Getting Fuel Tank Tested

L

LuckeCatanias

New member
Since getting Pearl (formerly Daydream) in July we've had the opportunity to do a couple of shakedown cruises.

One area we found work needed to be done was in the fuel tank.
We discovered at our first fuel-up that the gaskets on the inspection hatch were blown resulting in a fair bit of gasoline in the bilge.

We have a 100 gallon aluminum tank which I believe was installed near to 2005 when the boat was new.

We'll be taking her to Performance Marine in Everett at the end of the month.

Among other things, I'm asking them to:

- Clean the tank and remove accumulated water (approx 1 cup of water in
the tank)
- Pressure test the tank.
- Replace fill and vent lines.
- Test and possibly replace the sender unit (currently reading 1/4 tank low).

I'll be fabricating a new inspection hatch cover which was suffering from some advanced corrosion as well as new gaskets for the hatch and sender unit myself using 5052-H32 plate and 40A Nitrile, respectively.

I've also just replaced the fuel lines to the filter.

I wonder what I'm missing in my quest to refresh the fuel system?
 
colbysmith":20x8tks2 said:
Feel free to peruse my fuel tank issues on my 2009 CD-25... Colby

http://www.c-brats.com/viewtopic.php?t=31093&highlight=fuel+tank+removal
Click to expand...


Thanks Colby!

That's about as complete a job as one could imagine.
Also very similar to my config.

I think now I will be compelled to pull the tank entirely and inspect the bottom given the age of the tank (20 years).

- Looks like you were able to access the clamps for the vent/fill through the gunnel pockets? I.e., you did not have to pull the fill caps?

- Did you replace the grounding wires? The 2 black grounding wires that run FWD on port and starboard. Do you know where they run to?

- The aft retaining blocks that you removed -- after removal did you have to do any re-glassing of the hull? Also, how did you re-affix them?

- Did you at any point price out a new tank?

- Were you able to determine the alloy/temper of your tank?
 
- Looks like you were able to access the clamps for the vent/fill through the gunnel pockets? I.e., you did not have to pull the fill caps?

Yes, I was able to get to the clamps thru the access ports, and also with removal of the steps. Not always able to see what I was doing, but could at least reach and feel. The fill hoses are pretty thick and stiff, so it was a bitch to get them off and new ones back on, with little room to move the tank around. Also, the tank just barely fits through the floor cutout. I did have to jockey it around to get it out, and don’t think I could have done it without having removed all the gas first. It may have been easier to get the hoses off, if I had pulled the fill spouts. However, I think there was the issue of the ground wires and not easy access to them at the caps. Other than that, not sure why I didn't pull them off.

- Did you replace the grounding wires? The 2 black grounding wires that run FWD on port and starboard. Do you know where they run to?

No, I didn’t replace them. They were in good shape. Going from memory, I believe they attached to the fuel fill spout and then one ran to a negative ground post near the batteries.

- The aft retaining blocks that you removed -- after removal did you have to do any re-glassing of the hull? Also, how did you re-affix them?

They were somewhat loose, but I did have to cut part of the fiberglass matting holding them down. I did reglass over them to attach them back to the hull. (Use fiberglass to glue them to the hull, and then also placed some glass cloth over them and the hull.

- Did you at any point price out a new tank?

No. But I did learn that the supplier was Coastline Equipment in Bellingham. 1-360-734-8509. Ask for tanks.

- Were you able to determine the alloy/temper of your tank?

Not sure what you mean here. The tank was aluminum, so wasn’t too heavy. The inside looked fairly clean, for what I could see through the fill opening and access port where the guage transmitter goes. Only the outside bottom was pitted, likely from sitting in bilge water most the time. (I think I now have a dryer bilge with new hatches and finding a leak in the trim tab hydraulic line where it goes through the stern…but I’m sure there is still water that pools under the tank, due to the shape of the hull. At least I still get a little water out when I pull the bilge plug with the bow high. But nothing like I use to.

Hope this all helps. I was surprised to see the tank pitting, and wonder how many other C-Dorys are out there with tanks either leaking, or about to leak. I’m pretty sure if they are leaking, one would smell the gas as the bilge does have openings into the cabin. Good luck with your project. Colby
 
Aluminum comes in different alloys for use on boats. Saltwater and freshwater resistance, weldability, forming etc.

5052 is the most common. Probably what the fuel tank is made of. Bends fairly easy. Welds nice.

5086 is the best for saltwater and is more expensive. This is the preferred type for the lower part of an aluminum hull in full time contact with saltwater.

6061 is a structural aluminum and does not bend very easy.

There are many more alloy types, but these three are common.
 
To add to what Colby posted and in his reference posts, when that tank is out of the boat--which it should be if you are going to do a full "redo" of the tank. There may be pitting, and perhaps even thinning enough to have to replace the tank or the bottom of the tank. Another option is to epoxy the bottom of the tank as Colby did. (full outside coating is best)

While in there, it is a very good idea to check the tabbing of main aft cabin bulkhead to the hull in the tank compartment. This should be renewed in most boats. grind out the old tabbing, which is most lkely broken down and in adequate. After cleaning this up, repace it with layers of mat and cloth. I would suggest concentric starting with epoxy compatable mat next to the hull and the bulkhead. Then a layer of 6 to 8 oz cloth, then mat, and another layer of cloth with epoxy. The epoxy gives better secondary bonding than the polyester resin.

There is also a dry bilge setup referenced by Colby, and that is now available in one package for $150, or 4 suction stations for $ 180.
SeaFlow Drybilge commercial package

This will get all of the water out of that area under the tank, and help to keep it dry and prevent further pitting of the tank.

For a DIY dry bilge seeDry bilge DIY and commercial product
 
Update --

I pulled up the sole to pressure wash the area in prep for service/pressure test and found quite deep corrosion on the exterior aft vertical wall of the tank. About half way up the wall and maybe 10 inches port off the center line if anyone is keeping notes.

I'd estimate the depth of damage to be ~50% through the material --1/8" aluminum sheet.

Scattered, much more minor pitting on the order of 0.020-0.030 is descriptive of the other visible damage.

So, a new tank it is.

Coastline Equipment is currently quoting $1800 + tax and a 4 week lead time.


I'll be glad to know that I have a new 20-year clock going back in when it's all said and done.


Thanks to everyone for the excellent pointers. I'll document as well as I can and post on a new thread. With the new website should make adding copious photographs just that easy.
 
thataway":25x9k1kr said:
To add to what Colby posted and in his reference posts, when that tank is out of the boat--which it should be if you are going to do a full "redo" of the tank. There may be pitting, and perhaps even thinning enough to have to replace the tank or the bottom of the tank. Another option is to epoxy the bottom of the tank as Colby did. (full outside coating is best)

While in there, it is a very good idea to check the tabbing of main aft cabin bulkhead to the hull in the tank compartment. This should be renewed in most boats. grind out the old tabbing, which is most lkely broken down and in adequate. After cleaning this up, repace it with layers of mat and cloth. I would suggest concentric starting with epoxy compatable mat next to the hull and the bulkhead. Then a layer of 6 to 8 oz cloth, then mat, and another layer of cloth with epoxy. The epoxy gives better secondary bonding than the polyester resin.

There is also a dry bilge setup referenced by Colby, and that is now available in one package for $150, or 4 suction stations for $ 180.
SeaFlow Drybilge commercial package

This will get all of the water out of that area under the tank, and help to keep it dry and prevent further pitting of the tank.

For a DIY dry bilge seeDry bilge DIY and commercial product
Click to expand...


UPDATE:

Tank came out of the boat yesterday.

After pressure washing the bottom of the tank many holes appeared -- the pressure washer was able to punch two 0.350" holes in the bottom of the tank. Meaning that thing was just about to let go if not already -- I was likely leaking fuel or at the very least vapors into the bilge.

Very glad I caught it when I did.

Regarding the tabbing for the aft cabin bulkhead:

This is maybe a little hard to describe without pictures -- I'll post once the website updates this week.

On my boat the buildup of the bottom 7-8 inches of that bulkhead immediately adjacent to the hull (moving from fore to aft) looks like a (1) buildup belonging to the entire cabin bulkhead (unsure of the stackup) and then (2) a separate balsa core buildup scabbed on to that.

That second separate balsa core build up is as wide as the bilge and is only the 6-8 inches tall -- from the bottom of the bilge to just below the door. I can feel that the core tapers out at the upper edge. However, on the bottom edge it's fully exposed balsa core -- fully rotted out of course.

It seems like my action here is to cut the aft face sheet and core out until I get good material and then build back up with coosa core, mat, fabric, etc. as you describe, Bob.

Also, to clarify, you would expect the aft cabin bulkhead to be fully integrated to the hull?

I.e., when I build back up I should fillet transitions and run mat/cloth continuous from the vertical wall to the horizontal hull?

It is curious that this did not happen from the factory -- indeed does seem "inadequate".

For geometry, I am considering 0.5" minimum radii fillets and a 4-6" width of fabric on the hull to achieve adequate strength.
 
LuckeCatanias said:
Since getting Pearl (formerly Daydream) in July we've had the opportunity to do a couple of shakedown cruises.

One area we found work needed to be done was in the fuel tank.
We discovered at our first fuel-up that the gaskets on the inspection hatch were blown resulting in a fair bit of gasoline in the bilge.

We have a 100 gallon aluminum tank which I believe was installed near to 2005 when the boat was new.

We'll be taking her to Performance Marine in Everett at the end of the month.

Among other things, I'm asking them to:

- Clean the tank and remove accumulated water (approx 1 cup of water in
the tank)
- Pressure test the tank.
- Replace fill and vent lines.
- Test and possibly replace the sender unit (currently reading 1/4 tank low).

I'll be fabricating a new inspection hatch cover which was suffering from some advanced corrosion as well as new gaskets for the hatch and sender unit myself using 5052-H32 plate and 40A Nitrile, respectively.

I've also just replaced the fuel lines to the filter.

I wonder what I'm missing in my quest to refresh the fuel system?
Click to expand...
If your in the SALT constantly 5086 is better.
 
It seems like my action here is to cut the aft face sheet and core out until I get good material and then build back up with coosa core, mat, fabric, etc. as you describe, Bob.

Also, to clarify, you would expect the aft cabin bulkhead to be fully integrated to the hull?

I.e., when I build back up I should fillet transitions and run mat/cloth continuous from the vertical wall to the horizontal hull?
Click to expand...

Yes, you want to remove the bad balsa out, and your material of choice to full that area. Then mat and and cloth, on the hull, lay conconcentric out by about an inch each time, to spread any stress point to the hull out.
The fillet is about right I use a tongue blade radius for these fillets in the boats I built.

I agree the factory did not do adequate tabbing here. I have to guess that they did not realize water would stand there, and that this joint could break down, since often it was only a single layer of mat. I hope they are doing better today. Perhaps if NW Industries reads this forum they could comment on current best practices. Remember even C Dorys are built to a price point. Unfortunately many builders only consider the effect of use of the boat for the first several years. The difference in cost of materials is only a few dollars, and time is the greatest expense. Also this tabbing keeps bilge water out of the cabin, and is the usual failure boat where water appears under the cabin steps on floor--and the source is often under the shower or hanging locker.
 
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