Fuel tank vent filter, pickup tube

[Oldgray]

I just pulled out my fuel tank from my '88 C34 for cleaning, and have a couple of questions. This tank was previously cleaned in the boat by a commercial firm some years ago (10?) and they installed a cleanout port at the forward end of the tank. They also removed the screen in the pickup tube. Having just retired this year I've got time to invest on repairing the years of neglect my boat has suffered through. I naively assumed I could empty the tank then mop out the sludge from the handy cleanout port, only to discover a baffle less than a third of the way back blocking access to the rear of the tank. After the tank was completely drained by gravity through the supply line, I siphoned out another gallon of fuel and approximately 1/2 gallon of water, leaving behind a whitish to brownish layer of sludge (biofilm, I presume). My pickup tube ends about an inch or so from the bottom of the tank. I've read on this forum and other places two conflicting opinions of where the pickup tube should end. One opinion says the tube should go all the way to the bottom of the tank, and lay on the bottom, preventing the accumulation of water (assuming one actually runs the engine occasionally). The other says that the tube should end an inch or so above the bottom (like mine) thus preventing sucking water into the Racor (but guaranteeing the eventual accumulation of water at the bottom of the tank). I brought the tank home to clean out, and I'm wondering whether to put a longer tube on the pickup. Question 1: what is the current thinking on where the pickup tube should end, on the bottom, or an inch short of the bottom?
Question 2: Has anyone installed an H2Out vent filter in the tank vent line? Practical Sailor likes these, and the guy at the local marine supply store said they have gotten very positive feedback on the units they have sold. These things are very expensive ($130) for what they are, a clear silica gel-filled canister with 5/8" barb fittings at either end. The silica is blue, turns red when saturated, and can be removed and regenerated by heating. But they are well made and worth it if they keep water out of the thank. The big problem I see is that the only way I know when the tank is full when filling is when fuel flows out the vent. If the vent filter is flooded with fuel, then the silica gel is ruined. Even if one carefully calculates fuel usage, sooner or later everyone screws up and lets a little fuel out the vent. Any advice would be appreciated. Photos show the inside of the tank looking aft at the baffle, and looking down at the sludge after pumping residual fuel/water.

Steve
Sunshine #542

[Ken Juul]

my pick up tube has a rubber hose attached to it so it lays on the bottom of the tank.  Get the tank clean, use Biobor an other additives as directed and water should not be a problem.  I think most water enters the tank through  a bad seal on the filler cap or from contaminated fuel.  Can't see it coming in through the vent unless you are spraying it in with a hose.  With the biobor, the racor should stop any water from getting to the engine.

[Stu Jackson]

Steve, empty tank condensation thru the vent is an urban myth.

http://www.pbase.com/mainecruising/fuel_tankt_condensation

[Oldgray]

Empty tank condensation is not the issue. In an empty, vented tank, condensate evaporates when conditions permit. In a tank half full of diesel fuel, the water settles under the fuel where it can't evaporate. That's no myth.  Practical Sailor presents some pretty good evidence on the effectiveness of the H2Out filter, but it requires some elaborate (for me) venting with tees and check valves to protect the filter from fuel in overfilling, so I was curious if anyone has installed one on the C34. I will be much more disciplined in the future about adding biocide and corrosion inhibitor, but if there's a practical way to keep the air over the fuel dry, it can only help.

Steve
Sunshine #542

[Ron Hill]

Steve : I don't know where you are getting these pick up tube opinions from, but they are wrong!!
The pickup tube length should be above the tank bottom by about an inch or two. 
There should be about a 3/4" piece of 3/8" fuel hose attached to the pickup tube.  When the pickup tube is inserted back into the tank that hose is meant to curve down and have its opening so it picksup the fuel and any condensation from the bottom of the tank.  The Racor takes care of the condensation - that's why it's there in the fuel line just after the tank and before the lift pump.
All this has been written up in the Mainsheet Tech notes, WiKi, Projects, posts - so NOTHING NEW. 

All aircraft fuel tanks/bladders have a condensation sump built in to their tanks and that sump is drained(externally) daily before the 1st flight to drain out any condensation.  Too bad that boat designers didn't incorporate that feature into their fuel systems. 
I could never figure out how to do that on a C34, knowing where the fuel tank was located.  So have at it - come up with a design!!  Best thing to do is keep a 1/2 to topped off tank full of fuel.

A few thoughts

[Oldgray]

Thanks Ron. I'm familiar with the c34.org advice which I interpreted to mean that the fuel hose attached to the pickup tube should extend all the way to the bottom, curving to lie horizontal so that it is picking up right off the bottom. Other websites caution against this, because sediment forming on the bottom may clog the tube, and water will be picked up. I found that mine terminates with an angled cut, the bottom being about 3/8 in. above the bottom of the tank. Photo below. This was done by the commercial tank cleaning/fuel polishing firm that cleaned our tank years ago. I'll follow your advice, which, correct me if I'm wrong, is to install a longer fuel hose on the pickup tube. I'll also run the engine a lot more frequently to try and limit accumulation of sediment.

Steve
Sunshine #542

[KWKloeber]

I could never figure out how to do that on a C34, knowing where the fuel tank was located.  So have at it - come up with a design!!  Best thing to do is keep a 1/2 to topped off tank full of fuel.

A few thoughts

Does the tank sit perfectly level or slope to one direction?

=Ken

[Noah]

The tanks are supposed to sit level in MKI boats...not factoring in any list.