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Old 07-04-2012, 16:59   #31
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Re: Snapped Boom

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Originally Posted by delmarrey View Post
And that's why I run my main sheet blocks at the end of the boom. I'm willing to bet the crack started right where the aft block support is riveted to the boom.
look at the photo. No rivets. Its welded. Looks like a fatigue failure probably starting from resdual weldeing stresses and repeated loading. With the sheet eye welded directly to thin material, the local stresses will be high leading to early failure.

I agree on re-enforcing. Try to sleeve the inside if possible or replace the boom. I suggest adding a large patch of material over the boom and then weld on the sheet eye. The stresses need to be distributed over a larger area.
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Old 07-04-2012, 17:07   #32
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Maybe a misleading pic but that boom wall looks bloody thin to me. Maybe fine design/engineering but I would be looking for more wall thickness for this size yacht.
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Old 07-04-2012, 18:56   #33
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Re: Snapped Boom

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I like the way Selden attaches the mainsheet bails to their booms: the bail padeye slides in along a channel extruded under the boom. No welds or rivets to break and no threads to strip. Very good engineering.
And look at the section of a Selden boom not just a round pipe or slighyly ovalised one. The bail padeye and wang slides and lock in along a channel extruded under the boom. Selden boom are good value for money I am very happy with mine.
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Old 07-04-2012, 19:30   #34
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Re: Snapped Boom

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?
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Old 07-04-2012, 20:12   #35
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Re: Snapped Boom

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Originally Posted by Valkyrie654 View Post
Was the vang loose or tight and holding the boom down? If the vang was holding the boom down then the leech of the mail will pot a lot of load on the boom. I have seen external tracks peeled right off of the boom this way. Throw in some stress cracks from welding and there you have it.
Actually with mid boom sheeting I don't think a vang does a lot of work unless it's running before the wind.

Quote:
Originally Posted by chala
And look at the section of a Selden boom not just a round pipe or slighyly ovalised one. The bail padeye and wang slides and lock in along a channel extruded under the boom. Selden boom are good value for money I am very happy with mine.
Here's a Zspar. I made my own bail for the vang. Zspar didn't have any the right size.

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Old 07-04-2012, 21:25   #36
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Re: Snapped Boom

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Originally Posted by delmarrey View Post
Actually with mid boom sheeting I don't think a vang does a lot of work unless it's running before the wind.
That's also true with end boom sheeting on a traveller.
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Old 08-04-2012, 14:03   #37
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Re: Snapped Boom

Vang isn't adjustable, its the piston type.
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Old 08-04-2012, 14:06   #38
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Re: Snapped Boom

Ok... this is scary. I went to take some pictures. And then I thought about taking pictures of the other welds..... Well let me post them and without me giving my thoughts see what you guys think....
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Old 08-04-2012, 14:10   #39
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Re: Snapped Boom

This is the snapped off piece of the boom. Notice the black marks outlined in red. Corresponding black marks exist on the other piece of the boom. Also the area outlined in blue is darker than the rest of the metal. It doesnt show up in the picture though. This is exactly where the weld was.
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Old 08-04-2012, 14:13   #40
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Re: Snapped Boom

This is the weld where the boom snapped. Look around to the right side of it as well.
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Old 08-04-2012, 14:16   #41
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Re: Snapped Boom

Different weld - not same one as where the boom broke. Main sheet attaches at 3 points near each other. This is one of the other 2.
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Old 08-04-2012, 14:17   #42
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Re: Snapped Boom

Third weld for main sheet attachment.
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Old 08-04-2012, 14:18   #43
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Re: Snapped Boom

Break showing some of the black marks and the weld.
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Old 08-04-2012, 14:19   #44
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Re: Snapped Boom

Middle weld again.
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Old 08-04-2012, 14:20   #45
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Re: Snapped Boom

Weld at break again.
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