First, thanks for all the great discussions in this forum!
My Fiberspar boom (250 - 308; I use it for large sails) is breaking on both sides of the head clamp area.







My plan. Please let me know if any suggestions.
1. Sand both left and right side areas of trouble, until I get to underlying carbon rod.
2. Avoid center area under boom head.
3. Use carbon fiber. Starting with smaller strips and then move to larger ones.
4. Wrap with plastic tape as shown in the following to get layers to adhere.
5. Sand.
6. Not sure, but possible add a layer of fiberglass on outside to prevent damage to carbon fiber material.

Thanks!

The responsible reply should be, chuck it away, and buy a new one. But I guess you could give a repair a go, so long as you're not sailing on open sea.

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mark62 said..
The responsible reply should be, chuck it away, and buy a new one. But I guess you could give a repair a go, so long as you're not sailing on open sea.

I only sail on local lakes. Live in Colorado, USA. But, agree otherwise.

It's repairable.

Make sure you have a decent taper (ideally 25ish to 1) and remove all loose fibres.
Don't use short strips of fibre. Prepare multiple 25-50mm wide, 350-400mm+ long strips and stick masking tape to both ends while the fiber is dry.
Pre-wet the long strips on a board avoiding the taped ends, you want to keep these dry. Do not get resin on your hands as you need to stick the taped ends down hard with clean, dry hands.
Place one of the taped ends near the repair and stick the pre-wet repair tape to the dry boom using the masking tape.
You can now bind around the the repair over lapping with the wet out cloth keeping tension as you go around keeping the other taped ends dry.
At the end, stick the loose end down under tension.

Do this with 5-6 layers, resin will go everywhere so place a bucket or something under the repair to catch the mess. The more tension when binding, the less air in the laminate of the repair.

Once it's gone off, sand smooth and add a couple more layers. The aim will be to not sand these too heavily, clear coat and done.

Below is a pic utilising this technique, laminate completed and still wet. In this case I've also gone over the laminate binding peel ply to get even more resin out. Set the boom up so you have lots of room around it and use lots of disposable gloves. Bon chance!

Good rundown by Brent

but

(1) don't avoid the area under the head
you need to go as wide as possible with the bevel. I don't know what you mean by the underlying carbon rod?

(2). It looks like a poorly executed previous repair. Somebody has put some cracked carbon sleeve on the corners (?) due to previous crack or whatever (?) and just putting a bit extra on top never lasts.

I think it's not worth doing unless you do most of the front - I'd only leave about an inch in the middle u touched, helps with getting your diameter right later. Even then I think it may not be worth it given previous repair and age of the boom

Thanks, Brent and Mark - I really appreciate the suggestions!

If it were a standard-size boom, I'd just replace it, but large booms are nearly impossible to find around here (not many windsurfers left in Colorado), so I've decided to give the repair a go.

I made a first pass at it last night:
* I used the long strip wrapping method (similar to wrapping a bike handle), and it worked pretty well.
* I ended up covering the entire head area. As I removed the old carbon, I realized I needed full coverage to get a solid joint.
* Under the carbon was some kind of fibrous material - not sure exactly what it was, but I assume it was there to help wrap and hold the carbon in place.

I'm sanding and applying another coat today. I didn't see the tip about leaving an inch unwrapped until now - definitely a good idea to try next time.

One other question: In another boom repair thread, someone suggested using fiberglass as the outermost layer as a sort of "sacrificial layer" to protect the carbon. Have you tried this approach or have thoughts on whether it's worth doing?

Wrap repair with electrical tape, it stretches and you will be able to get it tight on the wet carbon, then prick the tape to release all the extra resin

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bwm6300 said..I made a first pass at it last night:
* I used the long strip wrapping method (similar to wrapping a bike handle), and it worked pretty well.

I'm not sure about this. you'll cover it in carbon, but what's needed is strength along the length of the tube not around it.
Maybe if you counter wind the strips in apposite directions that will help, and allow some flexibilit.

The more you wrap along the tube instead of just around it, the better it will be.

I'm scared. Don't go further than you can swim.

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decrepit said..

bwm6300 said..I made a first pass at it last night:
* I used the long strip wrapping method (similar to wrapping a bike handle), and it worked pretty well.

I'm not sure about this. you'll cover it in carbon, but what's needed is strength along the length of the tube not around it.
Maybe if you counter wind the strips in apposite directions that will help, and allow some flexibilit.

The more you wrap along the tube instead of just around it, the better it will be.

All good points. If you wanted to get technical you could place some zero degree fibers in between the binding layers. Never done it personally as the repairs are usually reasonably small but it makes sense. The primary points of the technique is to avoid bagging, tention the fibres and to get good resin ratios. I wouldn't use this technique on a mast for example where the loads are very different.

And heat cure the finished job, don't rely on ambient cure. Worst case, sit in direct sunlight for ages before the first 'close to shore' shakedown runs to make sure it all holds up. I hate long swims.

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Brent in Qld said..
All good points. If you wanted to get technical you could place some zero degree fibers in between the binding layers. Never done it personally as the repairs are usually reasonably small but it makes sense. The primary points of the technique is to avoid bagging, tention the fibres and to get good resin ratios. I wouldn't use this technique on a mast for example where the loads are very different.

And heat cure the finished job, don't rely on ambient cure. Worst case, sit in direct sunlight for ages before the first 'close to shore' shakedown runs to make sure it all holds up. I hate long swims.

The trouble with, "some zero degrees fibers" is they will take all the load. The angled fibers will allow some stretch, but 0deg ones won't allow any stretch.
Ideally you want every fiber to be taking it's share of the load. If a few fibers are taking most of the load, there's a good chance they'll snap. This places a point stress on the existing fibers, and they could also give way.
Getting a 0deg fiber to go round the bend and stay tight isn't easy, if it's loose it won't do much good.

I stick with counter wrapping at as low an angle as possible.

Fair call. Never had a failure and happy to be proven wrong

I use 0deg on straight arms, that's easy, but getting it round the bend nicely is beyond me.

I've just done this exact repair on this exact boom. It took three tries, and it seems to be holding very well now with 10+ hours of sailing. In my first two I did not get the layup right or not remove enough material as noted above. I used taped compression.
Luckily this failure is very forgiving and you get lots of warning. I never actually had complete boom failure, unlike when it breaks at the back end.
They are great booms - well worth repairing.