RedactedNarrative: A sailing vessel had an allision with the MacArthur Causeway bridge causing the mast to snap in half. The vessel owner/operator, stated he was returning from offshore and heading northbound in the Meloy Channel at approximately 7:30 pm and misread his navigational chart.  He thought the bridge clearance was 75’ when he was actually reading the channel width.  The bridge clearance is 35’.  He stated he was going approximately 3-4 kts at the time of the allision, and struck the bridge breaking his mast in half.  The broken mast landed on the solar panels on the aft part of their vessel.