Sidney/Anacortes = when do 48 hours start?

[techgirl]

I'm heading down to the US for a quick shopping trip and wondered if I clear into the US when I board the boat or get off? (I'm taking the ferry to Anacortes, and crossing by car back into Canada so just wanted to know when the "clock" starts on the 48 hours I need for my exemption

[Kahloke]

You clear Customs when you get off the vessel in Anacortes.