Yamaha 115hp 4-stroke lower unit

Howdy folks,
I'm in dire need of some help in trying to solve a problem with an outboard we use on a resident community only accessible by boat. In the past 2 months or so, we have torn up two lower units on the outboard pushing a 25' or so ferry across a river. The lower unit takes a lot of abuse as it is run, sometimes hard, in reverse every trip. I'm not fully aware of what was torn up in the first incident, but know a new lower unit had to be installed. Recently, the outboard has been chewing up cotter pins.

Can anyone offer any advice in trying to beef up the lower unit on this outboard to try to handle the abuse that our employees are putting it through?

Thanks in advance, and I will try to update any technical information that I can.

-Cody

You could change the props to a higher grade of steel and find one with a lower degree of pitch. You could also use a prop guard.

You may want to switch to synthetic lower gear oil. The oil holds up better under stress.