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Old 04-06-2011, 05:08   #16
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Re: Mystery Mast Welds - Explanation Please !

Quote:
Originally Posted by bangkaboat View Post
Personally, I wouldn't touch it, as is. Unlike welded steel, a welded joint on aluminum does not have the strength of the parent material, not even close, try in the neighbourhood of 35%. I'd suggest an x-ray, first. Providing that there were no gas pockets, full penetration, no other flaws & that there was a fair bit of overlay to the inner sleeve, I'd then want to add a collar, welded top & bottom. It doesn't matter that "They do this a lot", it is still compromised. Dye penetrant won't give you the answers.
Well, I don't know how you can be so sure of:

Weld strength, in particular the one pictured, without having all the welding parameters and the tests mechanical tests results...but let's see then:

X-ray : which technique will you use ( type of source, films, shooting technique...)?

Adding a collar will increase the risks of cracking, and will not specially add any advantage to the internal one, worse, it could damage the actual section and give unwanted stiffness to it.

About the dye penetrant, on such weld that is obviously ground flush, most of the critical defects ( an such thin wall thickness assembly as a mast can be) will be seen and, for the lack of penetration, you rather use UT compression waves, as the capping is flush, than X-ray.

And I won't worry too much about penetration as the internal sleeve act as a backing strip for the welding...which ususally help a lot in term of penetration for the welder.

But these are only asumption based on 30 years experience and qualification in QC and NDT work in welding industry.

And, as originally stated, DPT for a quick, easy and accessible to common people technique, is giving you much more answers than a simple visual inspection.

Shooting X-ray will oblige to fence a perimeter around the boat to do it (not to say that the whole perimeter will have to be forbiden for few hours), or to remove the mast and brought it to their facilities, to rent a qualified team of professionnals to come with a specific radioactive equipment, work few hours, process the film, may be re-shoot some and then read them in a dark room and have not 100% of the weld tested as the image will be spoiled by internals..easier than DPT obviously.

Personnally I prefer sound weld on aluminium mast, including for sleeving, rather than riveting (as riveting when not done properly initiate cracking), my 70'+ mast made by Marechal is all aluminium and all the fittings are welded, since 1990, the boat participate several transatlatique races without any signs of problem at welds location.

IMHO.
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Old 04-06-2011, 05:20   #17
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pirate Re: Mystery Mast Welds - Explanation Please !

Heh.

This always causes concern for me when two guys that sound very knowledgeable are diametrically opposed in their views.

I'd love to hear the outcome.

How about Brent Swain or Maine Sail weighing in?
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Old 04-06-2011, 05:26   #18
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Re: Mystery Mast Welds - Explanation Please !

The issue with welding aluminum is The most common and cheapest alloy is 6061 t-6 The t 6 indicated the metal is heat treated for strength So when this alloy is welded the heat treating is affected, well actually removed in the heat affected area There is a large reduction in strength something on the order of 40% I would think the inner sleeve on this mast add some strength back and the spot weld should not present a problem Of course we do not know what alloy this mast is there are non heat treated alloys that lose little strength from welding they are strain hardend
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Old 04-06-2011, 06:00   #19
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Re: Mystery Mast Welds - Explanation Please !

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Originally Posted by MikeMak View Post
I hope someone can help me.

I'm considering the purchase of a boat but the mast has me puzzled.

Approximately 18" above the boom, it has a seam all the way around it as well as various weld spots - all very sanitary. No apparent signs of a previous dismasting.

I've never seen anything like this before. Does anyone have an explanation. Mast is by Offshore Spars. I'll try them on Monday, but in the meantime, looking for some help.

Pictures posted.

Thanks.
From the photo - a good one, it looks like the mast was lengthened - I would suggest that it also has an insert - the photo appears to have circles
which were holes where the mast was welded to the insert. later all was ground down then anodized (or painted)
Could you see if the Gooseneck for the boom is attached to the area we are discussing ? That would be a reason to strengthen that section of mast.
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Old 04-06-2011, 06:00   #20
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Re: Mystery Mast Welds - Explanation Please !

I wouldn't consider not buying the boat based on the mast being potentially faulty, however do consider trying to adjust the price. The mast won't be worth a fortune to replace if required, it's not like it's a $100k carbon fibre racing mast...
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Old 04-06-2011, 07:29   #21
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Re: Mystery Mast Welds - Explanation Please !

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I wouldn't consider not buying the boat based on the mast being potentially faulty, however do consider trying to adjust the price. The mast won't be worth a fortune to replace if required, it's not like it's a $100k carbon fibre racing mast...
Agreed. I notice a trend on many forums where people start to argue the technical issues while forgetting the context of the problem. It starts to get like "what is the best steel for the needle to darn my socks?".

The question is a good one albeit academic since the professionalism of the weld indicates that this is not a home brew repair. As you know, there are gazillion things that could go wrong on a boat and you are always playing the odds. So yes, in line with what I just read above, I was wondering if you were considering an ocean crossing with this catamaran (sarcasm).

Continuing in the general subject; as to welds stronger than the surrounding material, I'm not sure a large strength difference is a good thing, because that creates adjacent areas of stress concentration. Sort of like patching tissue with canvas. In any case I'd try to look at the bigger picture here.

I see a lot of inexpensive inspection cameras for sale now in Home Depot, so that would be interesting to investigate from an interior view.
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Old 04-06-2011, 07:53   #22
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Re: Mystery Mast Welds - Explanation Please !

Allanpeda,

That was my first post intention, to give an easy way to assess the weld, deeper than by only visual and that should be enough for such assembly as it looks already well done.

An easy, cheap way, but able to find lack of fusion that are not usually visible with bare eye but really detrimental to the assembly.

The internal inspection will probably not revealed a lot, as it seems there is an inside sleeve in the mast, at least if you intend to see the root pass of the weld.
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Old 04-06-2011, 08:35   #23
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Re: Mystery Mast Welds - Explanation Please !

Quote:
Originally Posted by Eric50 View Post
Well, I don't know how you can be so sure of:

Weld strength, in particular the one pictured, without having all the welding parameters and the tests mechanical tests results...but let's see then:

X-ray : which technique will you use ( type of source, films, shooting technique...)?

Adding a collar will increase the risks of cracking, and will not specially add any advantage to the internal one, worse, it could damage the actual section and give unwanted stiffness to it.

About the dye penetrant, on such weld that is obviously ground flush, most of the critical defects ( an such thin wall thickness assembly as a mast can be) will be seen and, for the lack of penetration, you rather use UT compression waves, as the capping is flush, than X-ray.

And I won't worry too much about penetration as the internal sleeve act as a backing strip for the welding...which ususally help a lot in term of penetration for the welder.

But these are only asumption based on 30 years experience and qualification in QC and NDT work in welding industry.

And, as originally stated, DPT for a quick, easy and accessible to common people technique, is giving you much more answers than a simple visual inspection.

Shooting X-ray will oblige to fence a perimeter around the boat to do it (not to say that the whole perimeter will have to be forbiden for few hours), or to remove the mast and brought it to their facilities, to rent a qualified team of professionnals to come with a specific radioactive equipment, work few hours, process the film, may be re-shoot some and then read them in a dark room and have not 100% of the weld tested as the image will be spoiled by internals..easier than DPT obviously.

Personnally I prefer sound weld on aluminium mast, including for sleeving, rather than riveting (as riveting when not done properly initiate cracking), my 70'+ mast made by Marechal is all aluminium and all the fittings are welded, since 1990, the boat participate several transatlatique races without any signs of problem at welds location.

IMHO.
Well, not interested in a dick measuring contest. I've seen UT show gas pockets 40mm long, almost width of bead in weld that was visually sound & would've shown no flaws w/dpt. If you know anything about welding aluminum, you know the strength in comparison to the parent material. No, the addition of a collar won't cause cracking, provided done right.
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Old 04-06-2011, 08:39   #24
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Re: Mystery Mast Welds - Explanation Please !

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Originally Posted by tgzzzz View Post
Heh.

This always causes concern for me when two guys that sound very knowledgeable are diametrically opposed in their views.

I'd love to hear the outcome.

How about Brent Swain or Maine Sail weighing in?
Brent Swain shouldn't be giving anyone advice on welding. That said, better you go read the various discussions in boatdesign.net than to have them regurgitated here.
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Old 04-06-2011, 08:43   #25
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Re: Mystery Mast Welds - Explanation Please !

In the realm of possible reasons for the weld you can add that the previous owner may have overstressed the mast or it had a "weak" point in it that resulted in a crack appearing at that point in the mast. Rather than purchase a new mast, it was cut, sleeved and welded back together.
- - I did this with a Mizzen mast that would not - due to corrosion - come out of its mast step fitting. We had to saw the mast loose a couple of feet above the base of the mast. Then the mast boot and remaining portion were removed and separated. Finally the cut-off portion was sleeved and welded back onto the main mast tube.
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Old 04-06-2011, 08:43   #26
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Re: Mystery Mast Welds - Explanation Please !

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Well, not interested in a dick measuring contest. I've seen UT show gas pockets 40mm long, almost width of bead in weld that was visually sound & would've shown no flaws w/dpt. If you know anything about welding aluminum, you know the strength in comparison to the parent material. No, the addition of a collar won't cause cracking, provided done right.
I would not be interested in that contest either but I once owned a red porsche
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Old 04-06-2011, 08:51   #27
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Re: Mystery Mast Welds - Explanation Please !

The welded joint looks professionally done, and I want to make it clear that I'm making no criticism of the job done. I'm only saying that, personally, I wouldn't buy it myself, as it would be a weak spot in the mast. even if the joint were stepped, rather than straight, it'd turn me off, although it'd be a better "fix". The OP wanted opinions, that's mine.
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Old 04-06-2011, 08:59   #28
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Re: Mystery Mast Welds - Explanation Please !

For the OP:

This discussion has drifted away from your area of concern. I'll try to get back on track.

As I see it the issue is whether or not this welded mast is a reason to not buy the boat.

The welds appear to be either OEM or done by a competent welder, but there is the possibility that the conceal a defect. A full analysis would be awkward and expensive. What to do?

Well, first consider that in a deck stepped mast the loads in the subject area are nearly all compressive. To me this means that there is little stress on the welds, and that they are not an issue at all. Second, consider that there are no signs of cracking or distortion in the photos, which indicates to me that there have been no problems in the past usage of the mast, and that it is reasonable to expect no problems to develop as you use the boat. Third, consider that nearly all alloy masts have welded high stress fittings incorporated in their design... things like tangs at the masthead for the stays to attach to, winch bases, goosenecks, vang fittings and so on. The fears of welding reducing the strength of the mast to a dangerous degree seem to be allayed by the longevity of the other welded fittings.

So, to me the state of the mast would be of interest and worthy of some historical investigation, but would definitely not be a deal breaker.

YMMV.

Cheers and good luck with your decision.

Jim
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Old 04-06-2011, 09:04   #29
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Re: Mystery Mast Welds - Explanation Please !

Look like a factory weld. Cintrary to all the expert advice above, I wouldn't be concerned at all. But a call to the spar builder might calm you. They might put the sleeve and weld nead the boom because it makes the mast stiffer and therefore stronger just where the bending forces may be highest.
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Old 04-06-2011, 09:04   #30
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Re: Mystery Mast Welds - Explanation Please !

Bang, But aren't all large masts somehow fastened together because they are too big to transport on the road. For instance if you saw a super yacht with a 90' mast wouldn't it have to be a sectional?
PS As far as a dick measuring contest I've had 3 Porsches, not all at the same time and none were brand new. Does that make mine big or small?
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