Boom Bale Hole Repair

Wet Spreaders

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 I'm mulling on how to fix this. Options:

1. Some kind of composite/glass/bondo bodge-up, then use a strop around the boom for my main sheet.

2. Aluminum backing plate. Weld around the edges and then either fill with weld - use bales again for mainsheet, or fill with bondo and use a strop.

I'd like the outcome to be reasonably cosmetically good. Being strong enough to use bales again for mainsheeting is a bit of a bonus - most folks seem to be moving to strops anyway.  Ideas/advice?

boom slot.jpg

 

Wet Spreaders

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So that was where the mainsheet bail was thru bolted?
Yes. 30 years of salt and pressure and the stainless bolt holding the bail has drawn itself through the alloy. Hall don't make this section any more so I prefer to repair this one rather than get a new boom - it's otherwise in pretty good shape, just needs repainting. Trying to decide whether to weld it or use filler. Filler has a longevity problem and issue with getting material to adhere on the inside. But it's easy to use. My welding is "patchy" at best because I never get to practice and I was never an expert anyway, so there's a fair chance of a fuckup if I do that, but I think it will have a better outcome overall. I'm looking for other ideas in case I missed an option that has worked for someone before. For example, I could weld in thick wall tube that goes all the way across the boom, or just pull a small plate over the back of the hole and weld around the edges, then fill the divot with weld. Or something else...

 

SloopJonB

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Have a pro weld in the tube then finish it pretty with some epoxy filler.

Having doubler plates welded on both sides of the boom to thicken the area would also help.

 

randii

Member
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Sacramento area
BEST: Strip whole boom raw, weld in tapered reinforcements, then heat treat.

OK: bog, smooth, and strop.

DUNNO: mill oversized oblong holes to eliminate cracks/tears, then insert matching oblong section cross block with pivoting pin through a slightly wider mainsheet bale.

 

Zonker

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Folks - when you weld 6000 series aluminum (typical boom/mast extrusions) the yield strength drops significantly. Yield drops from something like 34 ksi to 20 ksi in the welded area. So you think you're making the boom stronger but you're locally weakening it. This is why most good mast fittings are bolted or riveted on.

So... welding a cosmetic patch isn't too wise. So my suggestions is pop rivet an aluminum painted cover plate (1 rivet at each corner looks tidy) and then use a strop for the mainsheet itself.

 

Gouvernail

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Old J-22 booms often have wallowed out holes as shown at the vang and mainsheet bales. 
 

i haven’t previously  seen one as bad as the OP’s example. 

Our go to welder guy has been piling aluminum around our wallowed out holes for  us.

His creation looks like somebody mashed a Hershey’s kiss into the hole. 
 

as the original J-22 bales had a 1/4 inch through bolt I figure more bearing surface is great.

we replace the through bolt with a 3/8” bolt. 
we make certain the shank on the bolt is long enough such that neither the boom nor the bale rides on threads. 
 

if your boom were my problem I would look through my extrusion pile  for a clean chunk of extrusion and, if I found something decent, move all my hardware to a fresh extrusion 
 

As it is a mainsheet attachment, I would  consider moving the bale about 6” aft and reinstalling it with a thicker bolt. Buying a new bake with larger holes so as to create a better beating surface wouid be a good option. 
 

if those options were not available I might slide a two foot long sleeve inside and simply drill a new hole for my bale’s bolt. At least that solution would  be spreading the load well away from the old holes and might preserve my old tited boom. 

 

weightless

Super Anarchist
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Mechanical fasteners, particularly rivets, might work here. You could probably get the old bail to work bolted through riveted on SS plates. Nicely polished they might look spiffy, too. Riveting on an AL sleeve or patch depending also seems reasonable.

 
I had this same issue, just not quite as bad. I just just cleaned up the area, left the hole, painted it and used a strop. I will not be going back. If you want to make it really pretty, fairing it out with filler (thickened on the inside as you have access) and painting it seems to be the way to go.

And strops are the way to go. I used some 3/16" SK78 with dyneema cover and it almost still looks new after 5 years except for a bit of staining. Weighs less as well... 

 

Wet Spreaders

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Yeah - I'm starting to think that the filler idea is better than welding. Lower chance of a fuckup. Here's the plan:

1. Take some FR4 PCB material (or thin G10), cut a little oversize and put a screw in the middle

2. Scrub up the damaged boom around the hole so it's nice and clean with fresh bright alloy showing inside (as much as feasible) and outside

3. Epoxy the FR4 to the inside of the boom - pull it tight against the inner wall with string pulling on the screw head

4. Remove screw, fill boom divot and screw hole with epoxy filler, fair, paint

5. Use a dynema climbing sling (20KN for $10) as a strop, held in place with a stainless slug and a screw into the track on top.

 

Crash

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Yeah - I'm starting to think that the filler idea is better than welding. Lower chance of a fuckup. Here's the plan:

1. Take some FR4 PCB material (or thin G10), cut a little oversize and put a screw in the middle

2. Scrub up the damaged boom around the hole so it's nice and clean with fresh bright alloy showing inside (as much as feasible) and outside

3. Epoxy the FR4 to the inside of the boom - pull it tight against the inner wall with string pulling on the screw head

4. Remove screw, fill boom divot and screw hole with epoxy filler, fair, paint

5. Use a dynema climbing sling (20KN for $10) as a strop, held in place with a stainless slug and a screw into the track on top.
Climbing gear usually not as UV resistant as marine rated…but if it lives under a boom/mainsail cover, then maybe no big deal?

 

DDW

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Folks - when you weld 6000 series aluminum (typical boom/mast extrusions) the yield strength drops significantly. Yield drops from something like 34 ksi to 20 ksi in the welded area. So you think you're making the boom stronger but you're locally weakening it. This is why most good mast fittings are bolted or riveted on.

So... welding a cosmetic patch isn't too wise. So my suggestions is pop rivet an aluminum painted cover plate (1 rivet at each corner looks tidy) and then use a strop for the mainsheet itself.
But is it 6000 series? I wouldn't weld it if it were, but some 5000 series aren't nearly that bad after welding. Maybe Hall can tell you, or you can have it tested. Also depends a bit on where the patch is. In some areas on a boom neither strength nor stiffness matter, some areas one or the other. The stiffness will not change much in the HAZ. For example if this is near the end of the boom, a 1/2 reduction in strength may not matter much - the section is way bigger than it needs to be there. 

 

Zonker

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Almost certainly 6061-T6 or some closely related 6000 series for 95% of mast/boom extrusions.

You can't (easily) extrude 5000 series especially big sections like mast and booms. More common in small sections like flat bars and angles. That's why you see 5000 in rolled plates and some stiffeners in aluminum boats but all the pipes are 6000 series.

Good point - if the bail is in the middle of the boom depth there is not much bending going on; but there is still shear forces. 

I still think a webbing strop is wisest. Spreads the load nicely, easy to inspect etc etc.

 

Wet Spreaders

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The boom is probably not under a lot of load at this point - the mainsheet has a 4:1 on the coarse tune and 6:1 on the fine. In a blow, I need both arms to pull the main in the last little bit, and I can probably row 160 lbs in a one off. So let's say 200 lbs max on the sheet, which means 800 lbs at the bail. Most of the tension will be along the underside, and the holes are 2ft from the end of the boom - so 1600 lb ft. That does not seem too bad for (say - bottom half of boom) 8 linear inches of (say) 1/16th aluminum with 34KSI strength. - 0.5 sq in = 3200 PSI. So it's a 10x safety factor.

 

DDW

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Right - it isn't just the location of the hole in the section, but how far from the end that is important. If the hole is very near the end, then all the aluminum has to do is stand up to the bearing of the bolts going through. I'd weld in a tube for that to increase bearing beyond the thickness of the walls (which should have been done from the beginning, then you wouldn't have this problem). If this was a vang attachment, then the strength might be critical as the bending stress is high. 

 

Zonker

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It's bearing strength you have to worry about, not a linear tensile tear.

That's the failure mechanism of the original setup which wasn't adequate.

 

Wet Spreaders

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It's bearing strength you have to worry about, not a linear tensile tear.

That's the failure mechanism of the original setup which wasn't adequate.
Not going back to bails. I was thinking about the strength needed in the boom and the strength of the strop. It looks like a 22,000 N strop would be fine considering 800lb is about 3500N - so plenty of over-design.

I wonder whether the strop can generate the same force as bails into the mast - how are boats usually set up for that? Do we rely on vang pressure only to create bend down low?

 

Zonker

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Hmm, I think I'm missing what you're asking. The strop just replaces a bail.

The strop takes the mainsheet load into the boom. It's pretty much a vertical force with a bit sideways when the boom is way outboard. Not much horizontal force going into the mast. 

image.png

 

randii

Member
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Sacramento area
...the holes are 2ft from the end of the boom...
Good access, so pop the end cap and and reach inside with a flapper wheel on a drill extension. You should be able to scuff it up nicely for good tooth, then epoxy in some internal reinforcement. If you do one side first with the hole facing down, gravity should help your layup okay flat. Cure, rotate 180 degrees, then repeat. With the inside reinforced, make a cosmetic fill of the remaining divots so your strop doesn't hang-up.

 
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