Fuel tank repaired in epic fashion

This is one of those projects I have long feared. The diesel tank on a Gulf 32 is below everything, and built into the bilge of the boat. Any trouble with it requires painful measures for either your wallet or your body. The tank on these boats is a generous 70 gallons, which is altogether wonderful except it makes the tank extra large and especially difficult to access or possibly remove.

Let me start with a little background. In this post I intend to fully document what I did and how I did it, because I know for certain this is a common problem on all sailboats past a certain age and like always I wish to aid my fellow sailors facing similar projects. I've previously replaced a leaking fuel tank on our old Ericson 28 and found that project straightforward as the tank was under the quarter berth and easily accessed. Not so easy on a Gulf 32. This project took a solid two months of time, and I estimate I put about a day a week, sometimes two, into it. It is now successfully completed on Aeolus, and I have the test of my repairs. I recognize there are several other ways this repair could have been completed, and I leave it to others to decide for themselves how they wish to proceed.

View of bow side of tank, showing lines marked for cutting. This was the easiest chamber to access. 

Beginning a few years ago, I n
oticed that when I filled the tank completely I would get leaking immediately. I was puzzled by the fact that I was not getting any noticeable leaking from around the fuel fittings at the engine side of the tank. None of my hoses were leaking, nor the sender. This led me to believe that I had a leak in the tank itself somewhere, and I thought it must be at the top in one of the welds or something. Some quick work with oil absorbent towels and the lesson learned, I stopped filling the tank all the way. Since the tank holds 70 gallons, it was never a problem to only have 50 in it. But I knew this was no good, and I put it on the list to finally resolve the problem of the leaking tank.

The general area of the stern side of the tank, showing sender location and area of hatch cut. Just out of view are the fuel lines in the tank. 

Gulf 32's have a deep, full bilge, and the tank is shaped as a V and placed down in the bilge. It is held in place by a fiberglass envelope, and this envelope holds it up off the actual bilge. Therefore, water and dirt and such is able to flow freely from the bow, head and cabin, under the tank, to the deepest part of the bilge under the engine, where it can be removed. So overall, the design is clever in that it fits a 72" long fuel tank that holds 70 gallons in a space that still allows for no expected contact with regular water or chemicals. For this to work, the tank begins just forward of the engine, and runs all the way to the bulkhead at the forward part of the cabin. This means it goes directly under the steps that lead from the galley down to the cabin sole, and beneath all the teak and holly and furniture of the cabinetry and seats and nav station.

View into bow chamber, and a sight no one wants to ever see. It came from the deep! 

Removing the tank would be a very ugly and expensive proposition indeed. I know one Gulf 32 owner who did so, and I can only imagine what he paid. Your cheapest and best option for removal, and I'm not even sure it would work, would be to remove the diesel engine entirely from the boat and put it on the hard, and then get in and cut the fiberglass from around the front of the tank, and try to pull it out and up through the engine access area. The tank, as I said, is 72" long, and I don't know that it can make the turn. This requires cranes and probably being on the hard. You would then have a new tank fashioned, and slid into place and glassed back in. My best guess is that the procedure alone would be a pretty $1-2,000, a boat unit or two, as my family would say. Then the new tank itself is an additional $1,000 or so. And the only other way would be to literally cut away what would amount to the entire cabin and sole of the boat and pull it up and out. That is impossible to contemplate.

View into bow most chamber after cleaning. You can clearly see the corrosion holes. 

At this time in my life I would rather not spend an easy $2-3,000 on the fuel tank. So I began to consider my other options. I have known for a fact that the tank had crud inside, as my fuel filters would clog occasionally and the boat is almost 30 years old. So I have long wished I had access hatches to get inside and clean things out. And that was the process I decided on.

I figured that no matter what, it was worthwhile for me to cut access hatches in the few places I could easily get into, and see what I saw. So now came the moment of truth, cutting into my tanks. Toward the bow, there is an access panel in the cabin sole that provides a view of the area just in front of the fuel tank, and of the top of the tank itself. This area is roughly 24" by 15". Beginning here, I knew I would have to later attach a new aluminum access hatch over this new hole I was cutting into the tank. For good measure, I decided to leave myself about an inch of aluminum on all sides so I would have something to work with when it came time to install the cover.

View into stern most chamber and fuel pick up. You can see the swiss cheese. 

First I had to pump the remaining fuel out of the tank, which is tedious, but straightforward. I took the outlet hose of my electric fuel pump and filled consecutive 5 gallon plastic diesel fuel containers.

View into second chamber from the bow. This is the chamber I had to access horizontally. I later replaced the baffle with a new sheet of aluminum bolted in place. 

This began the cutting and drilling phase of this project, which would continue for the next two months. I first drilled a hold at one corner of my desired cut out, large enough to accept the blade of my jigsaw. I bought metal cutting blades for my jigsaw, and found that fairly easy going. They dulled in the thin aluminum rather quickly but two sets of five Bosch blades did the trick. At this time, I had ye to employ my Dremel multimax, which I would essential later on, but I think the jigsaw would be still be the fastest option for this location.

Once the rectangle was cut away, I was horrified to look into my diesel tank for the very first time! What do I see but a layer of deep sludge. DEEP SLUDGE. Sludge so deep it had geological features. There was a Mt. Rainier in one place and Death Valley in another. I'm sure a more creative mind would discern the entire Cascades and Olympics but I was too eager to just clean the hell out of the mess. A sober assessment would say the crud was 1/4-1/2 inch think. My first approach was to get in there with a putty knife and start scraping stuff up. Gobs and gobs of stuff up. As I scraped my knife along the bottom, I would occasionally hit an edge, and this made me think. Maybe I have pits in the bottom of my tank? You think?

My marking of holes in the bow chamber. 

That first chamber cleaned produced a good quart or more of black crumbly crud. Dead bacteria, dirt, and whatever else might have found it's way in. I went back with a sharp blade in a scraper and got down to bare metal as much as possible. And guess what, not only did I have pits, I had swiss cheese. I used a series of terry cloth towels and acetone and cleaned the metal all around the bottom and near the sides of the tank. I was relieved to see that there was absolutely no sign of corrosion anywhere except on the bottom of the tank, and even there, it was in the low spots. Clearly, this was a classic case of water in the tank and bacteria producing acid. Always have wondered what species of bacteria we can blame for this, and if any microbiologists out there know, please let me know.

So all this work was only to access and clean one of the chambers on the tank. All tanks have baffles, and a tank as long as those on a Gulf 32 has many. However, there is no top side access to the next chamber of the tank as it is directly under the cabin sole. Have you priced teak and holly lately? So I decided to cut my way through the baffle horizontally, and into that adjacent chamber. Using the same technique, I left a border of good size, drilled a hole, and got in with my jigsaw the best I could and cut out the piece. Because of space restrictions, I couldn't get the jigsaw into all corners, and this was the first time I had to pull out my trusty Dremel. Attaching the specialized cutting wheels, I was able to Dremel the places I couldn't reach with my jigsaw. Slow going, but worked.

New aluminum plate being held in place for epoxy to set. 

Can I make a quick note here to say that all of this work, every bit of it, requires at the very least that you are laying down and reaching down into a smelly tank of diesel crud. At worst, you are upside down, sideways, hanging by your toes, and reaching blindly into a smelly diesel tank filled with crud. Not pleasant working conditions.

Back to our story. The second chamber looked like the first. Same deep layers of crud. I cleaned it in the same way, but it was far more difficult because I was having to work blind. I could only access the chamber by laying down and reaching sideways into the tank. Tedious. I found the same swiss cheese bottom in this chamber.

It was about this time I had my epiphany. All those years of leaking fuel when the tank was filled were not from a leak at the top, but from a continual and constant presence of diesel in the fiberglass envelope, and it only spilled over the top when the tank itself had enough fuel to rise above the level of the top of the envelope. Can you picture this? This meant that I just had to somehow fix the entire bottom of the tank, and my leaking should be solved.

View of Flamemaster 3204B2 applied around edges of aluminum plate and other spots. This stuff is incredibly tenacious and impervisou-just what you want in a fuel tank. 

My next chamber, and I thought my last, was the chamber closest to the engine and near all the fuel lines. This provides a smaller area to access, but sufficient. Cutting into this in the same way, I found the same sludge. Cleaning this was very hard because it is deep down in the bilge. I am a tall man at 6'2" and yet laying on the steps and hanging over as far as I could, my hands could not reach all corners of this deepest part of the tank.

Thinking I had found all my chambers of this tank, I set about doing my chosen method of repair. I would later learn my error here, but I'll tell that tale later on.

My chosen method of repair was two fold. Given the pervasive size of the swiss cheese holes in all three chambers, I decided to purchase aluminum sheeting from online metals and place new bottoms in large areas of each chamber. I used 5052 aluminum in 1/8 thickness. Fairly cheap stuff. I got pieces of 12" by 36" for $30. I needed several of these to form the bottom pieces mentioned here, as well as the new top hatches for sealing the tops of the tank. At this time I decided to take the step of drilling directly through the tank and the fiberglass envelope to drain any remaining fuel. When I pushed down on the tank bottom, diesel fuel would squirt up through the holes in the aluminum, so clearly there was diesel still being held. By drilling through the materials, I intended to allow this remaining diesel to drain away, and not compromise the bonding or sealing of my repairs.

New access hatch cover bolted into position and sealed with Aviation Gasket maker. 

This done, I set about using epoxy to glue the new aluminum sheet into the most damaged areas of the bottom of the tank. You can research the fuel resistance of epoxy til you are dead, and you will not find satisfying answers. Believe me, I tried. The companies both recommend it, and disavow it. People claim it to be fine, and others folly. I decided in my case it didn't matter, because the epoxy would never be exposed to the chemical soup that exists in my diesel, biodiesel, biobor, soltron and water fuel tank.

I researched all types of fuel tank sealants. You will too. I decided to go with a gold standard, and that was the stuff used on airplane tanks. I found examples of people who had used aircraft sealants on their tanks with great results, and I was persuaded that anything good enough for the aircraft fuels and additives would indeed work for diesel. I chose to go with Flamemaster 3204 B2. Flamemaster is the company, 3204 is the type of sealant, "B" is the thickness, with A being thin and self leveling and B being thick and able to cling to vertical surfaces, and "2" is how long you have to work with it. You can get anything from 1/4 hour to around 8 hours of working time. I thought 2 was just fine. So I ordered some from SkyGeek and had my materials.

One day I went and cut the aluminum plates to the required size, mixed my epoxy, and placed the new bottoms in the desired places using a generous bead of thickened epoxy for attachment. Days later, I went back and had my big sealing project. Because I could not get aluminum plate big enough to cover the entire tank bottom, due to the size of access hatch restriction, I knew I would have holes here and there that needed sealing.

Mixing the 3204 B2 is physically difficult. It is the thickness of thick peanut butter. Follow the simple directions carefully, and spread the stuff with a butter knife or whatever you wish, everywhere you need. I placed it around the entire edge of my new aluminum plates, thereby sealing the epoxy from ever being exposed to fuel. A quart of the sealant was sufficient to seal all the edges of new aluminum bottoms, and dab a bit here and there over the odd hole.

Letting this dry for a week or so, I went back and began to cut and create my new access hatches. The method I chose for this was to drill and tap bolts holes so I could thread bolts from inside the tank up through the hatch and place the nut and lock washer on the accessible top side. Straightforward, but a lot of drilling and tapping my friend! You can use whatever size bolt you wish. In order to get the bolt patterns to line up, I first drilled the holes in the access hatch at each corner. Using these guide holes, I drilled through the tank itself and tapped those holes for boats. Then, with the bolts in place and secured through the hatch, I drilled the remaining holes for all places. Quick note that I chose to use the same bit for initial holes for both materials, to avoid slop. Later, I had to expand the holes in the hatch by a size or two to allow the bolts to go through and provide some margin for error.

As for sealing the hatches to the tank, I decided to use the old classic of Permatex Aviation sealant. I researched every possible other gasket maker and sealant, and had a hell of a time finding one that would confidently work with diesel and biodiesel. I also decided I didn't need an actual gasket of cork of what have you, as the bolt pattern was tight enough to ensure a metal to metal fit in all places, and the Aviation sealant is thick and tenacious stuff. If this was not the top of the tank, I would have to use a different method.

My next trip to Aeolus brought the moment of truth. With the access hatches completed, I was ready add the fuel back. I poured back in the 25 gallons of fuel I had in containers and rushed down to look for leaks. To look under the tank requires you to hang your entire torso off the steps down from the galley and look into the small space under the tank. Again, being 6'2" this worked just barely. In fact, let me just say, it helps to be tall when doing this project. So I hung there for some time looking for drips, and didn't see anything. I was elated! My time was running out and so I started to clean things up a bit. Maybe an hour later, I was ready to leave, and look one more time.

DISASTER. Fuel in the bilge. Damn, Damn, Damn. Deep breathe. Zen. Life is beautiful. Go home.

My next trip to Anacortes and Aeolus was to investigate what the hell I missed. I had to pump back out all that fuel, and open up all my nicely sealed access hatches. I looked inside, and everything looked perfect, just as I had left it. Scratching my head, I had to consider there were some micro holes in corners or places where my naked eye could not see them. But another though occurred to me somewhat by accident, as silly as that seems now. As I was cleaning the last drops of diesel from the bottom most part of the tank closest to the stern, I kept finding new little puddles of diesel. I went and looked in the other chambers and they looked fully dry. Back again, and I got more puddling of diesel. What the heck?

It is so stupid of me to have not discovered this earlier, and let me say here I was once again reminded to be humble and keep beginners mind.

View down to where the windlass batteries and area for access to fourth chamber is located. 

I got out my tape measure and measured from the front of the tank to the first baffle going back. 18". I went to the stern of the tank and measured from the back to the first baffle. 18". I then measured from the stern chamber baffle to the next baffle of the second chamber from the stern. 18". Now, I can add 18 plus 18 plus 18 like the next guy, and I know that leaves me exactly 18" from the tank of 72". I HAD MISSED A CHAMBER.

Now before you think I'm a complete idiot, I have the minor excuse that all of this work is upside and sideways. It was an optical illusion to me that the back most baffle of the forward chamber was in the same location as the forward most baffle of the second to the back chamber.

Now I had the hardest problem of all, and made me sit and think for some time. I had no ready access to this chamber whatsoever. I had no top access, and my arms could not reach from any of the adjacent chambers. It lies directly underneath the starboard settee and nav station. I considered the horror of having to cut through the teak and holly. Oh dear Buddha. I even thought of throwing in the towel. Call in the cranes and empty out my savings. Fortunately, I am not impulsive and the better idea finally occurred to me.

Under the settee lies the batteries for the windlass, and under those batteries, is a plywood and fiberglass floor, and under that floor, must be the tank! So out came the batteries, and I began exploring. I began by cautiously drilling holes in a line from where I though the tank would be, to find it's edge. I would drill through the plywood and fiberglass and then there is a small space. If I hit metal, I moved 1/4" further to the side and began again. Soon enough, I found the edge. I then needed to gain access. I drew out the desired size of my access, knowing the hole through the plywood would have to be larger than the edges of the hole in the tank, because the access hatch needs an inch of material for attachment securely. To remove this plywood I needed to use my Dremel Multimax, which was vital. Using cutting heads on the device, I was able to remove the material above the tank and then cut into the tank itself as I had done elsewhere.

View from inside storage area under settee with the plywood cut away and the access cut into chamber. 

Once I had access, I knew I had found my problem. This chamber was the same as the rest, and my repair was the same.

After waiting a week or so, I went back and had another moment of truth. But this time, no leaks! I went away from the boat and and took a long walk, and checked again, no leaks! I hung upside down in that uncomfortable position and counted for a solid 120 seconds, and no leaks! The very next day was Friday, and we had plans to get away for the MLK weekend. When we drove back Friday night to Anacortes, I got right aboard and looked down to see if there had been some very slow leak over the past 24 hours. Nothing!

So ends this very long tale of a fuel tank repair. The previous post on this blog relates the story of our MLK weekend, and I will only add here that we experienced quite a bit of hobby horse bouncing and banging in the rough conditions. The tank was placed under all possible stresses for leaking, with the fuel being sloshed forcefully in all directions, including up onto the access hatches. I'm delighted to say no leaks.

Area around the fuel pick up. The tape was to prevent any accidental getting of sealant on the pickup  opening! 

An added benefit of this repair is that we had always had a slight diesel smell aboard Aeolus. Very slight, but present. Now that is gone. That persistent diesel in the envelope I described would of course be off gassing at all times. Now I have access hatches, and can clean her out whenever I feel the need.

And the whole project cost me about $200 in supplies. Of course, it took well over 40 hours of my time, but sometimes time is more abundant than dollars, or at least we would rather keep our dollars for something else. And the satisfaction of completing this job and knowing it is better than new, well that is priceless.

And all these repairs, and every other bit of effort, results in trips and times like these, and these are the most precious things in my life!