Mid-Boom Sheeting And A Broken Boom

[Pblais]

The insurance company wants to say that its a result of "corrosion" in the aluminum under the fixed bale but there's certainly more to this story.

This is always the answer the insurance cmpany gives. They like it even when there isn't any and should some surveyor hint that it might be an issue then it becomes the issue. The adjuster knows this too. "Must be corrosion". If you have the pieces you can get them analyzed by someone the insurance company will believe. They don't have to prove it was corrosion becuase it's their money.

I suppose it really comes down to if they want to deny or pay. If they want to pay then I would say the insurance company was right and you should collect and leave the sleeping dog alone. If not, then you'll perhaps want to spend some money on a engineering anylysis because a copy of this thread won't collect you any money. We are all well meaning and I think sincrere in what we say but we can't convince the insurance company to pay a claim.

A boom breaking in a 15 knot tack was already broken long before the tack. It just was that moment (pun intended) that it decided to break apart. How it eventually reached that conclusion is not anything we will be able to determine. An expert examination might tell the story different.

[Moonchaser2304]

See this thread also: Loose Footed Main OK?

To me part of the issue here is that on my mainsail (which is currently bolt rope with a large shelf, soon to be loose footed) the load on the boom from the main is ONLY at the tack and clew and the bottom 6" of sail that is mid-boom is floppy gumbo, loose even under full load. In that other thread people also state that the shelf itself should put zero load on the boom.

That being said, I also have mid boom sheeting and have to wonder if the sudden slap of the boom contributed to somedaypam's boom break? (I hope not because any of us could have that happen!)

I wonder if other boats of the same year and model as somedaypam's also have suffered from occasional boom breaks?

I wonder if that particular boom had more owner-installed screws near the mid boom point?

I wonder about corrosion too.

I wonder if newer Beneteau Oceanis 390's have larger boom cross sections..

Just thoughts...but I sure hope it was not the fact that the sail was converted to loose foot because I also have mid boom sheeting and am about ready to have my main converted to loose foot,

[Talbot]

I had a bolt roped main, and then swapped to a loose footed one. My main sheets are attached at the end of the boom, so that is not relevant to this discussion. What is relevant is that I discovered that the kicker was causing far more boom bending than had ever been the case before.

I would not have purchased a loose footed main if my main sheets were attached mid boom.

[Ex-Calif]

The numbers may be way wrong but there absolutely has to be a difference in single ppoint load - at the clew - vs. distributed load along the foot.

I agree with you 100% that you can design a boom to handle loose footed loads and mid boom sheeting.

However the original problem was - I changed my sail configuration to loose footed and the boom failed at the mid-boom sheeting point so what happened?

What happened is the scenario I described in my opinion.

[Pauls]

Having had personal experience with a broken boom at the bail attach area (mid boom sheeting) I can assure you that corrosion at this spot is a possible why for your failure. This is not a question that is going to be resolved on an internet forum. You have the boom. Look at it. Look at where it failed. Did it break along a line of stainless steel rivets/screws attaching the bail to the boom? That would be evidence of galvanic corrosion weakening the boom there. Inspecting the fastener holes will verify if the boom had galvanically corroded there. Is the boom heavily pitted under the bail? This could be galvanic or crevice corrosion, depending on the bail material. Etc. Observing the reality of the broken boom is the only way you will determine the cause of failure.

No siginicant corrosion combined with significant stretching/distortion of the boom metal at both sides of the break would be signs that the boom was under-engineered for the task. The break will show a granular appearance. Part of the break showing a smooth, kind of layered appearance combined with the rest of it showing a granular appearance is proof positive that the boom had developed a crack and had been operated for some time with the crack growing (the smooth, layered part) until it finally grew weak enough to fail completely (the granular part).

[carstenb]

Thsi won't help the OP, but I'm in the process of changing my end boom sheeting to mid-boom. I have a loose footed sail. Jeanneau told me I can get away with it if I change the boom out to a larger and stronger profile

Sparcraft 515 to a sparcraft 820

[Ostinato]

I also have experience loosing a mid sheeted boom. It had an internal rod to compensate for the increased stress. It also snapped in low winds after crossing from Bermuda to the Azores in storm conditions. I consider myself lucky in terms of when it happened. Bottom line it was not properly sized and I went up in size when I replaced it. I would also replace your insurance company. This would not be an issue with my current company.

[scotty c-m]

Rigs are designed for specific loads. I would suggest to the OP that he call the spar manufacturer and ask if his rig is designed properly. The same for those of you considering changing your rigs. I have had occasion to talk to technicians at both Charleston (US Spar) and Seldon. They have been happy to talk with me about issues, and I have found them very knowledgeable. There is no doubt that properly designed spars exist for this size yacht and mid-boom sheeting.

One aspect that might also be explored is the use that the rig has seen. Has there been a pattern of crash jibing, or other high impacts that might have weakened the boom over time?

[UNCIVILIZED]

On the boom breaking, it was underbuilt from the day it left the drawing board at the manufacturer. No boom should snap under those conditions, regardless of type of main, period. They should have (and did) calculate the stresses on the boom, over time, in conjunction with wear & tear, corrosion, plus different types of mainsail attachment. Though despite this, they knowingly put an undersized section on the yacht for the simple reason that it was cheaper.
Any competent rigger, of some experience, will tell you as much as well. And likely can do the math behind how strong your boom should have been vs. how strong it was. Ditto on any spar manufacturer..

As to fitting attachments, in this case, the bail. Sometimes when holes are drilled in booms, & definitely in spars, for load bearing bolts & fittings. A hole big enough for a supporting, compression tube is machined into the boom's side wall. Then an aluminum tube big enough for the bolt is inserted, & a reinforcing plate is welded onto the boom's wall on each side. Assuming, that is, that the boom's built so lightly (read close to it's calculated @ the factory, failure tolerance) that it's weak enough to need such reinforcement. Which it shouldn't be.

If there's any doubt, look at all of the booms on racing boats with HUGE, elliptical lightening holes cut into them. And they surely don't run mainsails which are attached along the entire foot of the sail. Plus the guys who race, & take care of them, attach fittings to their booms, pretty much on whims. I say this given 28yrs of racing (and boat care, plus limited building) experience. A good bit of it professional, up to the America's Cup & similar levels.

If you want to argue this issue with the insurance company, you'll need the pieces of the boom. Some qualified, Forensic Naval Architecture, & or qualified expert opinion to back you up. In addition to the original design specs for the boom. Also, professional metallurgical analysis of the failure wouldn't hurt. Nor would expert design analysis of the boom's design, & their comments on the boom section's strength & stiffness for it's intended purpose.
Though again, a well qualified rigger could do a lot of this, particularly one with experience in rig design.

As to Forensic Naval Architecture, here are links to a couple of examples:
Four Mast Failures
Forensic Naval Architecture
Also, take a look at his links page.

Realistically, in this case, given the cost of hiring those type of experts, plus attorneys, it may just be cheaper to either; sleeve the boom back together, & reinforce it. Or to pick up a stiffer/stronger section (likely used, & thus very cheap), modify it to your likings. And refinish it to match with LPU.
IE; Number of sheaves for reefing/reefing system design, attachment point style & number, etc.
Knock on wood, even starting with part of a spar section from a smaller vessel, to use as the basis for a custom boom, would work in a pinch.

In terms of attachments, most, if not all, high performance boats simply use short Spectra strops or Loups to attach blocks & other high load items to booms nowadays.
The exception being that depending on the design, a fair number use hard, aluminum "noses" for attaching vangs (or carbon fiber ones, when the boom's made of such).
Plus of course the appropriate reinforcement sections in proximity to the vang's attachment. Which are; riveted, screwed & glued, welded, & or laminated in place.

Or... if you're handy with tools, you could build your own tricked out custom one, out of carbon fiber (S-glass, & Basaltic Fiber), cores, & off the shelf components. Heck, you could even go all out, & build it in the Park Avenue style if such suits your fancy & application ;-)