Fuel system cracks

[Anonymous]

Hi All,

Please excuse the long story… we felt it important to get out the word..

Barb and I launched our Nauticat 44 a year ago. Prior to that, we were on the hard in Napa Ca for 3 1/2 years after purchasing her in 2011 in Florida. We trucked her there with mostly empty tanks.

After launching last year we filled both fuel tanks. We motored for a year on the port tank. Six weeks ago we decided to switch to the starboard tank to balance them out. I moved the twin three way valves to starboard mid week. Days later, we decided to run the engine for a 1/2 hour for a safety check, while we were making preparations to get underway. After 15 minutes the engine quit.

We checked the first upstream starboard Racor filter and found it was packed with silt and some water in the lower bowl. Filter area was dry. I cleaned the filter, replaced the cartridge, and primed it. We ran the engine again and after 15 minutes it stopped. The filter was empty. I primed it and it did it again. The was no additional silt or water. I figured I had broken suction somewhere in my cleaning efforts.

This was our mystery to solve what is the silt and why are we running our filters dry. On the upside, we were happy we ran the engine for a long test.

After a little research I found that the silt was algae residue. Unfortunately our local fuel polishing guy retired. We moved the fuel in and out of our tanks into 55 gallon drums while adding biocide. We equilized the tank levels and let the biocide work. We also added drain valves on the low point sumps and removed any water. Soon we will use our newly built large dual Racor filter set to polish the fuel and vacuum the tank bottom.

Their still remained the mystery of the Racor filter running dry. The double three way valve set was suspect as they were never quite dry (damp with fuel) so I replaced them with a new six port valve. We tried to pull fuel through the system and couldn’t. My friend suggested I buy a hand held “Mighty Vac”, (not the plastic version) which turned out to be a god send. It is used to pull vacuum on brake systems and bleed them. It will never leave the boat. It will speed up fuel filter changes, steering system work etc.

We changed the two inline filters on the engine as well. They were spotless so the upstream Racor did its job. We systematically checked the fuel tubing, valving and filters looking for leaks and found they all held vacuum. (all the way to the tank top) That left us with something inside the tank.

We thought the starboard suction tube might have broken or fallen off. We pulled the suction tube and at first glance it looked great. In bright light however we found hairline cracks running intermittently and offset down the full length of the brass suction tube top to bottom. I made a temporary duplicate suction tube using a new elbow fitting and soft 5/16″ copper we had on hand and installed it. The mighty vac pulled fuel through the system into the twin injection filters. The engine fired up without emptying the Racor filter. Our problem and mystery was solved, but now all four fuel suction tubes are suspect. (Eng and Gen, both tanks)

Any one of these lineal suction tube cracks could have changed the available fuel we could draw from the tank by breaking fuel line suction. Our fuel gauges could have shown a full tank when due to these suction line cracks only half or less was available.

I have never seen this type of cracking before so I took it into work and discussed it with our senior metallurgist. His determination was either sulfur or ammonia (or both) induced Stress Corrosion Cracking,(SCC) effecting the seamless brass tube where the mandrel induced stress on the brass tubing when it was manufactured. In his opinion it was those latent stress areas that cracked. Since it was around 20 to 30 years old either a replacement in kind or upgrade to CuNi would be ok. Newer fuels have less sulfur now.

We now have to change all of them as none of them can be trusted. We are using 5/16″ OD X .065″ Wall, rigid brass tubing with a Parker 1/4 MNPT X 5/16″ compression, 90 degree elbow. Tubing to be brazed at the 90 deg. ell and the crimped end. Four lateral holes are to be drilled in a pattern matching original.

So our mystery is solved. The algae didn’t come from the starboard tank (it physically couldn’t) it came from our running on the port tank. Probably the weekend we were out crashing waves seeing what she could do in higher knot winds. The algae could have come from a bad fuel stop. We should have been treating our diesel all along. We were lucky to discover the suction tube issue at the dock. The suction tubes are easy to duplicate. It should be only a days effort.

Hopefully our efforts are some help to you all.

Dave and Barb
NC 44 Babala
Richmond, CA.

[39Schuss]

Hi, Richard, could you please post a picture of your Racor installation? What Racor model did you use? 75500MAX2?

[Author]

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