Cracks in Hull - Storm Damage

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Cracks in Hull - Storm Damage

Postby bilbo » Tue Sep 06, 2022 7:09 pm

My boat was damaged in a storm early this year. Then I moved across the country and am finally getting time to fix the things that were broken. The boat and trailer was picked up by the wind and smacked into an electric utility box. The damage was some scrapes, broken bow eye (that was loose already), some dings on the rub rail, broken spreaders, and two big gouges on the bottom where it hit the electrical box. All things considered it didn’t fair too bad. Unfortunately the gouges on the bottom are leaking water. I filled the bilge with water and it was coming out at about a drop every three seconds.

Can I repair these from the outside? It would be easy to careen the boat and grind out the damaged areas. If needed, I can add glass cloth and resin. Would epoxy be ok or should I use something different? I can get some supplies locally but I believe it is polyester based. Any special considerations for either resin system?
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Re: Cracks in Hull - Storm Damage

Postby bilbo » Tue Sep 06, 2022 8:30 pm

Sorry, I can’t get the close pic of the cracks to upload, apparently the file is too big. I’m working off a phone at the moment and can’t figure out how to resize them.
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Re: Cracks in Hull - Storm Damage

Postby GreenLake » Wed Sep 07, 2022 3:36 am

Some variation of the technique I used and described in the thread "Gored: Crack Repair" should work for you. (That damage was from a wooden boat, and not a utility box, but the damage don't care).

When you grind away your damaged laminate and gelcoat, you may uncover more "milky" looking laminate. That is a sign the laminate is damaged and as a result, when you are done, you may have removed a bit more than you had originally planned on. And that means, that your repair may need a bit of support. (Or you find that where you had to create an actual gap, that the two sides no longer align correctly). In other words, your repair may need a bit of support from behind.

If you have no access from the inside, as is the case on a DSII, you can still use a bit of a backing plate to strengthen and align your repair. However, instead of pressing it against the inside, you need to use wires or zip ties other means to pull the plate flush after you've inserted it through a (widened) bit of crack. The other steps of the repair should just translate.
~ green ~ lake ~ ~
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Re: Cracks in Hull - Storm Damage

Postby bilbo » Wed Sep 07, 2022 7:39 am

Thanks GreenLake. Did you let the patch cure out before applying it to the hull? The way I'm envisioning the backing plate, if needed, is to pull it up against the back (inside) of the hull with something. Then lay wet glass on it so it's supported and allow to cure in place. Last, remove the bracing/support system.
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Re: Cracks in Hull - Storm Damage

Postby GreenLake » Wed Sep 07, 2022 12:24 pm

bilbo wrote:Thanks GreenLake. Did you let the patch cure out before applying it to the hull? The way I'm envisioning the backing plate, if needed, is to pull it up against the back (inside) of the hull with something. Then lay wet glass on it so it's supported and allow to cure in place. Last, remove the bracing/support system.


On a DSII where you can't access the inside of the hull, anything you put behind the repair will remain in place. That's why you use something like the thin (!) plate made from laminate. It's OK to glue that to the inside of the hull. You can then remove whatever you used to hold it while the glue (epoxy) sets. You then laminate over that from the outside. The patch on the inside supports the wet laminate, but also adds a bit of strength, which is a bonus though not strictly needed.

Because not strictly needed for strength, you can keep it thin and a bit flexible, just strong enough to ensure the edges of your gap are aligned, and you'll get a fair curve in your hull when you are done. Because you'll be gluing your backing plate, you can (and should) remove whatever you used to pull it against the hull before you add the laminate on the hull side. (In your case, that support is on the outside, so it would be in the way if you tried to laminate with it in place).

If you let the plate cure all the way before gluing in place, you need to sand it rough before gluing. You also need to reach in and sand the inside edges of hull so you get a good bond.

In my case there was some tension in the hull that pulled the edges of the crack out of plane very badly. I had to make the plate stiff enough to counteract that. I suggest you make a small sample to check your layup schedule for the backing plate; don't just use whatever I wrote in my other post.

You will sometimes read about laminating over something that's still in the "green" stage of curing. That will give you a better bond, but as you are gluing to the hull anyway which is a different resin and long cured, that's not something to worry about. Any surfaces that are not "green" epoxy need to be sanded before laminating. If you don't use a "blush free" epoxy, you may need to wash (water) the surface to remove amine blush before sanding.
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Re: Cracks in Hull - Storm Damage

Postby bilbo » Wed Sep 07, 2022 1:18 pm

That makes more sense; the patch piece would be just to support the backside of my repair from the outside while it's laid up. Since I can't really access the inside of the hull easily, and that part of the repair wouldn't necessarily be structural, would the sanding be necessary on the inside?

Here's kind of what I understand:

1. Remove material until I reach good laminate. Just guessing, based on the shape of the gouge, this will be about 1/2" X 6-8"
2. Feather back from the hole a few inches either side of the hole.
3. Make a thin, flexible plate similar to GreenLake's and let it cure out.
4. Sand the surface of plate
5. Drill one or two holes and run fence wire through the plate and apply epoxy to sanded surface.
6. Fish plate through hole and pull back to inside surface of hull with wires, tie to support until cured.
7. Apply stepped layers of glass/resin to outside for structural repair. Thickness/shape will depend on what I find when cutting the hull.
8. Fair, gelcoat, sand smooth, polish, etc.

Does that seem like a reasonable approach? I have been staying in a temporary house while all our stuff (and most importantly my tools!) is in storage 45 minutes away. We close on the 15th so hopefully we'll be moved in by the end of the month. I think I'm going to just wait until then as I'll have my own space to lay the boat down and have easy access to all the tools and equipment I need.
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Re: Cracks in Hull - Storm Damage

Postby GreenLake » Wed Sep 07, 2022 7:01 pm

All of that sounds about right.

You do want to reach in through the gap (widen it a bit to at least finger width) so you can sand around the edges on the inside. That will help that support piece to bond better and also contribute some to the strength of the repair. I wouldn't stress if your backing piece is slightly wider than the area you can sand this way.

Otherwise, sounds like you have a plan. Good luck!
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Re: Cracks in Hull - Storm Damage

Postby bilbo » Wed Sep 07, 2022 8:12 pm

Got it, thanks! I'll post back once I've started the repair.
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Re: Cracks in Hull - Storm Damage

Postby bilbo » Sat Sep 10, 2022 4:48 pm

Another question, as I'm putting together the shopping list for supplies. Most of what I've read says that fairing compound should be painted or sealed. Is there a product I could use that won't require painting afterward?
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Re: Cracks in Hull - Storm Damage

Postby GreenLake » Sat Sep 10, 2022 6:15 pm

Fairing compound is optimized for easy sandability.

As a matter of course, I would get something that's epoxy based, like SystemThree's EasyFair, but even that will benefit from a coat of neat laminating epoxy and then some paint. (Or gelcoat - I'm reading in a number of places that the prohibition on using gelcoat over epoxy may not apply as strictly as we were thought to believe, especially if the epoxy is mixed in the precise proportion and washed with soap and water to eliminate any "blush").

For very small repairs you might get away with using a dab of MarineTex which is a white epoxy paste, but it doesn't sand as well easily as fairing compound, so i would hesitate using it over a large area. I believe the pigment makes it somewhat UV resistant, but any other epoxy really needs to be covered (e.g. by paint) to be durable.
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Re: Cracks in Hull - Storm Damage

Postby bilbo » Sat Sep 10, 2022 8:52 pm

Thanks, maybe I’ll give gelcoat a shot. Worst case, I have to grind it out and redo. With a little experimentation I might even be able to tint the gelcoat to somewhat match the rest.
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Re: Cracks in Hull - Storm Damage

Postby GreenLake » Sat Sep 10, 2022 10:10 pm

Gelcoat thickness is a multiple of what you get for paint. So when you sand your fairing compound make sure you don't fair it to where it's flush with the existing gelcoat or you might have our patch end up proud of the surface or with not the full thickness for a gelcoat layer.
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Re: Cracks in Hull - Storm Damage

Postby bilbo » Sun Feb 12, 2023 5:57 pm

I have finally been able to work on this a bit. I ground away the gelcoat around the cracks to see how it looked. I saw the whitish areas where the matrix was damaged, then cut them out with the grinder. I was surprised how little thickness there is at the stern, maybe 1/8" there? Thankfully it appears nothing moved or warped when I made the cuts. Anyway, I've got some more gelcoat to remove but at least I think I've got the damaged stuff out now. How far on either side of the cut should I be adding material? I was thinking 2" either side.

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Re: Cracks in Hull - Storm Damage

Postby GreenLake » Sun Feb 12, 2023 9:23 pm

I think you have the right idea with about 2". Nominally, it's 1 in 12, or 12 times as wide as deep. That's for the portion that is the original fiberglass, not counting the area of adjacent gelcoat that also gets sanded in the process. For 1/8" thickness, you're getting 1 in 16 which is a slight amount of overkill, but better than the opposite.

For the places where you are left with an actual hole, you'll need something to use as backing, to support your new laminate as you are building it up. (Widest patch goes first, narrowest goes last, by the way.). A good backing material can be derived from plastic packaging with large see-through windows. That plastic is stiff enough to not wrinkle, very smooth and should not stick to the epoxy (if in doubt a wipedown with a bit of wax will make sure it comes off again).

Good luck getting her done.
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Re: Cracks in Hull - Storm Damage

Postby bilbo » Mon Feb 13, 2023 8:32 am

Thanks, I was going to make thin plates with FRP to use for backing. I should be able to fish them in and get them to stick from the outside. The holes are large enough to get my fingers in to clean/sand the backside.

Thanks for the tip on the patch stack. I probably would have done the opposite, narrowest first. Just to make sure I understand correctly, the patches should be as below with the top of the sketch being the outside of the hull?



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