint make a ship inoperable. All too often, what we can’t understand, we just ignore. And that is why lack of weight control is the silent killer for a ship.

2.0 Weight Consequences

BE AFRAID. To
understand weight control, we need to instinctively recognize the need for
it. I knew a passenger ship that
underwent major modifications. The owner
invested everything they had into this ship.
When it came out of the shipyard, the ship looked beautiful. And the vessel was not allowed to operate,
because improper weight control rendered the ship unstable. USCG would not allow an unstable ship to
operate. The owner had very limited
engineering solutions, since everything was already built. Even worse, they already invested their money
into a currently useless ship.

Lack of weight control can even kill a new ship. I joined project for new construction where
the owner had originally required weight control from the shipyard, which was
the right move. But the shipyard never
did their part, and the owner didn’t press the issue.

Fast forward 20 months to the end of construction. We discovered that the vessel only achieved
1/3 of its planned cargo capacity.
The ship was too heavy. Our owner
invested hundreds of millions into this ship.
Financially, they already committed to accepting that vessel. But the vessel missions were greatly
restricted, and the ship looked far less attractive as a business investment. I wouldn’t be surprised if that owner tried
to sell their new ship within the first year.

Stories like this happen more frequently than you
think. They all have a few things in
common. Weight control was ignored,
until after construction. The vessel
capabilities were seriously limited from being overweight. And very little could be done to fix the
problem after construction finished. All
the possible options were expensive, with limited effectiveness.

This emotional context is why we talk about weight
control. It isn’t about spreadsheets and
boring margins. Weight control is about
the fear of being overweight, with nothing you can do about it. That fear motivates us to control the vessel
weight.

3.0 Weight Limits

The process of ship design starts with making a guess at our
ship weight, and then refining that guess.
At the beginning of the design, we pick a hull shape and size. The hydrostatics of that shape dictate
certain limits on maximum weight and the center of gravity.

We then build inside that shape. (Figure 3‑1) We fill it with all the components required
for a ship: structure for the hull,
engines, propellers, beds, tables, paint, etc.
All these components add weight to the ship. But there are no guarantees that
construction weights match the limits of the hull shape. We need careful weight control to keep
everything within a narrow margin.

4.0 What is Weight Control

Weight control means different
things, depending on who you ask. The
offshore industry has a whole ISO standard for weight control. [2] In that context, it means specific standards
for reporting and communication.
Shipyards exercise different levels of weight control, varying with the
contract. For design offices, weight
control focuses on creating an accurate initial estimate.

Weight control starts with an
attitude more than a technique.

Create an accurate estimate of the weight
changes BEFORE starting construction.
Maintain consistent responsibility for tracking
and monitoring the evolution of the vessel weight.
Regularly check on the evolution of the vessel
weight.
1. During construction.
1. After construction, during vessel operation.
Ensure that key decision makers at all levels
recognize the importance of weight control.

The key element of this attitude
is to understand that without weight control, your ship runs very good chances
of going overweight.

4.1 Weight Estimate

Weight control starts with a weight estimate, where we
detail the weight and location of every single item on the ship. Very boring, and very important. A good weight estimate includes several
features:

Margins are added to the estimate, artificially
increasing the weight and vertical center of gravity. This provides breathing room during
construction.
Weight items should be divided and grouped into
logical structures. The estimate needs
to be organized so that anyone else can review it and determine if each item
seems reasonable.
Provide clear supporting documentation for all
weight items. Vendor information should
be readily available. Any calculations
should be easy to understand.
Revision control. The weight estimate is a living document,
frequently updated. You need a way to
track these changes.

Figure 4‑1: Example of Detailed Weight Estimate [3]

Weight estimates can also be combined with project
management techniques to track the evolution of the vessel weight during
construction. Just like a construction cost
budget, the weight estimate becomes your weight budget. Track its evolution to predict the final
weight at completion. Using these
methods, you shift from a reactive to a proactive strategy.

5.0 Conclusion

Weight control is not sexy,
but ignoring it leads to very dire consequences. Intuitively, we have a hard time believing
that little changes across the ship add up to huge penalties. That is why proper weight control needs a
champion, someone to remind us of the hidden danger. They stay vigilant to the evolving ship
weight, armed with their weight estimate.
It sounds overly dramatic, because weight control is not about the
process. Instead, focus on the
risk. Think of the consequences if we
ignore weight control: a potentially
unusable ship.

6.0 References

[1]	EES Shipping PTY LTD, “Disaster Strikes with Overweight Containers,” EES Shipping PTY LTD, 12 Feb 2014. . Available: https://eescair.com/?p=865. .
[2]	ISO Standard, “Part 5: Weight control during engineering and construction,” in Petroleum and natural gas industries — Specific requirements for offshore structures, International Standards Organization, 2016, pp. ISO 19901-5:2016.
[3]	ShipWeight, “ShipWeight: Item Dialog Basics,” YouTube, 11 Nov 2013. . Available: https://youtu.be/LA7GhBHSSgo. .
[4]	R. L. Beach, “Service Life Weight Control for Naval Ships,” in Society of Naval Architects and Marine Engineers Southeast Section, Charleston, S.C., 6 March 1970.
[5]	US Coast Guard, “Coast Guard rescue Golden Ray 14,” Wikimedia Commons, 11 Sep 2019. . Available: https://commons.wikimedia.org/wiki/File:Coast_Guard_rescue_Golden_Ray_14.jpg. .
[6]	Wikipedia Authors, “US Navy 090807-N-0000X-001 The Office of Naval Research E-Craft, an experimental high-speed transformable hull form vessel, is under construction at Alaska Ship and Drydock in Ketchikan, Alaska,” Wikimedia Commons, 7 Nov 2009. . Available: https://commons.wikimedia.org/wiki/File:US_Navy_090807-N-0000X-001_The_Office_of_Naval_Research_E-Craft,_an_experimental_high-speed_transformable_hull_form_vessel,_is_under_construction_at_Alaska_Ship_and_Drydock_in_Ketchikan,_Alaska.jpg. .

1.0 Introduction

2.0 Weight Consequences

3.0 Weight Limits

4.0 What is Weight Control

4.1 Weight Estimate

5.0 Conclusion

6.0 References

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