I have a 19'6" Sea Fox with a 115 Saltwater Mercury (2 months old). I towed a small jon boat about 2 miles back to a dock because it was out of gas. After I dropped the guy of and headed out on the river I noticed a bad vibration in my boat once I hit about 6mph and of course the faster the worse it got. When I tried to open it up it just bogged down. Does anyone know what could have cause this?