Dagger Repair

I tore up the trailing edge on one of my daggers recently. I've got enough experience w/ glass & epoxy (and a little carbon) that I don't think that the repair itself will be too troublesome.

I plan to grind out the damage, which is about 2" high and 3/4" deep in the trailing edge, about a foot from the bottom, and vacuum some carbon in it, then fair.

My question: Do I need to cover it in gel coat? Considering that it is in a spot that rarely sees the sun, I'm wondering if I need to do anything at all to the fairing compound after fairing it? I hate working with polyester resin.

Should I put a single thin covering of non-thinned epoxy over it?
or just treat the whole daggerboard w/ a poliglow-style UV inhibitor?
or re-gelcoat?

Any advice is welcome. Thanks

Rob

Anything you put over it for a finish is just cosmetic...if you don't care, leave it raw. Polyester resins are UV stable and, although it yellows, epoxy is structural stable with UV exposure. Heck, on small repairs, I hit it with a little krylon. Vacuum bagging is probably overkill on that too (did I just say that?).

To repair those dings, I mix up some finely minced glass fibers (either bought that way or self made) and fill the void with that putty. I tape a hotel key cards to both sides of the board to form the flat sides to leave very little fairing.

I have TONS of hotel cards/empty gift cards/vanilla reload cards (twice the size, good for squeegees), but I don't think I've used them the way you're talking..I've seen your pics. I have used them to help make a very square edge at the dagger trunk exit. Anyway, I'll try it like you say.

I have milled fibers from us composites, but I was planning to use carbon just to try to prevent this from happening again. Does that just make the rear of the dagger trunk more likely to get torn up? Is carbon even stronger in that situation or is it too brittle?

I hit a log floating under the surface, but the front of the dagger shows no damage at all. The rear got damaged from getting jammed into the trunk.

I've done repairs in all sorts of materials on the trailing edge of boards...it's all going to crush if it gets impacted with enough force and I'm not sure that it makes much difference what material you use. There is just so little material on the thin edge. I consider this type of repair as maintenance.

You should have had a Nacra infusion when they had "gybing" daggerboards. You would have to repair them after every regatta.

This is the standard 'Inter' rudder. Without looking I'm going to guess that the damage goes in far enough to be about 3/8" thick at its widest.

New semi-related questions:
Can fairing compound be polished smooth? I've never hit it with anything finer than 220 or so (usually just 80). It seems really porous to be on top.

How 'sharp' should the trailing edge be?

Thanks!

I hit a floating 2x4 (was looking/talking to another boat) doing around 8 knots.
it hit both hulls, both centerboards, both rudders. did similar damage in several places.
It was like a car wreck over, and over and over ...


What the heck is a "vanilla reload card"?

Jake what about on rudder bottoms? glass strands? kevlar? carbon cloth? sheet metal?

Goal being to reduce the loss WHEN you hit bottom (sand or mud around here)

Carbon is standard on the bottoms of the Gen3 rudder blades. Kevlar is the toughest in this type of application (I use it when building a composite part intended to skid along grass/concrete etc.). Trouble is it's the worst to work with and paint doesn't bond well to it. By worst to work with, I mean you need to modify scissors to cut it, and once it's in a layup its an absolute dick to finish cut or finish sand. Will require a hand sander and lots and lots of 60 grit sand paper to get to final shape. But it'll hold up better to repeated groundings, if it doesn't de-bond from the base layers.

http://www.fibreglast.com/product/Kevlar_Pulp_544/Fillers

It's about 3x the size of a CC, but still plastic, although a little more flexible than a typical CC/hotel room key.

Fibers only prevent a break and high modulus items are pretty useless at the tip of foils unless you really plan on hitting things hard. They won't prevent chips/scrapes/gouges. You need a hard shell to resist that kind of abuse and properly cured gelcoat is hard to beat in this regard.

Yeah, when I hit the thing, since it was completely submerged, I thought I snapped a shroud at first. Then 2 secs later it hit my rudder, and I drew the only obvious conclusion -- my boat and I were being eaten by a lake bound sea monster.

After nothing else happened, and sitting at a dead stop (from trapped out racing to the windward mark.) I moved on and came in last. When I came back to shore and the dagger was stuck I realized what happened. I had to rig a sort of up-@%#$er on the trap line to get enough purchase on the board to free it. The rudder had no damage at all...but I guess that makes sense since the front edge of the dagger didn't either.

You can push the board up from under the boat while someone pulls. Real pain but that's what we've done.

Jake, I think Kevlar pulp has considerable benefit in this application: "The results show that the incorporation of Kevlar pulp into epoxy contributed to improve the friction and wear behavior considerably. The maximum wear reduction was obtained when the content of Kevlar pulp is 40 vol%." From an abstract by J. Wu, seeing if I can get the entire paper now.

I would not paint over the kevlar, so the surface roughness may be higher but done right you can get a pretty smooth finish and no loss in performance.

Screw kevlar, from experience. he's not talking wear, he's talking fine edge impact. It won't help and it's certainly not worth the fuzzy headache it becomes unless you're getting paid by the government.

Not on the TE, on the bottom of the rudder blades and dagger boards. Kevlar is still half the price of carbon in lighter weights, at the sacrifice of 1/3rd the stiffness.

I fought a kevlar boat for 2 years and there is no way you can convince me of it's merits on a daggerboard repair, no matter where on the board. Not worth the headache. done right you have to put glass over it as a sanding barrier.If you're trying to offer the most laborious and frustrating method, then I commend you.

I'm sorry. We borrowed a kevlar A-cat last week, huge chunks of paint flaking off. Glad I don't own it.

I warned that Kevlar was extremely labor intensive. I hate using it outside of molds, and I did not use the filler I pointed at to fix the chunks in my rudder tips, elected to go with graphite. MN was asking for options on wear strips. Kevlar is amongst the most abrasion resistant materials the government has made commercially available. Translation, it is also extremely hard to fair.

About the only beachcat use I can see for it is the bottom of a cat that get's dragged up and down the beach, in which case the surface really doesn't matter.
p.s. A cat you borrowed a Waterrat?

I'll add another option for a tough surface, I tend to forget about as it's heavier than glass/carbon/kevlar, West Systems 420 Aluminum Powder. "Abrasion Resistance – Apply undercoats of epoxy modified for abrasion resistance or temporary UV resistance." Much easier to sand than kevlar.

We use it as the top surface on a fiberglass mold, as it forms a very hard coating, less chances of dinging the tooling when removing parts.

Kirk's H16 had kevlar strips on the bottom for that reason. We used Aluminum powder on the bottom of my H14 back when I was a toddler, it held up extremely well to the shells that pass for sand around here.

Yep, sailed the club A-cat, a Waterrat, too light to really get an opinion but J liked it for a solo play toy.

+1 for use of kevlar on the bottom.

I use this also already for years because of the high abrassion on my sharp assymmetric hulls. And by the way, it is not much harder to work with then other type of cloth.

On the bottom I use kevlar in ribbon format which covers exactly the sharp end of the bottom. To finish off the wet kevlar-laminate I always use PVC/tape (which I take off after hardening). The sand on the beach will sand it off very smoothly (only shells can make a hairy surface).

With regard to your damaged trailing-edge of the rudderblade, I wouln't suffice with some filler or so.
Sand it off with a overlapping "welding" section of about 4 cm on the sound part of the rudder. reconstruct any core if necessary and start laminating.
Do this for both sides of the rudder. Finally sandoff a nice sharp new trailing edge!

I would take a dremel with a cut off wheel and cut down the depth of the cut off wheel along the trailing edge where the damage is. A slot if you will. Then use carbon, I like around 15lb biax glass , lay up a layer or two a little longer than the slot and about 1-2 inches wide on some wax paper or use what method you like. After the glass has kicked, Trim so it fits into the slot. Mix some epoxy and glue it into the slot. From here you can make up a filler with epoxy, some West graphite powder will make it all black. Shape it up. Now you have a edge than can take some abuse without crushing.

+1

One trick is to lay a piece of plastic that is about the thickness of a ziplock sandwich bag over the repair and squeegee the air and excess resin out. There won't be much sanding to do after it hardens if you put the right amount of fibers in the repair. You would prooly want to tape off the repair area to protect the good part of the project. You can also trim the repair when it is partially hard to save time later on.
polyester won't go off when put over some types of epoxy. You can put pigment in surfboard epoxy, or just spray paint the repair for cosmetic purposes.
Also i have found that the most durable bog is a mix of aerosil, a little bit of finely cut up carbon, and epoxy. Works great on the bottoms and foil tips.
The rule for kevlar is bury it deep. It soaks up water and only forms a mechanical bond whereas carbon forms a chemical bond with the epoxy.

First I like to show you some explanation about how epoxies and polyesters do work:

epoxy and polyesters

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.

I used a thick slurry of milled glass fibers and epoxy per Jake. After grinding out the damage the edge I'd created actually cut me...which got me thinking: How sharp should the trailing edge be?

What Jake said, but forget about the plastic .

Make your own chopped fibers by rolling
some 4oz glass up on a +/- 45deg and dicing the end every
1/4" with some SHARP scissors. Mix 30% chopped glass fibers
with 70% WEST SYSTEM #404 High Density Filler, and add epoxy.
http://www.westmarine.com/webapp/wc...ord=404+high+dencity+filler#.Ulv93lNqkuQ

Make the mixture dry enough that it will NOT elongate off
the stirr-stick when pulled up out from the mixing can.

Tape the edges of your damaged aria with the Blue 3-M
painters mask , so when Ya sand down initially , you'll
hit the tape but not destroy it. At this point, i usually
paint on a bit of epoxy before mixing in the filler, then
use a Blue shop-towel to remove almost ALL of it.

Use a bit of 3" wide tape on the bottom side to hold
the mixture in place while it goes off.

SANDING
No need to wear a mask here, i use a File and water, till i
hit the tape, or 40grit wet/dry sandpaper. When Ya hit the tape
then pull it and switch to 100grit wet/dry ; then 180 ...

If you spend more than 1/2 hour labor on this job, then your
thinking Too much and need More Beer !!

Bille

Your gonna Laugh, but my sanding block is 1/8" thick
aluminum , (1" X 2"). i have 3 of them:
1) the exact length of my sandpaper
2) the exact Width of the papar, (i get 3 pieces of
sandpaper,after folding the edges)
3) is 1/2 the length of # 2.

Every time you drop your sanding block on the floor
then sand all 4 sides with 100grit by using one of
the other blocks. Do NOT forget this or your sanding job
will be screwed !!

Bille

What do you clean your files with? I've never found anything that I really liked.

Compressed air and a file brush works well with contact cement.

It's Ruff sanding, so i use a 1/2-round or round file
with a rather Heavy groove ; clean Before
the grooves full, and i do it with More water and a file
brush. It only sticks if you don't clean every very often.
Rotate the file every other pass.

Same goes for the Wet & Dry sandpaper, don't let the grit
get filled or ya got to toss that piece.

Wear Very Wet cotton gloves and use them to keep your
work wet; that also helps to keep your girlfriend happy
if you use your hands a Lot !!

Bille

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.

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.

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.

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!

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?

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.

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://m.iopscience.iop.org/0964-1726/22/2/025031

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://stiletto.wildjibe.com/portfolio/Port_4/photo_15.jpg

And that is why northsea junkie said this :



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.

For hum, sanding the trailing edge at an angle can get rid of it.

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

That was the best use of 7 minutes in quite some time.

Thanks for sharing those links. Certainly made it look easy!