Dismasting - Why Does it Happen - How to Prevent it

[ArtM]

I understand basically was dismasting is - under rough, windy conditions the mast either breaks or falls over due to some kind of stress failure in the rigging.

What I don't fully get is why this happens on modern, production-type boats - particularly a fiberglass catamaran with a good quality mast and rigging.

Is it sailor error? Poor maintenance? Construction flaws? Or an unpreventable eventuality that is going to hit sooner or later to anyone sailing blue waters?

IOW, is this a totally preventable mishap, or an endemic risk of sailing open seas?

[bruce smith]

A multi hull accelerates or it breaks. There is no heeling /saftey valve.
The cheapest possible materials are used , not the best.
It does not require rough or windy conditions.
On a marconi rig , not just a multimaran, the whole rig can collapse from a single rig failure.
no accident my boats are all gaff rigged.

[Sailmonkey]

90% of rig failures can be prevented with maintenance. but it's not always cheap

[roverhi]

Two recent dismastings I've heard about were chain plate failures. Crevice corrosion in the area enclosed in the deck. Removal and testing would have been the only way to discover the problem. Usually it's a fitting, turnbuckle or chain plate that goes. Only takes one wire to go for the mast to topple especially on the newer highly stressed rigs. Inspection and repair/replacement of parts can stop a lot of the dismastings but costs can be high. One of the chainplate failures would have required a major rebuild of the hull and deck in the area of the chain plate if they'd known a failure was imminent. Boat had just undergone a total rebuild with mast and rigging and been stripped to the bare hull below so it wasn't a matter of not looking for a problem.

A large number of dismastings could be prevented by inspection. Though the inspection needs to be more than just checking what can be easily seen. Very few dismastings are the result of poor design except on win at all cost race boats.

[Bash]

I was trimming mainsail on a less-than-one-year-old production boat that lost its stick when a cap shroud jumped off the spreader. A couple cents worth of seizing wire let go, probably the rigger's fault, and the mast, the sails, the jib furler and all the standing rigging were trashed in an instant.

[Factor]

Rig Failure is not a given. Sensible initial design and sensible maintenance result in no rig failure. There are production builders who have never had a rig failure.

[belizesailor]

Most rig failures I know of have been due to maintenance issues. A well built, well maintained rig is not going to collapse under any kind of normal conditions....regardless of the number of hulls.

Those that were not due to maintenance issues were really extreme conditions: hurricanes, roll-overs, and impact with bridges!

[Bash]

Originally Posted by belizesailor

Most rig failures I know of have been due to maintenance issues.

Interesting. Most rig failures I've witnessed have been due to poor judgement. Like when Boat A t-boned Boat B, or when Boat C snagged a jibe mark with its spinnaker.

One of my dock neighbors sailed his 75' mast under a 70' railroad bridge without asking the bridge operator for a lift. That was ugly.

[Roy M]

I once came close to a dismasting. I was sailing on a port tack in 12-15 knot winds in the Catalina Channel, when I heard a sound, similar to a "POP". Then I heard some metal parts falling on deck. I looked up and saw the mast head bending to starboard and the upper shroud swinging in the breeze. Instantly I tacked onto a starboard tack to take the load off the masthead, then headed up and got the crew notified. We fired up the engine and put it in gear for steerage, then pulled the main and headsail down. Motoring into a quiet cove in the lee of Catalina, I went up the mast in the chair to see what had happened. The nut and washer holding the chainplate at the mast head were the source of the POP and metallic rainfall. When I got secured on a mooring, I used the halyards to stabilize the mast, then went again to the masthead to get a clearer picture. Removing the remaining upper shroud (in quiet waters) I then tapped on the through-bolt holding the upper chainplates in place. I was careful to capture the through-bolt AND the compression tube that contained it, so as not to lose the tube down the mast. It took a few days for a new bolt to arrive at the Isthmus, but I was able to make a repair without pulling the stick. The original had broken at a thread, hidden inside the mast where it would only have been seen during an overhaul. Needless to say, I gained a new appreciation for Preventive Maintenance, and the knowledge that I had to change things from time-to-time even though they weren't "broke".

[belizesailor]

Originally Posted by Roy M

....I heard a sound, similar to a "POP". Then I heard some metal parts falling on deck. I looked up and saw the mast head bending to starboard and the upper shroud swinging in the breeze...

Had a similar experience in heavy weather many years ago...that moment when you see the rig start to bend is really heart stopping!

Amazingly, we did not lose the rig either.

[Stumble]

With the exception of hitting bridges, rolling over, of being hit by another boat, pretty much all demastings can be traced to a fundamental problem with stainless steel. While it has been the industry standard for years, stainless is highly susceptible to a nasty form of corrosion called crevice corrosion, that attacks burried and hidden portions of the structure much faster than the areas exposed to air. This means that what looks fine visually really doesn't mean much.

I don't have the study in front of me at the moment, but something like 50% of all dismastings are from chainplate failures. The primary cause of chainplate failures is crevice corrosion. For through deck chainplates it almost always happens right at the section hidden by the deck. For external chainplates it is typically either the bolts, or the back side of the chainplate where they marry against the hull.

Preventing this is pretty easy from an advice standpoint. You simply need to remove and dye test your chainplates on their 10th anniversary, and every five years after that. As a practical matter though many chainplates are buried, requiring significant work to access, remove, and inspect. There is also the all too human responce, well they are big, and have lasted this long, they're fine.

The next biggest problem is from failures of standing rigging. Most sailors don't know the expected lifespan of standing rigging, but all of the manufacturers give you between 6 and 8 years before every fitting should be x-rayed or dye tested for cracking. Then every year after that.

People always say, well my rigging is 20 years old and doing fine... It very well might be. But unless you have had it inspected you don't really know that, you just know it hasn't come down yet.

[impi]

Was chatting to a mate of mine who delivers new catamarans ... was out of port on the first day ... new cat and rig ... came down on him as had a few others on the same brand of new cats ... turns out they were buying a new brand of masts from China to save costs ... he felt it has something to do with the mast 'flexing on its self' (?)

[Stumble]

Impi,

I could imagine it happening once. I can't imagine a customer accepting a second, let alone a third new part failure like that from a supplier. Unless it was just significantly under designed, I can't see any builder going back to the same manufacturer regardless of cost with multiple news failures.

The cost to fix the boat, delayed delivery dates, new rigging sails and mast... Figure a demasting on a new sizable cat could cost $100,000 or more. No one eats that more than once.

[tenchiki]

I had a near dismasting once, and only doing a quick visual all-around saved us.
We were day-sailing an engine-less racing sloop. Fortunately, we were on the offshore tack when I looked around before tacking, and noticed the upper shroud swinging in the breeze... The clevis pin had fallen out of the chainplate, presumably because the cotter pin was lost. This was a college boat, and fortunately there was a small toolbox and it had a clevis pin that would fit. No spare cotter, however there was some twine that would work in a pinch.

It would have been quite the irony, since the boat had just recently got a new rig after the backstay was clipped in a race. (30-ft Shields sloop).

[impi]

Originally Posted by Stumble

Impi,

I could imagine it happening once. I can't imagine a customer accepting a second, let alone a third new part failure like that from a supplier. Unless it was just significantly under designed, I can't see any builder going back to the same manufacturer regardless of cost with multiple news failures.

The cost to fix the boat, delayed delivery dates, new rigging sails and mast... Figure a demasting on a new sizable cat could cost $100,000 or more. No one eats that more than once.

Yeah, I agree with you on that score ... not sure of the specifics but I am told they did loose a few.