Hi All, I am considering a 2008 Duroboat, but in the pics I am worried about what appears to be corrosion along the bottom edge of transom. See picture.
https://s16.postimg.org/9bi8hr2lh/01010 ... 00x900.jpg
https://s16.postimg.org/pl8eknd9h/01010 ... ned_up.jpg
I have not personally seen the boat yet, but what appreciate any advice on what I'm seeing here and what I should also look for to see if this boat is having serious issues in that transom.
James
Corrosion to worry about?
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kmorin
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Re: Corrosion to worry about?
jferrenb,
Welcome to the AAB.com Forum, the boat does look like it has some corrosion under the paint- coming out and showing through? Of course if that is salt or other minerals simply dried ON toP of the painted transom panel? Then the picture may show the skiff needs a good bath - not corrosion correction?
Since the paint seems to be lifted, but the photos aren't real close ups, and you've not been to inspect the boat yourself, I'll take the worst case and assume it is a pre-purchase inspection question? That is: you're asking for opinions before you buy this skiff and you're going to personally inspect and you'd like some ideas about what to consider when you inspect?
#1 Ask the owner to scrape those areas- pick the biggest most powdery and use a pocket knife- clean to bare metal. If the underlying corrosion is white chalky powdery, and flakes off with the paint, ANd the underlying metal is not smooth- you're right that is corrosion and you'd have to determine why its there in order to A)clean up B) stop it reoccurring and C) repair what's corroded if the depth is beyond surface pitting?
#2 If you're set on the boat (?) you may elect to buy and repair? If you're set on the boat- then I'd want a repair estimate independent of you or the owner- subtracted from the sales price- meaning you're going to have to find someone to do the repair, it will cost X and X should be subtracted from any sale price or you'll have to consider X cost added to your cost of the boat?
#3 It may be best for your to try to determine why this corroded in order to understand the full extent of the repair?
A) it could be just some expired or wrong alloy engine zincs and an engine bonding wire missing? with isolated engine mount clamps allowing the engine to be a stray current source?
B) it could be the engine's mount conductivity is fine, but some other onboard DC wiring errors are allowing the hull at this location to act as an anode so the wiring could be at fault? Notice the DC trolling motor- installing and running one of these and its charging system could easily be the stray current source of this type of corrosion?
C) it could be there is a wood panel inside the hull that is allowing a crevice/poultice corrosion cell to form and not dry out- in side the transom- and the corrosion is all the way through?
D) it is possible the paint applied to this area was not well adhered to the aluminum- poor prep- and the boat is trailered regularly; so, where the paint film is not adhered- that allowed a stagnate water cell (acidic corrosion) to form and re-wet without fully drying?
#4 The skiff may have other features not suggested here that contribute to that condition or what looks corrosion?
I'll note that builders who use, what looks like, extrusions along the transom and topsides seams are often those that use wood to inexpensively build up transoms, and those materials combined- wood and aluminum are sometimes not correctly installed?
I'd want to have an ice pick/pocket/screw driver knife along and ask the owner to peel the paint and explore those spots?
Cheers,
Kevin Morin
Kenai, AK
Welcome to the AAB.com Forum, the boat does look like it has some corrosion under the paint- coming out and showing through? Of course if that is salt or other minerals simply dried ON toP of the painted transom panel? Then the picture may show the skiff needs a good bath - not corrosion correction?
Since the paint seems to be lifted, but the photos aren't real close ups, and you've not been to inspect the boat yourself, I'll take the worst case and assume it is a pre-purchase inspection question? That is: you're asking for opinions before you buy this skiff and you're going to personally inspect and you'd like some ideas about what to consider when you inspect?
#1 Ask the owner to scrape those areas- pick the biggest most powdery and use a pocket knife- clean to bare metal. If the underlying corrosion is white chalky powdery, and flakes off with the paint, ANd the underlying metal is not smooth- you're right that is corrosion and you'd have to determine why its there in order to A)clean up B) stop it reoccurring and C) repair what's corroded if the depth is beyond surface pitting?
#2 If you're set on the boat (?) you may elect to buy and repair? If you're set on the boat- then I'd want a repair estimate independent of you or the owner- subtracted from the sales price- meaning you're going to have to find someone to do the repair, it will cost X and X should be subtracted from any sale price or you'll have to consider X cost added to your cost of the boat?
#3 It may be best for your to try to determine why this corroded in order to understand the full extent of the repair?
A) it could be just some expired or wrong alloy engine zincs and an engine bonding wire missing? with isolated engine mount clamps allowing the engine to be a stray current source?
B) it could be the engine's mount conductivity is fine, but some other onboard DC wiring errors are allowing the hull at this location to act as an anode so the wiring could be at fault? Notice the DC trolling motor- installing and running one of these and its charging system could easily be the stray current source of this type of corrosion?
C) it could be there is a wood panel inside the hull that is allowing a crevice/poultice corrosion cell to form and not dry out- in side the transom- and the corrosion is all the way through?
D) it is possible the paint applied to this area was not well adhered to the aluminum- poor prep- and the boat is trailered regularly; so, where the paint film is not adhered- that allowed a stagnate water cell (acidic corrosion) to form and re-wet without fully drying?
#4 The skiff may have other features not suggested here that contribute to that condition or what looks corrosion?
I'll note that builders who use, what looks like, extrusions along the transom and topsides seams are often those that use wood to inexpensively build up transoms, and those materials combined- wood and aluminum are sometimes not correctly installed?
I'd want to have an ice pick/pocket/screw driver knife along and ask the owner to peel the paint and explore those spots?
Cheers,
Kevin Morin
Kenai, AK
kmorin
Re: Corrosion to worry about?
Kevin -
How does wet wood allow corrosion to form / start?
Is it similar to what water and injected foam do to the inside of a aluminum hull over time?
Jon
How does wet wood allow corrosion to form / start?
Is it similar to what water and injected foam do to the inside of a aluminum hull over time?
Jon
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kmorin
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Re: Corrosion to worry about?
JonH, yes there is a case of similar behavior of wood and foam that is not bedded properly and holding a wetted interface. (first) the wood could be directly against the aluminum without any bedding or sealant. That interface can get wet and the water may form a thin film- when that happens the water can stagnate or loose its oxygen (initially to the bare metal's oxide film!) and shift ph to become acidic. This is true of wood or of even aluminum put flat to another piece of aluminum and left to wet by a film of water.
But the wood may hold water too, so when the boat is pulled/hauled and begins to dry out- the wood can act as a wick or supply of more water- not enough fresh water to rinse out the acid- but enough to keep the cycle of oxygen exchanges with the aluminum oxide going over and over. That is why the poultice cell got its name there is some water source in the organic matter that allows the acid to renew and 'eat more metal molecules'.
Treated woods may have copper chemicals too and there is a big galvanic (read battery) spread between copper and aluminum. The other potential with wood is the glue in some plywood when wetted can become acidic and finally, topcoats may seal the wood but not seal the interface like a mastic or calk. So there can be a few different wood contributions that rob water of its oxygen so its de-aerated/stagnated and therefore shifts ph toward acidic.
Last, if you use plywood build up in a metal boat transom its not rare to find screws, bolts or other fasteners used to hold the wood to the plywood - even it the two are glued/sealed/adhered to one another. These points of dissimilar metal (anything but hot-dipped galvanized/zinc coated fasteners have some galvanic potential with aluminum and so do these - but very little) intrusion can result in points of corrosion of dissimilar metals at any given entry point.
I've seen all these instances in metal boats over time, so I'm mentioning them all to help make the subject clear. However if wood is sealed with soaking epoxy, top coated with more, then bedded off the metal with some 5200 or that class of sealant, and has no thin film traps, it works fine for many applications especially if the interface is dry!
Cheers,
Kevin Morin
Kenai, AK
But the wood may hold water too, so when the boat is pulled/hauled and begins to dry out- the wood can act as a wick or supply of more water- not enough fresh water to rinse out the acid- but enough to keep the cycle of oxygen exchanges with the aluminum oxide going over and over. That is why the poultice cell got its name there is some water source in the organic matter that allows the acid to renew and 'eat more metal molecules'.
Treated woods may have copper chemicals too and there is a big galvanic (read battery) spread between copper and aluminum. The other potential with wood is the glue in some plywood when wetted can become acidic and finally, topcoats may seal the wood but not seal the interface like a mastic or calk. So there can be a few different wood contributions that rob water of its oxygen so its de-aerated/stagnated and therefore shifts ph toward acidic.
Last, if you use plywood build up in a metal boat transom its not rare to find screws, bolts or other fasteners used to hold the wood to the plywood - even it the two are glued/sealed/adhered to one another. These points of dissimilar metal (anything but hot-dipped galvanized/zinc coated fasteners have some galvanic potential with aluminum and so do these - but very little) intrusion can result in points of corrosion of dissimilar metals at any given entry point.
I've seen all these instances in metal boats over time, so I'm mentioning them all to help make the subject clear. However if wood is sealed with soaking epoxy, top coated with more, then bedded off the metal with some 5200 or that class of sealant, and has no thin film traps, it works fine for many applications especially if the interface is dry!
Cheers,
Kevin Morin
Kenai, AK
kmorin
Re: Corrosion to worry about?
I like Kevin's ideas, I'll throw a couple more onto the list of potential causes.
Water is getting trapped between the transom panel and the alloy extrusion at the bottom of the transom. The water is stagnant and turning acidic and leaching upwards under the paint causing bubbling and pitting. The other thing is that on these types of boats the alloys that the manufacturers use in construction are not typically the most corrosion resistant types of marine alloys so they are susceptible to problems particularly if they are painted.
Water is getting trapped between the transom panel and the alloy extrusion at the bottom of the transom. The water is stagnant and turning acidic and leaching upwards under the paint causing bubbling and pitting. The other thing is that on these types of boats the alloys that the manufacturers use in construction are not typically the most corrosion resistant types of marine alloys so they are susceptible to problems particularly if they are painted.
1987 24' LaConner pilothouse workboat, 225 Suzuki
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Re: Corrosion to worry about?
Thanks so much everyone for your input - this has been very helpful. I am considering buying this boat and noticed the "gunk" on the bottom of the transom - assumed it was some form of corrosion, but have not gone to check it out myself and being a novice REALLY appreciate the insights here.
https://seattle.craigslist.org/see/boa/5820369780.html
So I'll take a very close look at it - perhaps grab some additional pics to post here. I think, the price of the boat is unusually good, which tells me the seller knows his boat may have some issues.
Thank you again!
James
https://seattle.craigslist.org/see/boa/5820369780.html
So I'll take a very close look at it - perhaps grab some additional pics to post here. I think, the price of the boat is unusually good, which tells me the seller knows his boat may have some issues.
Thank you again!
James
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kmorin
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Re: Corrosion to worry about?
james, Chaps' remarks made me look at the image again, and I'd like to note a small curiosity on my part.
The transom panel's paint line seems to be separate from the extrusions- of course this may not be true as the photo is not a close up. What I'm driving at is the appearance of the extrusion being welded on the inside only?
Not sure on this, one side and inside only weld? But if that is the case, then the blue painted transom panel's insertion may not only be a source for water to wick up under the paint film (?) BUtttttt the sheet edge itself could have significant edge-on/perimeter corrosion hidden inside the channel of the extrusion?
What I'd want to inspect, if I were considering this boat is the inner seam/edge of the lower transom edge and bottom intersection seam. If this extrusion that is used a pair of U's at right angles? Is this extrusion - since it doesn't appear seal welded from the outside (?) welded only inside and if that is true- wouldn't this potentially be a source for standing water - even it were rain water?
Just a post script to your images that didn't occur to me before. I'd want to inspect this area inside the hull to discover the actual cross section and understand how that design is performing? If there is seal weld outside too, and I just can't make it out in the picture, my concerns are misplaced- to some extent- but you'll want to understand this construction detail before you pay anything for this skiff.
Cheers,
Kevin Morin
Kenai, AK
The transom panel's paint line seems to be separate from the extrusions- of course this may not be true as the photo is not a close up. What I'm driving at is the appearance of the extrusion being welded on the inside only?
Not sure on this, one side and inside only weld? But if that is the case, then the blue painted transom panel's insertion may not only be a source for water to wick up under the paint film (?) BUtttttt the sheet edge itself could have significant edge-on/perimeter corrosion hidden inside the channel of the extrusion?
What I'd want to inspect, if I were considering this boat is the inner seam/edge of the lower transom edge and bottom intersection seam. If this extrusion that is used a pair of U's at right angles? Is this extrusion - since it doesn't appear seal welded from the outside (?) welded only inside and if that is true- wouldn't this potentially be a source for standing water - even it were rain water?
Just a post script to your images that didn't occur to me before. I'd want to inspect this area inside the hull to discover the actual cross section and understand how that design is performing? If there is seal weld outside too, and I just can't make it out in the picture, my concerns are misplaced- to some extent- but you'll want to understand this construction detail before you pay anything for this skiff.
Cheers,
Kevin Morin
Kenai, AK
kmorin