Time to recore

[Zach]

An idea for finding your pads... at a later date.

Pick two points that aren't gonna go anywhere... Like the corner of a cabin top. Measure a straight line from each.

When you want to find the center of your solid glass spot, take a string, pin it down at the length of one leg, swing a pencil on the arc. Go to the other, repeat. Where the two cross is the location of your pad.

... Grin.

Zach

[Chris Campbell]

Getting ready to cut the cloth to do my layup (won't be able to actually lay it up today due to dinner plans, but I'll be ready for the next chance, hopefully tomorrow) - and am wondering about overlapping the pieces of cloth. If I were doing this with many layers of 10 oz. cloth I wouldn't ask - I'd overlap and stagger the overlaps. But since I'm doing this with 2 layers of 1708 it seems like any area of overlap will be much too thick, relatively speaking. Does it make more sense in this case to butt the fabric up against the next piece, rather than overlap? That'll be a weak point - will that matter?

Great advice on the solid pad locators, Zach, and exactly what I did in the end - and wrote it in sharpie on the balsa and photographed it and put it on my site. So hopefully I won't lose it!

Thanks,

Chris

[Quetzalsailor]

Sketch the layup in section. Lots of ways to stagger things.

Sounds like you should be using thinner stuff and more overlaps. Or bigger pieces. I think that halving the amount of fiber in any one place, along one line, is not good. Perhaps the joint can be placed over a thinner place in the core, with a third thickness of fabric dropped into the recess.

Entertainingly, my oldest FD is made of two layers of transverse strips of two-ply plywood with a longitudinal veneer added to the exterior. So, the interior veneer is transverse; the next veneer is longitudinal but only as long as the inner strip of two-ply plywood is wide (7" or so); the third veneer is also as long as the second strip of two ply plywood is wide, but staggered; the fourth veneer is transverse; and the fifth, exterior, veneer is the previously mentioned longitudinal. Thus effectively, the hull is four ply moulded plywood with the second, longitudinal ply spliced by virtue of the half-strip overlap. Perfectly clear, eh?

Unlike your plan, there are no butts in the longitudinal or transverse fiber.

[Chris Campbell]

I'll try to draw a pattern to include here in a minute, but for now here's a description: There will be four pieces per layer: one running transverse across the partners, one each side running aft from there to the back of the cabin top, and one filling in the small area behind the saloon hatch. I'll stagger the joints such that both of the joints between the forward, transverse, piece and the ones running aft are covered by my third transverse layer over the partners, so there will be no area without 2 continuous layers there. The small piece behind the companionway will also be staggered, but will not have a third layer - or that's my current plan. I could easily toss an extra piece of 6 oz. cloth on top of that area to tie it together, I suppose, although I don't know how much difference that would actually make, and it would mean I'd have a weave on top to fill in.

Sound like it ought to do it? Or do I need to continue thinking about it?

I'll draw a picture and get it up shortly.

Thanks!

Chris

[Chris Campbell]

OK, here's a diagram of my proposed solution, to make it easier to visualize:


And I've posted a description and my thoughts on my site, here.

Will this be enough? Do I need a third layer over the whole thing? Should I do what Doug suggested and dig a hole in the balsa to get a third layer under the staggered joints around the back of the saloon hatch?

Thanks!

Chris

[Quetzalsailor]

Ahh, I did not understand how thin the stuff was. I think you can lap it the right amount for full strength of embedment (if we were talking concrete and rebar, that's 30 diameters (I recall from the dim-dark)). Then you'll be coating out in faring compound and long-boarding it perfect. You can loose the 1/16" laps w/o trouble. Just don't sand through to the fibers.

If you were to put a recess into the core, rout it in after the core's as smooth and fair as you can get it.

I presume you're lapping onto the existing boat in a similar manner.

[Zach]

Why don't you stagger the joints 2 or 3 inches, then use a notched spreader with notches deeper than your cloth is thick to add fairing compound to each side to build up and flatten it quick with a long board, then trowel in more compound when you've got a fair surface... Or lay a sheet of finish cloth on the side you lapped over to bring it up to flush ish... just as filler.

[Chris Campbell]

Top skin's on. I went with more or less the layout planned above, although when I started cutting I forgot my plans and did something different - from which I had to recover. Oops. Anyway, the end result is good. I butted and staggered the joints (thanks, Tim) and will have a third layer over much of the cabin top, providing extra stiffness around the saloon hatch and extra strength around the partners.

Still a long way to go before I'm painting, but progress continues. As little fun as it is during the doing of it, there is quite a lot of satisfaction afterward!

Updates, as usual, on my site.

Oops! Had to edit the post to add a picture, can't post without a picture, silly me:


Cheers,

Chris

[bigd14]

Looks good, Chris! it is a good feeling getting it all put back together. I'm at the same stage. Adding a third layer to side decks, then I can begin fairing... Its just nice to have the boat sealed up again so i don't have to worry about accidentally stepping in the wrong place!

Doug

[Rachel]

I butted and staggered the joints (thanks, Tim)

Looking good, Chris!

Say, I'm interested in the idea of butting and staggering the joints - am I missing where you and Tim discussed it? If so, sorry, but could you point me to it (maybe it was mentioned in another thread or a rebuilding log?)

Thanks,
Rachel

[Chris Campbell]

Hi Rachel,

Sorry for the delayed response - first I was away (sailing!), then I forgot. Lousy excuse.

Tim's suggestion was offline, so I can't direct you to it - but basically he told me to butt the pieces together with staggered joints, as the whole thing being laid up together became monolithic anyway. That way I don't have to grind off any lapped joints or fair them up, neither of which would give extra strength.

That said, in order to satisfy my own need for strength beyond what is required I'm going to be putting a third layer of biax down this weekend - I realized that this is the time to make it strong, if I'm going to, and the extra weight and cost will be minimal.

Cheers,

Chris

[bigd14]

I decided to add a third layer as well on the side decks, and have 4 layers on the foredeck. Maybe overkill, but I'm a big guy and it is SOLID! For the weight I think its a good choice.

Doug

[Rachel]

Thanks, Chris, I appreciate your posting the info. Good to know.

Rachel

[Chris Campbell]

I got the third layer of 'glass down tonight, I'm done with laying up 'glass on the cabin top. Nice! Still a long way to go until she's ready for paint, but I definitely feel a sense of accomplishment for getting this part done. And I feel very confident that she's strong enough for anything that I (or, rather, Mother Nature) can throw at her.



Update and another picture on my site.

Thanks to all who have offered their expertise, words of encouragement, and assistance in the work! There is light ahead (note I didn't mention a tunnel), and I look forward to sailing into it!

Cheers,

Chris

[Bluenose]

Back in the days when I did structural analysis on aircraft we use quite a bit of graphite, Kevlar and fiberglass composites. And they all shared the same last name. Epoxy. We could have used any resin system we wanted but it was almost always epoxy.

At the time the homebuilt airplane scene was thriving and they made many different material and manufacturing choices from the industry based on cost, ease of construction etc. These were all valid choices for their application. The problems came when some of the homebuilt builders and designers needed to rationalize that these simple or cheap approaches were superior to the industry's methods. Apparently it was difficult to tell their potential customers that their approach didn't put quality of construction and materials first (perhaps third, but that was appropriate for their intended use and goals).

I get the feeling that the boat building world has worked the same way in the past.

Oh, and core failure has been a big deal in aircraft's as well. There was I believe a 70's vintage carrier fighter that had an aluminum cored horizontal control surface with composite skins. It was apparently very challenging to keep this structure water tight so water would eventually migrate into the core. During flight the moisture would freeze and cause delamination between the skin and core which would often allow more moisture in. Then the aluminum honeycomb core would turn to dust.

I also found it interesting that core boats have been around a very long time. Like the 1933-1939 German E-Boat



Constructed out of Kledgecell foam and fiberglass.

Makes me wonder just how much money the boat builders saved using balsa core.

With respect to cloth orientation (and I know I am late on this one) we chose our layup direction based on the intended loading. If we had say a bulkhead, it might get a larger percentage of +/- 45s to handle the higher shear loads. Where a large flat panel, like a foredeck, where the loads are beamed out to the sides might get a larger portion of 0/90 fibers. That said, we also occasionally used pseudo-isotropic layups to make black aluminum (a layup with the same properties in all directions).

Cheers, Bill

(Sorry for that last bit)

I also just spoke with a friend in the business about it and he tells me that if he were putting a skin on a cabin top he'd do it with mat/roving/mat, and use polyester resin since I'm not building a raceboat. Hmm. He has a point.

It's a point, but not a good one. But if you're looking for the absolutely cheapest possible way to barely squeak by, this is the way to go. It's not good, but it'll be cheap.

We have spent quite a bit of time and energy on this forum in the past making efforts to carefully explain why epoxy is the resin of choice for all repair work on fiberglass boats. It seems that there is a school of thought out there that refuses to differentiate between repair and new construction techniques. An all-epoxy laminate on a new boat might be expensive and exotic enough to limit it to the racers, and polyester resins still make good and viable new constructions, but that's not what we're talking about here. We're talking about how one goes about making the best possible repair to an existing vessel, with the benefit of hindsight into all the problems that cropped up over the first couple decades of fiberglass boat production. Using polyester and roving for repair work is simply stepping way, way backwards, and the use of epoxy resin in repair work has nothing to do with being "racy".

Similarly, advancements in fiberglass materials have made the old mat/roving process obsolete for all intents and purposes: yeah, it works, but it is inefficient, creates resin-rich laminates that are weak for their weight, and just doesn't make any sense any more. Ever. Yeah, I used some 10 years ago, but that was foolish and we have all moved on substantially from there.

You don't have to use biax; it's commonly used because it's so readily available, it has excellent strength/weight attributes, is economical, user-friendly, and is a good all-around fabric. However, there are choices, such as similarly stitched material that has its fibers oriented at 90°, in a variety of weights and weaves. This is the material from which late-model production boats are generally built. But lacking a truly compelling reason to go a different route, why would you?

[Chris Campbell]

Too late! I'm done!

But thanks for that background - very interesting. Surprising to hear that the Germans were building with cored fiberglass in '33 - especially surprising to hear that Kledgecell has been around that long!

I'm happy enough to have used balsa, and I feel confident that the protection I've given it will keep me out of trouble. I suspect that my use of epoxy and biax cloth weren't necessary for sufficient strength in this application, and probably the third layer of cloth on top wasn't, either - but I'd rather have it too strong - and know it - than not strong enough, or even just possibly not strong enough.

Is there anything special about using Kevlar? It seems to me that carbon requires cooking to achieve full strength, but could I have used Kevlar in exactly the same way I used the 1708 biax, and had it even stronger?

Thanks,

Chris

[bcooke]

Its the resin that needs the curing temperatures, not the cloth.

I used kevlar a long time ago and I seem to remember it being harder to wet out properly. You certainly could have used kevlar in place of glass. You could have used carbon fiber too. It would have been a waste of money though and quite possibly too rigid which would not allow the structure to flex properly and spread the loading.

Really, its a combination of the resin and cloth that give the composite structure its final properties. It isn't really fair to say 'kevlar is stronger'. It also depends on the resin used and what you qualify as 'stronger'. Typically, I think kevlar exhibits better impact resistance than say glass but with a reduction of flexibility (or am I thinking of carbon fiber?). It all depends on what characteristics are important to you (or rather your boat).

[Bluenose]

Too late! I'm done!

Chris,

Yea, sorry bout that. In any event my diatribe wasn't so much about which material to use as it was about why certain experts might say one method is best.

But thanks for that background - very interesting. Surprising to hear that the Germans were building with cored fiberglass in '33 - especially surprising to hear that Kledgecell has been around that long!

Yea, its funny how often we reinvent things.

Is there anything special about using Kevlar? It seems to me that carbon requires cooking to achieve full strength, but could I have used Kevlar in exactly the same way I used the 1708 biax, and had it even stronger?

Well I have a couple of thoughts here. First off, you don't "cook" the fibers, you cook the resin. So a wet laid up composite, whether it is fiberglass, Kevlar or graphite will never achieve the same strength and consistency of properties as a vacuum bagged, pre-preg (resin embedded in the cloth to precise ratios) laminate put in a pressure and temperature autoclave. I suspect that the reason that you don't see much wet laid up Kevlar and graphite is that they are quite expensive and it would be a waste using them with this method since you wouldn't achieve their strength potential.

And personally I would never, ever recommend Kevlar as a structural material. It has some interesting and attractive properties, high tensile strength and energy absorption, but it has pretty poor compressive properties. Back in the 80's I worked on a small remote aircraft for a foreign customer. One of our "brilliant" marketing types allayed our customers fear of small arms fire by promising to build their new aircraft out of Kevlar. It was one of the hardest job I ever worked on. Eventually the aircraft became mostly fiberglass (graphite wasn't exportable at the time) with a bit of Kevlar for show. Then they farmed out the manufacturing to Burt Rutan, who used wet laid up composite methods, so we got to redesign it again for the degraded strength properties of that method.

All that geeky-ness aside, I think that the limiting factor for boat strengths is more the design of load paths than getting the last bit of material strength. I am not a builder and don't have any real practical experience (yet) but I scratch my head sometimes when I see some of the choices that boat builder's have made.

[bcooke]

Bill, as an aside (and maybe because you know something about it) I read the other day that Airbus had succefully built a full sized wing with a room temperature resin. If one could get that kind of structure without autoclaves then I think the age of composites (as opposed to the bronze and iron ages) will truly be here ;-)

[Tim]

Makes me wonder just how much money the boat builders saved using balsa core.

I need to note here that balsa core is not chosen because it's cheap (though it does cost slightly less than some foams), but because it has such desirable properties as a core material that make it an excellent choice for many applications, particularly boatbuilding.

There are reasons to consider other materials, but one should never discount balsawood because of an impression that it's the cheap and easy way out for builders. It's simply not true. It's an excellent and viable core material that is still widely used not only in production boats, but in high-end custom, spare-no-expense boats as well.

[Bluenose]

Bill, as an aside (and maybe because you know something about it) I read the other day that Airbus had succefully built a full sized wing with a room temperature resin. If one could get that kind of structure without autoclaves then I think the age of composites (as opposed to the bronze and iron ages) will truly be here ;-)

Hey Briton,

I have been out of the business for about 10 years so I am not an expert on modern composite technology. Airbus has become the leader in incorporating composites in transport aircrafts but in the old days, 80s and 90s, the Achilles heel for composites was mechanical properties in a hot, wet environment. If my memory serves there was a strength degradation of properties in the order of 25 to 50 percent. My recollection is that autoclave composite (I believe our cures were 350 degrees F) resisted these degradations better than room temperature wet laid up. Perhaps a better room temperature resin system has become available or they are using so a large volume composites in their aircraft's that they can afford the "extra" weight of a room temperature cure and still achieve an overall weight savings. All of this is pure speculation on my part.

This conversation has long ago left the realm of boat building and repair. And I don't think that my experience in structural load paths, proper resin ratios and strolls down memory lane really add much to this forum.

But I do remember one of the things my first boss passed along to me. He said that complicated load paths required time consuming detailed analysis and advanced materials. And then they would still try to fail. A simple load path is safe, durable, low maintenance, easy to build and requires almost not thought or analysis.

[Bluenose]

Makes me wonder just how much money the boat builders saved using balsa core.

I need to note here that balsa core is not chosen because it's cheap (though it does cost slightly less than some foams), but because it has such desirable properties as a core material that make it an excellent choice for many applications, particularly boatbuilding.

There are reasons to consider other materials, but one should never discount balsawood because of an impression that it's the cheap and easy way out for builders. It's simply not true. It's an excellent and viable core material that is still widely used not only in production boats, but in high-end custom, spare-no-expense boats as well.

With just a small amount of reading I quickly discovered that my statement was a bit flippant and that Tim is quite right.

Cheers, bill

[Rachel]

Bill,

I found your notes to be quite interesting, so I'm glad you added them. You never come across as a know-it-all, or someone who has THE answer (which is what would bug me).

This thread got me to thinking about how we used to build fiberglass whitewater kayaks, in garages, back in the early 80's. At that point we were using Vinylester resin (although epoxy had been used by some of us at times), and the layup was two layers of S-glass, one layer of Kevlar, and one of Nylon. I have no idea who researched it, or if their conclusions were correct, but the "common knowledge" about it actually seems to mirror what's been said here.

We thought of it as S-glass for rigidity and strength, Kevlar for durability (but it was not rigid), and Nylon to hold the pieces together when they did break apart (not uncommon when bashing rocks all day long - we patched as a matter of course).

Ah, the good old days :)

Rachel

[Bluenose]

Bill,

I found your notes to be quite interesting, so I'm glad you added them. You never come across as a know-it-all, or someone who has THE answer (which is what would bug me).

This thread got me to thinking about how we used to build fiberglass whitewater kayaks, in garages, back in the early 80's. At that point we were using Vinylester resin (although epoxy had been used by some of us at times), and the layup was two layers of S-glass, one layer of Kevlar, and one of Nylon. I have no idea who researched it, or if their conclusions were correct, but the "common knowledge" about it actually seems to mirror what's been said here.

We thought of it as S-glass for rigidity and strength, Kevlar for durability (but it was not rigid), and Nylon to hold the pieces together when they did break apart (not uncommon when bashing rocks all day long - we patched as a matter of course).

Ah, the good old days :)

Rachel

Thanks Rachel, But you guys were taking it way to easy on that Kevlar. We use to use it as part of our blade containment for engine fan blades.



And to continue on this way off topic piece of nerdery, here is a video of a blade test failure.

http://www.msm.cam.ac.uk/phasetrans/2002/1510.mpg

This is the explosion from a single fan blade separating from the disk that holds it. On very rare occasions the disk itself cracks and fails which is asking just a bit much from the Kevlar.

And to think they worry about your tray table being in the upright and locked position.

Cheers, Bill

Oh, and the number for Amtrak is 1-800-USA-RAIL