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Anyone familiar with the different types of carbon fiber tubing?

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  • Anyone familiar with the different types of carbon fiber tubing?

    I bought a sailing rig for my kayak last year and capsized for the 1st time last week, snapping the upper mast made of 3/4" OD 6061 aluminum. I'm wondering if I would be smart to replace it with carbon, but I see many different types, different wraps, pultruded, etc.

    FWIW, here's the rig, the lower mast is supported by stays but the upper is held by sliding brackets on the lower, so when it hit the water hard it just bent and snapped. Would one type of CF tube be better than another to resist this kind of force? In that kind of event you produce both compressive and extension stresses focused on that upper bracket.

    Click image for larger version  Name:	kayaksailor for HSM.png Views:	0 Size:	440.2 KB ID:	1969284

    Location: Jersey City NJ USA

  • #2
    I would just stick to aluminum, but if you must go with CF don't use pultruted. Pultruded is very stiff in bending as all the fibers run lengthwise, but it crushes easy and has little hoop strength. Wrapped tubing is better because you will get fibers running not only lengthwise, but also at +/- 45 degrees in a decent layup. CF is a lot of money for no gain in this case. IMHO.

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    • #3
      Originally posted by polaraligned View Post
      I would just stick to aluminum, but if you must go with CF don't use pultruted. Pultruded is very stiff in bending as all the fibers run lengthwise, but it crushes easy and has little hoop strength. Wrapped tubing is better because you will get fibers running not only lengthwise, but also at +/- 45 degrees in a decent layup. CF is a lot of money for no gain in this case. IMHO.
      Why no gain? Do you think it would be just as vulnerable to breakage as the 6061? I was figuring it's threshold to catastrophic failure in the same dimensions would be much higher. I've found 19mm OD with 16mm ID on Ebay. I've worked with small diameter pultruded rods, like 6mm & 8mm, and they're much stronger than equivalent solid 6061.

      I was pretty disappointed that the 6061 failed the very 1st capsize, and now the rig's small mfr is trying to sell their business, don't have stock on the part, want $45 +shipping for a 110cm tube if they did, and sourcing anodized 6061 tubing in that size is not turning out to be easy.
      Last edited by gellfex; 11-08-2021, 05:39 PM.
      Location: Jersey City NJ USA

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      • #4
        Aluminium bends and flexes with stress, CF is more prone to breakage from what i know. Carbon fiber has a better strength to weight ratio in certain situation, but generally the application has to be engineered to play to CFs strengths, personally i duuno that i would trust doing a straight replacement, specially not on a piece like that

        Id just get a tube the right dimensions and paint it. Heck, get tube with a heavier wall and itll be stronger to boot

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        • #5
          CF can also fail internally without showing any external damage, whereas it's abit easier to see on alu. I'd do what the others suggest and buy a thicker walled alu replacement. Then make an anodising rig and anodise it yourself

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          • #6
            Originally posted by gellfex View Post

            Why no gain? Do you think it would be just as vulnerable to breakage as the 6061? I was figuring it's threshold to catastrophic failure in the same dimensions would be much higher.
            It is way more brittle. A lot of composite parts that might be subjected to any impact use Kevlar or CF with Kevlar outer layers, and they still won't outperform the aluminum for impact like you are speaking of.


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            • #7
              Be careful about making it too strong, it may survive but break something harder or more expensive to fix/replace. Bob
              Bob, 71193, Central Arkansas

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              • #8
                I played with windsurfing for a bunch of years and there's oodles of carbon masts out there that bend just fine. None of them are just standard tubing though. They are all done with a combination of bias and straight carbon so they are both stiff yet can flex to the curve needed when the sail is tensioned. And it's a LOT of flex. So no, a proper carbon sailing mast can flex a lot under normal sailing loads and even survive slamming into the water repeatedly with ease. And trust me. I was not the best of sailors out there so my masts were torture tested... A LOT ! ! ! ! Yet at the same time it's stiff enough to be able to haul on the sail for achieving the proper shape.

                If one of the now commonly found used carbon windsurf masts or a part of one would serve your needs you won't regret it. Just inspect the surface for any damage which is more than a slight scuff to very shallow scratch. Anything deeper than around .01" is reason to say no and move on to the next one. You don't want a mast or mast section (a lot of wind surfing masts are two piece) where the outer epoxy layer has been cut through far enough to cut into any of the carbon strands. There is an outer coating of just resin but it's only about that .01'ish of an inch thick.

                If I can measure some sizes for you for the typical base and top diameters I still have a two part mast and a couple of sails here. You see I've still got this crazy dream that I'll make up a nesting dingy that is a combo rowing and sailing design. So I kept the mast, a couple of suitable size sails and the wishbone boom that the sails need.
                Chilliwack BC, Canada

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                • #9
                  Originally posted by BCRider View Post
                  I played with windsurfing for a bunch of years and there's oodles of carbon masts out there that bend just fine. None of them are just standard tubing though.
                  Yeah, the problem is I need three quarter inch tubing and windsurfer masts are quite a bit bigger than that. While there can be big distributed stresses on a windsurfer mast it doesn't get the focused stress that this thing gets at that last support point when it hits the water. It's not long, the whole thing is 111cm, so I'm not sure that off-the-shelf rolled cloth carbon tube would not do it.

                  I'm really reluctant to just redo it with aluminum since my failure rate on capsize has been 100% so far! It's clearly the weakest point of the very clever design that I've discovered.

                  Location: Jersey City NJ USA

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                  • #10
                    I feel for you, that is just wrong. This seems like a case of a horribly flawed design with no/insufficient engineering. I mean I've been dunking sails for close to 50 years and have never broken a mast. What make was the kit so others can avoid it? (they imo should be named)

                    Be careful about making it too strong, it may survive but break something harder or more expensive to fix/replace. Bob
                    Yeah, who knows whether rest of the system is ready to break as well, but what choice is there with a mast that breaks on capsizing? I think you have to make it stronger or scrap it. Other materials? larger dia tube, windsurfer taper fiberglass tube cut off at the right length?
                    in Toronto Ontario - where are you?

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                    • #11
                      Originally posted by gellfex View Post

                      ......I need three quarter inch tubing.....It's not long, the whole thing is 111cm, .....
                      The picture of the rig is a bit misleading for scale. It took me an extra blink to realize that this is a sit on kayak with a sailing rig. So you're right and a windsurfing mast won't work at all. My first view last night had me thinking it was more of a sailing dingy.

                      For that size and length I honestly think I'd go with one of the more structurally strong alloys of stainless. The weight penalty will be very minimal and if you pick the right sort of alloy it'll be quite springy and should tolerate a basic capsize without any issue. And depending on how fragile the left over aluminium mast truly is perhaps you simply need a replacement of good thick walled aircraft aluminium with one of the more durable T numbers on the end which indicates a better springy behavior.

                      Assuming too that the failure was likely where the mast meets the socket in the hull if you were able to find the proper SS tubing and the size that didn't quite fit into the ID you could slit the smaller tube and force fit it up into the base so it gave the first part where it exits the deck and sees the highest force some additional support. The usual failure mode in tubing being that it deforms to an oval and then buckles. An insert of this sort aids with resisting that ovalizing under heavy load.

                      A suitable carbon thick wall tube MIGHT do it too. Likely would in fact. But with all the various parameters dealing with how it was made in terms of axial vs wound fiber ratios it would be hard to say if one is good where another might be more of a risk than the failed aluminium mast. I'd certainly feel more confidence myself working with stainless in this case.

                      Hope that gives you at least some ideas.
                      Chilliwack BC, Canada

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                      • #12
                        Originally posted by Mcgyver View Post
                        I feel for you, that is just wrong. This seems like a case of a horribly flawed design with no/insufficient engineering. I mean I've been dunking sails for close to 50 years and have never broken a mast. What make was the kit so others can avoid it? (they imo should be named)
                        Yeah, who knows whether rest of the system is ready to break as well, but what choice is there with a mast that breaks on capsizing? I think you have to make it stronger or scrap it. Other materials? larger dia tube, windsurfer taper fiberglass tube cut off at the right length?
                        The whole thing is actually amazingly clever and hits so many of the ideal requirements for a kayak sail in that it comes down completely while on the water so it doesn't catch the wind or interfere with fishing. The only criticism I've had up till now was the leeboards were too small in profile so it made too much leeway and pointed upwind poorly. That was what the project I previously posted about having to do with fiberglassing around a fairing shape was for.

                        But unfortunately, the design requires the topmast to be unsupported by stays, and that sliding connection is obviously a weak point. It also has bungee cord running up inside, so replacing it with solid wood or such is not an option either.

                        As for accountability, I fear it may be too late! The couple that ran the company posted on their site kayaksailor.com that they were retiring and looking to sell. So far they are unresponsive to my email and the phone is 'busy'. It could be that since their patent runs out shortly they decided they couldn't compete if someone copied them. It's possible, the unit was quite expensive, as much as a kayak costs!

                        Relative costs of stuff is a whole nother thread, I bought a single rocking potentiometer for a project for a price that could have bought me a low end smartphone. Strange times we live in...
                        Location: Jersey City NJ USA

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                        • #13
                          Sounds like it may have broke near the upper support. If it did break right at the attachment, there's a chance the tube was distorted by the clamp, setting it up for failure. A properly installed, identical replacement might be just fine.

                          Not sure if it would work at the same diameter, but a piece of straight grained spruce has been used for a lot of booms and gaffs over the years.

                          Edit, I see you can't go the wood route.
                          George
                          Traverse City, MI

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                          • #14
                            Originally posted by BCRider View Post

                            The picture of the rig is a bit misleading for scale. It took me an extra blink to realize that this is a sit on kayak with a sailing rig. So you're right and a windsurfing mast won't work at all. My first view last night had me thinking it was more of a sailing dingy.

                            For that size and length I honestly think I'd go with one of the more structurally strong alloys of stainless. The weight penalty will be very minimal and if you pick the right sort of alloy it'll be quite springy and should tolerate a basic capsize without any issue. And depending on how fragile the left over aluminium mast truly is perhaps you simply need a replacement of good thick walled aircraft aluminium with one of the more durable T numbers on the end which indicates a better springy behavior.

                            Assuming too that the failure was likely where the mast meets the socket in the hull if you were able to find the proper SS tubing and the size that didn't quite fit into the ID you could slit the smaller tube and force fit it up into the base so it gave the first part where it exits the deck and sees the highest force some additional support. The usual failure mode in tubing being that it deforms to an oval and then buckles. An insert of this sort aids with resisting that ovalizing under heavy load.

                            A suitable carbon thick wall tube MIGHT do it too. Likely would in fact. But with all the various parameters dealing with how it was made in terms of axial vs wound fiber ratios it would be hard to say if one is good where another might be more of a risk than the failed aluminium mast. I'd certainly feel more confidence myself working with stainless in this case.

                            Hope that gives you at least some ideas.
                            Thanks, but your idea of how it work is way off! there's no deck socket, when you pull the main halyard the main mast step slides towards the stern and the mast pivots up, tightening the forestay and shrouds till you lock the halyard. The topmast halyard pulls the sliding topmast up to fully set the sail. Don't know if this is clear, if you're really interested they have videos
                            https://www.kayaksailor.com/video-gallery/

                            As for carbon vs 6061, as I said the latter has 100% failure rate for me. I'd rather try something different, especially if the cost is comparable, as it apparently is given the difficulty of sourcing anodized tube. There's also the idea of 2024, but that I would definitely have to DIY anodize or pay a custom run.

                            This is the carbon I'm looking at, it appears from this image in the admittedly untrustworthy Ebay post to have numerous multidirectional layers. https://www.ebay.com/itm/143784564644

                            Click image for larger version

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ID:	1969433
                            Location: Jersey City NJ USA

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                            • #15
                              On the first read I missed that there's a few thicker wall options. I see that there's a 20mm OD option with a 14mm ID. So 3mm wall. If you can get the length you need that looks like your best bet. It's a trifle over your 3/4" but only a trifle. And the 3mm wall should result in a good ovalization resistance and thus it should resist shattering. But if it folds over and hits a hard edge of some manner such as a rigging lug on the deck all bets might be off.

                              Most of the other options and the write up in the body description make it look like the main focus is on model aircraft uses. But that 20 x 14mm option looks highly promising.

                              Last edited by BCRider; 11-09-2021, 01:09 PM.
                              Chilliwack BC, Canada

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