Why do you all try to invent the wheel again??
Go and visit a coach-worker and see how he repairs dented car parts with all kind of putties. These guys have special files for this work. I have some at home and they do work marvellous with there special profile which is designed to not slib up.
But it's all your punishment because you are using sort of putty for repairing cat's.
That has no constructual strenght at all. When hit again, it will break off.
I know it's a tempting and quick method, but don't do it!!!!!!!!!!!!!!
Hi northsea junkie,
Your linked essay didn't cover the difference between the bonding of epoxy to carbon vs. the epoxy to kevlar.
i am no chemist, but i was told by someone that i trust that the reason kevlar fuzzes up when you sand it is because there is only a mechanical bond, whereas carbon and glass have the mechanical and chemical bond. Also i have been told that the reason epoxy has part A and part B is because the part B isn't really a hardener like polyester has a hardener (also called catalyst). Ploy will go off eventually w/no hardener, but part A of epoxy will never harden on it's own.
Sure a sanded and unfinished surface of carbon will soak a minute amount of water, but exposed kevlar soaks water like sponge, plus you can't get it very smooth like you can with carbon. It's no big deal to put an unfinished board on the water that has exposed carbon or glass, but if there was any exposed kevlar the board would prolly be ruined. Bury the kevlar deep if you insist on using it because if you hit it while sanding you just created another step.
The plastic sheeting trick that i mentioned works really well for laminating areas about the size of a rudder or smaller. You will be amazed at the amount of air that you can squeegee out, and the surface is shinny when you peel the plastic. Also i have found that using clear surfboard epoxy which has uv inhibitors tends to save time in the long run. It's not the strongest epoxy but is good enough for most purposes, and some surfboard epoxies are better than others.
The fibers do most of the work, but there are resins with extremely good properties that will add a lot to the strength of the part.
First I like to show you some explanation about how epoxies and polyesters do work:
The cloth in a laminate will always suck up some water when the surface is damaged. (That's why they fill themselves with resin too)
Glass, carbon, kevlar or whatever, it makes no difference.
If the carbon molecules of the carboncloth really are bonded in the epoxy molecules during the hardening (the polymerisation), like you said, then this should mean less stable (disturbed)epoxy molecules.
The strenght of a laminate is largely determined by the fibers in the cloth you use. The resin only keeps all the fibers together; to be more precise, holds them at their fixed position to each other.
It fills the space between the fibres and fills them and holds them internally.
Let's remember too that most of these repairs are being asked to hold up to compressive loads...the fibers really don't matter that much when repairing a ding on the trailing edge of a dagger board.
i am no chemist, but i was told by someone that i trust that the reason kevlar fuzzes up when you sand it is because there is only a mechanical bond, whereas carbon and glass have the mechanical and chemical bond.
...
You ALMOST got it correct ...
When you place a cotton T-shirt in water, Ya get a WET
cotton T-shirt ; the water actually permeates the cotton
fibers.
When you place a carbon in water, Ya get a WET
carbon ; the water actually permeates the carbon
fibers.
NOT SO with Kevlar,when Ya place Kevlar in water
the water dos NOT permeate the actual fibers.
It's kinda like placing a plactic comb in water, Ya
get water dripping down the sides of the plactic, but
it doesn't soak through.
That's One reason Kevlar doesn't work for Squat for a bond
on Nomex-Honneycomb !
Bille
BTW, the glass fibers in that mix i suggested ...
DOES make it structural.
That's One reason Kevlar doesn't work for Squat for a bond
on Nomex-Honneycomb !
But on a honneycomb you always have a real problem with bondage of the two exterieur layers, regardless of the sort of laminate.
I'm still very surprised that they use it in boatbuilding. If you have followed the last Volvo ocean races, you certainly have seen the complete delaminated panels on the Imoca boats (all with honeycomb sandwhich core).
We in Holland have tried this honeycomb cores already 20-25 years ago in our surfboardconstructions. As editor of a surfboardmagazine in those days,I have tested prototypes with honeycomb. That was a disaster; they were all jumped to pieces!
BTW, the glass fibers in that mix i suggested ...
DOES make it structural.
It's not a structural repair in the sense that it doesn't see broad tension stresses over that area of the board (like the outer skin at the mid-point of the board would see). Also in the sense that if your repair fails, it will not compromise the structure of the board. High modulus fibers excel in tension as opposed to compression. The trailing edge sees crushing point loads (in compression) on impacts and my point is that placing high modulus fibers in something that sees this kind of focused compressive loads doesn't really add much over using fiberglass or even just fumed silica as a thickening agent.
At BMW we used a body filler that was somewhat flexible for repairing dings and dents. It seems for this application, something a little more flexible would be a little better. Any ideas?
BTW, the glass fibers in that mix i suggested ...
DOES make it structural.
...
*
...
Yes to ALL of that.
I should have added, that the size of
the repair will make a Big difference if i use Glass to
reconnect the skins after the repair. Anything over the
size of 1/4
square and I would use glass.
Glass over a repair, if an 8oz were sufficient, then
i Always use (3) layers of 3oz finish glass because
it has a very tight weave and it's rather thin. the first
layer would be 3' larger than the repaired aria, the second
is 1.5
larger, and the last is 3/4
larger than the repair aria.
Large repairs need a minimum of 2
overlap to all sides
of a repaired aria to reconnect the skins.
Adding a fairing coat of epoxy with West System 410
Microlight is the ideal low-density filler to make the final sanding easy.
That's One reason Kevlar doesn't work for Squat for a bond
on Nomex-Honneycomb !
But on a honneycomb you always have a real problem with bondage of the two exterieur layers, regardless of the sort of laminate.
I'm still very surprised that they use it in boatbuilding.
...
I would NOT use Nomex-honneycomb in boat building because
of everything you just stated ; it works rather well
on aircraft because the skin loads are much lower. Usially
the skins will only take twisting moments in an aircraft
wing.
I have a Rigid-Wing Hang glider that is 10 years old, and
i will pass-out before my wing will break ; the core is
Nomex-honeycomb. The stuff is a Bitch to work with if
a repair is needed. I nailed a wing-tip one day and it
took me 10 hours to repair it ; make a mistake and I'll be
tossing my reserve. That Really helps to focus on your
work !!!!
I was Lucky in that the guy who taught me is the same
guy who made one of the three prototypes of the F-35 .
I built a cantalievered rigid wing HG that he designed,
and had the good fortune to have him as my teacher on
the project. After which i was the test pilot because
at one time i was # 4 in the world at ACRO on a HG.
Bille
It's a worthy thought, but I can't think of a material that behaves appropriately outside of a university lab...essentially you are looking for something that deforms, but returns to original shape quickly, and has high fracture toughness...I had a prof working on a self-healing composite structure aimed at aircraft wings: http:/
All yours for $1 million. In the mean time, I'll continue putting thin webbing in the back of the trunk, has considerably reduced the number of these repairs, as has avoiding the bottom.
Avoiding the bottom.
There's an idea.
Didn't the Stiletto cats use Nomex cores?
I thought I saw a honeycomb core on one which had a porthole removed for replacement...
...
OUCH -- this will boarder-line on Mean :
http:/
And that is why northsea junkie said this :
I'm still very surprised that they use it in boatbuilding. If you have followed the last Volvo ocean races, you certainly have seen the complete delaminated panels on the Imoca boats (all with honeycomb sandwhich core).
...
Bille
Marstrom boats use a nomex core. At least their Tornado did.
@bille Adding resin to your example is what i am describing.
A tshirt saturated with rein won't soak up water after curing, but if you were to sand the edge exposing the fibers, would the fibers be able to soak up water?
My contention is that after carbon or glass is saturated with resin, even if you sand the edge, exposing fibers, that the fibers won't soak up much water. You can dry it off, lightly skuff it and bond to it/paint it etc.
If you try that experiment with kevlar water will soak in and if it's salt water you will never get the salt out.
You will need to glass the salt in and the fuzz down; being careful not to sand back thru.
There is a whole big thread out there in cyberworld about honeycomb & Acats. Some of them use it.
Billl Higgins' Stilletos most definitely were made using aircraft honeycomb and prepreg.
Problems with honeycomb delam seem to be worked out. Once honey comb got to Tornados, they never looked back.
They still have wood rudders and maybe the boards too. I think he does prepreg over the wood.
Also there were honeycomb surf boards in the 60's that are still around today.
So all the cool kids have honeycomb/prepreg these days. i assume: the AC 45's and 72's, some Ccats, those big 60 and 70' tris, but that isn't my field so not 100 percent sure about some of those boats.
As for trailing edge thickness-it's personal taste. You want them as thick as possible without slowing you down too much.. I think if you leave it perfectly squared off. you will get humm. rounded corners-no humm, but is it slower?
for future readers: For this particular repair it sounds like; try a small fill job first, and if it keeps chipping off, make it into a bigger job. one way would be to grind both sides down enough- (roughly the thickness of 3 layers of material), say 2-3" in from the trailing edge, so that after you glass it, the result will fair down nicely. The stronger the materials that you use, the better the repair will last. And off course customize the the trunk so that it isn't as likely to damage your precious foil.
A tshirt saturated with rein won't soak up water after curing, but if you were to sand the edge exposing the fibers, would the fibers be able to soak up water?
My contention is that after carbon or glass is saturated with resin, even if you sand the edge, exposing fibers, that the fibers won't soak up much water. You can dry it off, lightly skuff it and bond to it/paint it etc.
If you try that experiment with kevlar water will soak in and if it's salt water you will never get the salt out.
You will need to glass the salt in and the fuzz down; being careful not to sand back thru.
There is a whole big thread out there in cyberworld about honeycomb & Acats. Some of them use it.
Billl Higgins' Stilletos most definitely were made using aircraft honeycomb and prepreg.
Problems with honeycomb delam seem to be worked out. Once honey comb got to Tornados, they never looked back.
They still have wood rudders and maybe the boards too. I think he does prepreg over the wood.
Also there were honeycomb surf boards in the 60's that are still around today.
So all the cool kids have honeycomb/prepreg these days. i assume: the AC 45's and 72's, some Ccats, those big 60 and 70' tris, but that isn't my field so not 100 percent sure about some of those boats.
As for trailing edge thickness-it's personal taste. You want them as thick as possible without slowing you down too much.. I think if you leave it perfectly squared off. you will get humm. rounded corners-no humm, but is it slower?
for future readers: For this particular repair it sounds like; try a small fill job first, and if it keeps chipping off, make it into a bigger job. one way would be to grind both sides down enough- (roughly the thickness of 3 layers of material), say 2-3" in from the trailing edge, so that after you glass it, the result will fair down nicely. The stronger the materials that you use, the better the repair will last. And off course customize the the trunk so that it isn't as likely to damage your precious foil.
For hum, sanding the trailing edge at an angle can get rid of it.
Problems with honeycomb delam seem to be worked out.
What how??????????
Did you ever have a sheet of honeycomb in your hands and start wondering how in heavens name the exterieur laminate layers should bond to the extremely thin headsides of the honey comb. (without loosing too much weight in extra connections)
There's a test the Gov labs do to a honeycomb laminate
called the Peal-ply test ; they glue one side down, and
measure how much force it takes to remove the exposed side
from the honeycomb panel. Optimum skin weight for peal resistance
is 10oz skin or better. Adding more thickened epoxy
to disperse the energy to the cell walls, will add more weight.
I totally trust my Exxtacy to Not De-laminate while
i'm flying. But if it's Water i'm asking the honeycomb
to deal with than i'd keep the lamination width limited
to 1 inch strips to isolate the tears in a De-lam panel.
Remember they use honeycomb in the fins of Very high
speed rockets and also in some fighter-jet structures, and
it holds up Well ; i would Never trust my life to the stuff
on a boat , unless special precautions were utilized !!!
Bille
Digging up an old thread -
Goodall Design just published a series of videos on proper dagger/rudder trailing edge repair. Link here
Looks like I have a fun little project before the next regatta. Anyone have a preferred source for carbon cloth?
uscomposites.com
Goodall Design just published a series of videos on proper dagger/rudder trailing edge repair. Link here
Looks like I have a fun little project before the next regatta. Anyone have a preferred source for carbon cloth?
That was the best use of 7 minutes in quite some time.
Goodall Design just published a series of videos on proper dagger/rudder trailing edge repair. Link here
Looks like I have a fun little project before the next regatta. Anyone have a preferred source for carbon cloth?
Thanks for sharing those links. Certainly made it look easy!