William H. Seward Yacht Club

 Founded in 1975!

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Snow Loads Sink Boats!

Each winter, boats capsize or sink at the dock due to snow loads. Your club has created this page to inform you of the danger of snow loads. The stunning photo of a Valdez, AK vessel sunk under the weight of snow is from the USCG site which, each season, posts warnings of snow load hazard.

Snow loads sink boat in LaConner, WA

US Coast Guard in Valdez posts snow load warnings

"Before" and "After" photos show water line differences

Calculating the weight of snow on a boat in Seward.

How much snow weight can accumulate on a boat in Seward? Let's make some reasonable assumptions and find out.

We need to know the volume of snow on the boat. We can easily convert the volume of snow into a weight of water, and that's what we want to know. Fresh water weighs 62.4 pounds per cubic foot: a given value.

Snow Volume: We will multiply the snow's depth by the surface area of the boat.

This is the outline of a Passport 40 laid onto a square grid. The grid allows us to determine that the deck is 75% of a rectangle with the length and beam of the boat: Length of 40.67 ft X beam of 12.67 ft = 515 sq ft. 75% of the area is 386 sq ft. We believe that most sailboats are similar in deck-to-rectangle ratios.

Recently, Seward received 2 ft of snow. Let's assume the two feet of snow. How much will stack on deck? For utility, we will assume that it's like a cookie cutter of snow: two feet uniformly on the boat. Obviously, this is a maximum value. You can modify as your experience dictates by estimating the percentage of snow that stays on your boat compared to our "cookie cutter" model.

Volume of snow on the boat = deck area X snow depth = 772 cubic feet of snow.

Snow is not solid water! It normally varies between 15% and 60% water. We'll use both values to bracket snow loads. Very wet snow can exceed 60%, of course, and very light snow can be less than 15%. Use values that are consistent with your experience.

772 cu ft X 0.15 = 116 cu feet for 15% water equivalent, and 463 cu feet for 60% water equivalent.

Fresh water weighs 62.4 pounds per cubic foot. If the snow is 15%, the snow weighs 7,238 pounds (3.6 tons), and if 60% it weighs 28,891 pounds (14.4 tons)! The Passport 40 weighs 24,000 pounds (12 tons)!

For our 2012 Commodore's Nordic 34, Creola, the values are:

15% water equivalent = 2,630 pounds, 60% water equivalent = 10,521 pounds.

Each of the final snow weight values is halved for 1 foot of accumulation. Remember that loss of stability will capsize a boat long before she sinks under the snow loads! Ice-broken through-hulls, hoses, and sea cocks also take a toll.


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