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Visit this site, buy the book Home | Waggoner Cruising Guide
It will be your main cruising resource in the San Juan Islands.
If your time permits and you all have passports, consider hopping over to Canada. Two places in particular. Ganges on Saltspring Island. For a very (and then some) large splurge you could dine at the exquisite Hastings House. Or, you could have a beer and a burger at The Treehouse Cafe and take in some great music. This is a highlight of my family's summer. After that head over to Montegue Harbor. In May, the harbor may be peaceful. In the summer it's too crowded for my tastes. Instead, anchor on the north side of the peninsula by the "Shell Beach". Just ask a local in Ganges to point it out on a chart.
Get the Waggoner guide ASAP so you have time to dream and plan.
As far as charter outfits go, San Juan Sailing in Bellingham, WA would be my first recommendation. boats are maintained to the highest standards. They will also be able to suggest itineraries. Welcome to San Juan Sailing
. The next is Anacortes Yacht Charters. Anacortes Yacht Charters
A word of caution. May is "iffy" weather wise. It could be glorious. It could be wet, cold and rainy. The best Nw weather is July 5 - Sept 30.