Thread: Another UK GIS (Gizzle in Hants)

I think the carbon - wood composite concept probably works better at greater thicknesses. The further the high modulus carbon is from the neutral axis, the more good it will do in adding stiffness. I remain dubious as to how much good it will do on the outside of a 3.6 m by 40mm dia spar.

Do you have any data /claims on this sleeve material from the people who sell/ make it? Even a weight per metre and a rough idea of what percentage of that weight is longitudinal carbon, what % is in the spandex. Or an idea of what thickness of laminate will result from a sleeve added to a spar. With that we can start to make at least some (hopefully) intelligent guesses as to what stiffness it could add.

In the end, the only way to get useful/reliable data would be to build a wooden spar, get some good data on it's stiffness before adding the sleeve, then repeat the stiffness measurements after the sleeve has been added.

By 'good' data, ideal would be supporting it at either end, then adding increments of weight, and measuring the deflection at each weight. Say increments of 3 kg: 3, 6, 9, 12, 15, 18, 21, 24 kg, with deflection at each weight, done both before and after adding the sleeve. Once we've got the two stress-strain curves, we can ascribe the difference between them to the effect of the carbon sleeve.

Lots of work, if I wanted greater stiffness, I'd be inclined to just up the diameter a bit, (but I'd love it if you did the work and got some good before and after stress-strain data).

We can reasonably safely predict that if you increase the diameter of a solid spar by 20%, the stiffness will increase by 1.2^4=2.1, so just over double the stiffness for 1.2^2=1.44 so 44% weight increase. 10% diameter increase increases stiffness by 46% or so for a 21% weight increase.

If you have/can get any data on this stuff, perhaps we can get to where we can make some ballpark guesses so the first reinforced spar you make (if you go this way) will be in a stiffness range that is usable. I recall (woodeneye, I think) saying he'd talked to someone about these sleeves, and they were claiming of the order of 30% stiffness increase when added to a wooden spar of the kind of dimensions we are talking about.

Ian

I tend to agree with you about the impracticality of the small diameter carbon over already dense wood yard. Possibly the way to do it is to use a very low density wood, maybe hollow, increase the diameter and then add some carbon. This way you may end up with a reasonably light yard of the right stiffness.

I built a hollow (8mm wall) approx 52mm x 36mm and tapered slightly, douglass fir yard that deflects 20mm with a 10kg load and 37mm with 16kg but the sucker weighs 2.8kg (6lb 2oz). That's what I ended up using as a boom cause the sailmaker thought it was a bit too stiff. Don't have bend numbers on the second softer yard but it is more tapered and 48 x 38mm at the thickest point, made from cypress and weighs 2.9kg. This yard is probably not too far off for the sail I have.

The boat seemed fine with this much weight aloft but it's certainly not helping things, although the higher roll inertia may make the boat feel steadier, up until a certain point ......

Anyway I'm thinking that I'll play around with yard bend until I have something that works well and then build a lighter yard with the same flex characteristics. This will probably be an all carbon affair laid up over a foam mandrel that is later solvent melted out. The uni sleeves may be the ticket there as you can build the yard on the flexible side and add uni until the stiffness is right.

This is the web page for the sleeving with some thickness data.
* Soller Composites * Carbon UNI & Biaxial Tape Page

Can't wait to see how your carbon rig performs.

Originally Posted by SimonLew

...Possibly the way to do it is to use a very low density wood, maybe hollow, increase the diameter and then add some carbon.

Automotive parts and bicycle frames tend to follow this approach. Balsa wood or some sort of foam product (expanding or rigid) is used to provide shape, but the resin/carbon matrix is where the strength comes from. Of course, much of that strength is due to the appropriate alignment of the carbon fiber's weave with the stress forces, and the underlying mold plays a role in defining those paths, but the core is not a significant source of strength. In my opinion. Unless I'm mistaken. Your mileage may vary. Void where prohibited by law...

I built a hollow (8mm wall) approx 52mm x 36mm and tapered slightly, douglass fir yard that deflects 20mm with a 10kg load and 37mm with 16kg but the sucker weighs 2.8kg (6lb 2oz). That's what I ended up using as a boom cause the sailmaker thought it was a bit too stiff.

Simon, I'm reposting this in my own thread so this discussion can continue on with the cabon fiber momentum, but your flex data are very timely for me...

I did some calcs based on the thickness of carbon laminate that would result from adding one of these sleeves to a 40 mm round spar.

From the Soller website the sleeve material seems to be of the order of 0.03 inches thick, which is 0.76 mm.

I assumed there is a 0.76 thickness of carbon laminate around a 40 mm round spar and used a modulus of 65 GPa (I'm guessing here, standard pre-preg mandrel wound laminate would be about 85-90 GPa, but I'm guessing a hand layup on wood would be considerably lower modulus).

With these numbers, a sleeve around a 40 mm spar will add stiffness (EI) of 1.3 kNm^2 to that spar.

If the original spar deflects 40 mm with 10 kg weight hung from the middle of a 3.5 m span, the original spar has an EI of about 2.2 kNm^2.

So, adding one of these sleeves might add 60% to the stiffness of an existing, reasonably stiff spar. This seems reasonable and matches what woodeneye reports above in this thread from a conversation with Andrew Denman.

Such a sleeve might add 600 g to the weight of the spar, depending on how good a resin - fibre ratio you achieve, and how much you fill the weave for a smooth finish.

If you were going in the direction of a lightweight core with carbon sleeved on the outside, (ie all the strength in the carbon), you'd need at least three layers of sleeve to make it stiff enough. The spar might end up at a little below 2 kg.

Things that make these calculations less reliable are the unknown properties of this sleeve material - I'm just guessing the cured laminate's modulus based on values from mandrel wound pre preg (which goes on with optimal fibre to resin ratio, compression and heat while curing) I have no figures as to how this hand laid laminate performs in comparison, and the effective thickness of the laminate that results is a bit of a guess also. (Effective thickness of laminate will also depend on the size of spar it is stretched over)

Most helpful would be a real data point for this sleeve material, something along the lines of: "(Such and such) a sleeve will typically add (this many) kNm^2 of stiffness when added to a spar of (such and such) a diameter."

Critical is to know the diameter of the spar that had a sleeve added, and how much additional stiffness resulted.
With this, I'd be able to figure with more confidence how much stiffness it would add at other diameters, taking into acount the laminate will be thicker at smaller spar diameters.

Ian

Edit - I just started another thread on a different (and to my mind more sensible) approach to (reasonably priced) lightweight spars.
https://www.woodworkforums.com/f169/f...rboats-135248/

Hi all,
I have not completely disappeared but I have been away sailing so I think that is a pretty good excuse for not getting on with the goat in the garage. Getting back to work and real-life has been a struggle but I have managed to finish off the rudder and dagger board over the last weekend.


Pics here Tales of a Weekend Wood-Butcher

More progress soon....

Bit more progress, BH2, BH3, transom and stem all done. Also cut out the hull sides and joined them on the living room floor (I have a very tolerant wife). Great to make some decent progress.

Pics here Tales of a Weekend Wood-Butcher

Will try to get the chine logs on the hull sides this week but need to buy some suitable temporary screws to hold it all together. I assume the cedar can be easily persuaded to take the shape of the chine.

G

Another stem "maked"! Seems we're quite close in progress.

Originally Posted by Gizzle

I assume the cedar can be easily persuaded to take the shape of the chine.

No one seems to have reported an issue with cedar's ability to bend to MIK's fair curve.

Two other tips come to mind though:

1) This would be the time to bevel the top edge of the chine log if you're inclined to do so. The bevel would allow water to drain to the floor board. It's an extra step and you'll have to determine the angle yourself (I haven't seen a specific dimension documentated) but I believe it will be worth it.

2) There was a great analysis of the conflict between the two chine logs where they meet at the stem. Was it Simon? Or Ian? He diagrams what sort of taper is required at the bow for the two logs to meet peacefully.

Originally Posted by davlafont

No one seems to have reported an issue with cedar's ability to bend to MIK's fair curve.

Two other tips come to mind though:

1) This would be the time to bevel the top edge of the chine log if you're inclined to do so. The bevel would allow water to drain to the floor board. It's an extra step and you'll have to determine the angle yourself (I haven't seen a specific dimension documentated) but I believe it will be worth it.

2) There was a great analysis of the conflict between the two chine logs where they meet at the stem. Was it Simon? Or Ian? He diagrams what sort of taper is required at the bow for the two logs to meet peacefully.

Cedar chine logs bent without much drama. The last couple of feet at the stern are the least cooperative but nothing major.

The chine logs - stem fit sketch is here. I make no guarantees since it did not use it in my build but created it to understand what was going on after I had a bit of trouble. If you do follow it please report back your success/failure.

Originally Posted by davlafont

1) This would be the time to bevel the top edge of the chine log if you're inclined to do so. The bevel would allow water to drain to the floor board. It's an extra step and you'll have to determine the angle yourself (I haven't seen a specific dimension documentated) but I believe it will be worth it.

Bevelling the top edge of the chine log:

I think it's well worth the trouble, less of a sharp edge to get damaged, and lets water and dirt drain off onto the floorboards. Correct angle is about 25 degrees measured from that top edge.

Ian

Originally Posted by IanHowick

Bevelling the top edge of the chine log:

I think it's well worth the trouble, less of a sharp edge to get damaged, and lets water and dirt drain off onto the floorboards. Correct angle is about 25 degrees measured from that top edge.

Ian

Thanks chaps, yes I'm planning to do this for both of the reasons above. I just checked last night that I had a suitable router bit for the job.

Originally Posted by SimonLew

If you do follow it please report back your success/failure.

I made the cuts last night. I gave a little more leeway, 30mm vs. 28mm, 10mm vs. 12mm. It will be while before the two sides come together, but I'll be sure to share the feedback.

Quick question on the daggerboard case….

I’m just finishing off the bulkheads and the daggerboard case and looking at the instructions about adding some plywood spacers in the daggerboard slot. As I have made the daggerboard to the instructions (not using a ply or laser dagerboard), with the internal framing cut down to size such that there is 3-4mm of play (1-2mm each side of the board) do I need to add these ply spacers, perhaps just to the aft end of the slot?

I’m a bit concerned that if I make the slot too good a fit it may get stuck so I'm inclined not to bother.

Not sure how tight you want the board to fit but if you followed MIK's dimensions for the board and case, I'm sure it will work fine. I increased the case width slightly to accomodate outdoor carpet lining. This is working very well at protecting the board from scuffing and it also holds the board at any level you set.

I recently realized that the board holding feature can be duplicated without lining the sides of the centercase. Make up sacrificail spacers from some rubbery/carpety material that go in front and behind the board. If sized right they will pinch the board slightly and provide the friction necessary to keep it in place when partially raised. They will also save a lot of dings on the case and board from grounding impacts.