External Track For Batten Cars?

[Dsanduril]

The reason you can't find a ready-made conversion calculation from aluminum to carbon fiber is because there isn't one. It's not easy to compare properties of carbon fiber against steel or aluminium. Metals are (generally) uniform– they have the same properties in every direction.

Strength and rigidity of a carbon fiber component is created by positioning fabrics in a specific way. To compare a carbon tube to an aluminum one you need to know how many fibers are aligned longitudinally (to take that overall compressive/tensile load) and how many are crosswise (to take hoop stresses) and the nature of the fibers (are they continuous? discontinuous?...). This is really the same as all the glass work that went into the boat, if you are really building lightweight then you oriented glass fibers in specific locations to take specific forces. A carbon rig is no different, while an aluminum tube is built for the highest stress/strain case and the other dimensions are 'oversized' and just come along for the ride.

The perfect picture is the vertical fibers. If you only have vertical fibers they will split apart when put under bending strain. So you need hoop fibers to keep them together. In an Al design that hoop stress creates less force than the longitudinal forces and so the Al thickness required to carry the longitudinal load is overbuilt for the hoop stresses. With carbon you get to design both, and if you're saving weight you will balance them.

[Chotu]

Originally Posted by PirateFoxy

Generally speaking IME, what makes someone a pro of this sort is not being able to do the math, it’s knowing WHICH math to do when/where, and also knowing when what the math is telling you just doesn’t look quite right and that you’ve likely made a mistake somewhere.

Given that carbon fiber and aluminum have some quite different properties, wouldn’t the original design specify or assume a specific material? If so wouldn’t it need to be properly evaluated if the material was changed, to make sure stresses are still handled correctly and so on?

Of course. Yes to all that.

This discussion is getting tiresome since it’s not really about the topic.

It’s about bashing my boat (personal attacks) and people scared to death of a little math and mechanical analysis.

Also, no one has answered my questions so I can only assume no one here knows. When people don’t know I guess they put others down and sound the alarms of fear.

Guess what. People on boatdesign.net do know. And instead of fear mongering and personal attacks, they’ll tell me how to calculate this, or if indeed it can’t be calculated knowing the exact aluminum spar and moments as well as the properties of both materials. .

Over and out.

[zstine]

If Chotu knows the Aluminum mast section, and wants to specify the carbon one, he can do some reverse engineering. Stress = M c / I Start with you Aluminum (what alloy?) lets assume 35ksi yield...solve for M (bending moment) for his given mast section and now he knows what M the carbon mast must be good for... this assumes everything else on the mast is equal like length, spreader locations, etc. The same process should be repeated for buckling. He can even extrapolate from a 1 spreader rig to a 2 spreader rig, but it gets more difficult.

Masts loads are defined by the max righting moment of the boat hull (not sail area/forces). So another way to approach this mast design would be to start with that, max righting moment (beam/2 times loaded displacement) and do a force balance.

There are many free papers on how to do the detailed design of a mast, even the composite layup of one if you want to build your own. Sponberg has several papers if you want to design a free standing DIY built rig. They are easier to design since they aren't under compression and don't buckle. And Sponberg has helped many DIY mast constructions. You don't need to autoclave around a mandrel and use a huge hydraulic press to extract the section... there are back-yard methods that are very successful.
here....

https://www.ericwsponberg.com/wp-con...ring-masts.pdf

[zstine]

here's a paper on stayed mast design.. its a grad student thesis which I haven't gone through, but should give you a good understanding of the methods...
https://www.academia.edu/182815/Sailboat_Mast_Design

[zstine]

Originally Posted by Chotu

Of course. Yes to all that.

This discussion is getting tiresome since it’s not really about the topic.

It’s about bashing my boat (personal attacks) and people scared to death of a little math and mechanical analysis.

....
Over and out.

I hope what I posted above helps. I haven't personally done a mast analysis, though I think I understand the Sponberg calcs. So I may be able to answer specific questions about the above analysis if you have them. boatdesign.net certainly has people that can do this, I'm just not sure how forthcoming they are... worth a try.

[Jim Cate]

And all that is already specified on the plans. I guess you don’t realize I bought plans to build a boat from ?? Those details are included in the rigging plan, believe it or not.

And you don’t believe anyone can do anything they set their minds to? How do you think one becomes a rigger or designer then? They have the ability from birth?

Quote:

I'm far more comfortable with substituting a used spar whose details were successfully designed than starting with a carbon tube... bare as a baby's bum, no matter how stiff the tube might be.
I’m far more comfortable using the designed parameters of my boat’s ALREADY DESIGNED rig to build the rig in my plans than to substitute the rig from a similar boat. But you don’t seem to understand there is a rig specified in my plans for some reason. I may end up with the used aluminum rig anyway to save money depending on the cost of this carbon section. I’m going with the less expensive one most likely.

Sorry about the messy quotes above, but somehow they seem at odds with the first post in this thread where you say:

[QUOTE]So what if they just did me an oval and I added a track for batten cars on the outside of it?

1). Is that possible with a carbon fiber mast?

2). Is it advisable at all? Will it work or will they get jammed and stick or some other undesirable effect? We are talking large roach, flat top, full batten main.

3). How do I attach my tangs, spreaders, other hardware to a carbon fiber mast? Can I do this with fasteners somehow?

4). If I know the 2nd moment of inertia as well as an aluminum section that works for the rig, how can I specify a carbon section, given the material properties are different?
Moment of inertia only defines the shape of the mast. It does NOT define wall thickness. How do I know what wall thickness to use? The below wall thickness is for aluminum.
[QUOTE]

This does not sound like someone who is following a existing design, and that was the source of my concern. If in fact you have all these design details in hand, why are you asking such questions?

And I'm sorry if you found my post to be a personal attack. It was certainly not meant to be such. You have accomplished much... far more than most folks on this or any forum, but your own recent thread about the damage done to your boat whilst sitting on its own detracts from the idea that it is a completed sailing yacht of proven performance. I have faith that in time she will indeed be just that... whether with a carbon or an aluminium spar yet to be determined.

Finally, I still disagree that "anyone can do anything if they try". I know that I am not able to do things that require sharp vision or steady hands, or that require an artists view of the world. And not so many can compose symphonies or drive formula one race cars or do heart transplants no matter how hard they try.

I do agree that many yotties can learn to do many of the tasks that are commonly farmed out to "pros", and do them as well as said tradesmen... and I applaud such efforts and have encouraged folks to make them, right here on CF.

Jim

[Sherpa17]

I worked on a mast project for a Mount Gay 30 and an external carbon sail track was successfully vacuum bagged to a carbon mast. I happened to see the boat a few years later and it was still intact.

Ime, batten cars don't like a lot of bend, though. In the case of the Mount Gay, the track was heavily reinforced where the cars sat.

[contrail]

Would using an adhesive to attach the track to the carbon mast be better than screws to allow some flex, when the mast bends?

[waterman46]

Originally Posted by zstine

Masts loads are defined by the max righting moment of the boat hull (not sail area/forces). So another way to approach this mast design would be to start with that, max righting moment (beam/2 times loaded displacement) and do a force balance.


Yes, but don't forget to put in a healthy margin of safety since that sort of calculation is a steady-state and doesn't take into account the intense dynamics taking place, which are probably impossible to calculate with any accuracy.



There are many free papers on how to do the detailed design of a mast, even the composite layup of one if you want to build your own. Sponberg has several papers if you want to design a free standing DIY built rig. They are easier to design since they aren't under compression and don't buckle. And Sponberg has helped many DIY mast constructions. You don't need to autoclave around a mandrel and use a huge hydraulic press to extract the section... there are back-yard methods that are very successful.
here....

https://www.ericwsponberg.com/wp-con...ring-masts.pdf

Unfortunately, Chotu's cat probably was not designed to handle the localized stress of a free-standing mast mount.

[fxykty]

Originally Posted by Chotu

Thank you. I don’t know anything here so I’m trying to understand.



I just read tracks are typically put on a carbon fiber mast using adhesive rather than fasteners.



Does anyone know of a good system for an external track and cars or slides that works well with big catamaran full batten mains with a square top on a carbon mast?



Which is better? Cars or slides?

Cars are the only option with full battens and the size of main your boat will have.

Harken, Selden, Antal, Ronstan, etc. all have mast track and car solutions.

Regarding attaching the track, it will need to be reinforced at each batten car location and particularly the head cars’ location at full hoist and each reef hoist. That typically means mechanical fasteners in addition to however the track is attached to the mast.

[Matt Johnson]

Well, I hope the carbon works because the used mast on eBay just sold

Hopeful it was you that bought it.

Matt

[Moonskater]

Hi,
I just did this operation on my catamaran. I went from a heavy z-spar fixed aluminum mast to a 10% taller carbon rotating wingmast. The carbon profile had a fairly wide flat rear-end so i devised a aluminum profile extrution with the exact selden car profile that you show in your first post, glued to the back of the carbon mast.
I did have pro help with all the calculations for stress and load at all the different sail configurations and reefs. Quite large and complicated XL-sheets!
I bought the raw Carbon tube, made for my boat prepreg autoclaved and the me and dad built the complete rig ready.
We have sailed with this confiuration now for the third season and it is great! A totally new boat!
Imagine a Fontaine Pajot Antigua 37 from 1993 that sails TWS most of the time up to 8knots! 8 knots of wind, 8 knots of speed!
I still have aluminum extrution so if you go with the same carbon mast profile, i can supply the track extrution for the Selden battcars.
Had i known how i would have supplied a picture or two of the setup.
Henry Ford once said "Werther you think you can, or you think you can´t. You´re right"
That is my motto in many situations.
Let me know if i can help in any way.
/petter

[Chotu]

I had taken a break from the forum and this thread for a bit after the thread (as usual) went sideways.

What a great surprise to come back here and see so many thoughtful, helpful posts helping me learn.

Thank you soooo much for the references to the materials I need to get comfortable with this stuff.

I’m out running errands to provision for 2 days straight right now, but will revisit all these wonderful posts and see what I can come up with.

I cannot believe Moonskater is doing wind speed with the new rotating carbon rig on a 93 Fountaine Pajot. WOW! What sails are deployed during that? Do you think the rotating mast was more important than the spar weight? I had dismissed rotating masts as too much complexity even though my designer figured I’d probably use one. You’ve really achieved something there.

I’ve sat down with Eric Sponberg before he retired. Very nice man. He was patient and helpful with my very new/green questions. He helped me interpret some of the things that were ambiguous to me in my plans. He’s definitely the rigging master.

While I’d absolutely love an unstayed mast to reduce complexity and get rid of rigging (a central theme to my design is to get rid of things that annoy me about boats), I don’t have the localized reinforcements to hold up an unstayed mast.

My forward main structural beam is very precisely designed using finite element analysis and some interesting runs of glass to support a mast stepped on it at deck level and pressing down.

I could probably bury an unstayed mast all the way through the beam, but it was never designed to take a torsional load like that so it would be a huge modification.

This weekend, I’ll wade through some of the links here to the calculations provided. Thanks for the help.

Moonskater: what adhesive did you use to bond the track? Do you still have those Excel sheets so I could learn from them? I would definitely be interested in doing the same Selden track and cars you did. Do you remember the information on what your old Z spar mast dimensions were and what your new Carbon mast dimensions are? It would help me get a feel for what a successful “conversion” between the two would be. Just as a 10,000 ft/meter view to make sure my numbers are of the right magnitude later.

Zstine: I need to take some time to go through all the great resources you’ve provided. I’ll do this over the weekend.

I’m definitely not against getting someone to join in on exploring this idea. Does anyone know a mast designer that specializes in carbon? One in south Florida hopefully? But I’ll get all the details figured out BEFORE contacting them to consult briefly and double check everything.

I kind of want to build my own carbon mast in a lot of ways but the epoxy allergy precludes me from doing that. So as I’m doing the order for FRP pultrusions for various things I need (like my davits and some columns and stiffeners), I wanted to see what a carbon spar and boom pultrusion might cost while I’m at it.

[Sherpa17]

You might try to contact JB Braun. He knows this stuff. He might get back to you.

[Moonskater]

Chotu,
I guess i have all the data, drawings and nessesary info you might need. We just have to establish another connection so it is easier to show / send pics etc. I know it´s possible here but dont know how.
The track was of course bonded with a thick epoxy adhesive.. Sorry about your allergie! My mast pipe comes from Marstrom in Sweden and is 365x170mm. my added extrution with the sailtrack makes it a 405x17 mm wing mast. The main contributor to the added performance is larger sail area, new sails UK carbon type, and the rotation feature, in that order. My goal was not to gain higher topspeed but to improve average speed and reach 6-8 knots of boatspead sooner, as that is the speed that the boat and crew likes the best for comfort.
To sail windspeed i have a 64m2 Code0 on a prodder or with a mastheadhoisted spinnaker. Maybe i managed to attach two pics. with the spinnaker we are sailing steadu 10-11 knots there.