Late 80's OMC 15 loses prop

[thatone123]

I have a typical late 80's OMC 15 that I use for duck hunting in very shallow lakes. If interested you might view the UTUBE video "Who needs a Mud Buddie" My use is not that extreme but close to it. I find deeper sports to get up on plane then skim in the surface top 6 inches or less of the water. Boat, weight etc. is modified to do this. I run up an down a 5 mile stream to get to the lake. I was traveling under a fairly fast rpm and the motor was singing it's 2 stroke tune just perfect. When I got out of the boat and looked at the outboard at the boat ramp THERE WAS NO PROP. I looked out in the 4 ft water and there it was. I had hit some small submerged sand mounds and small branches and dead wood a little more than usual during the day but the last one was an hour ago. I guess the cotter pin must have failed, but the prop must have stayed on because of torque maybe? Never had this happen and I seldom looked at the prop pin or nut as never had a problem and took it for granted that that was a bulletproof component system. From now on I will pay closer attention and so should you if you don't already if you frequent areas like I do. I am either running on shallow water drive at a snails pace with the prop near the bottom or flat out with the prop near the bottom also. The prop blades get sandblasted and thinner over time, by the mud, sand and general gunk. What could cause the cotter/prop pin to come loose and break or fall out since it is protected by the prop exhaust flange?

 

[jimmbo]

Use of a non Stainless Steel Cotter Pin, repeated straightening and reuse of said Cotter Pin, improper torque of Prop nut, missing Fibre/Nylon washer between prop and nut

 

[thatone123]

That 1/4 inch fiber washer was there. I usually torque that nut tight then back if off til the hole lines up with one of the splits in the nut and that is where I put in the cotter pin. I usually put in new cotter pin. Do you mean a non-stainless pin rusts or is stronger...this is mostly fresh water.

 

[F_R]

I once lost a prop in 20 feet of water by using a common steel cotter pin that rusted away over time. But that was in salt water. Um..., you did say "mostly" fresh water.

 

[thatone123]

Yes, where I go it is fresh water slough that goes down to salt water. Only on a incoming big tide is the water brackish. The pin was not that old and I doubt that was the case especially as you go back upstream the water turns fresh again and the boat is never in the brackish water for very long. I guess it was just one of those weird things that happens once in a while.