Operator''s boat was heading south on Lake MIchigan, 1/2 mile from shore, between Chicago''s Palnatarium  and the entrance to Burham Harbor. The boat capsized in this area. According to the Chicago Fire Department ,they received 17 people with one male transported for his injuries. Not all passengers could be identified for this report. According to Operator, he picked up additional passengers while attending an annual but unofficial  boat party held off the shores of Chicago. 
Interviews were done with the identified passengers, including operator Operator. All passengers and Operator expressed the same  information concerning the accident. The boat capsized to the starboard when a wake and or wave hit Operator''s boat on it''s port. This, caused the boat  to capsize. The reason for this accident, according to witnesses on the boat, the majority of the passengers were on the starboard side of  the vessel. In addition 4 to 5 passengers were occupying the fly bridge when the boat  encountered the wake. Before the boat capsized into the water, passengers heard Operator shout, "Get to the other side of the boat."
With this for mentioned information, the boat  may of had a center of gravity (cg) and center of bouancy (cb) issue. A shift of the boat''s center of gravity occurred when most of the passengers standing on the starboard side, caused the boat  to tilt to the starboard. After the boat encountered the wake/wave to the port, Operator''s boat responded with the momentary shift of the center of gravity (due to the majority of people to the starboard) or a combination of cg and cb. One passenger  said, "As the boat tilted to the starbord, water was coming into the boat through a window and water coming over the gunnel. The 4 to 5 people on the fly bridge plus the water, caused the tilt to accelerate. The boat may have not had the chance to right it self as engineered, due to the positions of the passengers weight to the starboard and the added weight by the water.
A close examination of craft was done, when it was dry docked. No cracks were found to the hull. Seven pfds were found still inside their zippered compartments with each zippered compartment still below deck. Of the seven pfds examined 2 were not servicable.

Chicago                       