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Old 16-06-2008, 08:55   #1
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fuel system design

Thoughts appreciated
Have to start thinking about the routing of all the systems before the construction of the furniture starts.
The fuel tank is to be mounted on center just in front of where the mast would normally be, between the forward cabins. This is about 6 meters forward of the engine compartments. The 20 hp motors are about 6 meters apart in each hull.
I was thinking of a pair of Racor 500MA with a changeover valve mounted to one side in the seating across the aft main bulkhead. This would give a feed length of about 9 meters to the filters then about 7 meters to one engine and 3 meters to the other, seems a bloody long way. The top of the filters would be about level with the top of the tank. I could install the filters in the aft head which would shorten the runs by about 2 meters and they could then also be mounted just below the tank level.
There are many cats in the same situation with long runs so I may be fussing about nothing but .

Should I run bigger lines
Maybe a pump to prime the long runs
I was thinking of running the fuel return lines only back to the inlet of the filters
Access to the tanks will be somewhat difficult so a shut off valve at the tank may be problematic

Thanks
Mike
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Old 16-06-2008, 09:49   #2
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Quote:
Access to the tanks will be somewhat difficult so a shut off valve at the tank may be problematic
I would recommend that you make access to a shutoff valve at the tank a priority. Also if you mount the filters with the top even with the top of the tank then some kind of priming pump will be necessary, manual ones are now available as posted on the forum last week. If you install the filters lower, then you need a shutoff valve at the input to the filter.

Do yourself a favor and install a good fuel polishing system and ensure you have good access to all of the interior chambers of the tank for cleaning.
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Old 17-06-2008, 21:30   #3
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A NINE METER fuel line run?

That's a lot of 'Pull" for a lift pump.

Did you ever consider the idea of a "Day Tank" with an electric pump from your main fuel tanks.

And don't have good access....have GREAT access. You will thank us for that piece of advice later.
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Old 18-06-2008, 04:29   #4
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Try again, it seems my reply went astray

Quote:
Originally Posted by Chief Engineer View Post
A NINE METER fuel line run?

That's a lot of 'Pull" for a lift pump.

Did you ever consider the idea of a "Day Tank" with an electric pump from your main fuel tanks.

And don't have good access....have GREAT access. You will thank us for that piece of advice later.
Chief
9 meters is only to the filters. There is another 6 meters to get to one engine. It is the long pull that worries me the most. The only redeaming feature is that the tank is well above the motor so once a siphon is established it would help. I wasn't keen on a day tank as it would add quite a lot of wieght aft and I'm trying to achieve the opposite.
I spent a couple of hours pondering over the access aspect and I may be able to overcome it. If I move the anchor winch further aft into the same area I could have a smallish hatch access. The tank would most likely be about 500mm high which leaves a bit over 500mm above the tank to access the access ports. A transfer pump could also live on top as part of a polishing system.

Mike
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Old 18-06-2008, 20:07   #5
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suggest since you are at ground zero that you put in a multi stage spin on high capacity fuel filtration secondary and
tertiary
filter set up also include an isolated bulb primer hand pump-for more info look up these
issues
author tony
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seaboard marine CA USA-net result will be high capacity easy filter change no bleeding needed
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Old 19-06-2008, 05:14   #6
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Quote:
Originally Posted by eyschulman View Post
suggest since you are at ground zero that you put in a multi stage spin on high capacity fuel filtration secondary and
tertiary
filter set up also include an isolated bulb primer hand pump-for more info look up these
issues
author tony
Athens
seaboard marine CA USA-net result will be high capacity easy filter change no bleeding needed

eyschulman
I was going to use 2 Racor 500's with a valve to select either. As these are way overkill for a pair of 20 hp motors I was thinking of using 10 micron filters, the primary on the motors will be very easy to change. I will most likely fit a polishing system at the tank so I think anymore is getting excessive.
I spoke with a builder who has built many similar configurations and he claims it has never beeen an issue but then he runs a 1" fuel line back to the filters. Coupled with the siphon this may be the solution
Are the green words meant to be links?

Mike
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