Grand Banks Fuel Tank Corrosion

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Ron T

Senior Member
Joined
Oct 13, 2007
Messages
328
Location
USA
Vessel Name
Grand Yankee
Vessel Make
1981 49' Grand Banks Classic
Just finished another Grand Banks survey. Every 49' Banks shows rust on the out side forward bottom area. WHY? where is the water coming from. The rust around the base of fuel fill/vent lines is understood, but the rust in the lower corner is not. Looking at the fact that engine exhaust hose runs veryclose to that area an wonder if the heated steel draws moisture to that area. Any ideas out there ??
 
Ron, I think it comes from moisture from condensation (changes in temperature). Our components in the engine room were frequently wet. I could see the water running down the forward face of the tanks where it would accumulate on top of the bottom lip of the tanks. That was several years ago. I have since kept an electric oil heater (passive, no fan) in the engine room. The temp stays at a steady 68*F. The ER has been dry ever since. Look into Por-15 or other rust "sealers" should you purchase a GB with a little rust in places.
 
Ron,
I have a 1990 Grand Banks 46 Classic. I am just now starting the process of cutting out the port side fuel tank that developed a slow leak in the lower outside corner that you mention. I first thought it was from the leaking fuel filler on the teak deck, as there is much rust around that filler pipe on the top of the tank. However, one day I was in the engine room checking this and that, while my wife washed the decks. Our boat has a freshwater filler pipe near the fuel filler on the starboard side. I noticed a rather nice trickle of water running down that water filler pipe, and because of a "sag" in the large water filler line near the front of the port tank, I observed water dripping into that corner. This is where our problem originated, as I am sure much salt water has come in this area, and my guess is there are more "sagging" water fill lines out there, with leaking deck filler plates. We have begun the dreaded task of cutting out the 300 gallon steel tank, and replacing with three custom built tanks. Not been too much fun so far with this project.
 
Just finished another Grand Banks survey. Every 49' Banks shows rust on the out side forward bottom area. WHY?

Water/moisture can find its way into an engine room in a lot of ways. One way with boats like GB is around the deck-mounted fuel fills that may look properly bedded but aren't anymore. Water can migrate under the fill fittings, sometimes along deck seams that have pulled away from one side of the groove or the other, and from there run down the filler tube, onto the hose, down the hose, and eventually pool on top of the tank. If the top of the tank is not absolutely level the water can meander over to the lowest side or corner, run down the side of the tank, and end up sitting between the tank and whatever the tank is sitting on---wood frame, solid platform, etc. Once there the moisture and the salt from the water gets rust going in short order.

And the fill fittings don't even have to be involved if water is getting down under the teak planking via separated seams. Once there, it can migrate down into the sub-deck alongside the zillions of screws that are holding the teak planking down. While it's unlikely the deck screws penetrated all the way through the subdeck it can happen.

Another route into the boat is via failed bedding of the bulwark hawses or the rail stanchions. This can let moisture/water get into the "gap" between the deck and hull molds and eventually find it's way down into the hull or migrate across the underside of the deck mold until it drips off, possibly onto the tops of the fuel tanks.

The shaft(s) can throw off a fine spray of salt water as they turn in their logs. This happened with the starboard shaft of our boat at some point before we bought it. The victim was the sound shield on the Onan generator which rusted badly where the fine spray off the shaft was constantly hitting it. Today the packing glands are adjusted such that they don't drip even when turning (maybe once over ten minutes or so if I stay down and watch them that long) but they don't throw a spray out anymore.

The engine room air intakes can be another source of moisture/water ingress although their designs are supposed to minimize this.

But based on what I have been reading on the GB owners forums for the past many years, the fuel fill deck leak seems to be the number one killer of GB iron fuel tanks. It' probably why the previous owner of our boat had the three original iron tanks removed and replaced with five new tanks.

You might pose your question to the GB owners forum Grand Banks Owner's Resources You'll probably get some good suggestions there, perhaps from owners who have observed the same thing you have but know why.
 
Someone knew this was coming ... so, not to disappoint:

"shows rust on the out side forward bottom area"

So exactly where is this rust? Your not very nautical or surveyor-like description reads as if it is in way of the forward end of the tank(s), outboard, and at or near the tank bottoms. It is not clear if the rust is internal or external.

Where are these tanks located because it is odd that ...

"Looking at the fact that engine exhaust hose runs very close to that area ..."

Are the tanks located that far aft of the engine and inboard far enough that the exhaust runs outboard of the tanks, between the tank and the hull?

"... wonder if the heated steel draws moisture to that area ..."

Conventional thinking says that the application of heat to any material will drive moisture from it, not to it.

The next question is, what is wrong with the exhaust system that makes it capable of heating the fuel tanks?

Perhaps you could post the relevant portion of one of your survey reports.
 
Somebody got up on the wrong side of the bed:lol::lol::lol:
 
To Capt. Waldo

I had the tanks fabricated out of 5052 aluminum, 1/4" thick, by RDS in Perry Fl. I designed three tanks, each different size and shape, stackable, to replace one 300 gallon steel tank. (our final capacity with the three port tanks is 292 gallons) The tanks were drop shipped to me in NC, and I lightly sand blasted to get the mill finish off, then acid etched them. After neutralizing, I coated them with two coats of Macropoxy 646, a Sherwin Williams marine epoxy. A final coat of a two part high solids white polyurethane was the last step before installing.

Cutting the large 300 gallon tank out was one of toughest jobs, as my wife and I did all this work ourselves. Took about 18 hours, and 23 heavy duty sawzall blades to get the old tank out. Ear plugs, face/arm protection, knee pads, and heavy gloves and lots of pads were required. The hole in our port tank came from water/sea water dripping off the 2" freshwater filler hose from the deck plate, down the side of the tank, and rusting the bottom where the tank was bedded to the crossmember. It was a small pinhole less than 1/8" in dia. While the 10" exhaust is directly beside the tank, I am confident in our boat that it had nothing to do with any moisture issues, nor did the engine room vents or other things that other owners have discussed and mentioned. We replaced every fitting and valve, new sight glass, new and larger vent lines, and new filler hose and deck fill plate. I designed a sump in the bottom tank with a valve. I will say the interior of this old iron tank was surprising clean for a 20 year old tank.

Job is complete on the port side, and hoping that I can simply ospho and epoxy the starboard side tank which has some surface rust, to avoid going thru this process again.

Hope this helps.
Chuck
 
Rick.. The saddle tanks in our boat, both the two originals and the four new ones, are located in the aft portion of the engine room and are just aft of the engines. They are not hard against the side of the boat, and there is enough space between the tanks and the hull sides for the exhaust hose runs.

I don't know the tank configuration in a GB49.

Whether the mere presence of an exhaust hose would encourage rust is something I don't know, unless the hose was leaking. Tank rust and replacement is a frequent topic on the GB owners forums and while I have seen a lot of reasons given for external tank rust I've never seen that one despite the fact that apparently all or most GBs run the exhaust hosed back alongside the tanks.
 
I am looking at a GB 46 that is of a 1986 vintage not commissioned until 1987. The boat is decent shape, but it has the original fuel tanks. This scares me a bit since most of the GB's of that vintage have had their tanks replaced.
Upon inspection, I did not find or see any evidence of rust but a yellow drip stain on the starboard tank. I really could not see the top of the tank. There are no leaks at this time. I am wondering about what your thoughts are. Grand Banks owners that is.
I am also looking to find out the fuel burn of a 46 at about 8 knots with 3208Na
 
Diane-- First off, I suggest you join the Grand Banks owners forum Grand Banks Owner's Resources and ask your questions there. Unlike a general forum like this one, the GB owners forum will get you answers from people who have in many cases owned and been involved with GBs for decades. Even more beneficial, there are participants on that forum who have been or are yard owners and shipwrights who have specialized in the maintenance, repair, restoration, and upgrading of Grand Banks boats for the better part of a career. These people have an intimate knowledge of these boats, their construction and components, care and feeding, and all their quirks and flaws. Instead of speculation you'll get answers that directly pertain to the specific type of boat you're interested in from people with in some cases a good chunk of a lifetime of involvement with these boats.

There are actually two GB owners forums. The one linked above is the most active. However there is another one sponsored by Grand Banks itself. http://gbbeacon.com. Select "Discussion Forums." This forum does not have as much participation but it is worth joining as well because it has Mike Negley as a regular participant. Mike and Bob Lowe (Bob's a founder of the first forum I linked) are probably the two most knowledgeable people on the planet when it comes to repairing, maintaining, restoring, and upgrading Grand Banks boats. By joining both forums you get the benefit of their collective knowledge and experience.

That said, you need to inspect, or have inspected, the tops of the fuel tanks in that GB46. Moisture-- rain, deck washdown, spray, etc.-- can get underneath the fuel fill fittings on the deck if they are not properly bedded or if the bedding has hardened, shrunk, or cracked over time. Once under the fitting the moisture will follow the fuel fill hose down to the top of the tank and sit there. And that is where these tanks will begin to rust.

Other causes of rust can be moisture trapped between the tank and the platform or bracing it sits on, the fine spray sometimes thrown off by a spinning shaft where it enters the packing gland. and as Ray noted, a generally damp engine room that encourages condensation to form on the outside of the tank that can get between the tank and it's supporting structure.

The fact the boat is a 1986 model does not automatically mean the tanks are suspect. There are GB woodies from the 60s out there that still have their original tanks and they are in great shape. If iron tanks are not subjected to the moisture issues described above and the engine room is well ventilated and kept dry, there is no real life limit to the longevity of iron tanks.

So use mirrors, lights, whatever it takes to get a good look at the tops of all the fuel tanks.

The other concern, of course, is rust inside the tank. This can occur if the boat has sat for a long time or is not used very often and water has accumulated in the bottom of the tank. As part of a survey, fuel should be drawn or pulled from the very bottoms of the tanks if their configuration and construction permit this. Then the situation inside the tanks can be assessed.
 
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Here are your fuel consumption figures:
 

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Grand Banks Tank Corrossion

To Capt. Waldo

I had the tanks fabricated out of 5052 aluminum, 1/4" thick, by RDS in Perry Fl. I designed three tanks, each different size and shape, ste, to replace one 300 gallon steel tank. (our final capacity with the three port tanks is 292 gallons) The tanks were drop shipped to me in NC, and I lightly sand blasted to get the mill finish off, then acid etched them. After neutralizing, I coated them with two coats of Macropoxy 646, a Sherwin Williams marine epoxy. A final coat of a two part high solids white polyurethane was the last step before installing.

Cutting the large 300 gallon tank out was one of toughest jobs, as my wife and I did all this work ourselves. Took about 18 hours, and 23 heavy duty sawzall blades to get the old tank out. Ear plugs, face/arm protection, knee pads, and heavy gloves and lots of pads were required. The hole in our port tank came from water/sea water dripping off the 2" freshwater filler hose from the deck plate, down the side of the tank, and rusting the bottom where the tank was bedded to the crossmember. It was a small pinhole less than 1/8" in dia. While the 10" exhaust is directly beside the tank, I am confident in our boat that it had nothing to do with any moisture issues, nor did the engine room vents or other things that other owners have discussed and mentioned. We replaced every fitting and valve, new sight glass, new and larger vent lines, and new filler hose and deck fill plate. I designed a sump in the bottom tank with a valve. I will say the interior of this old iron tank was surprising clean for a 20 year old tank.

Job is complete on the port side, and hoping that I can simply ospho and epoxy the starboard side tank which has some surface rust, to avoid going thru this process again.

Hope this helps.
Chuck


To Seaisleman

I am German, so please excuse my bad English. My Grand Banks 42 Classic
also has got serious Corrossiono at the port Diesel-tank and I am planning to cut the tank and replace by new tanks. I will empty the tank and clean it with water. But before starting with sawing I want to be sure about the risk of explosion. I would like to know what you did.

Hope to get reply

Seapilot
 
What did you have to move out of the way to do this job? And congratulations for getting it done!!!

To Capt. Waldo

I had the tanks fabricated out of 5052 aluminum, 1/4" thick, by RDS in Perry Fl. I designed three tanks, each different size and shape, stackable, to replace one 300 gallon steel tank. (our final capacity with the three port tanks is 292 gallons) The tanks were drop shipped to me in NC, and I lightly sand blasted to get the mill finish off, then acid etched them. After neutralizing, I coated them with two coats of Macropoxy 646, a Sherwin Williams marine epoxy. A final coat of a two part high solids white polyurethane was the last step before installing.

Cutting the large 300 gallon tank out was one of toughest jobs, as my wife and I did all this work ourselves. Took about 18 hours, and 23 heavy duty sawzall blades to get the old tank out. Ear plugs, face/arm protection, knee pads, and heavy gloves and lots of pads were required. The hole in our port tank came from water/sea water dripping off the 2" freshwater filler hose from the deck plate, down the side of the tank, and rusting the bottom where the tank was bedded to the crossmember. It was a small pinhole less than 1/8" in dia. While the 10" exhaust is directly beside the tank, I am confident in our boat that it had nothing to do with any moisture issues, nor did the engine room vents or other things that other owners have discussed and mentioned. We replaced every fitting and valve, new sight glass, new and larger vent lines, and new filler hose and deck fill plate. I designed a sump in the bottom tank with a valve. I will say the interior of this old iron tank was surprising clean for a 20 year old tank.

Job is complete on the port side, and hoping that I can simply ospho and epoxy the starboard side tank which has some surface rust, to avoid going thru this process again.

Hope this helps.
Chuck
 
At the moment I did not start with the work, its still in planning. I hope that only the connections to the tank have to be removed.
 
I didn't wash or clean the insides of my tanks when I cut them out...I took the inspection plates off and blew a little ait in there...a compressed air hose or vacuum on blow would be fine...an explosive mixture has to be pretty concentrated/exact....

Once a decent sized hole is there to air out the tank...no worries...anyhow the Milwaukee brand "Torch" blades never created enough heat or sparks to worry about.
 
Seapilot,
I would suggest to drain all fuel, and open as many inspection plates as you can. With a strong water hose nozzle, add about 10-15 gallons of water, and some non-ionic detergent, such as JOY, or DAWN. I probably used half of one of the small bottles. The detergent will help disperse the diesel. If you can find something like a long paint stick, or most anything to agitate the water/detergent/diesel mixture, try that. Then drain all of this mixture out of the tank. If a really heavy diesel residue remains, you may want to try the same procedure again. I used a small pump attached to my tank fitting to pump into five gallon buckets.
Diesel needs heat and compression to explode. As others suggest, you may want to blow some air into the tank when you first start, but it will not be needed as you get large areas open. Work in small sections, as the iron is heavy. You’ll need a couple dozen good heavy duty reciprocating saw blades. You will know quickly when to change them out, as they will become dull faster than you might think. Let the saw do the work as much as you can, in other words, don’t force it. There will be some sparks, but don’t worry too much. I kept a fire extinguisher nearby, but never needed it. Try to vacuum up the small steel shavings each day, as they will quickly become rust spots overnight. As I mentioned in my earlier post, have plenty of good eye/ear/face and hand protection. The noise of the reciprocating saw in black iron is deafening. Good gloves and long sleeves are a must. I have heard of these tanks being cut out with a small grinder, but that produces a LOT of sparks, and a lot of metal filings all over the engine room. I am not sure it is any faster than a reciprocating saw.
You will find that the interior baffles are the most difficult to remove, but you’ll make it. They have big round holes in them so you can use those as starting points. Just know it takes some time, and take plenty of breaks.
Bglad,
I removed the upright stainless support post from the stringer to the cabin floor support, the Racors, the fuel lines, numerous raw water lines to shaft bearing and such, transmission shift cable, and the exhaust system from the turbo to the 10” exhaust line behind the tank. (Make sure to seal the end of the turbo) Of course numbers of clamps, fasteners, etc. Suggest you make lots of pictures, as putting it all back will be made easier if you do so.
I did not remove the generator. But, I spent a lot of time with measurements, calculations, and mock ups made from luan to make sure the three tanks I designed would fit through the doors, hatches, etc.
Hope this helps. Let me know if you need any more information.
Good Luck,
Chuck
 
Cutting with a sawzall will not produce heat or sparks if you go at a reasonable pace and spray a little lubricant on the blade every few minutes. On the advice of my old employer who removes underground heating oil tanks and cuts them up for a living.

Washing the tanks will just produce a lot of goo that you now have to dispose of.

I drained my tanks down to the fuel system outlets and a few diapers did the rest..no muss no fuss...and yes the saw residue did produce rust spots that are easily cleaned with any of the acidic cleaners.

I used a Home Depot Rigid one handed recip saw with the Milwaukee "torch" blades and did about 4 hours a day for a week to get the 2 tanks out and cleanup as I went along...I wasn't in a rush and didn't feel like I had to torture myself. Te bat was in the water for the summer so it was an "as I felt like it schedule"...

The thing that took the longest was not removing all the floor bracing (as we are liveaboards) that would have allowed me to move the tanks around more and cut without fear of cutting other supports or into the hull....but it still was no big deal.
 
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RickB,
I enjoy reading your responses and replies, due to your extensive technical knowledge. I did read the article you posted, and as most news articles do, it left a lot of details out, as to what kind of welding he was doing, where on the tanks, how much fuel was in the tank, etc. etc. If someone were stick welding on a tank below a fuel level, then I could certainly understand how it could get hot enough to explode.
So, from that, my opinion here is that we are talking about apples and oranges.
Thanks,
Chuck
 
Just passing along the other side of the story. Most fuel tank fires and explosions occur because people thought there was no risk involved in whatever they were doing. Call it due diligence.

Having done a few jobs like that I am fond of using CO2 inerting via dry ice or a bottle until the tank has been opened enough to ventilate fully.
 
Rick,
The dry ice is a very good idea. I have used that procedure in a very different non boating situation. My fuel tank had been cleaned and well ventilated for over two weeks before I started sawing on it, so I felt the risk of fire was very minimal in my situation. I hope that any person who would attempt a DIY project of this magnitude would of course do their due diligence also.
Thanks,
Chuck
 
Seapilot, some years ago, at Alice Springs in remote central Australia, half way through a 16000km car rally, we had a cracked leaking auxiliary gasoline tank successfully welded. We did remove it from the car first. Only one guy would touch it, we were surprised he did, staying well clear while he welded.You should be ok,with planning.
 
I just cut my tanks out... At times the blades on the saws-all got so hot they started smoking, so I'd stop for a minute and keep cutting. Used a sledgehammer to break the welds holding the baffles on.

Take a cup of diesel outside and put a match in it and see what happens.....
 
Sea Moose
In the meantime I finished removing the port dieseltank.
I did it the way seaisleman reported in this forum.
When the sawblade became hot I dipped it in cold water and
could continue sawing immediately.

Best Regards
Seapilot
 
To those who have cut out their old iron tanks: how did you get your new tanks in? In parts, that were then welded within the engine room....or?
 
I went with smaller (many use multiple) tanks so they slid right in with just barely moving one vertical deck support.

Because the new tank bottoms are flat versus shaped like the hull...they sit up on platforms now.
 
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