Weighting for the Ferry

The M/V Guemes rides lower in the water now, but it meets US Coast Guard stability requirements. This is the conclusion of the Stability Letter issued to Skagit County by the USCG on December 5th, 2007. The engine replacement and hull work done in 2006 had a larding effect on the vessel.

The heaviness of the ferry’s rolling was noted immediately by the crew after the completed engine project. When the channel got lumpy, veteran ferry riders also could hardly miss the ponderous rolling and decks awash.

The crew was concerned enough to request a formal stability check. Last June the ferry was tested in Anacortes and witnessed by Coast Guard personnel in a standard procedure from USCG regulations. While the ferry was sitting normally in the water at dockside, a measured amount of weight was added on the deck a specified distance outboard from the boat’s centerline. This weight tilted the ferry to the side, and the degree of list was carefully noted. From this data the center of gravity and center of buoyancy were determined. The purpose of the test was to confirm that the ferry could still easily right itself after heeling over in a seaway.

The left hand image was taken January 1, 2004 and the one on the right February 19, 2008. Both photos were taken of a fully loaded 1pm run.

The good news is that the ferry is stable. It will still return to upright like a weighted punching bag when smacked over on its side.

The bad news is that the ferry is considerably lower in the water and heavier than she was when new. How much lower? About six inches. This was confirmed in the test. The original allowable minimum freeboard (the distance from the deck to the water) has been reduced from 2 feet 11-¾ inches down to 2 feet 6 inches. Before-and-after photo images of the ferry confirm the half-foot lowering stemming from the 2006 work.

What was done to make the ferry so heavy?

The 2006 haul-out included several changes to the vessel, most of which added tonnage. First, the original Detroit Diesel engines were replaced with Cummins engines. The Cummins are four-cycle units and heavier and bigger than the two-cycle Detroits. Larger engine houses were also installed. Second, some weight was added to make a wheelchair-capable ramp over the doorsill in the passenger cabin. But the greatest weight gain came from the third project, extending the decks outboard three feet on each side of the boat.

The deck extensions were needed to keep the ferry from getting damaged from hitting its own dock pilings. The new pilings installed in 2005 on the Anacortes terminal side were placed at the mid-point of the vessel, rather than towards the ends of the boat. These pilings were also driven into the channel bottom at a very vertical angle, so when the ferry rolled from side-to-side, while tied up at the dock at low tide, the pilings threatened to hit the ferry’s pilot house. The deck extensions gave the pilot house safe clearance.

How much heavier is the ferry?

The M/V Guemes is now approximately 60,000 pounds heavier after the 2006 work. This can be calculated by figuring the area of the vessel at the waterline multiplied by the half-foot added displacement of seawater. To give some idea of the added weight, it’s roughly equivalent to twenty 3,000-pound cars. So it is no wonder that the ferry is rolling heavily.

The ferry has packed on some pounds in its middle age, about as much as a full ferry load of cars. Unless the County is prepared to correct much of the work done in 2005 and 2006, the ferry will remain obese.

Tim Rosenhan, 3.2.8

 

Tags: Ferry Haul Out
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