Someone asked for the location. Here is my description. I'll try to get a Chart Graphic, but I am not sure how to do that.
NOAA Chart 13275 - Danvers, MA where the Danvers/Porter Rivers meet near RN #8. Link: Chart 13275
Upper Left corner of Chart (not inset).
Basically between RN#8 and 11 ft depth on chart, I made my turn and headed towards 8 ft water depth just off the unnamed point near Foster's point. Route was to pass over 6 ft depth between the 8 and 11 depths and continue to the 8 ft depth area. This is the position of the channel markers. Incident occurred in the sy
symbol area. Was at ~9 ft (7.5 on the depth meter) when depth went from 7.5 to 4.2 then back to 7.2 during impact. At 9 ft I have just over 3' under my keel. Low tide was +1.91 feet that time/day, so I should have had plenty of water even in the lower areas. The basic route is to follow the CAUTION buoys placed up the river which have been dredged to be no less than 6' at MLLW. Again instructions were made clear from several marina folks that once leaving Danvers river, straight line follow the buoys up to the marina. Did it with same tide conditions 4X before without incident.
I fired an email to the Harbormaster, told the marina, and made an entry on Active Captain. For most boats, probably not an issue as most boats in the marina during summer are power boats. Only in winter/spring do sailboats make the journey up/down river as the marina is a popular storage facility. My draft isn't that bad for the river. There are several boats in winter storage at the marina that have 8 ft drafts that make the trip.