I thought I would start a thread for windsurfing repairs gone wrong so others can share bad experiences and maybe some "constructive advise" about what to improve.

I recently broke a carbon boom and decided to repair the boom myself. After reading a previous forum thread on carbon boom repair it looked a fairly straight forward fix- wrong!

The insert I made was from a foam sheet (normally used to protect head of sail in new sails) rolled into a tube and used electrical tape to maintain the shape. I then used 4 sheets of carbon fibre and epoxy resin to create a carbon tube insert. I wrapped this in glad wrap and inserted it into the broken section to create the tube insert. Unfortunately during the insertion, some part of the gladwrap must have ruptured which left half the insert stuck and epoxied into the boom. Not to be put of by this minor setback I continued with the fix by removing the glad wrap from the half insert still sticking out from the boom to continue the fix. Once cured, I epoxied the insert and reassembled the boom before wrapping the outside section with 4 layers of carbon fibre and epoxy. Again, I used gladwrap to squash down the layers of carbon.

At this point everything was looking good.

After leaving the layup to cure for 4 days I decided to do some fine sanding to prepare for re gripping. I tested the boom for strength and it felt ok. However during the sanding process it appears I didn't have good adhesion of the wrap to the boom. Parts of the new warp can be lifted with my fingernails.


At this point I decided the fix was a fail and will consider sanding all layers back and going again. What went wrong? Poor adhesion suggest my surface preparation was not adequate. Did I leave too much old glue on the boom. Would a vacuum pump have helped to make sure layers were in good contact with the surface. Happy to hear other opinions on whether to try and fix and what went wrong. Be kind, my board repair skills are limited to the odd ding repair!

Safety is priority number 1.
Repairing masts and booms is not.

Too much renin IMHO. In lamination you want the material to be hard down onto the area. I think in your case the carbon cloth was sitting/foating on a layer of resin. A good cheat it to wrap the cloth once wet out and on the boom with insulation tape. After the first wrap twist it so the sticky is on the out side and them wrap it as tightly as possible. then prick holes in the tape to allow excess resin to come out. once set, the tape comes off easily and there is no sanding required. also consider cutting the boom ends at 45deg that way you are not point loading the join under the load so much.

What solvent did you use for the final wipe after sanding the outer? Should be acetone or MEK.

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JakeNN said..
Safety is priority number 1.
Repairing masts and booms is not.

Carbon boom's generally can be repaired successfully by those who know what they are doing. At a replacement cost of $1200-$2000 for an equivalent, I'll take my chances.

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Bender said..
Too much renin IMHO. In lamination you want the material to be hard down onto the area. I think in your case the carbon cloth was sitting/foating on a layer of resin. A good cheat it to wrap the cloth once wet out and on the boom with insulation tape. After the first wrap twist it so the sticky is on the out side and them wrap it as tightly as possible. then prick holes in the tape to allow excess resin to come out. once set, the tape comes off easily and there is no sanding required. also consider cutting the boom ends at 45deg that way you are not point loading the join under the load so much.

One additional step I didn't go into too much detail on was when I wetted the fibre cloth, I placed it between two plastic sheets and squeegeed out as much resin as possible. This method was suggested to me by another repairer. I like your suggestion to prick holes in the tape though. I do believe that my cloth was floating in some areas, as you said and maybe just poor adhesion wasn't the only cause. I not sure if a 45 deg cut was made on how I could maintain the curvature and correct length.

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airsail said..
What solvent did you use for the final wipe after sanding the outer? Should be acetone or MEK.

Probably where it all went wrong Airsail. I used a rust stripper wheel from Bunnings, which was very effective at cleaning the area of all visible residue. I didn't use any solvents to do the final clean.

i repaired my carbon boom by adding a carbon tube sized to fit the internal diameter of the boom arm. it extends well into both sides of the break. one advantage of this method is you can push the break back together so it's not really that visible and the grip remains in pretty good nick. it's an easy process with almost no sanding, cutting and mucking about.

it's a solid repair. actually stiffer than the original boom now.

i would not trust a repair without a dowel.

Yes I've a couple of carbon booms with multiple repairs, none of which have given way.
But I wouldn't dry the carbon out so much, how much weight did you save? A few grams at most. To get a good bond, you need enough resin to completely wet the area, if the carbon is too dry this won't happen, I don't clean with solvent, but I've sanded/ground the area down with 80grit paper, to remove all damaged material, and form a tapered surface. It will then take more than 4 layers of carbon to restore the original diameter, but I normally would add a few more layers to be on the safe side.

I also would not say just a wrap is sufficient. On a SUP shaft I sleeve it with commercially manufactured carbon tube and have still had a re-break when the mould release still existed and it let go.
Clean clean clean, rough it up, clean again, sleeve and maybe then a bit of a wrap externally.

Done right its fine, I have a Maui carbon slalom boom that had 5 breaks and put back together by a pro repairer. Its got many years of big guys sailing it overpowered, no issues.

I recently repaired a boom with in insert similar to the way Mike described (no surprise since I asked him about how to do it). It was in the straight section so I could use part of an old end piece for an insert. On one side where it was loose, I wrapped it with glass to make it fit better. Cut a few cm off the broken parts, sanded them down to a taper, and wrapped them with carbon. I used relatively long pieces that I could wrap around tightly several times, and finally wrapped it with plastic. Sanded everything down afterwards. Looked good, but had only one session with it so far. My wife liked that the repair area is thinner due to the shrink wrap tubing, and asked me to re-wrap the entire boom with it. Won't happen, though .

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flatchat said..
At a replacement cost of $1200-$2000 for an equivalent, I'll take my chances.

At a replacement cost of $1200-$2000 for an equivalent, I'll reduce my safety risks.

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JakeNN said..

flatchat said..
At a replacement cost of $1200-$2000 for an equivalent, I'll take my chances.

At a replacement cost of $1200-$2000 for an equivalent, I'll reduce my safety risks.

No you dont, you take a gamble on manufacturing defects. A repair will be stronger than original.
In the above case it could be not adequate pressure (I prefer using peel ply or sticky tape upside down), wrong ratio of resin/hardener, resin too old (that would stay tacky).

Every goes on about how great carbon booms are yet there seems to be a lot a bust ones here being repaired

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Ben1973 said..
Every goes on about how great carbon booms are yet there seems to be a lot a bust ones here being repaired

All the broken aluminium ones are in the bin

Thanks for all the suggestions. I'll take it that another go at fixing the boom is worthwhile. Although I also have a much newer Severne carbon boom, this NP boom is still my favourite go to boom for smaller sails.

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Mark _australia said..
I also would not say just a wrap is sufficient. On a SUP shaft I sleeve it with commercially manufactured carbon tube and have still had a re-break when the mould release still existed and it let go.
Clean clean clean, rough it up, clean again, sleeve and maybe then a bit of a wrap externally.

Done right its fine, I have a Maui carbon slalom boom that had 5 breaks and put back together by a pro repairer. Its got many years of big guys sailing it overpowered, no issues.

It can be done but it takes a lot of time & effort :-)

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flatchat said..
Thanks for all the suggestions. I'll take it that another go at fixing the boom is worthwhile. Although I also have a much newer Severne carbon boom, this NP boom is still my favourite go to boom for smaller sails.

Tim,
Remove all the ragged ends from the break even though there will be a gap, sand inside & out and thoroughly clean inside & out.
Making the sleeves is the trick, they need to be a goof fit.
The sleeve below was fitted to a small diameter wave boom with no increase in actual diameter.
The grooves were filled with carbon roving.

Agree with what most are pointing to here. A few extras to consider when doing epoxy repairs.

Resin ratio. Mixing small quantities by volume can be very hit & miss. Find the ratio by weight & use a set of digital scales. Mixing by weight will reduce one of the major variables.

Surface prep. once sanded, a combination of vacuuming & wiping down with clean rags is more than enough. Surface residue & dust are the two most common cause of secondary bond failure. I never solvent wipe a composite surface to prep it for glassing/bonding. The risk of residue remaining & contaminating wet resin is too high. Keep in mind if a solvent is able to etch or soften the surface, it will be done so permanently thus stuffing up the secondary bond. If possible avoid compressed air to blow down the job, even with air traps etc... the risk of oil, moisture being blasted into the composite ain't worth it, blowing down simply pushes dust around the shed to land on the job at a later time!

Temp. Assuming you bind or vacuum the laminate, lightly heat the laminate for a while as the resin initially sets. A small heater blowing over the job will make the world of difference to the job going hard quickly & accelerating the curing process. Can also sit the job in the sun occasionally rotating so all surfaces get a hit. The cure times Vs temp will be part of the resin MSDS.

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AUS 808 said..

I fix tube batten by inserting a solid piece or a sleeve over both ends so similar fix but on a buch smaller scale with way less consiquence if i stuff up.

Slightly off course, not a repair gone wrong, but i figured i'd put it on here to open the thread up a bit more. Managed to ding the nose on my JP 175 today (i did it just for this thread) typical mast impact.

Relevant info: board is made of carbon. Previous openings have revealed that what will probably be underneath is straight to styro. I've had to do enough repairs now that i have my own ideas how im going to fix it (it's actually an easy fix) but thought i'd put on here anyway, see if i can learn anything new....

How would you fix it?

edit: it bled some water out whilst sitting in the sun, so needs opening up.

Small nose repair like that just sand out to a nice bevelled oval about 50% larger than the cracks and about 2mm deep (max) hopefully seeing hi density foam there not styro!
4 or 5 layers of 4oz glass getting progressively bigger and cap with a 2oz bigger than all (helps with less fill)
blend edges out with a bit of filler once cured.

If no hi density foam I'd be going much wider and over the top with more glass as it would be like bloody eggshell nose.

Make that charcoal colour with black, white, little bit of green and purple, matting additive.

No HD foam in JPs from what I've repaired

Geez I wouldn't mind knowing what is in the back half. Something, I hope.

I pushed a broom handle 4 feet in to my Maui carbon boom to push the stopper away as there was water stuck in the boom.

This was four days ago and the broom handle is still there.

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Mark _australia said..
Small nose repair like that just sand out to a nice bevelled oval about 50% larger than the cracks and about 2mm deep (max) hopefully seeing hi density foam there not styro!
4 or 5 layers of 4oz glass getting progressively bigger and cap with a 2oz bigger than all (helps with less fill)
blend edges out with a bit of filler once cured.

If no hi density foam I'd be going much wider and over the top with more glass as it would be like bloody eggshell nose.

Make that charcoal colour with black, white, little bit of green and purple, matting additive.

You might be right. being the nose, they might've had a brain fart and put some high density in there...

I'll post a picture when i've opened it up on monday or tues night.

Im pretty sure they've put some through the back half. Thats where all the load is. but theres none through the front half on the bottom. I doubt theres any through the front half on top.

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petermac33 said..
I pushed a broom handle 4 feet in to my Maui carbon boom to push the stopper away as there was water stuck in the boom.

This was four days ago and the broom handle is still there.

You're a funny one Pete.

Bottom of a JP
Definitely has high density foam layer.

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Ben1973 said..
Every goes on about how great carbon booms are yet there seems to be a lot a bust ones here being repaired

Carbon ones are worth fixing and last a hell of a long time, Ali will bust unexpectedly and then are worthless.

I must admit to never trying to fix an ali boom.

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petermac33 said..
I pushed a broom handle 4 feet in to my Maui carbon boom to push the stopper away as there was water stuck in the boom.

This was four days ago and the broom handle is still there.

Was it a teak broom handle? That'll make a good boom.

Latest Nico Prien video has a short bit on a quick nose repair. FWIW, if you have carbon about, I'd use that on the nose instead of so many layers of glass. It'll be easier to fair back into the board. That's just me, though.

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petermac33 said..
I pushed a broom handle 4 feet in to my Maui carbon boom to push the stopper away as there was water stuck in the boom.

This was four days ago and the broom handle is still there.

Don't be so lazy, take it out & sweep the floor