Building Shesha, a Hunter Valley GIS, Australia

[woodeneye]

Ian/MIK

As an exercise, I'm just looking at some standard carbon tube on the Aussie CST website.

35.2 ID; 1.8 wall; 38.8 OD; 319 Weight (g/m); 2.30 Flexural rigidity kN.m^2; 4100mm standard length available; $102 Price/m

Would this be stiff enough do you think? Would it need stiffening in the middle do you think? If so could I just use the cut off bit, split it and slide it in?

By the way, they have shorter, cheaper sections which they say can be "bonded and joined using standard laminating techniques". Another way would be to buy two shorter lengths with one size that just fits inside the other nicely, and then simply epoxy them together.

I'll ask them about freight cost.

[IanHowick]

Ian/MIK

As an exercise, I'm just looking at some standard carbon tube on the Aussie CST website.

35.2 ID; 1.8 wall; 38.8 OD; 319 Weight (g/m); 2.30 Flexural rigidity kN.m^2; 4100mm standard length available; $102 Price/m

Would this be stiff enough do you think? Would it need stiffening in the middle do you think? If so could I just use the cut off bit, split it and slide it in?

By the way, they have shorter, cheaper sections which they say can be "bonded and joined using standard laminating techniques". Another way would be to buy two shorter lengths with one size that just fits inside the other nicely, and then simply epoxy them together.

I'll ask them about freight cost.

Hi Bruce,

If your assessment of the stiffness required from comparing your old wooden yard and your new alu one is correct, then a stiffness of 2.3kN.m^2 is too flexible.

I'd go up a size in either wall thickness or diameter.

For a idea/comparison, 2.3kN.m^2 is about the stiffness of your wooden yard.

Your alu yard (and my carbon yard) have a stiffness of about 4 kN.m^2

My yard is 38mmID, 1.8mm wall, 41.6mmOD, stiffness 3.9kN.m^2

If you go up a size in wall thickness to say 2.4mm wall at 35.2 mm ID you will get about the right stiffness, and the yard will be absolutely bombproof due to the solid wall.

If you go up a size in overall diameter to say 38mmID at 1.8mm wall, you also get the right stiffness, but it would be worth adding a bit of reinforcing to the 200mm either side of where the halyard attaches.

Second option was the way I went, it ends up a little lighter for the stiffness, and a little cheaper I think due to less carbon required.

I got my spar makers to put the extra reinforcement in the middle, if you're buying a piece of tube of the shelf, maybe you could do this yourself with some carbon cloth or tape wrapped around, I guess you could use fibreglass if you added a little more.

The problem with using two sizes that sleeve inside each other is the wall thickness of the piece that goes inside is probably restricted to 1.4mm, which I think is too light for this application. (Usually there is a 3mm jump between the inside dia of tube sizes available)

I'll have a look on the Aussie CST website when I get the chance, see what options I can come up with if you like.

Ian

[woodeneye]

Thanks Ian, I had no idea on how to relate the data to actual flex. I'll see if I can get something around the 4 kilo N watsies squared!

The website is CST Composites: Carbon Fibre Tubes and Rod

[IanHowick]

Thanks Ian, I had no idea on how to relate the data to actual flex. I'll see if I can get something around the 4 kilo N watsies squared!

Hi Bruce, if you want to learn how to relate "kilo N watsies squared" to "how much it flexes under a sailing load", I can fire you some information/equations/possibly a spreadsheet. The maths isn't too bad.

Hugely useful is having the data/pictures/feel for what's happening on the water that you are providing so we can relate theory to practice, try out what we've figured, hopefully go through a few iterations of that.

Ian

[Boatmik]

I just looked more at the Moth site, they are dealing with much smaller sticks than we are - because they are stayed - but a few years ago they were just gluing tubes inside one another with some resiney carbon to bond.

Might be a cheaper but more fiddly alternative that a lovely tapered spar.

MIK

[IanHowick]

Thanks Ian, I had no idea on how to relate the data to actual flex. I'll see if I can get something around the 4 kilo N watsies squared!

The website is CST Composites: Carbon Fibre Tubes and Rod

Hi Bruce, I just had a look at the CST website, compared their tube dimensions with their stated EI (Flexural stiffness) values, their EI values come in quite a bit lower than those for the same dimension tubes from either C-Tech or a carbon tube manufacturer in the UK.

My calculations based on (what I think is standard) 87 - 95 GPa carbon match exactly the quoted values from the later two manufacturers, but the stiffness values quoted by CST are much lower. (For example I would expect their 38.3 mm ID/1.8 Wall/41.9 OD to have a stiffness of 3.97kN.m^2, but they quote this tube to be only 2.9kN.m^2)

Only thing I can think of is their carbon is a lower specification (by about 30%, modulus must be about 63GPa, not 90GPa) than what C-Tech are using, or possibly a carbon-glass mixture. If this is so, we'd need to take that into account when specifying what is needed, possibly go up one more size.

Sorry for all the numbers/weird terminology, hope it all makes some sense. I'm also not trying to persuade you to go the carbon route, just make sure that we get it right if you do.

Ian

[woodeneye]

Hi Bruce, I just had a look at the CST website, compared their tube dimensions with their stated EI (Flexural stiffness) values, their EI values come in quite a bit lower than those for the same dimension tubes from either C-Tech or a carbon tube manufacturer in the UK.

My calculations based on (what I think is standard) 87 - 95 GPa carbon match exactly the quoted values from the later two manufacturers, but the stiffness values quoted by CST are much lower. (For example I would expect their 38.3 mm ID/1.8 Wall/41.9 OD to have a stiffness of 3.97kN.m^2, but they quote this tube to be only 2.9kN.m^2)

Only thing I can think of is their carbon is a lower specification (by about 30%, modulus must be about 63GPa, not 90GPa) than what C-Tech are using, or possibly a carbon-glass mixture. If this is so, we'd need to take that into account when specifying what is needed, possibly go up one more size.

Sorry for all the numbers/weird terminology, hope it all makes some sense. I'm also not trying to persuade you to go the carbon route, just make sure that we get it right if you do.

Ian

Thanks Ian, now that I know the numbers, when I do decide, I'll go with the most important of them which is the "kilo N watsies squared"

[IanHowick]

I just looked more at the Moth site, they are dealing with much smaller sticks than we are - because they are stayed - but a few years ago they were just gluing tubes inside one another with some resiney carbon to bond.

Might be a cheaper but more fiddly alternative that a lovely tapered spar.

MIK

Hi Mik,

Carbon (and aluminium) yards:

I think on this size of (hollow, thin walled) spar, that 'lovely taper' is more aesthetic than necessary for function. I did some measurements on the tapered and untapered ends of my yard, the difference in bend with the same weight between tapered and untapered end was only a couple of millimetres - less than 10%, so hardly noticeable. Weight saving from tapering one end would only be about 5% of the total yard weight, so if you did it by glueing in a smaller piece, it wouldn't save you any weight.

My take on what would be sensible in terms of an 'off the shelf' carbon tube, would be to get a piece at 38 mm ID / 1.8 mm wall / 41.6 mm OD, (so EI of about 4 kN.m^2) then wrap some extra carbon tape or cloth or tape around the middle 600 mm or so where the halyard attaches so it has more hoop strength there. While you're at it, add some to either end to make sure it doesn't split at the ends.

You could do this yourself, but it probably wouldn't / shouldn't be hard to get the people making the tube to do it for you - they'd just wind some prepreg laminate on the middle 600mm of the mandrel first, then run the rest end to end at a 1.8mm wall setting.

I think 'off the shelf' carbon tube is a bit of a missnomer, these websites list all their 'standard' sizes, but they don't have 10 of every possible size and wall thickness just sitting on the shelf.

What they have is all the mandrels on the shelf, some prepreg tape in the fridge, a winding machine and a long, skinny oven nearby. You place an order, they find the correct mandrel, put it in the winding machine, wrap it in celophane, take the prepreg tape out of the fridge, set the wall thickness to wind it, then wrap more cellophane around it after the carbon is on, then pop it in the oven to cure then send it off.

The point is, 'standard size' or not, it's all really custom done, so asking for a specific wall thickness or thickness distribution on a mandrel shouldn't be difficult or particularly more expensive.

Ian

(All these numbers are still dependent on some on the water testing of these stiffer yards, we should have a much better idea if we are correct once Bruce can get on the water with his aluminium yard, and of course I'm itching to get mine on the water as well.)

By the way, Bruce, what is the amount of edge round on the head of your sail?

Thanks for this very useful picture:


Because we know the flex characteristics of the aluminium tube quite well, we can pretty much calculate the forces on the yard from this picture showing how much it is bending. Another picture exactly like this when you are on the water under full sailing load conditions would be good!

Ian

[woodeneye]

By the way, Bruce, what is the amount of edge round on the head of your sail?

Thanks for this very useful picture:

Ian

I'll have to measure and let you know this w/e. Planning on going freshwater sailing this time if I can get some decent time on Grahamstown Dam, which is a lovely big water supply dam near where I live. However, quite restrictive regulations with opening times, closing times and requirements for rescue boats, plus launching fees etc. None of that rubbish for briny sailing!

I have to get my new trailer registered before I can get going though. Have dumped my old box trailer arrangement as it was too cumbersome to manage.

[Boatmik]

I had a thought on the way home from Duckflat tonight - there are two approaches here.

One is that the Duckworks sail has been flattish till this point with the standard spars.

The other is that the UK McNamara sail which has been modified to work well with the standard spars with a larger edge round.

I can't comment about the broadseaming as it is not really obvious.

This has been one of the big debates in most racing classes too - with them flipping from one to the other in many classes each few years.

That is with boats that are highly evolved - of course the goat has a long way to go before we start flipping between these two alternatives as well - thus the value of these discussions.

Best wishes
Michael

[woodeneye]

Hi Bruce, I just had a look at the CST website, compared their tube dimensions with their stated EI (Flexural stiffness) values, their EI values come in quite a bit lower than those for the same dimension tubes from either C-Tech or a carbon tube manufacturer in the UK.

My calculations based on (what I think is standard) 87 - 95 GPa carbon match exactly the quoted values from the later two manufacturers, but the stiffness values quoted by CST are much lower. (For example I would expect their 38.3 mm ID/1.8 Wall/41.9 OD to have a stiffness of 3.97kN.m^2, but they quote this tube to be only 2.9kN.m^2)

Only thing I can think of is their carbon is a lower specification (by about 30%, modulus must be about 63GPa, not 90GPa) than what C-Tech are using, or possibly a carbon-glass mixture. If this is so, we'd need to take that into account when specifying what is needed, possibly go up one more size.

Sorry for all the numbers/weird terminology, hope it all makes some sense. I'm also not trying to persuade you to go the carbon route, just make sure that we get it right if you do.

Ian

To be fair to CST, they do offer a very wide range of Youngs modulus carbon fibres for various applications, from 220 - 550gpa, depending on application. They seem to have quoted the numbers for the lowest and most commonly sold, ie. for general cruising boats, as 550gpa is generally used for aerospace, satellites and robots. They quote 4 different YM ranges are available, so I guess they will choose the type depending on the job it has to do and the customer's appetite to pay!

In the email I sent you, they appear to have quoted me for a spar than will meet the flex requirement while keeping the diameter around 40mm.

[woodeneye]

I had a thought on the way home from Duckflat tonight - there are two approaches here.

One is that the Duckworks sail has been flattish till this point with the standard spars.

The other is that the UK McNamara sail which has been modified to work well with the standard spars with a larger edge round.

I can't comment about the broadseaming as it is not really obvious.

This has been one of the big debates in most racing classes too - with them flipping from one to the other in many classes each few years.

That is with boats that are highly evolved - of course the goat has a long way to go before we start flipping between these two alternatives as well - thus the value of these discussions.

Best wishes
Michael

Good thought. Perhaps we should start collecting some data regarding the amount of edge round and what spars they are matched to?

I still have a strong gut feeling that the 4 sided sail needs a stiffish yard tip to support the leach. If that can be achieved with a tapered spar then the aesthetics are looked after as well.

I have all the bits I need now to try out a kicker when the time is right too. It's an 8:1 cascading system with just 3 little cheapie blocks. Perhaps too powerful, but so simple and cheap. I just wish I had discovered or worked out cascades in my racing days...so much simpler, cheaper and more powerful...

[BradLH]

I have all the bits I need now to try out a kicker when the time is right too. It's an 8:1 cascading system with just 3 little cheapie blocks. Perhaps too powerful, but so simple and cheap. I just wish I had discovered or worked out cascades in my racing days...so much simpler, cheaper and more powerful...

Pulling my 6:1 vang on a broad reach or run can be a bit of a struggle with the 90 sf OZ sail. The cleat is located at the back of the centercase so it's a sideways pull toward the transom, if it were located so the pull were toward me it would be better.

[woodeneye]

Pulling my 6:1 vang on a broad reach or run can be a bit of a struggle with the 90 sf OZ sail. The cleat is located at the back of the centercase so it's a sideways pull toward the transom, if it were located so the pull were toward me it would be better.

Mmm, maybe not too powerful then. Thanks Brad.

[Boatmik]

It is a little bit less than 90.

Maybe I should make the plan $19.95?