From: Krivo, Stan

Sent: Monday, June 24, 2013 2:19 PM

To: Shepherd, Lorinda

Subject: FW: Statoil Support Vessels pictures

Attachments: Peyton_Candies.jpg; Otto_Candies-Claire.pdf; Otto_Candies-Peyton.pdf; 

Gulf_Tiger_OSV.pdf; Graham_Gulf-Sybil_Graham.pdf; Maersk Developer 

Sample VOLUME sources.xlsx

Lori,

This is for your information and project files.

...sjk

From: Bart Brashers [mailto:bbrashers@environcorp.com] 

Sent: Monday, June 17, 2013 8:14 PM

To: Krivo, Stan

Subject: Statoil Support Vessels pictures

Stan,

Enclosed are a sampling of boats we looked at to find a typical crew boat and OSV. I believe the Peyton 

and the Otto are pretty much identical, just different years.

The Sybil is 10.7m wide, the Candies are 18.3m wide, and the Tiger is in the middle at 16.5m wide. If we 

average the Sybil and the Candies we get 14.5m. This would give a conservative Sigma-Y of 6.744m.

For Simga-Z, it’s a bit harder because they don’t give the height of pilothouse above the waterline. You 

can see from the JPG enclosed that the exhaust ports are actually angled back by 45°, but clearly near 

the top of the pilothouse. Estimating the height of the pilothouse on the Sybil, it looks like at least 25 

feet (at least 4 times as tall as the person I think I see on deck). For the Candies, it’s about the same 

height above water as the width of the boat. So the average of 18m and 25ft is 12.81m. Divide that by 

2.15 and we get a conservative Sigma-Z of 5.96m. This also gives a volume source Height of 6.41m. In 

reality, the turbulence from the ships’ wake, along with the buoyant plume rise of the exhaust, should 

make sigma-z be larger than that, but we’ll test this conservativism and see if it works.

(I also set the Forklift’s Sigma-Z to be based on 6 ft, just in case you also thought that 10 was too 

generous.)

I take the sum of the emission rates for each pollutant (SO2, SO4, etc.) over both boats, and divide by 

the number of volume sources used. I’ll try with both 10 and 100 volume sources overnight, and see 

what we get.

I’ve also enclosed a sample spreadsheet that shows how I calculated the emission rate from each 

VOLUME source. Basically, I sum the total OSV + Crewboat emissions, then divide by the number of 

VOLUME sources used to represent those emissions. I removed the links to other sheets (which make 

the XLSX file huge) and did a “paste values” instead.
This is equivalent the phrase in the ISC manual (last sentence of page 1-48) that says “The doubling of 

[sigma-y] by the user in the approximate line-source representation in Figure 1-8(b) is offset by the fact 

that the emission rates for the individual volume sources are also doubled by the user.” The number of 

VOLUME sources is cut in half, so that

Individual VOLUME source emissions = TOTAL emissions / Number of volume sources

So if you double the denominator, you have doubled the magnitude of the individual VOLUME source.

Bart

Bart Brashers | Atmospheric Scientist

Senior Manager, ENVIRON International Corporation

19020 33rd Ave W Ste 310 | Lynnwood WA 98036

T: +1 425-412-1812 | F: +1 425-412-1840 | M: +1 206-550-2606

bbrashers@environcorp.com

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