Hull repair questions

[Ryan]

I have a Hughes 25' boat that is a new project for me to learn a little more about glass boats. This boat has a three foot gash in the foward part of the starboard hull. It looks like the previous owner tried to cut out the fiberglass hull liner inside the vee berth with a sawzall and cut through the hull as well. The cut is above the water line. My repair plan is to dish out the area around the cut inside and out around two inches on each side of the cut, then fill the gap made by the saw blade with collodial silica-thickened epoxy. Then I will laminate a couple of layers of glass tape in the dished out areas of the hull inside and out. Once this cures, I'll sand it smooth and fair with more silica thickened epoxy. Does this seem like a sound plan to you folks? Please feel free to chop this idea to pieces and correct any errors that you veterans can find. Thanks!

Ryan

[CharlieJ]

Sounds like exactly what I'd do. The only thing I'd suggest is plan on more than a couple layers of glass. I'd go at least four on each side, starting with the 4 inch wide piece to cover your 2 inch each side dish out. Then a 3 1/2 inch wide one, then a 3, then 2 1/2, etc. PLus I might alternate a layer of matt in between the layers of cloth.

Otherwise sounds like you have a handle on it.

Do you intend to use polyester or epoxy?

[Ryan]

Thanks for the reply. I plan to use epoxy. For the most part, I'm not a fan of polyester and the hull will be Awlgrip painted when I'm finished, so no need to use polyester to be compatible with gel coat.

So you would lay down the widest layer of glass first? Although I have only done a few fiberglass repairs, I have always started with the narrowest strip of cloth and worked my way out to the widest strip. This way the "dished out" area is filled in more evenly. the part of the hull that I am repairing is only about 3/8" thick, so I don't want to grind down too far. Thanks again

Ryan

[CharlieJ]

If you lay in the widest piece first you get a total bond, new glass to old surface, then the next smaller gets a total bond to that, etc.

If you put in the small one first, you get THAT bond, true, but then the next size only gets to bond to the hull around the edges- the rest is bonded to the other new piece. Plus, when you grind it smooth you cut away even more of that bond.

So the BEST bonding overall comes by using largest first, then stepping down.

This is the way the Gougeons recommend by the way.

[Jason K]

I was under the impression that smaller pieces should be laid up first, both because the bonding is superior as it bonds to a uniform substrate and because the final layer is more uniform and easier to fair.

It looks like the previous owner tried to cut out the fiberglass hull liner inside the vee berth with a sawzall and cut through the hull as well.

I could see myself doing that. In my enthusiasm, I tend to do demolition with less than surgical precision. Fixing the results can be a pain though. Of course, I would likely be a bit more careful if the work posed a risk of putting a hole in the hull.

By the way, what was the reason for cutting in the first place? The boat doesn't have a cored hull, right?

[CharlieJ]

Many people are under that impression, but the recommedation is for what I told him. Take a look at this article from the Gougeon's EpoxyWorks magazine-it's pretty thorough on the subject.

http://www.epoxyworks.com/21/practical.html

Since you have to final sand and apply a final finish coat anyway, the ease of grinding fair isn't any different, In fact, you will actually lose LESS fiberglass by having the small patch last. By putting the largest one last, you'd wind up grinding most of the final layer away in your finishing.

[Ryan]

No, the hull is not cored. He was cutting out the interior liner in the vee berth and got carried away with the depth of the cut. The saw line in the hull matches the cut in the interior liner perfectly.

And I agree, I can certainly see myself doing the same thing.

Ryan

[The Good Goose]

Ryan
I would use microballoons for the final fairing it is easier to get a smoother surface

Brock

[Rachel]

Thanks for the link to that informative article, Charlie. It's a keeper!

(One thing to note is that it looks like that "V" was added to the end of the link inadvertantly; once I removed it, I got to the article just fine.)

I, too, had heard to put the smallest piece in first and go bigger from there, although in the old days of patching holes in our whitewater kayaks, we did used to do it the way you and the article recommend, with the largest piece first and subsequent onces smaller.

I think that we would tend to get air/bubble problems between the layers' edges otherwise (althought that's waaaay back in my memory). Of course we also didn't fair or sand our patches in any way, as we weren't going for looks or smoothness to any great degree. We just put clear plastic wrap on the outside as it cured (Vinylester resin) and let that amount of smoothness suffice.

I believe that other board members do it the opposite way, so, as an information-hound, I look forward to hearing their perspective(s). I *know* I'm going to be patching some holes one of these days :-)

--- Rachel

[CharlieJ]

Rachel- I got rid of the V - thanks. Don't have any idea where that came from, but it is correct now.

[Tommy Bahama]

If you lay down the largest ply first, the entire repair is at the mercy of delamination if that ply should fail. Each smaller ply is only bonded to the largest one and nothing else. Impact wize, I think you'd be fine but for "peel" strength of the ply I believe that the large ply first theory compromises strength or shear.

If you place the smallest ply first to span the repair it adheres to the entire surface. The next larger ply not only bonds to the first ply but also bonds to the original surface and so on. The layup should be "wet" so that air bubbles do not form and the excess can be squeegied off when finished.

The idea here is that if the top ply is compromised for any reason, the remaining plys are still bonded to themselves plus the original surface. This is important because the "peel" strength of any given ply is only about 7 pounds of lifting force (varies depending on epoxy type).
I know that we are splitting hairs here for a boat surface but the Rutan brothers have spent years developing glass ply and composit techniques for aircraft. The testing includes repetive motion of the pieces to the point of failure plus the aging data for aircraft in the field.

This is just intended to validate another method for performing a repair based upon studies by another relevent industry.

Keepin' the dirty side down,

Tom Jordan

[Ryan]

For the fiberglass used in this repair, would you guys/girls reccomend for or against some biaxial tape like West System 727? This stuff is easy for me to get and I feel like the +/- 45 degree fibers give me the best strength in all directions. Thanks!

[Tim]

I think biax is an excellent choice for bulkhead tabbing, as none of the fibers end up parallelling the joint. Strong stuff. I've had good luck working with the West System tape (I think it's 15 oz.), as well as the heavier biax available elsewhere.

[Ryan]

Tim

Do you suggest the same biax for the above mentioned hull repair as well as bulkhead tabbing? It seems that you would get the same benefits. Thanks.

Ryan

[Tim]

I like biax for just about all general purpose fiberglass work.

[CharlieJ]

I think the bias glass would be great for the first layer perhaps, but to do a glass repair like that I always try to orient the cloth so the strands don't line up, one layer to the next. You're talking about 6-8, maybe 10 layers of material all told , counting both sides of the patch. Using the bias is great, just don't lay each layer JUST like the one under it, or you lose the advantage. SOME of those strands SHOULD cross the repair at 90 degrees, some at 45, some in between.

You can, and perhaps should add a few layers of matt into the matrix. It DOES work with epoxy, and does give a randomness to the orientation of the strands- it also helps soak up excess resin, which is a very good thing. You want the patches to be as dry as possible, without having dry spots. In other words, a heavy glass to resin mix, rather than the other way around. Excess resin does nothing but add weight.

[bcooke]

[matting] DOES work with epoxy

So why are there so many warnings against using matting with epoxy? Has the matting material changed in recent years?

The biax I have lying around has a thick buildup of loose fibers attached to one side -like matting- so I would think biax tape or cloth alone would work fine.

Just my 2 cents

-Britton

[Figment]

Mat is not just a bunch of random fibers held together by magic. It's a bunch of random fibers held together by a "binding agent" that is supposed to dissolve or otherwise go away when it comes in contact with resin.

The binder used in some mat goes away when it meets polyester resin, but not epoxy resin. I have actually had this problem happen to me. Happily, it wasn't in an application that made this a dealbreaker. This was probably ten years ago. I haven't run across this problem since. It may be that mat producers have universally switched over to epoxy-friendly binder, or it may be that I've been buying my stuff from epoxy-oriented suppliers. Even money on that bet.

Britton, if you got your biax from Jamestown or from Fiberglass Supply, it'll be fine with epoxy. I've used both with epoxy without incident.

I personally am not sold on the notion that mat adds any structural advantage over biax alone. I think it just makes for a nicer finished surface.

[Tim]

Many fabrics and tapes include the mat on the back side. The mat is there for much the reason that Charlie mentioned above, and helps layers of the material integrate together in the laminate. This is a similar notion to the old-fashioned manner of laminating using woven roving alternated with layers of mat, though the mat is not an essential component with modern stitched and woven materials.

The mat also helps stabilize the fabric so that it retains its structural integrity when wet out, and helps keep the biaxial fibers in their proper orientation. Material lacking the mat will often stretch in odd directions, which can be an issue at times.

Mat stitched or otherwise adhered to the back of your material, be it biax or other, also adds a bit of weight to the material, and acts as a laminate bulker of sorts. Biax with mat on the back is a very good all-round material for most repair work. The West System biax does not have the mat attached, and is lighter weight, but works very well for many applications thanks these very traits.

[CharlieJ]

Britton- I'd heard that too, for years. Then the Gougeon's did some tests on it. Take a look at this article from EpoxyWorks Mag, put out by the Gougeons on using epoxy and matt.

http://www.epoxyworks.com/21/chopped.html

So I tried some in a matrix with cloth. Two layers cloth, one layer matt, two cloth, one matt. Worked very well.