Snapped Boom

[PyotrBee]

Completely different weld. This one is one of the runners where the line runs along the boom. Very low stress compared to others.

[PyotrBee]

Looks like SN.... but while I was reviewing it... see the cracks??? And there isnt even any stress on these points....

[PyotrBee]

Another weld.

[PyotrBee]

Another lower stress point where the line runs up the boom, but....

[PyotrBee]

Same weld as above, close up.

[PyotrBee]

After seeing all this... I got really worried about the mast. But the mast appears to have rivets for things attached to it, not welds.... Despite the mast being also manufactured by Sparcraft.

[Ziggy]

I'd replace the boom. Your photos show pretty clear evidence of cracks at the welds. I suppose you could get a welding inspector to look at it, but I think it would be just throwing good money after the bad.

[delmarrey]

I sure as hell would be calling Sparcraft and show them the pictures.

Aluminum shrinks up to 15% after a weld, Unless it is preheated. And even then there is shrinkage, but cracks are less likely to appear. The pictures in post #45 and 50 definitely looks like a cold weld.

I really think the wire used in welding the boom (6082) may have been the wrong material>>> Aluminium Alloys - Aluminium 6082 Properties, Fabrication and Applications, Supplier Data by Aalco

http://www.gruppofrattura.it/pdf/ext...oy%20welds.pdf

http://www.alcoa.com/adip/catalog/pd...Alloy_6082.pdf

[s/v Jedi]

Originally Posted by Cheechako

Some cruisers have gone to loose footed mains and nylon strops around the boom for th e mainsheet. I kinda like the idea....Did you guys both have rigid vangs?

Here's the key in post #34 of the thread... and it is ignored

no welding for attachments: webbing or netting or spectra strops around the boom for sheet attachments and for reefing lines. Look at the racers, ingenuity by simplicity.

The boom vang attachment needs a reinforcing sleeve on the inside. Next, a rectangular slot cut in the right spot and then a fitting for the vang sticking out from inside the boom, held in place by a couple of rivets or screws, but the load taken by just not fitting through the slot as the vang pulls. The reinforcing sleeve spreads the load of a couple of feet of boom.


Nick.

[PyotrBee]

Originally Posted by Ziggy

I'd replace the boom. Your photos show pretty clear evidence of cracks at the welds. I suppose you could get a welding inspector to look at it, but I think it would be just throwing good money after the bad.

Yes thats exactly my thought as well. But no money for now, so it seems like Ill be sailing with just the foresail for quite some time. And it sucks because we just paid to have the main sail and sail bag repaired

[PyotrBee]

Originally Posted by delmarrey

I sure as hell would be calling Sparcraft and show them the pictures.

Definitely going to do that - but Im not sure I have much of a chance with them... although if I flog these posts and pictures enough it might look pretty bad for them....

[PyotrBee]

Originally Posted by delmarrey

Aluminum shrinks up to 15% after a weld, Unless it is preheated. And even then there is shrinkage, but cracks are less likely to appear. The pictures in post #45 and 50 definitely looks like a cold weld.

I dont do welding - but I do soldering on electronics. And to me it looked very much like the aluminium was heated/cooled to quickly and thus the cracks....

[DumnMad]

Combination of location of load points, high stress, welds and fatigue. Too much muscle on the winch? Leech and vang a bit tight. Broke when it had no wind loading because with no upward loading along the middle of the boom to counter the load from the vang the bending moment from the end load was at a maximum.

[PyotrBee]

I called to South Africa today after some investigations. SparCraft Cape Town was part of a company that is now been bought out by a NZ company. It is now known as Southern Spars (Southern Spars - world leaders in carbon spar design, manufacture and service). The SA factory produces masts and booms for Southern Spars and they also still produce aluminium masts and booms under the name and license SparCraft Cape Town.

They asked for some pictures and would take a look at them but given the buyout etc the gentleman I spoke with was very frank and was doubtful if the new company would take liability on a 10 year old mast which was produced before the new owners bought it.

[Talbot]

The mid-boom sheet attachment like this puts a lot of stress onto the boom. I am amazd that the three seperate block connections are as close as they are. All other variants of this have had a lot of space between the blocks and thus spread the load along the boom. I have a loose footed sail, and recognise that this is totally unsuitable for mid-boom sheets (luckily mine connect at the end of the boom) However, the same stresses exist in a boom when you are using the 3rd reef, and have an end boom sheet connection, (or if you have a gorilla on the vang!)