Repairing stress cracks in a riveted aluminum boat

JonM · Jul 12, 2024

I have 5 stress cracks in my riveted aluminum boat on the starboard side and one stress crack on the port side. All the cracks are under the ribs closest to where the hull meets the sides of the boat. I've done some extensive research and it seems the best way to repair this is to drill a hole at each end of the cracks and make a riveted patch with 5200. I have one issue, I can't access this from the inside because of the floor so I'll have to use aluminum closed end pop rivets (sealed rivets). I'd appreciate some opinions on this repair and would also like to know if I should remove/replace the rivets where the cracks are. Thanks in advance!

Axhammer · Jul 13, 2024

Your research has served you well. A proper lap patch riveted in place “wet” with 5200 will be a permanent repair.

You have five separate repairs or patches that need to be fabricated & installed. If you post more pictures we can figure out what needs to happen in each situation. You might want to post several pictures of the first one you want to make, and call it repair one. Your closeup pictures are great, but you need some pictures from further away, and both sides.

Are you going to install solid rivets where possible, or pop rivets everywhere. Solid rivets are preferred, but both style rivets will work fine.

Axhammer · Jul 13, 2024

You always want to “stop drill” the cracks.

When there are rivets in the repair area, the standard practice is to pick up those holes in the patch. When the patch gets installed, new rivets will go in those holes. The lap patch normally consists of one patch. Like a bandaid, and it’s called a doubler. When required a doubler will go on both sides.

JonM · Jul 14, 2024

Axhammer said:
Your research has served you well. A proper lap patch riveted in place “wet” with 5200 will be a permanent repair.

You have five separate repairs or patches that need to be fabricated & installed. If you post more pictures we can figure out what needs to happen in each situation. You might want to post several pictures of the first one you want to make, and call it repair one. Your closeup pictures are great, but you need some pictures from further away, and both sides.

Are you going to install solid rivets where possible, or pop rivets everywhere. Solid rivets are preferred, but both style rivets will work fine.

Thank you for your input, I will try my best to get more pictures today. It's going to be a couple weeks before I can attempt this repair because I'm recovering from a broken leg. But in the meantime I'm buying all the materials I need to successfully make this repair. Also I work at West Marine and I can get almost everything I need from there, I saw someone recommended G-flex instead of 5200. What are your thoughts on this?

JonM · Jul 14, 2024

This is repair 1 and it's the only repair that's accessible from the inside. What's concerning to me is how the hull is kind of peeling away from the edge of the rib inside the boat. Those lines that look like hairline cracks are just scratches. The cracks that go through to the inside are visible in the close up pic of the last rivets on the rib.

JonM · Jul 14, 2024

Repair 2, can't see this one from the inside because it's under the bench and floor/deck

JonM · Jul 14, 2024

Repair 3, this one is also under the deck. Also all of these cracks are under the ribs. This boat is a 1997 Monark 16 SF (16' V bottom)

Axhammer · Jul 14, 2024

G-flex is some strong stuff, but it isn’t very flexible compared to 5200. I started a test of different adhesives, and I need to evaluate my results and share with everyone.

LDUBS · Jul 14, 2024

Axhammer said:
You always want to “stop drill” the cracks.

When there are rivets in the repair area, the standard practice is to pick up those holes in the patch. When the patch gets installed, new rivets will go in those holes. The lap patch normally consists of one patch. Like a bandaid, and it’s called a doubler. When required a doubler will go on both sides.

Hey @Axhammer, when installing the patch, is it OK to replace those solid rivets with pop rivets?

Axhammer · Jul 15, 2024

There are many types of pop rivets (blind rivets).

There are blind rivets approved for structural repairs on aircraft. Cherry Max and Huck rivets are two that are very common.

https://huckaerobolt.com.au/blogs/n...etlabels for,sound rivets make when installed.

Axhammer · Jul 15, 2024

A tool should be used to determine the required grip length for a blind rivet.

Axhammer · Jul 15, 2024

https://www.docdroid.com/AwvlaY3/general-aircraft-structural-repair-manual-pdf#page=120

NAVAIR 01-1A-1. The Structural repair manual…lots of good info.

Axhammer · Jul 15, 2024

A very rough idea of what a lap patch might look like.

JonM · Jul 15, 2024

Axhammer said:
A very rough idea of what a lap patch might look like.

View attachment 121774

This was very helpful, thank you for the info and drawing

lckstckn2smknbrls · Jul 15, 2024

Any reason why there's no dot between the two original rivets in the upper row?

Axhammer · Jul 16, 2024

No, I missed it. There are guidelines to work with but when a patch is laid out it could be done several ways, and there is usually no truly wrong way. Edge distance and rivet pitch have variables.

JonM · Jul 17, 2024

Axhammer said:
No, I missed it. There are guidelines to work with but when a patch is laid out it could be done several ways, and there is usually no truly wrong way. Edge distance and rivet pitch have variables.

Is there a way to pull everything together from the outside of the hull before riveting on the patch? My concern is when I drill out these rivets holding the ribs to the hull, the ribs will separate and create a gap. Will the rivets pull everything together? There's also an indentation in the hull where the rivets are, should I lightly hammer the patch to take the shape of the hull/indentation before I start riveting? Thanks

Axhammer · Jul 19, 2024

I noticed the indented area. I would reshape the hull skin in that are, trying to get it back to the original shape. You want to shape and form the doubler, so it fits the area it is being attached to. Being a boat, it will have compound curves. You can use a hammer, (body hammer) or rubber mallet, to strike it against a vice, anvil or short section of railroad track. You can also use a sand bag to shape it. Either way you want to doubler to fit closely, creating less stress.

They make a style Cleco that has a wing nut to tighten, allowing the metal to be pulled together. I’ll post a picture of one, they work good for what you are talking about.

How thick is the skin, and doubler metal you have to work with?

JonM · Jul 20, 2024

Axhammer said:
I noticed the indented area. I would reshape the hull skin in that are, trying to get it back to the original shape. You want to shape and form the doubler, so it fits the area it is being attached to. Being a boat, it will have compound curves. You can use a hammer, (body hammer) or rubber mallet, to strike it against a vice, anvil or short section of railroad track. You can also use a sand bag to shape it. Either way you want to doubler to fit closely, creating less stress.

They make a style Cleco that has a wing nut to tighten, allowing the metal to be pulled together. I’ll post a picture of one, they work good for what you are talking about.

How thick is the skin, and doubler metal you have to work with?

I don't know exactly how thick the hull is but it looks close to 1/8th of an inch thick. I bought 1/16th aluminum sheets from Amazon and two different sized 3/16th's rivets from "Jay-Cee Sales & Rivets, Inc". One pack of rivets with grip from .251-.375 and another pack with grip from .376-.500 . I included a photo showing how my hull is starting to bend where I circled in red. It's not so bad towards the transom but the hull starts to bend down more and more towards the middle of the boat. The hull is fairly thick and difficult to bend back into it's original shape. I might have to shape the patch to the hull, please let me know what you think. Thanks

LDUBS · Jul 20, 2024

JonM said:
Is there a way to pull everything together from the outside of the hull before riveting on the patch? My concern is when I drill out these rivets holding the ribs to the hull, the ribs will separate and create a gap. Will the rivets pull everything together? There's also an indentation in the hull where the rivets are, should I lightly hammer the patch to take the shape of the hull/indentation before I start riveting? Thanks

Axhammer said:
I noticed the indented area. I would reshape the hull skin in that are, trying to get it back to the original shape. You want to shape and form the doubler, so it fits the area it is being attached to. Being a boat, it will have compound curves. You can use a hammer, (body hammer) or rubber mallet, to strike it against a vice, anvil or short section of railroad track. You can also use a sand bag to shape it. Either way you want to doubler to fit closely, creating less stress.

They make a style Cleco that has a wing nut to tighten, allowing the metal to be pulled together. I’ll post a picture of one, they work good for what you are talking about.

How thick is the skin, and doubler metal you have to work with?

To me it looks like there is already a gap (see image 4250 in post #5). That is probably what caused the dimples and cracks in the skin around the rivets. If the hull is returned to original shape it seems that gap would be even larger. When new rivets are installed, would you not have the same problem again? I don't have an answer. Seems bending that floor brace would be a no-go. Just scratching my head on how this would all come together. Probably overthinking it.

Repairing stress cracks in a riveted aluminum boat

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