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  #1   IP: 199.68.38.6
Old 10-19-2011, 11:25 AM
RUSSELL RUSSELL is offline
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Planning Engine Install for C30: Fuel System

Now that I have the engine compartment prepared and the engine sitting in the boat, I'm trying to think through what needs to happen for all of the supporting systems.

I note a large number of threads dealing with dirty fuel and Don Moyer's admonition regarding clean fuel (in the MMI manual and literature that came with the replacement engine).

The gas tank was 32 years old; I decided to replace. The piece of plywood the gas tank was sitting on was rotted and weak; I tore it out. So, I will be implementing a fuel delivery system from scratch.

My first thought is to move the gas tank to the aft locker in the cockpit.

(1) Gas tank outside the cabin rather than under aft berth.

(2) Eliminates the gas line fitting on the deck (one less hole in the deck).

(3) Only one gas line running inside the cabin rather than two (fuel line feeding the tank and fuel line from tank to engine is two lines - there would only be one fuel line from tank to engine this way).

(4) The area where the gas tank was originally installed under the aft berth would make a nice place for four house batteries.

My thinking is to build a box for the fuel tank, fiberglass up well, and fiberglass into that aft locker. I would also add some "reinforcing struts" between the hull under the floor of the locker and the locker floor due to the additional weight of the gas tank in the locker. (I expect to do a good bit of glass work here because I am going to add a deck plate so I can access the exhaust thru-hull as well as improve the area where the blower hose passes through so water can't leak in).

I assume I would place an anti-siphon valve on the fitting on the gas tank; from there to a shut-off valve mounted on the gas tank box in the aft locker, down through the boat to the fuel filter/water separator, from the fuel filter to the electric fuel pump, from the electric fuel pump to the polishing filter, and from the polishing filter to the carb. I was thinking maybe a second fuel shutoff valve right before the fuel filter/water separtor would be handy for purposes of working on the system (less gas to have to drain out of that long line) as well as increased safety. I was planning to encase the fuel line in a bilge hose as it travels from the gas tank along the hull of the boat and through the bilge until it gets to the fuel filter/water separator to prevent chaffing of the fuel line. I was planning to drill holes in the encasing bilge hose so that if any water got in the encasing hose it would drain out.

I am not sure what gas weighs; around eight pounds per gallon? The 12 gallon tank, box, and glassing in would weigh around 120 punds (gas tank full). This seems like a negligible weight movement for a boat the size of a Catalina 30 to me (but, I don't really know).

Any time one talks gasoline it seems one needs to think about safety. I assume I would mount a fire extinguisher in the aft locker. I also saw these little ports with a scored glass so you could shove a fire extinguisher nozzle through them on another thread. I was thinking of putting one of those in the middle of the each engine compartment access hatch. Anything else to consider?

I would appreciate feedback, especially if someone sees a significant weakness with this approach.

Again, I would never have even considered doing this without the good folks on this forum. Thanks in advance.
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  #2   IP: 24.152.131.155
Old 10-19-2011, 11:58 AM
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ndutton ndutton is offline
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Yeah, I have a couple of problems with the plan. Don't get me wrong, I like the reasoning behind everything but here are a few factors to consider:
  1. The fuel tank in the aft cockpit locker will result in a MUCH higher mounting position than under the quarter berth resulting in MUCH higher head pressure to the system. Without doing the math the pressure could be greater than the output of the electric pump. I'm not clear on how an anti-siphon valve on the tank would work because under normal operation the pressure at the tank valve is negative, the same as in a siphon condition. Wouldn't an anti-siphon there also mean an anti-flow during operation? And as mentioned in another recent thread, you're counting on the carburetor float valve to hold back the tide.
  2. Distance to the engine: Moyer sells a different electric pump for the Catalina 30 to specifically address the distance and that's with the tank in the stock location. You're nearly doubling that. The higher mounting mentioned above would likely negate the issue but still . . .
  3. Powered ventilation of the new fuel compartment: Engine spaces and fuel storage compartments are required by the USCG to be positively ventilated. If using the same blower system, this new tank location will have to communicate atmospherically with the engine compartment which also means the entire rear half of the boat will now be included. This brings in a variety of additional potential ignition sources such as the engine control panel, refrigeration if so equipped and so on. Note that the USCG requires our starters, alternators, battery switches and blowers to be either ignition protected or vapor tight for this reason due to their normal location in the engine space. If the new tank location is sealed off from the rest of the boat and ventilated separately you may be better off but that means a separate set of vents, additional blower, wiring and ducting. The inevitable spills may be better managed with a sealed off compartment too.
  4. With a sealed off tank compartment, if you install a Xintrex gasoline vapor alarm you'll need two to be fully protected.
I hate to be a pain, just thinkin'.
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prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others

Last edited by ndutton; 10-19-2011 at 12:26 PM. Reason: just one more comma
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  #3   IP: 199.68.38.6
Old 10-19-2011, 01:07 PM
RUSSELL RUSSELL is offline
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Neil,

Not a pain at all; I assume there is far more to things than I realize.

I never understood why the gas tank was placed where it was originally; your reply clarifies some.

I don't understand this term: "higher head pressure." Do you mean that as gravity pulls the gas down from a position above the engine it will create enough pressure to overcome the fuel pump, force back the carb needle valve, and leak gas out? That is a bad sitiation I do understand.

I read somewhere that USCG requires an anti-siphon valve at the gas tank. It has a male end and attaches to the gas tank fitting; I just looked for the part on a web supplier.

It sounds like maybe movement of the tank creates as many issues as it solves.
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  #4   IP: 71.183.233.249
Old 10-19-2011, 04:19 PM
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Where is your fill going to be at the new tank location? The big question is where will spills go? There are always spills.
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  #5   IP: 96.239.165.126
Old 10-19-2011, 08:52 PM
RUSSELL RUSSELL is offline
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A good question and an issue I had not considered. With the current deck fill, a spill would basically run down the deck and overboard (into the lake; not good, but it would not remain in the boat).


In my initial thought a spill would pool in that aft locker. As I said, I had not considered; it seems like a very bad thing to have a splash of gas trapped next to the gas tank.

Thanks for raising the issue.
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  #6   IP: 24.152.131.155
Old 10-19-2011, 09:09 PM
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Quote:
Originally Posted by RUSSELL View Post
I don't understand this term: "higher head pressure." Do you mean that as gravity pulls the gas down from a position above the engine it will create enough pressure to overcome the fuel pump, force back the carb needle valve, and leak gas out?
Basically the greater the difference in elevation between the tank and the carb the greater the pressure. It's the basis for nearly all city water systems. That's why you see water tanks on hill tops or towers. Once the water is pumped up into the tank the whole system is gravity fed. With such a great difference in elevation pressures exceeding 100 psi are common. Our systems are simply on a smaller scale.

Also the electric pump will not hold back flow. My float valve issue a while back (see USCG Fuel Line Shutoff thread) allowed the fuel to siphon right through the pump and out of an overflowed carb bowl.

You and I need to chat off list so as not to bore the forum with minutiae. I have some ideas for you specific to the Cat 30. PM coming your way.
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1977 Catalina 30
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prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others
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  #7   IP: 148.170.241.1
Old 10-20-2011, 08:05 AM
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ILikeRust ILikeRust is offline
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Don't forget USCG and ABYC standards for fuel systems. Since you're totally redoing it, now is the opportune time to make sure it meets all the latest and greatest safety standards.
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