filling holes in an unstayed carbon mast

Depends on it being active or passive.... i.e. did you pay for the good (passivated) stuff.

I doubt they were passivated- I have not seen passivated 316 screws from suppliers like mcmaster, but I did find one company, fairwindfasteners.com that seems to sell them.

It sounds like passivation is a really simple process I could do at home... basically just let it sit for an hour in warm citric acid solution, and then rinse really well with deionized water.
 
This is the sort of thread that I find entertaining;lots of replies,each describing a more "perfect" way to fix a problem that doesn't really exist.If it did,the mast would have failed a good while ago.
AI is jet fuel for forums
 
Step 1: Evaluate the Structural Risk
Whether this is a major structural problem depends on three factors:
  • The Location: Holes drilled near high-load zones—such as the masthead, the hound/forestay attachment, the spreadsheet brackets, or right above the gooseneck (boom attachment)—are highly critical. Holes right in the middle of a freestanding Wyliecat unstayed mast are also high-stress points. Holes in low-load areas (like a lazy jack attachment midway up an stayed mast) are less dangerous. [, 2]
  • The Hole Alignment: If the four screws were drilled in a perfectly straight horizontal line, it creates a "perforation line" (like a piece of tear-away paper) that severely weakens the tube. A vertical or staggered pattern is safer. [1]
  • The Screw Material: If they are stainless steel screws threaded directly into the carbon without an isolating barrier (like Tef-Gel or a plastic washer), they will cause severe galvanic corrosion. The carbon will literally eat away the metal and degrade the surrounding resin. [, 2]

Step 2: What to Do with the Screws
Do not just yank them out or leave them ignored. Follow this sequence:
  1. Back them out carefully: Try to unscrew them gently. If they are seized due to galvanic corrosion, do not force them, as you risk cracking the surrounding carbon laminate. Use a penetrating fluid or localized, minimal heat if necessary. [1]
  2. Inspect the holes:Look closely at the carbon around the holes using a magnifying glass and a bright light. Look for:
    • Delamination: Milky white rings or peeling layers of carbon around the hole.
    • Cracking: Micro-fissures radiating outward from the drill site.
    • Corrosion: A bubbling texture or white/grey powdery residue inside the hole. []

Step 3: How to Repair the Mast
If the carbon around the holes is not cracked or peeling, you do not need to replace the mast. You can repair it permanently using an epoxy-bonding method:
  • If you want to keep using the holes: Do not use self-tapping screws. Instead, coat the inside of the hole with epoxy, insert a plastic or fiberglass rawlplug/sleeve to isolate the metal, and use a machine screw. Better yet, bond an external carbon plate over the area to act as an isolated pad for any fittings. [1, 3, 4]
  • If you want to close the holes: Slightly chamfer/sand the edges of the holes, clean them with acetone, and fill them completely with a structural epoxy paste mixed with chopped carbon fibers or high-strength fillers.
  • If there is minor delamination: You (or a professional composite tech) can grind back the damaged area locally and wrap a few localized plies of carbon fiber tape over the section, wetting it with structural epoxy to restore 100% of the tube's original hoop strength

    make sure you got a magnifying glass, as for which one is cooler AI knows

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  • The Stereoype: Seen as highly stable, practical, financially secure, and a capable "fixer."
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No one falls in love with a degree or a corporate title alone. Success in dating invariably comes down to universal human traits:
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In terms of attracting romantic partners, neither profession has a built-in advantage; individual personality, confidence, and social skills matter vastly more than a job title.
However, people do hold different social stereotypes about each field. Here is how those perceptions break down.

Please don't put AI slop in here, I could ask LLMs for advice myself, but was looking for advice from real people here. It's already getting increasingly hard to find real info online, with all of it getting drowned out by this stuff. I'm not going to trust an LLM for repair procedures on a 45 foot carbon spar whose failure at sea could be a life or death thing for myself and my crew.

I had a crewmate on a Melges 24 try to tune the rig with LLM advice, and we would have lost the mast if I hadn't stopped him... the LLM was instructing to overtension the rig by a factor of 3x.
 
So what is your plan on fixing these 4 holes?
 
So what is your plan on fixing these 4 holes?

I said earlier that I am leaning towards following the advice from @jehardiman - epoxy in monel studs or rods, and then layup some carbon cloth over the area. I may try to do a thick tapered cover as the spar engineer recommended, but I do not want to enlarge the holes to use his carbon plug method, as they will cut more of the unidirectional fibers that provide tensile strength. As jehardiman said, my repair won’t be able to recover tensile strength but can recover compressive strength and protect from further damage by reducing stress on the hole edges.
 
If you see this microcracks, you are in trouble. If none yet, do not be too complacent. Carbon fiber laminate belongs to the "brittle" material and failure is catastrophic. The load on the mast is complex as it is a compound load. You have flexing (tension/compression) and torsion. Better mitigate the loss of strength by plugging and fixing it it with the same material (solid carbon fiber rod laminate + high strength epoxy or industrial adhesive).
 

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If this is a filament wound mast, then it consist of unidirectional fibers wound in three axis in a standard 20/50/30 % proportions. 90 degree (hoop) on the inside to handle compression and buckling, 0 degree (axial) for stiffness, and 30 to 45 degree final layer to wrap it up and handle torsion. Hard to replicate but short fibers cut from uni fibers mixed with epoxy can be presssed into a die (drilled metal plate + plunger) cured under pressure will approximate the original lamination. 3M 2216 or other industrial high strength epoxy can be used to secure it.
 
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How are you planning on laying it up

Sand under the fibers are just visible, and then lay alternating layers of cloth with unidirectional vertical weave, and regular woven cloth, tapering the edges.

Still undecided about how to install a new mast track, but considering the option of metal clips through bolted in the small holes already there, but also bonded on with high strength methacrylate adhesive. The other option is to also lay new cloth the entire length of the mast over those holes, lay cloth over that, and just bond the clips on.
 
If this is a filament wound mast, then it consist of unidirectional fibers wound in three axis in a standard 20/60/30 % proportions. 90 degree (hoop) on the inside to handle compression and buckling, 0 degree (axial) for stiffness, and 30 to 45 degree final layer to wrap it up and handle torsion. Hard to replicate but short fibers cut from uni fibers mixed with epoxy can be presssed into a die (drilled metal plate + plunger) cured under pressure will approximate the original lamination. 3M 2216 or other industrial high strength epoxy can be used to secure it.

It appears it is not filament wound, but is alternating layers of unidirectional and woven cloth, such that 75% of the fibers are in the vertical direction. The mast/boat were built in 1996.
 
It appears it is not filament wound, but is alternating layers of unidirectional and woven cloth, such that 75% of the fibers are in the vertical direction. The mast/boat were built in 1996.
Vertical means 90 degree (hoop). Usually it is the 0 degree fibers that are dominant. 50 to 60%. Hand layup mast have very low modulus (and heavy) unless it was vacuum bagged during curing. At least filament wound ones approximates the modulus of a T6 aluminum.
 
fixing it it with the same material (solid carbon fiber rod laminate + high strength epoxy or industrial adhesive).

What do you think about filling the holes with these unidirectional carbon fiber rods, with the fibers aligned in the vertical direction to match most of the fibers in the mast?

"High-Strength Lightweight Carbon Fiber Rods: Their fibers are aligned in a single direction, so they hold up to bending across the fibers but will splinter and separate like string cheese when bent along the length of the fiber"
 
Vertical means 90 degree (hoop). Usually it is the 0 degree fibers that are dominant. 50 to 60%. Hand layup mast have very low modulus (and heavy) unless it was vacuum bagged during curing. At least filament wound ones approximates the modulus of a T6 aluminum.

I'm very confused, I assumed vertical meant lengthwise along the mast. Here is the exact text, but I will e-mail him to confirm:

"The mast has 75% of the fibers vertical, so if you can find both woven and unidirectional carbon fabric, it would make sense to alternate vertical uni and fabric layers"

I honestly don't know much about how this mast was made, that text above is all of the info I have. Ted Van Dusen who engineered the mast certainly knows what he is doing, he engineered virtually all of the unstayed carbon spars used in production sailboats (Wyliecat and Nonsuch), as well as a big fraction of the carbon masts used in high end offshore racing yachts, and his masts are known to be extremely light and not break unless misused. The mast is 46 feet long, supports a large 650 sq*ft mainsail without stays, and weighs about 100lbs.
 
Just using the same formal terminology as used in filament winding method and as used by Eric Sponberg, a member and contributor to this forum and a contributor to Professional Boatbuilder magazine.
 
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