bottom corrosion 18'bayrunner
bottom corrosion 18'bayrunner
Changing bunks on the trailer today and found alot of corrosion pitting on the bottom of the boat today always herd this problem with bayrunners any help on how to repair would be great. THANKS SUSHI KING
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peterbo3
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Corrosion is never good but do not despair. How thick is the alloy? Can you scrape away some of the corrosion to determine how deep it is? If you have plenty of good alloy left then it may be simply a case of finding out WHY this has occurred & taking remedial action.
If you can deal with the first two points & provide some pics I am sure that a
satisfactory solution can be found.
If you can deal with the first two points & provide some pics I am sure that a
satisfactory solution can be found.
Regards,
Pete in Brisbane
Pete in Brisbane
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gil marlin
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- Location: La Mesa, Ca.
I had some corrosion issues on the transom of mine. I remedied the problem by installing a battery negative switch to go with the existing battery positive selector switch. Now when it's not in use I switch off both and the battery voltage is completely isolated from the hull. I have had salt accumulate on the carpet of the trailer bunks but it has not caused any pin holing. As said before, if the hole is not too large you should be able to seal it with marine tex, or have it welded, the bottom plate is pretty thick...
Is that a real Poncho or a Sears Poncho?
repairs
weld and grind , and go forever . I have been told of instances of corrosion occuring in the area of contact with carpeted bunks if left for long periods . dampness and exposure to the air has something to do with it .its not the same as being submerged .
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kmorin
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Poultic Corrosion on Trailers' Bunks
sushiking,
wooden trailer bunks covered with carpet can create a type of corrosion in aluminum called poultice corrosion because the cause of the acidic cell is a wet sponge like material against the metal.
Wood will stay soaked and help carpet or other bunk covering to stay damp allowing the water to be in constant contact with the metal. The water isn't the problem, alone, but what happens to the water as it stays in the carpet or on a wood bunk is that the dampness slowly becomes acidic. If the boat is not moved too regularly this acidic 'wet spot' will cause pits as the aluminum looses its oxide to the acidic water.
If the hull has bunks located in the after half the hull that are spaced near the riveted on, or press-formed rails (?) then the rails unfortunately work to keep fresh air from drying the carpet and bunks. This keeps the acid in liquid contact with the hull and hull panel deterioration can be fairly severe. The same boat tuned keel up and left in the rain will last for decades, but with a poultice site it can be pitted through.
I'd suggest you consider hull doublers to repair. Usually welding to a formed hull isn't as effective as we'd like. The hull's original scantlings are light and semi-flexible compared to welding plates in the field on hull panels. You'd do fine to add a welded transom or even repair a welded chine, but adding welded panels to the riveted and press formed bottom isn't as successful. The rigidity of the weldment often ends in edge cracking within a season.
I'd suggest you consider a series of strips of hull thickness material blind riveted over the areas of pitting and bedded in 5200 or some other marine mastic. Of course, riveting is 'ten times' the work of welding and riveting with bedding compound is more frustrating yet.
My reasoning is that the thin doubler would add original hull outside the damage, avoid heat distortions always associated with welding super thin sheet, and to make the entire project a cold worked repair.
Hope you save your boat from becoming un-seaworthy.
Cheers,
kmorin
wooden trailer bunks covered with carpet can create a type of corrosion in aluminum called poultice corrosion because the cause of the acidic cell is a wet sponge like material against the metal.
Wood will stay soaked and help carpet or other bunk covering to stay damp allowing the water to be in constant contact with the metal. The water isn't the problem, alone, but what happens to the water as it stays in the carpet or on a wood bunk is that the dampness slowly becomes acidic. If the boat is not moved too regularly this acidic 'wet spot' will cause pits as the aluminum looses its oxide to the acidic water.
If the hull has bunks located in the after half the hull that are spaced near the riveted on, or press-formed rails (?) then the rails unfortunately work to keep fresh air from drying the carpet and bunks. This keeps the acid in liquid contact with the hull and hull panel deterioration can be fairly severe. The same boat tuned keel up and left in the rain will last for decades, but with a poultice site it can be pitted through.
I'd suggest you consider hull doublers to repair. Usually welding to a formed hull isn't as effective as we'd like. The hull's original scantlings are light and semi-flexible compared to welding plates in the field on hull panels. You'd do fine to add a welded transom or even repair a welded chine, but adding welded panels to the riveted and press formed bottom isn't as successful. The rigidity of the weldment often ends in edge cracking within a season.
I'd suggest you consider a series of strips of hull thickness material blind riveted over the areas of pitting and bedded in 5200 or some other marine mastic. Of course, riveting is 'ten times' the work of welding and riveting with bedding compound is more frustrating yet.
My reasoning is that the thin doubler would add original hull outside the damage, avoid heat distortions always associated with welding super thin sheet, and to make the entire project a cold worked repair.
Hope you save your boat from becoming un-seaworthy.
Cheers,
kmorin
kmorin
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kmorin
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Seal'em, Drain'em, Change'em
mojomizer,
if the bunk is carpet then it can be changed for a vinyl covering. The black vinyl is not reactive like rubber with aluminum, and most often has ridges that allow the water to drain away from the metal being supported.
If that option isn't realistic then epoxy soaking [ almost any sealer that would waterproof ] the wood a few times would keep the acidic development down. Some trailers actually have treated wood for the bunk longs, and that copper solution would really corrode, but the ones I've seen were capet wrapped on top of the treated wood so the combination was pretty hard on the hull.
Another idea would be to tilt the tongue up enough to insure that whatever moisture was in the bunk's covering was drained. If the tongue jack is put on a tall block and jacked to the top, that should give some pitch up by the bow.
Last resort would be to rinse with the garden hose on a semi-regular basis. If the water in the carpet can be 'freshened' the ph stays mid range enough for the aluminum to handle.
Odd as it may sound, baking soda is a great acidic neutralizer, although dilution with fresh water usually works. I've mixed baking soda in 5 gallons of water to 'store' in the bilge of aluminum (commercial) fishing boats that were having internal corrosion problems and its been extremely helpful.
Cheers,
if the bunk is carpet then it can be changed for a vinyl covering. The black vinyl is not reactive like rubber with aluminum, and most often has ridges that allow the water to drain away from the metal being supported.
If that option isn't realistic then epoxy soaking [ almost any sealer that would waterproof ] the wood a few times would keep the acidic development down. Some trailers actually have treated wood for the bunk longs, and that copper solution would really corrode, but the ones I've seen were capet wrapped on top of the treated wood so the combination was pretty hard on the hull.
Another idea would be to tilt the tongue up enough to insure that whatever moisture was in the bunk's covering was drained. If the tongue jack is put on a tall block and jacked to the top, that should give some pitch up by the bow.
Last resort would be to rinse with the garden hose on a semi-regular basis. If the water in the carpet can be 'freshened' the ph stays mid range enough for the aluminum to handle.
Odd as it may sound, baking soda is a great acidic neutralizer, although dilution with fresh water usually works. I've mixed baking soda in 5 gallons of water to 'store' in the bilge of aluminum (commercial) fishing boats that were having internal corrosion problems and its been extremely helpful.
Cheers,
kmorin
I believe this subject deserves more discussion as I have encountered this problem (bunk board/alloy hull bottom corrosion) on several occasions. Chemical reactions occur between many dissimilar materials especially when salt water and or electricity are part of the mix. Keep in mind also that many anchorages, berths, docks, marinas can have stray electrical currents propagated by other vessels or shore power or? that can melt your alloy away in short order. High water and hull temperature can accelerate the electrolysis. As some members have mentioned, improper vessel electrical and electronic system design/materials/implementation can be a major contributor to alloy hull erosion problems. Retained moisture between bunk structure, bunk surface and alloy bottom hull surface can result in major headaches. Roller wheel and plastic bunk trailers certainly have some merit.
Regards, Don
Regards, Don
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kmorin
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Trailer Bunks versus Rollers
Calloy,
I'd like to remark about trailering alloy boats on rollers versus bunks. My experience with both, as a repair shop and builder, has left me with some experiences that might be worth discussing.
First, flat bunks, especially carpeted flat bunks might create poultice corrosion cells if they don't dry out- but the do distribute the hull's weight along larger areas than rollers.
Rollers are more likely to damage an aluminum alloy hull- welded OR riveted- than bunks- but not by corrosion.
Not very many boats travel 50 to 80 mph but those that do are 'loaded' uniformly over the wetted area as the hull enters the water. [Yes, I agree that there might be a very stiff ride at those speeds primarily because these boats are not as heavy as GRP hulls.]
But even a hull designed for 70 mph on the water can be damaged by the 'point loads' developed during hauling a hull on a trailer at those speeds if the hull is balanced/supported/held up on rollers.
If the hull weighs 2000 lb. hull, engine,fuel, and gear and is moving at 50 mph there is a momentum or force much greater than just 2tons; its the mass times the velocity so lets call it 100,000 p.
If the hull's beam is 6' and the bottom is about 18' long the area is roughly 70 square feet. So the force of 100,000 p is divided over this area, in our over simplified example, and the loading is about 1400 p per square foot.
Now if the rollers are about 3" wide they'd each have about 3" or 0.02 square feet each. So lets say there are 24 rollers or about 0.5 square feet. So now that same 100k p of force is being supported on less than one percent of the area when on the water.
That decrease in area of support cranks the point loads up by roughly 130 times more when the boat is on the trailer, WITH ROLLERS compared to when its on the water.
Bunks can contribute to corrosive cells but they do help 'cushion' the ride on the highway.
I've seen more damage from roller trailers than I have from corrosion. So I always try to position the rollers on hull longs, and if possible to keep them close to internal framing elements and to add as many as reasonably possible.
I've seen owners take four 2 ton nylon cargo straps, one at each corner of the hull, and winch the hull to the trailer- tight. They're putting four times the hull mass in deflection onto those rollers and then they wonder why there are structural problems?
Cheers,
I'd like to remark about trailering alloy boats on rollers versus bunks. My experience with both, as a repair shop and builder, has left me with some experiences that might be worth discussing.
First, flat bunks, especially carpeted flat bunks might create poultice corrosion cells if they don't dry out- but the do distribute the hull's weight along larger areas than rollers.
Rollers are more likely to damage an aluminum alloy hull- welded OR riveted- than bunks- but not by corrosion.
Not very many boats travel 50 to 80 mph but those that do are 'loaded' uniformly over the wetted area as the hull enters the water. [Yes, I agree that there might be a very stiff ride at those speeds primarily because these boats are not as heavy as GRP hulls.]
But even a hull designed for 70 mph on the water can be damaged by the 'point loads' developed during hauling a hull on a trailer at those speeds if the hull is balanced/supported/held up on rollers.
If the hull weighs 2000 lb. hull, engine,fuel, and gear and is moving at 50 mph there is a momentum or force much greater than just 2tons; its the mass times the velocity so lets call it 100,000 p.
If the hull's beam is 6' and the bottom is about 18' long the area is roughly 70 square feet. So the force of 100,000 p is divided over this area, in our over simplified example, and the loading is about 1400 p per square foot.
Now if the rollers are about 3" wide they'd each have about 3" or 0.02 square feet each. So lets say there are 24 rollers or about 0.5 square feet. So now that same 100k p of force is being supported on less than one percent of the area when on the water.
That decrease in area of support cranks the point loads up by roughly 130 times more when the boat is on the trailer, WITH ROLLERS compared to when its on the water.
Bunks can contribute to corrosive cells but they do help 'cushion' the ride on the highway.
I've seen more damage from roller trailers than I have from corrosion. So I always try to position the rollers on hull longs, and if possible to keep them close to internal framing elements and to add as many as reasonably possible.
I've seen owners take four 2 ton nylon cargo straps, one at each corner of the hull, and winch the hull to the trailer- tight. They're putting four times the hull mass in deflection onto those rollers and then they wonder why there are structural problems?
Cheers,
kmorin
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gil marlin
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- Joined: Thu Jul 03, 2008 10:53 am
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- Location: La Mesa, Ca.
I have noticed more salt build up on the ends of my trailer bunks at the stern since replacing them a couple of years ago with pressure treated wood and carpet. I don't think there was a better choice for materials, but I could have painted the wood first. I guess I'll just keep an eye on the carpet for salt build up and rinse occasionally. I agree that slick materials or rollers create their own set of problems and that wood and carpet is still the way to go as far as supporting the hulls load when trailering on bumpy roads as I do a lot of in Baja...
Is that a real Poncho or a Sears Poncho?
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kmorin
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- Location: Kenai, Alaska
pressure treated wood and aluminum
gil marlin,,
Copper is one of the main fungus inhibitors impregnated into pressure treated woods and that metal and salt water will corrode aluminum.
I don't think carpet and pressure treated wood are the best choices for trailer bunks, I'd prefer to see epoxy encapsulated wood or even painted steel covered with sheet plastic over carpet. UHMW strips on metal bunks will do fine, even if the boat might move more easily on the slick material. If you can arrange the bunks near spray rails you could stop the side-to-side movement as long as some tie-down were to hold the boat snugly to the trailer over bumps.
I hope the additional salt you see isn't copper salts reacting with your hull? I did inspect a smaller production boat with a refurbished transom that used treated wood which only lasted one season. The copper in the pressure treatment reacted with the aluminum since this transom panel was sandwiched into the transom and was wet a good deal of the time. This was a combination of galvanic and poultice corrosion inside the transom and the first signs of problem were a white crystal looking chalking at the top butt seams near the outboard clamp. When opened, the entire wood to metal surface areas were pitted beyond use and the owner tried to ask for costs to replace the entire transom from bottom to topsides.
I'm not in favor of treated wood in use to support aluminum.
Cheers,
Copper is one of the main fungus inhibitors impregnated into pressure treated woods and that metal and salt water will corrode aluminum.
I don't think carpet and pressure treated wood are the best choices for trailer bunks, I'd prefer to see epoxy encapsulated wood or even painted steel covered with sheet plastic over carpet. UHMW strips on metal bunks will do fine, even if the boat might move more easily on the slick material. If you can arrange the bunks near spray rails you could stop the side-to-side movement as long as some tie-down were to hold the boat snugly to the trailer over bumps.
I hope the additional salt you see isn't copper salts reacting with your hull? I did inspect a smaller production boat with a refurbished transom that used treated wood which only lasted one season. The copper in the pressure treatment reacted with the aluminum since this transom panel was sandwiched into the transom and was wet a good deal of the time. This was a combination of galvanic and poultice corrosion inside the transom and the first signs of problem were a white crystal looking chalking at the top butt seams near the outboard clamp. When opened, the entire wood to metal surface areas were pitted beyond use and the owner tried to ask for costs to replace the entire transom from bottom to topsides.
I'm not in favor of treated wood in use to support aluminum.
Cheers,
kmorin
When I built the trailer for my boat I used Trex with a full length piece of square tubing under it for the bunks. It does leave some marks on the hull, but they are under the water so they are never seen. I didn't want to have to replace carpet and figured the Trex would be safer than pressure treated lumber. You could easily cut grooves in the Trex with a router for drainage which is probably what I will do having read this discussion.
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gil marlin
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I used wood because it contours to the shape of the hull and has some give to it. I used pressure treated so it would resist rotting. I considered trex but it sags too much and backing it with tubing would make it rigid. Maybe trex with some aluminum angle as a support would be one way to go. The carpet in my opinion protects the hull from scratches and keeps the boat from sliding around too much, unlike plastic or vinyl. Thanks for the information, I was aware of the copper in P/T but never considered the fact that it might leach out into the carpet.
Is that a real Poncho or a Sears Poncho?
This site is great. With any boat it's easy to overlook small details that can lead to major problems down the road. It's great to have access to other people's experiences.
I've used wood bunks for my aluminum boats for all the reasons listed above. I have to drive down rough dirt roads quite a bit and the support supplied by the long bunks is mandatory. I always use large tie-downs in several places so the boat won't separate from the trailer bunks. With the tires aired down the trailer takes the bounce and the boat and trailer don't "slap" against each other. Of course, going slow is the key.
From a support stand point the bunks are right for me. At the same time, I hate having salt water trapped under there - even without treated wood. I've thought of using Trex or a similar material but it doesn't have the same "give" as the wood and flexes a little too much. When it's time to change them out I might give the Trex with aluminum angle a try.
I've used wood bunks for my aluminum boats for all the reasons listed above. I have to drive down rough dirt roads quite a bit and the support supplied by the long bunks is mandatory. I always use large tie-downs in several places so the boat won't separate from the trailer bunks. With the tires aired down the trailer takes the bounce and the boat and trailer don't "slap" against each other. Of course, going slow is the key.
From a support stand point the bunks are right for me. At the same time, I hate having salt water trapped under there - even without treated wood. I've thought of using Trex or a similar material but it doesn't have the same "give" as the wood and flexes a little too much. When it's time to change them out I might give the Trex with aluminum angle a try.
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kmorin
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Vinyl is Great
Vinyl is a perfect choice for bunks, it won't hold water at all, it won't interact with aluminum like carbon rubbers- neoprene or some sheet rubber materials. Its slippery when wet so loading wouldn't be dragging the hull on gravel or sand, then vinyl drys off fast as water is running off it not out from between fibers as might be the case with carpet products.
The shapes here 'give' or cushion; the wood is separated from the metal so poultice cells are eliminated; and there seems to be a size/width for different displacements. By combining these sizes, shown on the link from skfmj, with adjusted lengths and bunk count and layout- I'd say this was as good as it gets for an alloy boat out of water.
[I love the fact that this country has so many people solving so many problems - if there's a need - someone is going to offer a way to fill it.]
cheers,
kmorin
The shapes here 'give' or cushion; the wood is separated from the metal so poultice cells are eliminated; and there seems to be a size/width for different displacements. By combining these sizes, shown on the link from skfmj, with adjusted lengths and bunk count and layout- I'd say this was as good as it gets for an alloy boat out of water.
[I love the fact that this country has so many people solving so many problems - if there's a need - someone is going to offer a way to fill it.]
cheers,
kmorin
kmorin
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Bayrunner19
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Re: bottom corrosion 18'bayrunner
Are you bunks made of pressure treated wood by chance? I've been told that can cause pitting on the hull. It's a reaction to the chemicals in the wood. I never knew it.
Getting ready to do the transome on my Bayrunner glad to have this web site.
Getting ready to do the transome on my Bayrunner glad to have this web site.