How full can you fill fuel tanks on newer C-Dorys?

[pcg]

I’ve read that EPA rules (that went into effect around 2011/2012) for marine vessels require a fuel system that allows fuel vapors to be captured and also that will work with the newer auto shut-off fuel nozzles. This means that there is a fill limit vent valve on top of the tank that closes before the tank is full, creating a pressure surge that allows the fuel nozzle to shut off. Some have complained online that this substantially limits how full the tank can be filled.

Are the newer C-Dorys required to have this technology? (If there is a carbon canister in the fuel vent line then I’m guessing they do.)

If so, how many gallons of fuel can you actually put into a “25 gallon” tank, in a new C-Dory?

 

[thataway]

If you want to see the rules as noted by ABYC here.

Generally I have found some C Dorys more difficult to fuel than others, depending on route of both the fill tube and the vent/vent tube. I try and allow for air and vapor venting around the nozzle when filling (This may not be possible in some states like Calif.--I believe Oregon has the same rules-- where there is a closed vapor system when filling tanks). Also Oregon has "no topping off tank" rules, so those, are going to be restrictive. If I was filling a tank in Oregon (and I don't know if you are allowed to do that in a service station or not), I would go very slowly for the last few gallons.(probably not a bad idea anywhere to avoid spills.)

One of the reasons that the C Dory 25 was given two fills, was to allow complete filling of the tank in about the 2004 era. (It is also much more convenient for taking on fuel to have fills on both sides).

Theoretically, you should be able to fill a tank as completely prior to and after the 2011 deadline, if you go slowly enough. The vent valves are 1 PSI.

 

[pcg]

Here's a video that shows what happens during filling. To save time, start at 0:55. https://www.youtube.com/watch?v=FszARiU ... e=youtu.be

Theoretically, you should be able to fill a tank as completely prior to and after the 2011 deadline, if you go slowly enough. The vent valves are 1 PSI.

Yes, apparently even after the fuel level rises enough to close the fuel limit vent valve, there is enough pressure leakage somewhere to allow the inlet check valve (common name, but called an inlet control valve in the video) to open up, allowing remaining fuel in the line to drain into the tank. At that time you should be able to keep filling, as long as you go slow enough to prevent the buildup of sufficient pressure so that the inlet check valve doesn't close again.

However, my understanding is that this process defeats the safeguard provided by that air space, and that is to protect the carbon canister from getting wet with fuel, which will prevent it from absorbing gasoline vapors. Filling to the top and eliminating the air space would make it much more likely that a full sloshing tank will inject some fuel up into the canister.

My reason for asking is that I'm thinking through the process of possibly building custom aluminum saddle tanks, and what would be involved if I chose to build them to EPA specs. (They would certainly be built to USCG and ABYC specs). They wouldn't be certified, of course, but could still function as a certified tank would. The only compatible fuel limit vent valves I've been able to locate shut off at 1-1/2" below the top of the tank. So, unless one wanted to defeat the EPA system by filling the remaining space very slowly, one ends up not being able to utilize the top 1-1/2" of the tank.

I assume that new C-Dorys implement this feature, but I don't know. I was wondering if there was an exemption that they fall under. If so, I still have to decide if I want to do my part in keeping the air clean by implementing it anyway, as I'll be replacing the fuel system with at least new hoses, and possibly new tanks, and so have the opportunity to do it.

 

[Wefings]

The "party line" from tank Mfgs is that you lose 7-8% of the tanks capacity due to the EPA required equip. That is really an issue for the long range fishermen and cruisers . The tanks are supposed to hold 1 atmosphere of pressure to prevent fumes or liquid to escape with normal daily temperature changes [expansion and contraction], hence the name "diurnal system".

I wonder how the recreational boat pollution per day compares with the pollution created by a weekend golf outing to Maralago on Air Force One ...........

Just a thought ........

 

[ssobol]

The "party line" from tank Mfgs is that you lose 7-8% of the tanks capacity due to the EPA required equip. That is really an issue for the long range fishermen and cruisers . The tanks are supposed to hold 1 atmosphere of pressure to prevent fumes or liquid to escape with normal daily temperature changes [expansion and contraction], hence the name "diurnal system".

I wonder how the recreational boat pollution per day compares with the pollution created by a weekend golf outing to Maralago on Air Force One ...........

Just a thought ........

I wonder how boat designers deal with the change in tank size due to containing the expansion. I know that the plastic can I keep my mower gas has the same constraints on venting as the new boat tanks (Moeller makes a lot more portable gas cans than boat fuel tanks). I have seen very noticeable changes to the size and shape of this can due to thermal expansion.