bent top section

G

g1gaumond

Member
The young princess was out in some good strong wind, testing her limits and thus of our vintage laser:cool:. Came back with a bent top mast section.

It is only slightly bent above (1 feet) the joint portion with the bottom section. Can I safely try to "un-bend" using force or am I simply going snap it? The bend is only a few degrees, more like a curve than a angled break.

As is now it is usuable but I am afraid it could (could it?) snap next time out in similar conditions (Got myself an adrelanine junky!!:D). Is it fixable or should I start shopping around for a new top section.

Apparently, choosing less exciting conditions do not seem acceptable to her. ;)

Thaks for your help as usual.


Ghislain
 
You have a few options:

1. Do nothing - if the spar is not being used for racing, a small bend is nothing more then cosmetic at this point.

2. Try and straighten it, either by hand or by sailing (put the top section in with the bend facing forward and sail, checking at the end of each day's sail)

3. End for end the top section - This is probably the best thing to do IMHO, especially if the spar is more then a few years old - you can then decide if you still want to try and straighten the section, but having the bend section away from the joint should help it last longer then keeping it at the joint.
 
hi if youve bent your top mast section yes you could bend it back, but why not leave it as it is? i wont snap if you try to straightern but if it worsens then it might be time to do some shopping but the older top mast section had two rivets holding the upper sleve that fits into the bottom section, if it has two rivets the forward one is more likely to break as there is already a weakness in he mast section! if it only has one rivet that is facing the stern then youll be ok and is less likely to break!
 
You guys are outstanding.

Thanks for always having the answer...I love this forum!:)

Will try to see if it can be fixed.

Cheers.

G
 
After trying to bend it back, you might consider to give it a new life by using it upside down. It's much stronger.
The only thing you have to do is refit the upper mast sleeve. :rolleyes:
 
Did the end-to-end change earlier on, it actually bent after that. Perhaps, I should have waited a bit longer before making the change.;)

It is sailable and she's not attending any class legal regattas yet, so will try to un-bend. Meanwhile I am shopping for replacement one.

Thanks again.

G
 
I have a top section that was also slightly bent after it was end-for-ended. Is there any reason to not return the collars back to the original position? It was end-for-ended simply as a matter of practice by the previous owner.
 
I recently read a Laser book where the author told of a regatta he went to with a poor top section. Every day after racing, he would have to straighten his mast to remain class legal. This comtinued for a few weeks. The mast never broke (at that event, anyways), and he did quite well. Laser masts do in fact have a good reputation for repeated bending and straightening, despite the stories of broken masts you will hear everywhere.
 
Finally stopped procastinating about this one for fear of snapping the mast. Could not bare looking at my daughters eyes if this had happened before an outing, or after one.

We were taking the Laser with us for a week holidays at a friend's cottage, so did not want to try before that was done;).

Followed steps as described on the link above, it went really well. Must do it slowly to ensure that it does bend the other way, I was surprised to see how flexible this aluminium was. It is now nice and straight again...this is until she hits the water again and seek the adrenaline rush she so enjoys.:D

Thaks again guys.

GG
 
Good glad the link info worked, years ago I worked as an engineer manufacturing shop fittings, part of the job was tube bending with a mandrill tube bender, what we found was that on steel tube it had a seam that ran down the length of tube & on tight bends the seam had to run on the inner edge of the bend, if not 5 times out of 10 times the tube would snap.
My point now comes is on the laser aluminum masts the seam in a random place ? is this why some masts are more prone to bending than others & some just snap ? Is this something laser has ever looked at or anyone else ?
 
Different manufacturing processes, your steel tube is likely to be welded using just the heat and pressure of being forced through the die. There is no seam on the laser spars, only die marks as it's typically extruded.

The reason why some mast bend and others don't is related to wall thickness variations as the die wears and variations in heat treatment. The spar tubes are artificially aged at elevated temperatures (the ageing process varies for different alloys but it might be 4 hours at 120 deg. Celcius for the precipitation process to occur) in a process that increases the yield strength of the material, as this happens in a furnace, you'll get some variations within the batch inside the furnace and some variations between batches.

I'll also add that despite the stickers placed on the spars in Australia, their is now metallurgical reason for work hardening to occur in the normal usage of the spars, for work hardening to occur the material must be worked (deformed) above the yield point, normal flexing of the mast occurs below the yield point.
 
Thanks Alan I had asked the very same question to someone today who said the tube would more than likely be extruded so no seam, & yes the wall thickness variation definitely sounds the true reason for some masts appearing to be stiffer than others, just out of interest has anyone done any studies on the mast thickness variations ?
 
Stiffness is only related to wall thickness, diameter and the modulus of elasticity. However the modulus of elasticity for aluminium is the same for almost aluminium alloys irrespective of the type of alloy, the heat treatment etc. So bacically how much a mast flexes is solely dependent upon the wall thickness and diameter.

The dies used to extrude the aluminium turn out tube that are within the class tolerances, but a new die will turn out thinner tube and as the die wears, the wall thickness and diameter will slowly increase.

So the flex of a spar is dependent upon the wall thickness (and diameter). How easy it is to permanently bend the spar is dependent upon the yield strength which is dependent upon alloy, the ageing process and the wall thickness (and diameter).

Basically, the issues with spars permanently bending easily is really an engineering specification problem, choosing a different alloy with a higher yield strength or increasing the minimum thickness of the tube would significantly reduce or eliminate the problem.
 
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