I have a 55hp Yamaha on 16 ft flatbottom. I am worried that if I hit a log or rock that it will tear out my lower unit or worse when I run it in the river. Is it a good idea to disable the trim so the motor will kick up. Any suggestions would be appreciated.

I had one with no trim and the lock was broken. A real PIA and embarrassing every time I tried to back the boat up, the prop would want to fly up out of the water. While it probably would cause less damage, if you hit a log or rock running at speed you lower unit is going to pay a price.

Not sure about the smaller Yamahas but Mercs will release if you strike something. At least my 1985 175V would. I hit a rotten log on Texoma once and the motor kicked up completely out of the water. Cleaning out the speedo pickup was a real pain. Buddy was behind me and was cracking up. He said there was a pile of sawdust.