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Old 05-27-2014, 02:36 PM   #1
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Leaking Fuel Tank on 1981 Mainship 34 II

Greetings all,

This forum is new to me, so I am a newbie here, but I am not a newbie when it comes to boats.

The reason I decided to post is becuase of a recent issue and I have not been having luck finding the root cause of the problem... Here goes:

I keep my boat up in Saxon Harbor, WI. As anyone who plies the waters of the Great Lakes knows (and Lake Superior in particular) the ice is finally starting to go away and winter appears to have lost her grip. So it wasn't until Friday of last week that I was able to get the cover off of my baby and start to get her ready for the year. I did the usual things, checked every square inch of her, started to clean, and etc. I noticed a little bit of red fluid by the rudder shaft, but otherwise nothing. As I did some steering work last year, I just chalked it up to steering fluid as it did not exactly smell like diesel.

Then on Sunday night, I got a call from the Harbor Master saying that my boat is leaking fuel! So Monday (yesterday) morning I zoomed up there to find out what is going on, and sure enough there was fuel held between the stringers and was seeping down into the bilge, and then through the drain in the keel. In all total, about two gallons (give or take a few ounces) had leaked out.

Thinking it was fuel lines, I checked those. There were not any leaks in any of the fuel lines, all as dry as a bone. Sure enough, it must be the tank! I pumped the tank dry, cleaned everything up, and of course the leaking stopped. I have been wracking my brain trying to figure out what the heck is going on and more importantly, why did it suddenly start to leak the day after I started to get her ready.

In particular, it "seems" to be leaking from the aft end of the starboard fuel tank. Both tanks are located under the cockpit deck, and as usual, are completely inaccessible with exception to the fuel connection points. You can see the sides of the tank through the cockpit hatch, but that's about it. Heaven forbid any boat manufacturer ever make a HATCH over a crucial item of the boat.

All of this being said, I have been looking around and it appears as though this model commonly has fuel tank issues. My question, is does anyone know the root cause of the failures? Is it because they are aluminum? Is it because the welds break? Does the starboard tank always fail or is there an even failure between starboard and port? Has anyone seen a port tank fail? I cannot find any information out there as to why it would fail, other than they do fail. I know that aluminum has a finite fatigue life, and right now I am thinking it was a fatigue failure at a weld. But as I have not removed the tank I am unsure.

I am fully aware of what I need to do to fix the problem. I know that no matter what, I need to cut the deck off. And when I do, I am going to replace BOTH tanks regardless of the fact that my port tank is not leaking. I am also going to go one better and actually put in access hatches to get to key items (like the fuel sender for instance). Besides, the end grained balsa core has some spongy spots, and the deck needs work anyways.

The conundrum I also face, is should I chance this year running on one tank, in this case, the port tank before I tear the deck off in the fall. The fuel return line empties into the port side tank, so I can isolate the starboard tank without any issues. Of course, I would need to ballast the boat accordingly since over 700 lbs would be sitting on the port side. But, without knowing WHY these fail, I am scared to death. What's to say that the port side tank decided to pop a leak while she is in the water, the bilge pump kicks in, and dumps a ton of fuel into the water. NOT GOOD!!!

At this point, I am thinking of draining the port tank and centralizing into a "temporary" permanent tank under the cockpit hatch, something in the neighborhood of about 40 gallons so that when we do go out for the weekend, we can hit our normal spots and still have enough to make it back to port with plenty to spare. She is a very fuel efficient boat, so that should give me more than enough cruising capacity at this time. But at the same time, I would rather not spend money on a fuel tank that I will not be using next year since I am going to be putting in new tanks. The kicker of course is that a fuel tank is a LOT cheaper than a fuel spill, so I know what route I am going to follow here.

Can anyone inform me as to the failures seen out there? Why they failed, pictures, anything? It would be greatly appreciated!!!
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Old 05-27-2014, 02:55 PM   #2
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Greetings,
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Old 05-27-2014, 06:37 PM   #3
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I have a Puget Trawler in Seattle with 2-200gal aluminum tanks that have developed pin hole leaks near the bottom seams. Was tracking down the fuel odor and discovered that the Port side tank had been leaking for some time. So far what I have read is that tank sediments (bacterial growth, algea, gunk, rust, etc...) settles in the bottom of the tank and eats away at the aluminum. Thus the corrosion effect that takes hold of the metal.
I am not eager to rip up my floor to access both tanks for removal. Have found a company here Felix Marine, that does an epoxy reline on the tanks. Said they have done over 300X over 15 years with no call backs or leaks. Im tempted to try this route since it is apparently effective and costs less (without tearing up my salon deck). Apparently they have been doing this in the Aviation world for some time now which is where the idea came from.
If someone has experience with this solution I am all ears! I talked to a couple full service yards and they recommended re-weld or replace $6-10K. This epoxy process should be under $6K. Granted all that I want is to have a functional system that is safe money aside. But if the epoxy works, is safe and is less expensive and doesnt take my boat out of service for 2 weeks, then Im good with that.
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Old 05-27-2014, 06:38 PM   #4
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BTW, I will be having both tanks cleaned and epoxied, not just the port side. so that amount is for both tanks.
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Old 05-27-2014, 08:05 PM   #5
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Here we go..Your 110 gallon tanks are secured by metal straps, insulated from your aluminum tanks with what appears to be tarpaper. Any electrical contact from those straps will set up electrolysis and aluminum will get eat away, anywhere on the tanks a dissimilar metal touching will do it. Even the screws holding down the decks the tanks sit on. My fix: Carefully pull floors from salon, will reuse, empty tanks, tanks come out easy. Cut windows 8x8" widows 3 per tank to access baffles. Get alum plates 10"x10" to cover windows with gasket material and Permatex. Get orange cleaner and scotch brite, reach in each baffle and scrub like hell until the 33 years of shi* is gone. Use saw horses..good ones to save your back. After tanks r clean inside, scrub outside top and bottom. Orbital sander 80 to 120 grit, sand them down. Where you find pits, and you will, heavy wire brush on grinder to clean pits. Now set tanks top up put in ten or so gallons of water and look for drips, air pressure if you like but I did not. Holes identified, get a kit of heavy epoxy called Splash by Peddit. Follow directions. Turn tanks up and do the water test again. Once you are sure the leaks are plugged flip tanks back over and cover with very light weight fiberglass cloth. Use EPOXY and go 2 or 3 inches up the sides with cloth and thick coat. Replace sub floor that got saturated with diesel, counter sink and seal all screws. Roll on coat or 2 of epoxy. Set repaired tanks back in boat on top of heavy coating of 5200..NO METAL STRAPS... Hook em up, fill em up and go another 30 years. My buddy used a welding shop and had to do it twice. This works and new boats manufactures epoxy the bottom of their tanks now. This works, been a couple of years, no leaks. I know of this fix going on 10 years now. No need to replace tanks/

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Old 05-27-2014, 09:32 PM   #6
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I would run the 4 months or so on the one tank.

But carry a good transfer pump just in case. You can usually find someone to take on a load of fuel to help you out if need be.

YMMV
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Old 05-28-2014, 09:58 AM   #7
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You hit the nail on the head there about how they are secured... Never even thought of that being the culprit, although I have seen similar issues on aluminum radiators; that being electrolysis. But again, I have also seen fatigue failures as well.

When you did this, about how much did it cost you to do the whole shebang? And, if you reused the floor, how did you end up securing the floor back down?

I did order a temporary "permanent" tank yesterday and it should be in tomorrow. Not a big one (31 gallon) but that will give me plenty of run time even though I will need to refuel at the start of every new trip. The risk of dumping diesel into the harbor when I am not there is just too much to handle and I wouldn't be able to sleep. Then when I tear into all of this in the fall, I am going to move the tank into the bow and use either as a day tank, or more likely, a tank for the head since the current holding tank for the head is extremely small, especially when there are three females on board. Granted, two of them are kids, but they are growing fast and soon that itty bitty tank is not going to last half the weekend instead of a full weekend like it does now.
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Old 05-28-2014, 10:03 AM   #8
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Here is what we did one more time....

@ TheOffice: September 2013

Hope this helps
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Old 05-28-2014, 11:16 AM   #9
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Lets see, +- $350 total. 1 gallon epoxy kit, 20 feet light weigh (150wt?) cloth orbital sander and 50 pack of disk, 2 gallons of citrus cleaner. Box (100)#8 self tapping stainless screws, gasket material (cork?), gasket sealing goo..Permatex. Aluminum plates to screw down over your holes. A 6 to 8in hole saw would work good on the soft aluminum for access holes, then have your machine shop fab you some plates to close. I cut 6 in holes square and used 9in square plates but I think round might be better, as would bigger thicker plates with more surface area to screw into around the ports would be better with more screws. Maybe even 1/4 inch plates going over the 3/16 tank. Make no mistake about it, this is the way to go on a Mainship 34 MK1,2,3 because the tanks come out so easy. Just replace floor as you took it out. Even if you had them welded or bought new, still the epoxy process should be done to electrically insulate and access ports should be in place. With the small weeper type leaks the splash putty will do fine. I had no problem with the securing straps, but it was coming. My issues were with the bunk securing screws, even though they were countersunk. There is enough moisture in the air in the bilge to create an electrical path. Were I to do it again, I would cloth and epoxy the entire tank(s), top bottom and sides leaving only the ports, pickup plumbing holes and the area around them bare. Also epoxy the bunks before the 5200 glue down.. If you push it you might spend as much as $500.00.
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Old 05-28-2014, 11:56 AM   #10
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Thanks!!!

Well that isn't too bad then... definitely more cost effective than buying new tanks. Did you stay with the original fuel lines as well or did you replace them with new lines? I am not sure how yours was, but all of mine are solid copper. I know that copper and diesel are not supposed to be mixed (also corrosion issues there), and I am thinking of replacing all of the lines in the boat with new stainless lines.

When you took the floor off, did you just take the sections above the tanks off or did you take the entire floor off as one piece? I assume you left all of the floor stringers in place.

As I had said, my floor has some spongy areas. When I bought her, they weren't as big as they are now, and the surveyor said that I would be looking at replacing the floor at some point. My thought was if I remove the floor but keep the stringers (the stringers are still in very good shape) I can place the new floor over the existing stringers rather than run all new stringers as well and epoxy the floor down to the existing stringers. Then I can just build the floor in my garage over the winter months so that in spring I can just "slap" everything back together.

Thanks again for all of the insight!!
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Old 05-28-2014, 12:52 PM   #11
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After you get into it all will fall in place. You seem to be a hands on guy. Leave the lines, if they ain't broke then don't fix em. It has been 2 years so I may have forgot some things, however I will add: evaluate everything. You want to go in there once and only once. Let your grandchildren watch their Dad undo your work while you sit on in a lawn chair using only your index finger to point. If it is questionable, like my vent hoses were then renew. Replace fuel sending units. Once you close it up u be done. Flooring...3/4 in plywood is cheap.
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Old 05-28-2014, 01:54 PM   #12
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Well, I suppose so... Again, I appreciate it. It is certainly sounding "easier" than I thought it would be. I know it is going to be a lot of work, but that is fine. I will have plenty of time over the winter to get thnigs squared away.

As for the kids comment... Back when I was a little squirt, my Dad rebuilt the rear end of the backhoe. Then in October of last year, I had the honor of doing it again. So there were his Grandchildren watching and helping me undo the work he once did. So, I can certianly relate!
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Old 05-28-2014, 01:58 PM   #13
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Funny side note... Back when I first bought her, I replaced all of the scupper hoses and the exhaust system. I crawled around under that dang deck for days getting those hoses fixed. And as I am not short, it was not easy. Got stuck a few times, it was a grand old time. I wrote a note in there on the "cieling" that said, "If you are laying here reading this, you have reached the 7th level of hell."

And now here I am, looking at pulling that entire deck off... ohh the irony.
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Old 06-09-2014, 09:38 AM   #14
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Just an update...

I ended up getting a 31 gallon temporary "permanent" fuel tank and put it in below the cockpit hatch. With the short distances we go, it will be more than enough, especially since she sips the fuel instead of guzzles it like usual boats.

Then I disconnected both starboard and port side tanks. The port tank was not leaking, but I know it is a matter of time before it does.

She is now in the water ready for a season of boating. The fun will begin when I tear into her in the fall, but as my Father once told me, "It all comes with pride of ownership." Truth be told, I am actually looking forward to it too!
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Old 06-09-2014, 04:14 PM   #15
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Why would a person go to all of the trouble of removing and reinstalling a tank and not have a new bottom welded in or at least weld or patch the holes. Epoxy is good stuff, on the outside of tanks. And yes I have heard and read countless testamonials to its effectiveness as a sealer on the insides of fuel tanks. But, folks dont tend to brag about things that dont work as they were told they would, especially after considerable expenditure of time and money. Then they get to pay to do it correctly. Do it right, do it once. I cannot rest knowing I didnt do something to the best of my ability, and gooping the inside of a fuel tank is not something I will do. But its not my boat or decision. And, I do tend to go way past what is considered normal when it comes to things like this. However, If I was looking to buy a boat "new" or even "reconditioned with documentation" fuel and water tanks would be a major factor to consider. Patched, epoxied, splashed, or otherwise fixed at would be a deal breaker.
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Old 06-09-2014, 05:28 PM   #16
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Oh make no mistake... I plan on doing all of that.

I am one who also goes "overboard" with things as well. Looking at what this fix will cost me, versus getting entirely new tanks, has me thinking that it wouldn't hurt at all to re-weld any holes shut, epoxy the inside, glass the outside and etc. for the simple fact that the extra cost of welding is going to be negligible in the long run.

I am also going to replace the entire fuel system on the boat. Copper and diesel fuel do not mix eithe. I work for a diesel engine distributor, and have extensive experience repowering boats with diesel engines. New engine installation / application guidelines all say "do not use copper" due to corrosion. Plus, with the way that this government is going, you know darn well that at some point there will be mandatory biodiesel concentrations just like we are dealing with ethanol in gasoline now, which I am sure all of you know the fun of ethanol in older (and newer) boats that are not set up to run on it. So, I have elected to replace all fuel lines with 316 stainless steel lines. Again, it will cost a bit more, but at least I will also have peace of mind. Plus I can update some of the outdated fuel system components.
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Old 06-09-2014, 06:27 PM   #17
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Excellent. Glad to know I'm not the only "nut case" out there that insists on proper procedure. On the issue of copper tubing, I like the plastic coated stuff. I have even ran copper tubing for steering systems in blue plastic electrical flex tubing, just for corrosion protection. I also like stainless tubing, but it is not immune to corrosion either. Some say that diesel and ss dont mix well, maybe the sulphur in it, I dont know. I do know that stainless is not recommended for diesel tanks. Plain old mild steel piping works exceptionally well for diesel plumbing, especially if epoxy coated. Of course you would need a flexible section at the engine whatever type of system you use. Properly rated rubber fuel line can be used there, or everywhere if you so choose.
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Old 06-09-2014, 08:36 PM   #18
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Kulaks,
Sometime back GPS was developed. epoxie for public use became affordable. Fiber optic cable became the standard over twisted pair. I watched a bilge of a Mainship 34 start filling with diesel due to a bad welder that had his pay and a careless owner not checking the welders work. That being said, I will try to get back to you in 30 years or premature failure of my fix recommended by some very savvy industry people. I believe in science, people smarter than me and previously proven methods. I even drive a truck rather than using a horse and buggy. Go ahead and hire a welder, as for me, until proven different I think I will do as I have successfully. Please tell me of similar experiences you have executed and the end result...I am waiting, ...thank you
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Old 06-09-2014, 09:01 PM   #19
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I just didnt understand why, when the tank was out and clean, it was not welded. I dont have any experience gooping a tank and reinstalling it, I would never do that. All leaks, cracks, pinholes, etc. have been tig welded then the tank is pressure tested, then reinstalled correctly. The risk is to great to do otherwise, and I like my sleep. If you look a little you will find people that will tell you anything, usually what you want to hear. When it comes to old boats with old tanks the easy way out is almost never the "proper" way. As for me, I will use best practice.
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Old 06-09-2014, 09:54 PM   #20
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Mule, after re-reading your post I see that mine and your fix is similar in several ways (minus the welding). I dont epoxy the inside but dont see any problem with it. I dont "glass the ouside but thats ok to. I do epoxy the outside. I use 1/4 inch thick neoprene strips under the hold down straps, glued to the tank with 5200. I use 3/4 inch thick rubber strips (horse trailer pads, cut in 2 inch widths) glued to the underside to allow air circulation. I use 2 inch by 1/4 inch aluminum strapping for hold downs, substantially bolted to the stringers if possible. I cut square holes in each baffled section for cleanout/inspection ports. The covers are made 4 inches bigger than the hole for a 2 inch overlap. I use rubber gasket material that is fuel rated. I rivet a ring of 2 inch by 1/2 inch thick aluminum bar stock inside the tank around the perimeter of the cutout. I drill and tap this to give my lid bolts more material to thread into. This is the only way that I know of that is industry accepted everywhere. Some yards will do the job however you want it done, but any yard would do it this way. This is what is considered "best practice".
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