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Old 04-27-2016, 08:25 PM   #41
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Plus, by the time you cut the tank up enough to get inside and cut and grind smothered the baffles that are usually in there, it is more trouble than it is worth.

I guess you could rough out the baffles and line the tank with foam....but I see that as a weak repair versus a new tank. If the bladder moves at all it could flex the tank enough that may be in bad shape anyhow and have it split at a corner.

Big difference in an engineered plastic tank and shoving a bladder in an old rusty tank.

Properly installed I would trust bladders, but I don't know of any new boats with them so something is a detractor.
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Old 04-27-2016, 09:52 PM   #42
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What they need to figure out is an airfree tank with no vent to the air. No air, no water, no bugs, no acids, no bad fuel. Maybe a floating membrane on top of the fuel that moves up and down with changes in fuel level. that is sealed away from the air.
Maybe like a balloon of fuel in a rigid box.
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Old 04-27-2016, 11:40 PM   #43
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I`d suggest caution in relying on an older bladder.
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Old 04-28-2016, 07:10 AM   #44
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A nearly one inch thick tank must must have been pretty heavy.
Good eye! That was supposed to be 0.090"
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Old 04-28-2016, 07:18 AM   #45
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Sdowney, you just described a standard production foam filled tank. You can even buy the foam to retro an existing tank. Race cars, offroaders, high performance applications, etc. use it. All of these things are appropriate in there element. But its JMO that a boat that has the fuel tank coated on the inside with whatever latest greatest goop or fiberglassed or replaced with plastic or any number of other stop gap measures is not indicative of an owner that cant really afford to do it right. Or that the boat is not worth the cost of doing it right. I do understand that tank replacement in a early 80s taiwanese boat probably is not going to be cost affective. The value of the boat cannot increase enough to offset the cost. Another problem is that the current owner has usually bought that boat because it was in his price range, and the dollars per foot looked better than say a Hatteras or Bertram of the same age. When confronted with the prospect of fuel tank replacement he has to look at the cost of basic boat ownership and now a large outlay of cash. Or cut corners and do it on the cheap. He becomes an "end user". When he's done using the boat, thats the end of it. Any (good) surveyor looking at a boat over 10 years will insist on a complete fuel tank inspection. If he finds any of the afore mentioned "repairs" he will advise the buyer to get estimates for tank replacement, and deduct that from the purchase price or look elsewhere, ie, walk away.
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Old 04-28-2016, 08:09 AM   #46
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Sdowney, you just described a standard production foam filled tank. You can even buy the foam to retro an existing tank. Race cars, offroaders, high performance applications, etc. use it. All of these things are appropriate in there element. But its JMO that a boat that has the fuel tank coated on the inside with whatever latest greatest goop or fiberglassed or replaced with plastic or any number of other stop gap measures is not indicative of an owner that cant really afford to do it right. Or that the boat is not worth the cost of doing it right. I do understand that tank replacement in a early 80s taiwanese boat probably is not going to be cost affective. The value of the boat cannot increase enough to offset the cost. Another problem is that the current owner has usually bought that boat because it was in his price range, and the dollars per foot looked better than say a Hatteras or Bertram of the same age. When confronted with the prospect of fuel tank replacement he has to look at the cost of basic boat ownership and now a large outlay of cash. Or cut corners and do it on the cheap. He becomes an "end user". When he's done using the boat, thats the end of it. Any (good) surveyor looking at a boat over 10 years will insist on a complete fuel tank inspection. If he finds any of the afore mentioned "repairs" he will advise the buyer to get estimates for tank replacement, and deduct that from the purchase price or look elsewhere, ie, walk away.
Thanks for the info.
I have been wondering if in existing tanks, some kind of thin plastic small plates could be floated on top of the fuel to reduce fuel exposure to moist air. Sort of like overlapping scales. They could be dumped into any tank and would float on top right to the tank edges.
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Old 04-28-2016, 02:38 PM   #47
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A small leak in a tank dosen't automaticly mean replacement. If the area of the leak can be determined, a repair may be an option. We know of several tanks that had been leaking from the inside as a result of pit corrosion along the bottom or at a seam and repaired with Flamemaster 3204. One of the repairs was still good after 10 years. The 3204 is a 2 part polysulfide that's been around for years and does have a good track record.

Hobo has 2-350 gallon tanks that we cleaned and coated the forward chambers with the 3204 a few years ago just for pm. We didn't have any leaks but we did have some pits in the forward chamber where sludge had accumulated. The 3204 went on like molasses and sticks to everything it touches. We're happy with the results and can see how it would seal the interior. The most difficult part is you're doing everything through a 10" inspection port.

We looked at replacement tanks of similar size and volume; north of $25K complete. The engine needs to be removed and the engine room basically stripped. We have 8335 hours on our engine so if we were going to replace the tanks, why not rebuild the engine? What's another $12-15K? That's a bucket of money plus the time and inconvenience.

Flamemaster can be a viable option for minor leaks.

http://flamemaster.com/wp-content/up...-rev-01-07.pdf
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Old 04-28-2016, 02:48 PM   #48
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Hobo has 2-350 gallon tanks that we cleaned and coated the forward chambers with the 3204 a few years ago just for pm. We didn't have any leaks but we did have some pits in the forward chamber where sludge had accumulated. The 3204 went on like molasses and sticks to everything it touches. We're happy with the results and can see how it would seal the interior. The most difficult part is you're doing everything through a 10" inspection port.
Larry, what is used to clean the inside of the tank? I assume you have to remove all petroleum residue prior to coating with 3204, correct?
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Old 04-28-2016, 03:00 PM   #49
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Has anyone thought of talking to bladder/ fuel cell replacement, could be a lot easier . Cut the top out or part of the top large enough to get the bladder into the old tank . The bladder manufacturers can fit all your required inlets and out lets.
Must be worth a call ?
That doesn't work for a large marine fuel tank.

At least not easily in most cases for several obvious reasons.
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Old 04-28-2016, 03:02 PM   #50
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Oops, double post
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Old 04-28-2016, 03:04 PM   #51
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I'm fine with that (flamemaster) as long as your willing to tell the next guy what you did, and his surveyor. I also understand that when, or if, you pull the engine for rebuild that would be the time to refit the engine room and replace the tanks. I dont know what the difference in value of a KK42 with new tanks would be compared to one with originall steel tanks. The boats have almost a cult following so they have good market value, even with all there normal problems (similar to lots of "other" tiawanese boats of the same age) so I would think you could expect a better return on that investment. Personally, I've always just bit the bullet, pulled them out and had new tanks custom built. HUGE PITA and on my 50 foot Krogen it would have been about a $150,000 job if done by any boat yard. It has a 250 gallon "belly tank" amidship under the sole that required complete removal of everything. Basically completely gutted the entire boat from the middle ahead of the engine room to the bow pulpit. It also has a 250 gallon SS water tank under the sole of the forward stateroom that I pulled out, inspected, added access ports and reinstalled. The only good thing about all that is it allowed me to do everything to my standards. 3 new 1 1/2 inch thick heavily glassed in (with epoxy) full width and hiegth bulkheads, new sole with cutouts to access tank ports, etc. Like they say "go big or go home".
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Old 04-28-2016, 03:27 PM   #52
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Larry, what is used to clean the inside of the tank? I assume you have to remove all petroleum residue prior to coating with 3204, correct?
Acetone, acetone and more acetone.
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Old 04-28-2016, 03:41 PM   #53
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I'm fine with that (flamemaster) as long as your willing to tell the next guy what you did, and his surveyor. I also understand that when, or if, you pull the engine for rebuild that would be the time to refit the engine room and replace the tanks. I dont know what the difference in value of a KK42 with new tanks would be compared to one with originall steel tanks..
It's a secret. Kidding. I'm all for disclosure that's why I'm not afraid to post pictures and posts on the internet. If the tanks do leak? Then they'll be replaced. Same if we rebuild the engine.

I think you're right, other than the hassle factor we could probably get the tank/engine dollars back on resale or if nothing else, it would make for a quicker sale.
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Old 04-28-2016, 07:35 PM   #54
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I sincerily appreciate the input. Due to weather and life, I'm only now getting the boat towed to the yard tomorrow. Figure Saturday to finally get the tanks out for inspection. Done a good bit of research (much due to the informed comments to this post.

Several observations -

1. Al tanks are not bulletproof.
2. I owe Viking bigtime for configuring tanks that can actually be removed from the vessel without turning the boat into sashimi.
3. There are as many theories about tank failures as there are boats.

I have not had time to update this thread simply due to the fact I have a real job, but y'all have provided valuable info for working through the problem.

As my sons would say, "TF rocks." Much appreciated.
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Old 04-28-2016, 09:59 PM   #55
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Larry, that's like the stuff used in aviation on 'wet wings' or "integral tanks'. These are sections of the wing that are riveted together to form a tank. The entire structure would leak if not for the sealant authorized for that purpose in airplanes. The key here is that the structure is strong and not compromised.

Catching it early with minimal roughness and sealing it with this product like Larry has sounds very prudent and effective.

I can't count the number of airplanes I've flown with integral tanks.
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Old 04-29-2016, 04:28 AM   #56
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Bias. A couple a times a year I am asked about buying a Krogen 42. My response usually includes a comment that if the tanks have not been replaced on a 20+ year old boat subtract $20,000 US and figure a big hassle. Right or wrong this is the belief of many / most buyers and thus I don't know if an owner is saving any money in the long run attempting a repair on a mild steel tank. Granted there are exceptional cases. But when I opened my tanks we found numerous spots where the rust would have eventually worn through the tank wall.
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Old 04-29-2016, 07:09 AM   #57
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i sincerily appreciate the input. Due to weather and life, i'm only now getting the boat towed to the yard tomorrow. Figure saturday to finally get the tanks out for inspection. Done a good bit of research (much due to the informed comments to this post.

Several observations -

1. Al tanks are not bulletproof.
2. I owe viking bigtime for configuring tanks that can actually be removed from the vessel without turning the boat into sashimi.
3. There are as many theories about tank failures as there are boats.

I have not had time to update this thread simply due to the fact i have a real job, but y'all have provided valuable info for working through the problem.

As my sons would say, "tf rocks." much appreciated.
Coming in a bit late on this I realise, but in view of my great experience with replacing water tanks with food grade plastic, if I was ever faced with replacing the fuel tanks, it would be with fuel grade plastic, without doubt. Especially in view of the constant pressure everywhere nowadays to move to green, ethanol based fuels and biodiesel.

Think of the logic of tanks made with a substance that is resistant to galvanic, (electrical), oxidative, (e.g. rust) and chemical corrosion, and if the worst should happen, and one ever did need replacing, it could be easily cut out and replaced without any sparking/fire/explosion danger. They can be made to order, even to fit unusual shapes, like the insides of boats usually are. If getting yours out is easy, and without engine removal or cutting, you are lucky. It will be more straightforward and cheaper than otherwise, but if it was me, I would still go fuel grade plastic anyway. As Barney said, it is used for racing cars, off road vehicles, and most road cars now, all of which are much more shaken and stirred and vulnerable to damage from crashes. Just sayin'...
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Old 04-29-2016, 09:35 AM   #58
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I agree that plastic is great, installed properly, For vehicles and small boats, but the problem is that in sizes large enough for most of our purposes they dont work because they cant be baffled.
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Old 04-29-2016, 10:25 AM   #59
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I agree that plastic is great, installed properly, For vehicles and small boats, but the problem is that in sizes large enough for most of our purposes they dont work because they cant be baffled.
Rotomolded or blowmolded plastic tanks may not have baffles, but hot gas welded tanks certainly can have them integral to the tank construction. I agree with Peter, plastic tanks certainly deserve consideration. I know I would price out a fabricated plastic tank if I was in the same situation.
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Old 04-29-2016, 11:26 AM   #60
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I am not familiar with "hot gas welded" tanks. Sounds very interesting. My only problem with plastic tanks has been the lack of proper baffling.
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