Tiny Holes in the Aluminum Hull

[mattevans24]

I am fixing up a 1987 Blue Fin 17' aluminum boat. I am through the tear down stage and its time to repair then rebuild. There are about 30 tiny holes in the bottom of the boat. I don't know what may have caused this. I did a punch test with a screwdriver and aluminum around it isnt brittle at all. They are all in the center, from where the poured foam starts, to the transom.

Anyhow, I am going to drill each of them out and use blind rivets, at the recommendation of jigngrub. After sizing up the holes, 3/16 seems like the appropriate size.

My Question is what length rivet do I need? I have never worked with rivets and I don't particularly know the thickness of the aluminum. It is only going through the aluminum in the hull, it won't be traveling through anything else. Below are some photos. The dark photo is one from under the boat and I turned off the lights in the garage and placed a light in the boat.

Anyone else have this problem with their aluminum hull? Any ideas on how the holes were formed?

Thanks!

 

[Bondo]

Re: Tiny Holes in the Aluminum Hull

My Question is what length rivet do I need?

Ayuh,... The hull is probably 'bout .060" or so, so the shortest closed-end pop-rivets you can find, oughta work, Just Fine...

 

[Willyclay]

Re: Tiny Holes in the Aluminum Hull

Anyone else have this problem with their aluminum hull? Any ideas on how the holes were formed?

Yes, BTDT with my 1965 Lonestar. It looked like Swisscheese. I concluded it was caused by corrosion but could be wrong. Good luck!

 

[FastFission]

Re: Tiny Holes in the Aluminum Hull

Looks like corrosion to me. Any chance the hull was in contact with something wet for a long time (either inside or outside surface)? Is the material thinned in the area, or just where it's pitted?

 

[Grandad]

Re: Tiny Holes in the Aluminum Hull

Anyone else have this problem with their aluminum hull? Any ideas on how the holes were formed?

Thanks!

I believe what you have is a case of "crevice corrosion". It's my understanding that when fresh water becomes trapped between 2 metals, even those of identical, normally corrosion resistant materials, it turns corrosive. I don't know the entire process, but I believe the oxygen content in the water is depleted such that the oxide that normally forms a protective film on aluminum is absent. This occurs anywhere that there is no fresh exchange of water, such as where wet foam is in constant contact with aluminum.
http://en.wikipedia.org/wiki/Crevice_corrosion

Unless you're absolutely certain that the strength of the aluminum sheet in the area has not been weakened, I would add a piece of aluminum sheet over the entire suspect area. Apply 3m 5200 without gaps over the entire mating surface to exclude the possibility of trapping water between and avoid further crevice corrosion. Then rivet the patch in place. I would use solid aluminum rivets bucked in place with air tools, however others recommend using blind pop rivets. Under no circumstances would I use a rivet that uses steel in its construction in an area that will obviously be wet. Such materials that are more "noble" than the surrounding aluminum will promote corrosion of the aluminum. - Grandad

 

[CheapboatKev]

Re: Tiny Holes in the Aluminum Hull

Usually that corrosion is actually caused by the poured in foam
It can get damp and keep water forever..Also it's own chemical make up will eat into tin boats.
Not cool.
After the rivets, Gluv-it is your friend for years of worry free boating.

 

[jigngrub]

Re: Tiny Holes in the Aluminum Hull

These are the rivets you need:

http://www.rivetsonline.com/closed-end-blind-rivet-pr62asph.html

They have a grip range of .020-.125", that about 1/48-1/8" thick material they'll work on.

I've ordered lots of rivets and a setting tool from JayCee's, they have good service and timely shipping.

 

[mattevans24]

Re: Tiny Holes in the Aluminum Hull

These are the rivets you need:

http://www.rivetsonline.com/closed-end-blind-rivet-pr62asph.html

They have a grip range of .020-.125", that about 1/48-1/8" thick material they'll work on.

I've ordered lots of rivets and a setting tool from JayCee's, they have good service and timely shipping.

Alright rivets are ordered, Thanks!

I checked the strength of the aluminum surrounded the corroded areas and it is solid. I used the jab and stab technique and it didnt even make a mark. Excited to get those rivets and get em in. Then its on to gluvit.

Any estimates on how much gluvit I will need? It will just be applied to the rivets and seams.

 

[kfa4303]

Re: Tiny Holes in the Aluminum Hull

It seems like 1 qt. of Gluv-it is enough to do a whole boat (,18') usually with a bit leftover. Good luck with the rivets!

 

[kfa4303]

Re: Tiny Holes in the Aluminum Hull

You shouldn't need more than a quart to do your whole boat.

 

[jigngrub]

Re: Tiny Holes in the Aluminum Hull

Alright rivets are ordered, Thanks!

I checked the strength of the aluminum surrounded the corroded areas and it is solid. I used the jab and stab technique and it didnt even make a mark. Excited to get those rivets and get em in. Then its on to gluvit.

Any estimates on how much gluvit I will need? It will just be applied to the rivets and seams.

Did you order the rivet setting tool as well? Or do you know someone that has one you can borrow?

You can set those 3/16 rivets with the small one hand setting tool, but it'll require a substantial amount of effort. The larger two handed heavy duty setting tool makes setting them much easier. These aren't your typical little 1/8" aluminum rain gutter and downspout rivets, they're very strong and tough rivets used in aircraft and boat construction. You'll see what I mean when you install them.

If you find out you need the heavy duty setting tool, you can get one hear for cheap:

http://www.harborfreight.com/heavy-...and-riveter-with-collection-bottle-66422.html