"Capt. JG" wrote
This is exactly what the guy with 30+ years of experience said on
Saturday. It was recommended to add a dual (filter)....
So you are going to add that second filter ARE you not? In view of the high
current conditions in SF Bay and your responsibility to your students I'd
hate to be you if something happened due to fuel contamination after posting
that you were aware of this recommendation.
While you are at it, consider this:
I think my system has gotten a bad rap for complexity due to the dual tanks
which does drive up the cost and complexity a lot. Here is what it would
look like in yours or the typical single tank boat:
http://home.maine.rr.com/rlma/1tankFOsystem.gif
The Shelco Filter was about the same cost as a Racor. The second pump was
about 60 bucks and is also a good redundancy feature. This redundancy would
be especially desirable in a boat with a low mounted tank that will not
gravity feed. Otherwise, there are only one or two additional valves and a
few fittings more than in the dual filter system. The cost difference is
insignificant in boat bucks.
Fuel contamination and degradation is always going on to some extent. This
system is constantly removing it whenever the engine is running. The system
will filter a volume equal to the typical sailboat tank every hour of
running time. Your dual filter OTOH is just sitting there doing nothing
useful.
Fuel flow at the tank inlet is vastly greater than in the typical system.
This increases the uptake of water and anything else floating around in the
bottom of the tank waiting for rough water and a tight spot to get sucked
into the system at the worst possible time. Since most of the fuel is going
through the polishing filter and being returned to the tank, getting this
stuff into the fuel system is a good thing.
In the event of the primary filter (Racor on the drawing) loading up, OR the
primary fuel pump failing, just turn one valve and you are back in business
with full fuel flow. Some tank configurations or engine driven fuel pump
problems may require partially or completely closing the second valve. In
any event, it doesn't take any longer than switching filters.
Let's say you do pick up a load of bad fuel and calling a fuel polishing
contractor isn't an option either because you are cruising or there isn't
one as is now the case here in Portland. (BTW, none of this has anything
to do with an old and neglected tank that has gotten thouroughly coated and
filled with slime. That's a different issue all together.)
Duel Filter Setup:
Switch filter.
Change first filter element - 16 bucks.
Run for a while.
Repeat as often as necessary at about 16 bucks a filter element.
The only way to get fuel flow is to run the engine That means doing these
repeated and expensive filter changes underway or with the engine running at
the dock and sucking very little fuel. With an engine the size you have on
your boat, it will take 20 - 30 hours to run all the fuel through the
filters. And, you have to consume it which adds to the expense.
Polishing Setup:
Turn red valve and isolation valve if necessary and deal with it when you
get back to the dock. The high capacity of the Shelco makes its load up
time much higher than the Racor or similary filter. You can change it's two
buck element while the engine runs on the Racor, just as on a dual filter
system if it does load up.
When you get back to the dock, you can plug into shore power and let the
polishing system run with the engine off, changing two dollar filter
elements as necessary.
Based on the amount of crud I found in my Shelco and the pristine condition
of the sediment bowl in my Racor, I would say loading up of the Racor is
unlikely in any event.
Here's a challenge. Usually after you've taken a seminar like the one you
just did, they will entertain a few follow up questions. Take this
schematic to your guy and let us know what he thinks.
--
Roger Long