[jollyburger]

This is from 2008 so it seems like it's been an issue for a while?

Then a few weeks ago, The Tyee reported, the company performed an unusual test using as many as 18 gravel trucks to weigh down one of the vessels. The company is yet to say whether the full load helped. Nor is it clear how adding weight permanently to the vessels would affect fuel consumption should the company decide to do that.

The test points to the suspicion that the noise and vibrations are related to how high the ships sit in the water.

It’s a theory confirmed by Stefan Krueger, an engineering professor at Hamburg University of Technology, who helped design the new ferries. When the ships are at berth, the propeller may draw some air, said Krueger in an e-mail. It is “absolutely harmless for the ship or the propeller, but it can cause some noise,” he wrote.

Once loaded and underway, the propellers will be “sufficiently submerged” to prevent the problem, he said.

In an essay on the design of the new ferries, Krueger and two co-authors describe how the propulsion system was chosen.

They chose “a propeller diameter as large as reasonably possible,” arriving at five metres. They based the size on the maximum draft of the ships, the amount of the hull that would be under the water line when fully loaded. That maximum draft is 5.75 metres.

Twenty centimetres below

When the ship is unloaded, however, the blades come much closer to the surface. According to one analysis, when unloaded, the draft is just 5.2 metres, so the blades would be within 20 centimetres of the surface.

Or as an FSG employee, Markus Brinkmann, put it participating in a web forum discussion of the Tyee’s first article on the design problems with the ferries. “When the Coastals are in the dock, the propellers suck air -- yes, no doubt.” It won’t happen while they’re moving, he said.

It is also key that the propellers turn at a constant speed of 127 revolutions per minute, even when docked. Krueger said in an e-mail that he does not consider a long idling time “normal or useful, because of the related fuel consumption.” He did not, however, respond to a further e-mail asking how long would be needed to shut down the ship and start it back up again.

And as neighbours of the ferry terminals like Franklin in Nanaimo know well, the ships on the major routes spend a significant amount of time empty at the dock. They are there when they start in the morning, when they shut down at night and for 25 or 30 minutes while unloading and reloading between hour and a half crossings.

https://www1.thetyee.ca/News/2008/12/15/NoisyFerry/

From 2013 after one of the Coastal Ferries crashed into the berth:

Marine Investigation Report M11W0211

After the Coastal Class vessels entered into service, it was discovered that the bow propeller caused excessive vibration and noise as well as terminal erosion and damage to propeller blades if the motor was kept running while the vessel was berthed. In order to reduce these problems, the bow (or inshore) motor is stopped.

The Coastal Inspiration's bow propeller caused excessive vibration, noise, terminal erosion, and damage to its blades when it was left running at the dock. To avoid this, British Columbia Ferry Services (BCFS) adapted the designed berthing procedure by requiring the crew to stop the bow propeller motor. To stop the motor without triggering the automatic feathering of the propeller, the crew were instructed to "freeze" the pitch at zero by setting the pitch to zero with the handles, and then switching from normal to emergency mode to bypass the automation. Freezing the pitch does not involve use of the emergency push buttons associated with emergency mode.

https://bst-tsb.gc.ca/eng/rapports-reports/marine/2011/M11W0211/m11w0211.html

The rotors (rotating part of electric motor) have a service life of 30,000 starts.

https://www.bcferries.com/web_image/h19/h60/8993956593694.pdf