Shear pin went 2x in 2 weeks, didn't hit anything!! 5HP Honda ??? Help???

Posted By: Bill Wickett, M17 and Norseboat 17.5 (for sale)
Date: 8/17/09 9:12a.m.

Report: outside forum guidelines

I am looking for any experience/insight/best guess on why a shear pin would go without hitting anything. Here is the story of 2 occurences on back to back weekends. Last week at the Ruff Ruff get together, we were nosing into shore to pick up some driftwood for the campfire. I reversed out, then into neutral and then into forward again, and the shear pin went. Changed it out on the lake. Thankfully it was calm. Just a LOOOONG reach to the prop on the stern of the boat, doing it basically one handed, hoping I didn't drop anything into the 40+ foot depth. Did it okay with Julie handing me the tools etc, and me handing her back the cotter pin, hub, prop, then lining it up so the new pin was horizontal and everything back on again. Yesterday, out on Lake Ontario great sail, drifting/swimming and keeping cool in the humid heat of the summer that finally arrived. Heading back in 4 hours later, we were about halfway up the channel to the ramp. Had to slow down and put the motor in neutral due to slow traffic ahead (larger sloop taking a student Laser in tow, as the wind had died up in the harbour). Put the motor back in forward, started to move, then she revved higher, as the pin sheared. This is the one I put in the week!! Enough forward momentum to steer to the pier wall at the side and make a quick landing. Waited till the traffic cleared and hailed a runabout going past to the ramp. He kindly took us in tow to the ramp finger dock, and we hauled out as usual. If it had happened out on the lake yesterday, conditions would not have allowed changing the pin hanging off the stern. Could have sailed in part of the way. It is a busy channel, and narrows down in a couple of spots. In both cases we were at slow throttle. The motor is a Honda B5A 4 stroke. Same model of motor we had some years back on our Naiad (1000 lbs). This boat is 1600 lbs, plus crew of 4 yesterday. Only thing I can think of was there was pretty good wave action yesterday and as we headed into wind to drop the sails the stern was pitching up and down somewhat. Throttle setting was at slow or less at that point, and I was playing the throttle down and back up if it came out. Same case 2 weeks previous to the Ruff Ruff trip, we had experienced some pitching of the stern. The Montgomery seems to move pretty easily with the 5HP motor, and we have not had to go over 1/3 throttle yet in 6 times on the water with the rig in the last 5 weeks. I believe several other M17 owners have the same set up. When I shift from forward/reverse, I make sure the throttle is idled before putting back into gear. I am not sure why I lost the shear pin in "normal" operating conditions. The pin I put in at Ruff Ruff was one of the pins that was in the little holder under the motor cover. Bronze look. So was the first one that broke. I can't be sure they are original equipment as the motor is a 2003, and we are the 3rd owner of the boat/motor combo. Since I had no spares after the first one breaking, I did pick up a couple of original Honda shear pins on Saturday. They are not the bronze look I have seen before, but are shiny silver. Some kind of plating on them I think. 2 weeks running is a bit concerning. Could be a problem in busy channels. Has anyone else experienced this happening? Other questions: - possible that the pins were not matched for this motor. Are there different strengths available? - could the boat be too heavy for the motor? (1600 lbs) - could cavitating and or clearing prop out of the water while pitching into the waves weaken the pin? It was not revving very fast at that point. (This is the only common factor I can come up with in both occurences) Lessons learned: - be ready to hoist sail to manoeuvre or anchor at a moment's notice if you lose power. I am thinking of leaving the main up and luffing while transiting the harbour channel. (I knew this, just has not been front of mind) - keep lots of spare pins on hand. (We only ever had to change a pin once on the old 5HP after a line wrapped the prop)