Apr 6, 2019
Blameless Postmortem
This was originally an interview homework assignment from the company Mapbox. The task was to write a blameless postmortem on some kind of failure I’ve experienced, technical or not. I chose to write about my first sailboat dismasting while racing in Oregon.
Date: August 6, 2016
Author(s): Cory Dominguez
Status: An insurance claim was filed and collected. But as of January 31, 2018 a new mast has not been procured and the sailboat has not been refitted.
Summary: The Cal 20 racing sailboat Sirena dismasted 6.5 miles (15%) into the Double Damned Regatta on the Columbia River Gorge in Oregon. The crew roster was: Chris (driver) Cory (trimmer) Mark (pit) and Andrew (Foredeck)
Impact: Approximately $15,000 in damage to the boat. No crew injuries.
Root Causes: A soft shackle that was incorporated into the back stay had an unknown defect and failed under high load. The sudden release of support suffered the mast to break in half six feet above the deck of the boat.
Trigger: A gust of wind coincided with the boat being in a “bow down” position in a wave resulting in a high load on the mast.
Resolution: We verified that the crew was uninjured and determined that the boat was not in immediate danger. The mast, sails and rigging were collected and lashed onto the boat. An emergency electric motor was installed and we traveled directly to the nearest dock. After securing the boat we called the race committee and our support team to report the accident and abandon the race.
Furthermore, we now discuss prior to races possible catastrophic failures, how we can mitigate them and how to properly handle them when they happen. Dismasting, crew overboard, broaching, and collisions are common topics.
Detection: It was rather dramatic and obvious to all on board, although no one anticipated the failure.
Action Items:
Lessons Learned
What went well
- The correct recovery tasks were decided quickly and efficiently carried out.
- All of the crew were wearing PFDs.
- The boat was prepared with a backup motor.
- We had several ways to communicate our distress including VHF and cell phones.
What went wrong
- There are several pieces of the boat that are fault intolerant. The supporting structures of the mast (e.g. shrouds and stays) are such pieces. The shrouds on either side of the mast and the fore stay in front are single pieces, factory constructed, and rated. The back stay needs to be adjustable in order to affect the shape of the sails. This makes it much more prone to failure. It is common practice to attach a looser safety line from the deck to above the running rigging so that if that rigging failed the mast would not become completely and instantly unsupported. Prior to this race we had incorporated a defective soft shackle into the back stay but had never set a safety line.
- We had not talked about the possibility of dismasting even though we knew that this race and location has notoriously high winds.
Where we got lucky
- When supports to the mast fail under load, the mast will fall to leeward. It is natural for the crew — especially the foredeck crew nearest the mast — to be upwind of the mast for purposes of weight distribution. Nonetheless we are very lucky that no one was injured by the falling mast. We are all experienced sailors and have good instincts about where to position ourselves on the boat but it would have been much better if we had talked about a possible dismasting before the race and made our positions more explicit.
- Our location in the race was very convenient. We were not near shore or any other obstruction and had plenty of time to collect our broken gear and install our emergency motor. Once we were under power the nearest dock with a boat launch was only a quarter mile away.
Timeline
August 5, 2016 (all times PT)
- 0800 we arrived at the Cascade Locks a day before the race.
- 1400 install the mast and prepare the boat for a test sail.
- 1430 the defective soft shackle is installed into the leeward deck attachment of the back stay. The reasoning is that because this race is almost exclusively downwind it would be to our advantage if we could elongate the back stay by six inches and orient the mast more upright. This is considered to be a faster configuration for high downwind sailing.
- 1300 launch the boat and start our test sail. The winds are ~ 22 kts and are similar to conditions we anticipate during the race. We make several maneuvers on our test sail and everything appears to be functioning correctly.
- 1600 dock the boat in the marina, put away the boat and retire until the next day.
August 6, 2016
- 0700 arrive at the boat and set it up for racing.
- 0730 Skippers meeting and check in with the race committee.
- 0830 Leave dock and proceed to starting area. The conditions are very windy ~25 kts.
- 0900 Race starts. The boat is handling well, although there are moments when the bow of the boat digs into the water. This produces a large bow wave and loads up the sails and the mast. This is a common occurrence in these conditions so we are not worried.
- 1030 While the boat is bow down in a wave, a large gust of wind ~30 kts comes and produces a high load on the mast. The defective soft shackle fails and the mast breaks six feet above the deck and falls with the sails into the water.
- 1050 We have recovered all the broken gear and have installed the emergency motor.
- 1104 we arrive at the dock, secure the boat and call the race committee and our support crew to inform them of the accident.
- 1400 We pull the boat out of the water and secure it to the trailer for its trip back to California.
