Mid-boom sheeting and breakage

Does anyone know if there is a history of (or higher than "normal" incidence of) booms breaking when rigged with mid-boom sheeting? My boom broke recently and I'm needing to deal with the insurance company and want to educate myself on the dynamics of a break of this type. On my Beneteau Oceanis 390 the main sheet bridle is located in the middle of the boom. There are three blocks- 1 is connected to a bale that's attached to the boom (this is where the boom break occurred) and the other blocks are on bales that slide along a track (groove in extrusion) on the underside of the boom. I was tacking in 15kt winds and going from a beam to a beam, didn't pulled my sheet in and when the boom came over it just kept going and split in two pieces just at the fixed bale. Not sure if its significant or not but I'd just changed to a new loose footed mailsail. I also had the vang on but not too tight and I'd tightened the toppinglift about 3 inches earlier in the day in order to take up excess stretch from the new line. 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. I've been sailing for 28 years and never seen anything like this. Any info, insights or similar stories would be helpful. Thanks

 

Well, the rule is :not less than 55 % of the boom. It' s because of the extrem flexion of it due to the mainsail.If you didn't change your mainsail for a bigger in E dimension , if you have not moved your blocks foward , it must be a aluminum problem( so be carefull with your mast!!) . Because this value of 55% is already seen by the naval architects who have drawn the boat. This value is higher for a multihull.

The mast and boom are old enought to think about buying a new one. And your oceanis 390 would be happier with.

Have a nice week-end