filling holes in an unstayed carbon mast

[marlinspike]

Would this work for plug building? For $100 and shipping; if it can work…

I suppose that would get the fibers going in a more appropriate direction than a unidirectional pultruded rod? I really wish I had more composites engineering knowledge, it always seems like there are good sounding arguments for doing things different ways, and I am not sure how to evaluate them. If the plug is tapered and has high density, I could imagine most of the compression force is actually trying to essential delaminate it lengthwise and squeeze it out of the hole, so in that case the unidirectional rod would be oriented correctly?

Buying a sheet of CF, I can repurpose the leftovers as some ultra strong but light - and nice looking - backing plates for tether and jackline mounting points, which would be nice to have aboard.

 

[tropostudio]

@rx composite - Curious if you think the OP's holes are only a compression issue. @jhardiman, in post #15 figures it's only a compression concern. Are there criteria where someone 'made a hole by mistake mistake' where you worry about compression and ignore tension? Does that change the approach to a repair? This thread is interesting in that we see advice ranging from 'ignore it' to 'pretty elaborate.' Are there general guidelines for sizing up a repair like this in the marine and aero industries?

 

[fallguy]

I only offered the commercial CF sheet if you insist on a tapered plug. It would be hard to do with the rod and the bonding gets real important for errors in the plug or hole.

My personal view is to bore out the holes and replace with a cylindrical plug, but to stay close to the thread majors versus a big overbore to suit some plug cutter or rod size and to follow RX.

I can’t see it as wise to layup 25 sheets of CF by hand to make the tapered plugs.

If the mast is in compression, my intuition goes against a tapered plug, but I am trying to offer my go to solution when struggling often .. buy it..

 

[Fellies]

I jsut dont understand why people are trying to give aerospace engineering and formulas to a mast with 4 screw holes in?

You could lay up any carbon stack cut it and plug it in with a taper or without one with with a technical glue regardless of the orientation. Its still going to be fine. The boats been used for ages with the screws in and its been fine. One would think an Americas cup mast is being repaired here.

This is so ridiculous the guy might as well buy a new mast.

 

[marlinspike]

The boats been used for ages with the screws in and its been fine.

It does seem to me like with the way carbon fails progressively over time, not having failed yet isn't really evidence that there isn't much to worry about. I race on SF Bay where it's pretty windy in the summer, and during the summer racing season a whole lot of 30 year old racing sailboats finally lose their mast in a 40 knot gust after decades of racing with no issues. It's happened on two boats I'm a regular crew on.

One of the 20 or so wyliecat 30s built has lost it's mast before, and it broke in the exact spot where these holes are, also from mounting a spinnaker pole, however it was flying the spinnaker in 30 knot winds at the time.

 

[tropostudio]

Sounds like OP has gotten a recommendation and OK for a repair procedure by the designer/manufacturer. Signifigant credibility there.
My last question to rxcomposite - another person with signifigant industry credibility - was about guildeines and rationale for deciding on a repair procedure for holes in CF.
'Fuggedaboutit' is also an option. Nothing learned by not asking. Cheers.

 

[rxcomposite]

@rx composite - Curious if you think the OP's holes are only a compression issue. @jhardiman, in post #15 figures it's only a compression concern. Are there criteria where someone 'made a hole by mistake mistake' where you worry about compression and ignore tension? Does that change the approach to a repair? This thread is interesting in that we see advice ranging from 'ignore it' to 'pretty elaborate.' Are there general guidelines for sizing up a repair like this in the marine and aero industries?

It is a complex issue. Attached is my study on mast design covering wood, carbon fiber, aluminum. Sorry, it is a preliminary before the final spreadsheet. I am still into modified elliptical section study.

As you can see, there is bending and torsion. This deforms the round hole into an oval shape. Deformation causes compression (sort of).

So far we are talking only of small hole so the response of most is not to worry about it. Those who are engaged in mast design knows that the Factor of Safety (FoS) is small to keep it light. 2 is standard, even in the aerospace industry. If computations are rigorous and there are coupon samples made, they go down to 1.87. It is better to have a mast break than build it so strong the boat will capsize first before the mast break.

 

[fallguy]

I jsut dont understand why people are trying to give aerospace engineering and formulas to a mast with 4 screw holes in?

You could lay up any carbon stack cut it and plug it in with a taper or without one with with a technical glue regardless of the orientation. Its still going to be fine. The boats been used for ages with the screws in and its been fine. One would think an Americas cup mast is being repaired here.

This is so ridiculous the guy might as well buy a new mast.

Seriously?

Why would you be upset I offered him a link to carbon sheet?

If he decides to go tapered hole; he won’t have to do a 25 layer layup. That was his original advice and then someone offered carbon rod may shatter easily.

I already told him to follow RX.

But the choice to complexity is his own. All I tried to offer is a way to simplify the original proposed option and a query about the bond thickness; of late..

 

[rxcomposite]

Sounds like OP has gotten a recommendation and OK for a repair procedure by the designer/manufacturer. Signifigant credibility there.
My last question to rxcomposite - another person with signifigant industry credibility - was about guildeines and rationale for deciding on a repair procedure for holes in CF.
'Fuggedaboutit' is also an option. Nothing learned by not asking. Cheers.

If you can patch it with the same material and the same strength/modulus plus a strong adhesive that will withstand the shear, good but it won't be as good as new as it is only a repair. Patching it by taper grinding to 1:12 ratio then replacing all the lost laminate + 1 is not recommended (standard repair). The last patch will be a bulge and it will be unsightly. You just made a tiny hole become obvious.

 

[Fellies]

It does seem to me like with the way carbon fails progressively over time, not having failed yet isn't really evidence that there isn't much to worry about. I race on SF Bay where it's pretty windy in the summer, and during the summer racing season a whole lot of 30 year old racing sailboats finally lose their mast in a 40 knot gust after decades of racing with no issues. It's happened on two boats I'm a regular crew on.

One of the 20 or so wyliecat 30s built has lost it's mast before, and it broke in the exact spot where these holes are, also from mounting a spinnaker pole, however it was flying the spinnaker in 30 knot winds at the time.

Just plug it with a carbon rod. make on or, buy one like this other guy mentioned, use spabond and your sliding of the fibres which is the worst ,will easy match the carbon around it on such small holes. If you pushed a small piece of paper or foam in first and fill the hole, the hit a slightly tapered plug in you will hopefully get some on the inside which helps you on the tensile. If the plugs tapered your compressive is fine. If the mast flexes and your shear lap spread is bad, spabond will easily transfer the load with any carbon orientation plug inside. Regardless I dont think this is as bad as you seem to think it is. Just my opinion, Im sure your can trust what ted said.

 

[Fellies]

Seriously?

Why would you be upset I offered him a link to carbon sheet?

If he decides to go tapered hole; he won’t have to do a 25 layer layup. That was his original advice and then someone offered carbon rod may shatter easily.

I already told him to follow RX.

But the choice to complexity is his own. All I tried to offer is a way to simplify the original proposed option and a query about the bond thickness; of late..

Im not saying you wrong im just saying what i would do, sorry for the confusioin

 

[rxcomposite]

Here is how they make forged carbon parts. Same thing when making round tapered plugs.

 

[marlinspike]

Here is how they make forged carbon parts. Same thing when making round tapered plugs.

Wow, that actually sounds pretty easy, I have a 3D printer and a good vice, I could probably manage to replicate that process at home. Forging the actual small plug directly would avoid the thermal runaway of a large layup that I planned to cut down to plug size later.

Man, I can see endless applications for creating sailboat parts like this... I never knew about that process, but it sounds way stronger than the CF-PETg parts I've been printing directly, as those just contain microscopic carbon dust embedded in a fairly weak substrate.

 

[Fellies]

Wow, that actually sounds pretty easy, I have a 3D printer and a good vice, I could probably manage to replicate that process at home. Forging the actual small plug directly would avoid the thermal runaway of a large layup that I planned to cut down to plug size later.

Man, I can see endless applications for creating sailboat parts like this... I never knew about that process, but it sounds way stronger than the CF-PETg parts I've been printing directly, as those just contain microscopic carbon dust embedded in a fairly weak substrate.

Would you really get thermal runway on a part you made for a small plug?

 

[gonzo]

It is better to have a mast break than build it so strong the boat will capsize first before the mast break.

I disagree. Demasting is a bad thing. A properly designed and built sailboat should recover from a capsize with an intact rig.