filling holes in an unstayed carbon mast

[marlinspike]

I have a Wyliecat 30 with a flexible unstated carbon mast, and a previous owner drilled holes (I think 3/8") to mount various hardware, which weren't part of the engineering specs for the mast. At this point, it's pretty time tested with those holes in place, as they were installed decades ago, and the boat has been raced and sailed a lot with them, but I'd like to properly fill and repair them anyways. Is it reasonable to just fill with thickened epoxy, or should I perhaps also install a carbon patch over it? Does adding a patch risk creating a hard/less bendy spot in the mast that could be worse than just leaving the hole?

Sorry for asking a maintenance and repair question in a construction/engineering forum, but I feel this is really a technical spar engineering question, given the complex engineering that goes into designing a composite mast like this. I will also try to get ahold of the engineer that designed the spar and ask for their opinion, if possible.

 

[montero]

Where are these holes? What's the mast profile and wall thickness? Any photos?

 

[fallguy]

So, my opinion…if there was hardware mounted, something filled the void. Removing it now creates a void. Assuming the hardware was attached with something to reduce stress on the mounting; I’d say it would show more stress now under load. So, I’d be inclined to leave it with hardware or repair, not remove and do nothing. My dime..

I am reluctant to offer repair advice on something of this nature. It would be rather difficult to get anything proper on the inside and tapering it for a flush repair seems like it weakens the structure further if any error in the repair. So, I’d be inclined to hire a composites engineer and see if they would specify a repair. My guess is they would want to wrap the entire mast or part of with sleeve type patches, but it is well beyond my wheelhouse and they may offer a cosmetically superior option. I’m only answering because I don’t like the idea of leaving voids and wanted to share the opinion.

We have not had much commentary from the one composites expert lately.

Another thought would be a 5200 patch, of sorts, but again, I’m not fully sure how and won’t pretend, but something moulded over the mast and then removed and then bonded back comes to mind.

So the mast might be a male plug and you create a female mould by adding some thickness to the plug for the laminates before the takeoff and then the part you build in the female mould gets bonded to the mast…or perhaps another plug to get to a male mould for best fit to the mast and some manual work for cosmetics, etc. The most important piece is making sure nothing gets perm bonded to the mast during taking off and also getting dimensions right. Basically, you are building part of a sleeve. How many is based on the number of holes.

I’m not confident a taper grind repair is best here and would not recommend it. If the mast is not uniform dimension, then the takeoffs are done location specific to each sleeve.

Hope I at least stir conversation.

 

[marlinspike]

Here is a photo of the 4 machine screws installed where the spinnaker ring used to be, about 5 feet off the deck. I'm not completely sure, but I think the carbon mast walls are about 1cm thick. I have also contacted the firm that engineered and built the mast for advice, but haven't gotten any info from them yet. Yes, I know it looks like wood, but I promise the mast is actually carbon!

 

[marlinspike]

I’m not confident a taper grind repair is best here and would not recommend it.

Yes, no way am I removing even more material for a patch... I think this is an axial-wound/filament-wound carbon mast, rather than woven cloth, so enlarging or tapering the holes means further destroying the hoop like thick carbon filaments, in a way that a patch isn't likely to compensate for.

One idea is to fill the holes with epoxy, and then epoxy an ugly patch to the outside to strengthen it, but I think that will likely look awful, and could risk making a 'hard' spot that doesn't bend like the rest of the mast.

 

[fallguy]

I’d say it does not look tapered; you did not mention. No matter; skip the sleeve idea…

I’d want to repair it: looks boogered from a prior repair as well.

So, on further, I think building any sleeve starts to add potential for stress risors.

Here is an easier way to go.

Just add a small epoxy plug to the holes. A light sanding and an overcoat one more time of fairing compound.

Then get a really cool sticker from a vinyl shop and cover it all with something related to the name of the boat or something you like…a conversation piece instead of ugly patches and simple repair that doesn’t change the strength anymore than the screws did.

 

[marlinspike]

I’d say it does not look tapered; you did not mention.

I’d want to repair it: looks boogered from a prior repair as well.

So, on further, I think building any sleeve starts to add potential for stress risors.

Here is an easier way to go.

Just add a small epoxy plug to the holes. A light sanding and an overcoat one more time of fairing compound.

Then get a really cool sticker from a vinyl shop and cover it all with something related to the name of the boat or something you like…a conversation piece instead of ugly patches and simple repair that doesn’t change the strength anymore than the screws did.

Thank you, that is what I was leaning towards as well. I am pulling the mast soon to sand and repaint it, and will at least plug the holes with silica thickened epoxy instead of machine screws, and do some fairing.

I'm not sure what you are asking about tapering, the holes themselves are not tapered, the mast is a tapered design, it gets much narrower aloft.

I'm definitely concerned that it would be easy to accidentally make the mast even weaker by engineering a repair wrong- adding any type of sleeve or patch that creates stress points, or opening the holes up and cutting more filaments.

These masts are strong as heck, 30 years later the only one of these boats that has ever broken a mast was when someone was flying a massive spinnaker plus an unreefed 650 sq ft main in 30 knots of wind, when they are not designed to carry a spinnaker at all... that mast did break right at the ring bolts, the location I am trying to repair here.

I will, hopefully, also get the input of the composites engineer that designed the mast, Dr. Ted Van Dusen, before finalizing any plans.

 

[fallguy]

O

Thank you, that is what I was leaning towards as well. I am pulling the mast soon to stand and repaint it, and will at least plug the holes with silica thickened epoxy instead of machine screws, and do some fairing.

I'm not sure what you are asking about tapering, the holes themselves are not tapered, the mast is a tapered design, it gets much narrower aloft.

forget about that query; it was only related to the notion of a sleeved patch ~ the water has flowed past the bridge on that

 

[montero]

If you're worried about breaking it in this spot, reinforce it with roving along the mast. The question is, what will you glue it to?

 

[gonzo]

If it is cosmetic, use a polyester filler and match the paint.

 

[Barry]

With the mast off, do you have access through the bottom of the mast?
There are two possible goals here
1) fill the holes for appearance
2) introduce a strengthening repair

1) easy as Gonzo suggested.

2) Sleeve from the outside, If the sleeve is tapered you would not have to worry about increased stress concentrations. The current holes will be causing some stress concentration BUT if it has worked this way
for years as you stated, the holes have not been a problem.

Sleeve from the inside

If you have access through the bottom of the mast, even if it is several feet up, you could sleeve from the inside. I have attached a process that can line a pipe hundreds of feet long, with a changing internal diameter.
It would take a bit of creativity. But basically you would build a dry carbon fiber sock, flexible, impregnate this with the resin, insert it into the mast. Before you insert it, you
install a bladder, I am thinking perhaps a short
small inner tube, (some type of collapsible bladder) You then wet the dry carbon fiber sock, insert the collapsed bladder (which would have an valve stem on one end, saturate the sock, insert the bladder and saturated sock into the mast as far as to get on the far side of the holes, then blow up the bladder so it forces the saturated sock onto the ID of the mast.

The process is used to line broken sewer pipes up to hundreds of feet long to line them instead of excavating or breaking up concret under a floor. In one situation that I have seen first hand saved the building owner
close to $100k by lining the pipe from the inside of a building with the only access to the split and corroded section of the pipe through a toilet 4 inch hole)

Google Search

Two videos of the process. As you do not need to get the sleeve up the mast very far, it would be simple to make this a DIY process. Alternatively, get the contractor to come to the mast and do it for you.

 

[wet feet]

I would suggest a variation on montero's proposal.Carve or saw a wooden block to the radius of the mast at the point of concern.Cover it with parcel tape and lay up a piece with alternating layers of cloth and rovings to about 1.5-2mm thick.Release it,trim to an oval shape and bond it over the area it is intended for.Visit a vinyl sticker company and have them make a large enough sticker to cover the new piece and have something like ACME CUSTOM SPARS printed on the face.

 

[marlinspike]

If you have access through the bottom of the mast, even if it is several feet up, you could sleeve from the inside.

Yes, I do have access from the bottom, but it is probably ~10 feet up. Could be doable as you describe though with some custom tools. I will need to get the opinion of a professional composites engineer to see if it is necessary before I try something that complex.

 

[Barry]

This is a better look at the process. You would not need the elaborate bladder mechanism with the wheels

 

[jehardiman]

I have a Wyliecat 30 with a flexible unstated carbon mast, and a previous owner drilled holes (I think 3/8") to mount various hardware, which weren't part of the engineering specs for the mast. At this point, it's pretty time tested with those holes in place, as they were installed decades ago, and the boat has been raced and sailed a lot with them, but I'd like to properly fill and repair them anyways. Is it reasonable to just fill with thickened epoxy, or should I perhaps also install a carbon patch over it? Does adding a patch risk creating a hard/less bendy spot in the mast that could be worse than just leaving the hole?

Sorry for asking a maintenance and repair question in a construction/engineering forum, but I feel this is really a technical spar engineering question, given the complex engineering that goes into designing a composite mast like this. I will also try to get ahold of the engineer that designed the spar and ask for their opinion, if possible.

Ok, they have been there for years...so this is not a tension issue, but a compression and cosmetic issue.

I’d want to repair it: looks boogered from a prior repair as well.

Yep, is that staining on the lower two screw holes cosmetic or delamination?

So, on further, I think building any sleeve starts to add potential for stress risors.

Here is an easier way to go.

Just add a small epoxy plug to the holes. A light sanding and an overcoat one more time of fairing compound.

Then get a really cool sticker from a vinyl shop and cover it all with something related to the name of the boat or something you like…a conversation piece instead of ugly patches and simple repair that doesn’t change the strength anymore than the screws did.

Based on how we have repaired CF and S-glass vacuumed formed items for deep submergence, I'd do it this way. Get a short NI-CU (CF will corrode regular SS) set screw that fits the hole. Screw it in with epoxy and set it just below the surface. Once that is set, use a fiber thickened top coat covered by a piece of tape/wrap to get it smooth. Cover as you see fit. You can never repair the tension without HUGE structural cutouts, but the compression issue is relatively easy.