Bent Boom

[harpo]

I've recently discovered that my boom -- bought with a new boat last summer -- has a permanent bend aft of the vang fitting.

Anyone else seen this before? I do sail in windy places (the Gorge, SF), I sail several days a week, and we use a lot of vang.

But I don't remember any of my previous booms doing this. Wondering if there might've been a manufacturing or other issue with last year's spars in North America.

 

[LASERNUT]

I've bent/broken loads of booms. Never really up to the job.

 

[Matt B]

i think most laser booms are bent but you can bend it back like you would a top section but that just weakens the boom. By the way ive heard rumor that aluminium hardens with age so if you store one for a year or so before using it it shouldnt bend as badley when i got my laser the spars had been stored for three years by the previous owner and mine have not bent so maybe theres some truth in it.

 

[laserxd]

bending it back will weaken the boom, I would only bend it back if its severely deformed, it won't really effect performance except that you might need to tune the boat differently

 

[cskudder]

aluminium hardens with age

FWIW, as I understand it ...
Any hardening effect is a process of slow oxidization on the surface layer and slightly into the metal. I *suspect* that the alloy they use for booms+ mast parts is selected to minimize or eliminate oxidization, and/or they use an anodization process to slow or prevent it. However, the oxides are generally STIFFER (harder surface, less flexible, more brittle) - without being STRONGER. So an oxidized part generally will break rather than bend, at the same level of force on it, or sometimes less force. Even without it, most alloys wouldn't harden enuf in a year to matter.

And yes, bending most metals back + forth generally both hardens and weakens the metal. You can see this easily by bending a wire coathanger back + forth -- it's pretty hard to straighten it out again completely cuz the first bend hardens that part of the wire, and eventually it breaks.

I'm not a metallurgical engineer but have been around small planes made of aluminum which led me to look into these things.

FWIW, and as I understand it. Maybe there's a real materials engineer on here who can confirm or correct.

 

[AlanD]

I am a Metallurgical Engineer and you are incorrect, no time to fully take your comment to pieces but on most points above, you are incorrect. Give me a few days.

 

[jeffers]

FWIW, as I understand it ...
Any hardening effect is a process of slow oxidization on the surface layer and slightly into the metal.<snip>

This has been extensive covered in various threads about top sections and, from AlanD who is very knowledgeable in these areas, is proven to be completely false.

The reason older spars do not tend to bend as much is likely that they are made of a slightly different spec of aluminium rather than any kind of 'age hardening' or 'work hardening'.