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PostPosted: 26 Jul 2016, 13:19 
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Location: New England
Well, now that I have all the tools and materials to re-rivet our beloved tin boats projects, a friend brought me his to look it. His tin hull weighs 800-lbs by the book, without motor or gear and it was always stored on the trailer that has two 8’ long bunks to support the hull, one down each side. He’s been complaining of a water leak for years now, but this season it became too much, where he won’t trust going away for any length of time with the boat in the water, even though it has an operable automatic bilge pump.

Knowing it is a boat used in saltwater and that the bunks are carpeted, I asked him if he ever looked at the hull where the bunks are located? And of course the answer was ‘No’. She we carefully blocked off and then jacked up one side of the hull at time, lifting it a good 6” off the bunk and placed deadman supports in place so we could work under there without losing a finger or arm … careful – they’re attached!

Look at that corrosion damage! We cannot verify that the bunks were made out of pressure treated wood (20-year old trailer), but it definitely is a saltwater boat and the area where the boat sits on the bunks has never been painted. He would scrape the bottom while it in the water once or twice per season, using a mask and snorkel, but he never looked close at the tin surface. I think it is indicative of crevice corrosion, as aluminum protects itself by the oxide layer of oxygen present in the atmosphere. Stainless steels too are very prone to crevice corrosion … cut off some part of the material to “free air” and it will corrode.

Most surprisingly the pin hole or crevice damage as shown was confined to the 1st foot of the bunk on each side, forward towards the bow end, with barely any – if any – signs of corrosive damage on the rest of the bunk length. I think this is caused by the sheer weight of the hull, being a 16’ hull only supported for 8’ of its length, where the bunks stop about 6” from the stern. This supports the contention that it is most likely caused by crevice corrosion. As even though the stern holds the 250-lb motor, the complete forward part of the boat is probably all borne the 1st foot of each bunk up the front, completely squeezing the carpet and shutting out any free air. Then too, that carpet was soaked in saltwater 2X per season – hopefully just once in and once out, LOL.

Our plan of attack is to scrape and sand the bunk areas – then vinegar wash them (working in one direction only) with a copper scrubby pad and then coarse wet paper – wipe down (1 direction only) w/ vinegar-soaked clean rag – air dry – spray with etching zinc chromate primer – sealing with G-Flex flexible epoxy – and finally adding a copper-free ablative bottom paint to these areas.

Whaddya think?

I will say that any rivets in the surrounding area, and even the chine areas, and all over rest of the bottom of the hull look in an amazingly great condition for an otherwise old hull!


Hull Leaks-01.jpg

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#1) 1st tin rebuild, 18' Lund viewtopic.php?f=21&t=36583
#2) 25' Parker refurb from EMPTY hull http://www.classicparker.com/phpBB3/vie ... p?f=15&t=6
#3) 16' V-tin rebuild viewtopic.php?f=21&t=36465
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#5) 16' Starcraft entirely NEW Transom Skins viewtopic.php?f=3&t=37548
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PostPosted: 26 Jul 2016, 21:00 
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Part 2 - After prepping, vinegar wash/sand and priming:

Mixed up some G-Flex flexible epoxy and slathered it on using a 1" wide flexible metal paint scraper blade (new). Using a plastic single-serving cup, like kid's applesauce comes in, that is maybe 2-3/4" round by not even 2" deep with a slight bowl taper to it, this entire side about 4" by 8+ feet was done just by mixing up 3/8" deep mix of both Parts A & B.

That G-Flex covers really well! And it is tenacious on properly prepared surfaces, as I've intentionally tried to gouge it off using a worn but good quality paint scraper blade and man ... you really need to dig at it and apply muscle to even skim a surface or piece off.

We also got lucky, as on the port side, the only crevice corrosion showing where the boat sits on the bunks is at the forward part of the bunk, a spot no longer than 4" total, as shown in the picture. Glad we caught it now!


Hull-Leak4.jpg
Hull-Leak4.jpg [ 17.17 KiB | Viewed 309 times ]
Hull-Leak5.jpg
Hull-Leak6.jpg

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#1) 1st tin rebuild, 18' Lund viewtopic.php?f=21&t=36583
#2) 25' Parker refurb from EMPTY hull http://www.classicparker.com/phpBB3/vie ... p?f=15&t=6
#3) 16' V-tin rebuild viewtopic.php?f=21&t=36465
#4 Procraft SV14
#5) 16' Starcraft entirely NEW Transom Skins viewtopic.php?f=3&t=37548
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PostPosted: 27 Jul 2016, 07:39 
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Joined: 19 Dec 2015, 20:40
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Location: S.C.
A couple of years back I got a good deal on a used 16' tinny that I would use for saltwater fishing. It came with an undersized fresh water trailer and knew it would only last a season maybe 2. For a little extra support I added a small v bunk near the bow. The trailer did break and while jacking the boat up to slide the new trailer under I noticed 2 areas about 4"x4" each with several pin holes in the hull. They corresponded to where the v bunk was located ... I inadvertently had used pressure treated [-X I prepped the surface areas and coated each with clear JB Weld. A year later and no problems.



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PostPosted: 27 Jul 2016, 12:57 
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Joined: 21 Apr 2012, 17:11
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Location: rural SW Wisconsin
Nice catch and repair.

Is there any possibility of structural weakness where the corrosion occurred? Place where the pinholes were and the metal around them did not show damage, but were reduced in thickness which was not readily apparent?

Have fun, be safe.



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1955 Alumacraft Model A
http://www.tinboats.net/forum/viewtopic ... 08&start=0
1959 Alumacraft Model F
http://www.tinboats.net/forum/viewtopic.php?f=3&t=25386
1980 Alumacraft Model F7, 1955-56? Johnson 10hp
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http://www.tinboats.net/forum/viewtopic.php?f=3&t=39249
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PostPosted: 27 Jul 2016, 13:09 
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Location: New England
Kismet wrote:
Is there any possibility of structural weakness where the corrosion occurred?

Great question! But I highly doubt it ...

None of the 'porosity' appeared clean through and none of it is anywhere near a rivet or chine or any other structural feature. I also put a high-powered LED work lamp into the forward bilge access hole above the areas - at night - and couldn't see anything shining through.

Believe me ... we'll be keeping a good eye on the area!

But for it to have taken 20-years to do that, I'm really confident in the flexible G-Flex epoxy being the right choice. Steel-Flex or that Coat-It others here are using would probably work too, but just in case of any hull deflection, we opted for the superior flexibility properties of the G-Flex epoxy.

In a few years I'll report back just how well the repairs (1) sticks to the hull and (2) is working and/or wearing.



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#1) 1st tin rebuild, 18' Lund viewtopic.php?f=21&t=36583
#2) 25' Parker refurb from EMPTY hull http://www.classicparker.com/phpBB3/vie ... p?f=15&t=6
#3) 16' V-tin rebuild viewtopic.php?f=21&t=36465
#4 Procraft SV14
#5) 16' Starcraft entirely NEW Transom Skins viewtopic.php?f=3&t=37548
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PostPosted: 27 Jul 2016, 14:37 
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Joined: 15 Mar 2014, 16:57
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Location: CT
Any reasoning behind using G-Flex vs Gluvit?



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PostPosted: 27 Jul 2016, 15:03 
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Location: New England
onthewater102 wrote:
Any reasoning behind using G-Flex vs Gluvit?

G-Flex flexes ... Gluvit is or becomes brittle ...

Technically speaking, the modulus of elasticity of the G-Flex is about 1/3rd that of a standard epoxy, so where other epoxies may lift or fail when subject to bends, vibration, shocks or even expansion/contraction due to thermal changes ... G-Flex was designed to stay adhered. That's why we went with it. I myself have witnessed epoxy 'glue' seams fail years later due to repetitive expansion and contraction cycles. So I hope this works!

Cost-wise, if one only used it on structural areas, like rivets or seams, it's not bad, as an 8-ounce kit is $19 to $20. Whereas a quart of Gluvit is $40. If someone wanted to coat an entire hull as a prophylactic (proactive) measure, then Steel-Flex or Coat-It would surely be more economical.

Our choice was also more based upon the fact that this was a repair to an area with corrosive porosity. On an otherwise sound hull, I would use another epoxy product, if going for total bottom coverage for example.



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#1) 1st tin rebuild, 18' Lund viewtopic.php?f=21&t=36583
#2) 25' Parker refurb from EMPTY hull http://www.classicparker.com/phpBB3/vie ... p?f=15&t=6
#3) 16' V-tin rebuild viewtopic.php?f=21&t=36465
#4 Procraft SV14
#5) 16' Starcraft entirely NEW Transom Skins viewtopic.php?f=3&t=37548
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