Join Date: Oct 2011
Location: New England
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Re: Irwin 10/4 centerboard info
Unless you luck into someone here who knows, try googling "irwin owners", there are several groups and forums and you are more likely to get a knowledgeable response.
Here is the brochure for the 10/4 which describes the centerboards as "hand laid-up fiberglass and lead ballast", so it is ballasted.
Irwin 10/4 Sailboat: The Sailing Sloop Orion