How much does the ocean weigh?

Quick – how much does the ocean weigh?

Let’s say you’ve recently been spending a lot of time at home with a small child. You foolishly told them you can’t play right now because you’re busy doing important work calculating the weight of stuff. This has sparked their interest. And they won’t let go of that question.

Sigh. I don’t know how much the ocean weighs. I couldn’t even guess how many zeroes are in the number.

Or could I?

70% of the Earth’s surface is covered in ocean. I’ve watched enough nature shows to remember that’s about right. What would that surface area be? Let’s assume the Earth is a sphere (it’s not, but it’s close enough). What’s the formula for the surface area of a sphere? I don’t remember and my Weight Engineer’s Handbook is in the office. No matter – let’s assume Earth is a cube instead. I know how to find the surface area of a cube.

I know what you’re thinking – working from home with a hypothetical kid asking dumb questions all day has driven me bonkers. We can’t assume the Earth is a cube. But for this estimate we can. All I’m looking for is a number within a few orders of magnitude of reality. The difference between a sphere’s surface area and a cube’s (with the cube’s edge the same length as the sphere’s diameter) is negligible.

The surface area of a cube is six times the area of one side of height H, or 6xH². Since our cube’s height is the same as our sphere’s diameter, we need to know Earth’s diameter. Because “Apollo 13” is an awesome movie I know that a spacecraft in low Earth orbit moves about 17,500 miles per hour and takes 90 minutes to complete an orbit. That gives a circumference of 26,250 miles and a diameter of 8360 miles. Let’s call it 8,000 miles because I read somewhere that low Earth orbit is about 50 miles up, the Earth is rotating under the spacecraft and I’m kidding myself if I’m going to assume any precision in this calculation.

That gives us an ocean surface area on our Earth-cube of 70% x 6 x 8000² = 269 million square miles.

I don’t know the average depth of the ocean, but I know most of it’s deep. I’m guessing between one and ten miles because I heard “miles” and ocean depth mentioned together somewhere. Let’s say two miles deep. That gives us a total volume of 538 million cubic miles.

Every weight engineer knows the density of water – it’s 1 gram per milliliter. That’s fresh water – salty ocean water is denser, close enough. I remember it that way because I’m an expatriate Canadian and the metric system is a tenacious thing. No matter, I can convert. There are 454 grams in a pound (thanks, Canadian food packaging!), a milliliter is the same as a cubic centimeter and there are 2.54 centimeters in an inch. Put that all together and you get a water density of 0.036 lb/in³, or 9,181,017,236,653 pounds per cubic mile. Time for scientific notation: 9.2x10E12 pounds per cubic mile.

At a volume of 538 million cubic miles, our ocean weighs 4.9x10E21 pounds.

How did I do? According to the internet, “Earth’s ocean is made up of more than 20 seas and four oceans, weighing an estimated 1,450,000,000,000,000,000 short tons” – or 2.9x10E21 pounds.

There you go, kid. My estimate came within 2x the real value. That’s pretty good for starting out with no earthly idea!

This is called “Fermi approximation”, named after World War Two-era physicist Enrico Fermi, who was known for making good approximate calculations with little to no data. It’s a great way to get a quick rough guess before moving on to more precise methods.

My first boss when I was a brand new mass properties engineer used this method to devastating effect. He would send me off to spend days researching, interviewing designers and analysts, drawing sketches and running calculations to estimate the weight impact of a potential design change. When I returned, he would knock off an estimate in a few seconds that would invariably be within spitting distance of my hours of work. It was humbling, and I would ask him why he made me go to the effort. He’d say his method is quick, but now I have the data to back it up. He didn’t say it also made me a better mass properties engineer, by giving me a powerful tool to quickly understand the size of a thing, whether it’s a potential weight impact or the number of hours a task might take – or the answer to a childish question.

If you like hearing about the techniques, methods and experiences of other weight engineers, I encourage you to attend the 2020 SAWE Tech Fair, starting June 22. A wide range of technical presentations, industry seminars and training classes will be featured, all live and online, presented by your mass properties colleagues.

SAWE’s first ANSI standard has been published!

ANSI/SAWE STD M-4-2020 “Supplier Weight Control for the Marine Industry” was approved by ANSI on January 9 and will be published on January 17, 2020. It supersedes Recommended Practice M-4 (2012) “Vendor Weight Control for the Marine Industry”.

Congratulations go to Greg Roach, Terri Husley-Crawford, Andy Schuster and the Marine Industry Committee for their hard work and dedication to this task. All members of SAWE should be proud of this achievement.

With this publication the SAWE has shown it has the capability to create Voluntary Consensus Standards aligned with the USSS, (United States Standards Strategy) which in turn supports creation of ISO, International standards. Publishing our Recommended Practices as ANSI/SAWE Standards brings increased visibility to those documents and recognition to the SAWE as a standard developer.

The SAWE has been a member of the American National Standards Institute (ANSI) since 2012 and an accredited Standards Developing Organization (SDO) since 2014. The SAWE participates in International Standards Organization (ISO) sanctioned standards development work as an SDO for the United States’ sole member to ISO, which is ANSI.

The benefits of ANSI membership were described in a previous blog post by Jeff Cerro here (https://www.sawe.org/blog/2018/08/20/the-benefits-of-ansi-membership-to-the-sawe-society-corporate-and-individual-members/).

Standards and Practices – A Call to Action

At the kickoff of Standards and Practices Day at the 2019 International conference in Virginia, I talked about donuts.

An internationally known chain of donut shops noticed their sales dropping. To find out why, they asked their customers if there was a problem with the donuts. The answer was no – the donuts were as good as ever. But sales kept dropping. Then the donut shop asked a different question: what do the customers think of their donut shop experience? The response surprised them: the donuts were great, but the coffee was bad. That’s something the owners had not considered: get better coffee, sell more donuts. And it was only learned because the donut shop asked an open-ended question, allowing the customers to communicate what was important to them.

SAWE Recommended Practices (RPs) are a vital resource available to a wide range of customers. Mass Properties Engineers refer to them. Companies and government agencies require their use. But there are significant gaps in what our RPs cover. As the new Vice President of Standards and Practices, my role is to shepherd the development of new RPs and the revision of existing ones to ensure they stay relevant to our customers.

But what to do first?

At the International conference I asked all of the Industry Committees to emulate the donut shop and  ask their customers what is important to them. Understanding their customer priorities will allow the Industry Committees to know which RPs to focus on and will motivate them to complete their tasks on time.

My call to action is this:

By the end of 2019, each Industry Committee should document their customers’ needs, the Committee’s priorities, and the time-based plans to create Recommended Practices which support their customers’ needs.

This does not mean that all current work should stop. A small number of RPs, such as those being converted to ANSI standards, have been identified by the SAWE  executive as high priorities and should continue to be worked. I have asked the Industry Committees to review and update the development schedule for each of these to ensure they will be published on time to meet the customer needs.

Developing and updating Recommended Practices is a vital part of ensuring the SAWE remains a professional society relevant to our industry needs. The Industry Committees need volunteers to help with this important work. If you wish to help out, please contact me at standards@sawe.org.